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Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 553
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 554
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 555
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 556
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 557
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 558
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 559
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 560
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 561
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 562
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 563
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 564
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 565
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 566
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 567
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 568
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 569
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 570
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 571
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 572
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 573
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 574
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 575
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 576
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 577
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 578
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 579
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 580
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 581
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 582
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 583
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 584
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 585
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 586
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 587
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 588
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 589
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 590
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 591
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 592
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 593
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 594
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 595
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 596
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 597
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 598
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 599
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 600
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 601
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 602
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 603
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 604
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 605
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 606
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 607
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 608
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 609
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 610
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 611
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 612
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 613
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 614
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 615
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 616
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 617
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 618
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 619
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 620
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 621
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 622
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 623
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 624
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 625
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 626
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 627
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 628
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 629
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 630
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 631
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 632
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 633
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 634
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 635
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 636
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 637
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 638
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 639
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 640
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 641
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 642
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 643
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 644
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 645
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 646
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 647
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 648
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 649
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 650
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 651
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 652
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 653
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 654
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 655
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 656
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 657
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 658
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 659
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
×
Page 660
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 661
Suggested Citation:"Earth Satellite Program." National Research Council. 1965. Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958. Washington, DC: The National Academies Press. doi: 10.17226/26118.
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Page 662

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XV EARTH S A T E L L I T E PROGRAM E x p l o r e r I V l a u n c h e d f rom Cape Kennedy D u r i n g t h e I G Y

EARTH S A T E L L I T E PROGRAM Page A. O r g a n i z a t i o n o f T e c h n i c a l P a n e l on E a r t h S a t e l l i t e Program 553 B. Summary o f P a n e l A c t i o n s 554 C. P r o j e c t O b j e c t i v e s and R e s u l t s 565 30.3 I n i t i a l D e velopment o f O p t i c a l T r a c k i n g S y s t e m 567 30.5 O p t i c a l T r a c k i n g S y s t e m - I n i t i a t i o n 568 30.6, 30.8 - E s t a b l i s h m e n t and O p e r a t i o n o f O p t i c a l T r a c k i n g S y stem. . . . 569 30.9 V i s u a l O b s e r v i n g Program - Moonwatch 571 30.10 O p t i c a l T r a c k i n g D a t a R e d u c t i o n , A n a l y s i s and H e a d q u a r t e r s O p e r a t i o n 573 30.12 A d m i n i s t r a t i v e C o s t s o f O p t i c a l T r a c k i n g S y s t e m 586 30.20 I n t e r i m O p t i c a l S a t e l l i t e T r a c k i n g Network 586 30.21 V o l u n t e e r S a t e l l i t e T r a c k i n g P r ograms: P h o t o t r a c k & Moonbeam. . . . 587 31.1 P r o c u r e m e n t o f S a t e l l i t e L a u n c h i n g V e h i c l e s 592 32.1 C o s m i c - R a y O b s e r v a t i o n s 593 32.2 M e t e o r i c E r o s i o n & E l e c t r i c C h a r g e o f a S a t e l l i t e 598 32.3 E x t r e m e U l t r a v i o l e t S o l a r R a d i a t i o n 600 32 4 Measurement o f I n t e r p l a n e t a r y M a t t e r from E a r t h S a t e l l i t e s 601 32.5 M e t e o r o l o g i c a l Measurements from an E a r t h S a t e l l i t e 604 32.6 E l e c t r o n D e n s i t i e s i n t h e A t m o s p h e r e 606 32.7 S a t e l l i t e E n v i r o n m e n t a l M easurements 607 32.8 Lyman-Alpha and X - R a y s 609 32.9 S a t e l l i t e G e o m a g n e t i c Measurements 611 32.10 Measurement o f C o s m i c L i g h t & R a d i a t i o n from a S a t e l l i t e 615 32.11 S a t e l l i t e Measurement o f t h e E a r t h ' s R a d i a t i o n B a l a n c e 616 32.12 D e t e r m i n a t i o n o f F l u x o f Heavy P r i m a r y C o s m i c Ray N u c l e i 621 32.30 S p e c i a l E q u i p m e n t & E n g i n e e r i n g S e r v i c e s f o r S c i e n t i f i c E x p e r i m e n t s 625 32.31 S a t e l l i t e E q u i p m e n t & E n g i n e e r i n g S e r v i c e 628 32.32 M i c r o m e t e r D e t e c t i o n 629 32.40 R a d i o I n t e r f e r o m e t r y & D a t a A n a l y s i s 630 32.41 I n t e r f e r o m e t e r & D o p p l e r Measurements o f S a t e l l i t e R a d i o T r a n s m i s s i o n s 633 32.42 A u r o r a l I o n o s p h e r e S t u d i e s I n v o l v i n g S a t e l l i t e R a d i o T r a n s m i s s i o n 636 32.43 E l e c t r o n D e n s i t y & R a d i o P r o p a g a t i o n S t u d i e s U t i l i z i n g S a t e l l i t e T r a n s m i s s i o n s 641 32.44 S a t e l l i t e D o p p l e r Measurements from S p a c e d L o c a t i o n s 643 32.46 A b s o l u t e S i g n a l S t r e n g t h & F r e q u e n c y Measurements 650 32.47 E l e c t r o n D e n s i t y P r o f i l e s from lonograms 653 32.48 P o l a r S a t e l l i t e P r o p a g a t i o n Measurements 655 33.1 R a d i o T r a c k i n g E q u i p m e n t and O p e r a t i o n s 657 33.2 R a d i o T r a c k i n g - O r b i t C o m p u t a t i o n s & D a t a A n a l y s i s 659 34.1 S c i e n t i f i c T e l e m e t e r i n g & S a t e l l i t e I n s t r u m e n t a t i o n 660 34.2 T e l e m e t r y R e c o r d i n g & T e c h n i c a l A s s i s t a n c e 661 552

XV. EARTH S A T E L L I T E PROGRAM A O r g a n i z a t i o n o f T e c h n i c a l P a n e l on E a r t h S a t e l l i t e P r o g r a m 1 E s t a b l i s h m e n t o f t h e P a n e l F o l l o w i n g a d o p t i o n o f a r e s o l u t i o n c a l l i n g f o r geo- p h y s i c a l o b s e r v a t i o n s w i t h s c i e n t i f i c e a r t h s a t e l l i t e s a t t h e l l i r d R e u n i o n o f CSAGI, Rome, 1954, t h e U.S. announced on J u l y 29, 1955, i n t e n t i o n t o a t t e m p t t o l a u n c h s u c h e a r t h s a t e l l i t e s d u r i n g t h e IGY P r e l i m i n a r y s t u d i e s had a l r e a d y been c o n d u c t e d by a w o r k i n g group o f t h e T e c h n i c a l P a n e l on R o c k e t r y ( s e e C h a p t e r X I - R o c k e t s ) , and a new p a n e l was o r g a n i z e d t o d e v e l o p the e a r t h s a t e l l i t e program D u r i n g t h e c o u r s e o f work o f t h e P a n e l , some new members were added and a number o f w o r k i n g g r o u p s o r - g a n i z e d 2 C o m p o s i t i o n o f t h e P a n e l ( A f f i l i a t i o n a t time o f a p p o i n t m e n t ) P a n e l Members R.W. P o r t e r , C h a i r m a n G. M. C l e m e n c e (From 1957) M i c h a e l F e r e n c e , J r ( F r o m 1957) J o s e p h K a p l a n W.W. K e l l o g g (From 1958) H. E . N e w e l l , J r Hugh Odishaw W.H. P i c k e r i n g A l a n H S h a p l e y (From 1957) A t h e l s t a n F S p i l h a u s Lyman S p i t z e r , J r ( R e s i g n e d 1956) J.A. Van A l l e n F r e d L W h i p p l e G e n e r a l E l e c t r i c Company U.S. N a v a l O b s e r v a t o r y F o r d Motor Company U n i v e r s i t y o f C a l i f o r n i a , L o s A n g e l e s Rand C o r p o r a t i o n N a v a l R e s e a r c h L a b o r a t o r y N a t i o n a l Academy o f S c i e n c e s J e t P r o p u l s i o n L a b o r a t o r y N a t i o n a l B u r e a u o f S t a n d a r d s U n i v e r s i t > o f M i n n e s o t a P r i n c e t o n U n i v e r s i t y S t a t e U n i v e r s i t y o f I o w a S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y C o n s u l t a n t s and DOD L i a i s o n W.W. B e r n i n g R.B. C a n r i g h t A.M. G e r l a c h George G r i m m i n g e r J . P . Hagen J.W. J o y c e T . J . K i l l i a n J.G. R e i d , J r J.O. S p r i g g s C.S, Weaver H a r o l d Z a h l C.L. Z a k h a r t c h e n k o H.K. Z i e g l e r B a l l i s t i c R e s e a r c h L a b o r a t o r y A d v anced R e s e a r c h P r o j e c t s Agency A i r F o r c e Cambridge R e s e a r c h L a b o r a t o r y U.S. A i r F o r c e N a v a l R e s e a r c h L a b o r a t o r y N a t i o n a l S c i e n c e F o u n d a t i o n O f f i c e o f N a v a l R e s e a r c h Army E l e c t r o n i c s P r o v i n g Grounds Advanced R e s e a r c h P r o j e c t s Agency O f f i c e o f t h e D i r e c t o r o f D e f e n s e - R e s e a r c h 6t E n g i n e e r i n g U.S. Army S i g n a l R e s e a r c h & Development L a b o r a t o r y N a t i o n a l Academy o f S c i e n c e s U.S. Army S i g n a l R e s e a r c h & Development L a b o r a t o r y S e c r e t a r i a t ( I G Y S t a f f ) G.F S c h i l l i n g (To J u n e 1956) J.G. R e i d , J r (To J a n u a r y 1958) G A D e r b y s h i r e (From J a n u a r y 1958) 553

EARTH S A T E L L I T E 3 P a n e l M e e t i n g s . T h e r e were twenty m e e t i n g s o f the P a n e l . F i r s t M e e t i n g O c t o b e r 20, 1955 W a s h i n g t o n D.C. Second M e e t i n g November 21, 1955 W a s h i n g t o n D.C. T h i r d M e e t i n g J a n u a r y 28, 1956 Ann A r b o r , M i c h i g F o u r t h M e e t i n g March 8-9, 1956 W a s h i n g t o n D.C. F i f t h M e e t i n g A p r i l 20 , 1956 W a s h i n g t o n D.C. S i x t h M e e t i n g J u n e 7-8 , 1956 W a s h i n g t o n D.C. S e v e n t h M e e t i n g Septembe r 5, 1956 W a s h i n g t o n D.C. E i g h t h M e e t i n g O c t o b e r 15, 1956 W a s h i n g t o n D.C. N i n t h M e e t i n g December 3-4, 1956 W a s h i n g t o n D.C. T e n t h M e e t i n g F e b r u a r y 7, 1957 W a s h i n g t o n , D.C. E l e v e n t h M e e t i n g May 1, 1957 W a s h i n g t o n , D.C. T w e l f t h M e e t i n g O c t o b e r 3, 1957 W a s h i n g t o n , D.C. T h i r t e e n t h M e e t i n g O c t o b e r 22, 1957 W a s h i n g t o n , D.C. F o u r t e e n t h M e e t i n g November 6, 1957 W a s h i n g t o n , D.C. F i f t e e n t h M e e t i n g J a n u a r y 7, 1958 W a s h i n g t o n , D.C. S i x t e e n t h M e e t i n g F e b r u a r y 12, 1958 W a s h i n g t o n , D.C. S e v e n t e e n t h M e e t i n g A p r i l 3, 1958 W a s h i n g t o n , D.C. E i g h t e e n t h M e e t i n g May 27, 1958 W a s h i n g t o n , D.C. N i n e t e e n t h M e e t i n g J u l y 17, 1958 W a s h i n g t o n , D.C. T w e n t i e t h M e e t i n g J u l y 21, 1959 W a s h i n g t o n , D.C. B Summary o f P a n e l A c t i o n s 1 R e s p o n s i b i l i t y f o r the S a t e l l i t e P rogram a Ob l e c t i v e s The s p e c i f i c o b j e c t i v e s o f the U.S. e a r t h s a t e l l i t e p rogram were ( i ) t o p l a c e an o b j e c t i n o r b i t and p r o v e t h i s by o b s e r v a t i o n s , ( i i ) t o o b t a i n a p r e c i s i o n o p t i c a l t r a c k f o r g e o d e t i c and h i g h a l t i t u d e a t - m o s p h e r i c d r a g s t u d y p u r p o s e s , and t o ( i l l ) p e r f o r m e x p e r i m e n t s w i t h i n t e r n a l i n s t r u m e n t a t i o n b O r g a n i z a t i o n a l R e s p o n s i b i l i t i e s By m u t u a l a g r e e m e n t , the f o l l o w i n g d e f i n i - t i v e a r e a s o f r e s p o n s i b i l i t y f o r the p r o j e c t were e s t a b l i s h e d ( i ) N a t i o n a l Academy o f S c i e n c e s e x e c u t i o n o f C o o r d i n a t i n g t h e p l a n n i n g , d i r e c t i o n and ( a ) t h e s c i e n t i f i c a s p e c t s o f the s c i e n t i f i c program, i n c l u d i n g e s t a b l i s h m e n t o f p o l i c i e s and p r o c e d u r e s r e l a t i n g t o budget and t o r e l e a s e o f i n f o r m a t i o n , (b) t he i n t e r n a t i o n a l and i n t e r d i s c i p l i n a r y r e l a t i o n s i n v o l v e d i n the o v e r - a l l I G Y e f f o r t , ( c ) t h e o p t i c a l t r a c k i n g program and a s s o c i a t e d o r b i t c o m p u t a t i o n s , (d) t h e s e l e c t i o n o f the s c i e n t i f i c e x p e r i m e n t s t o be a c c o m p l i s h e d t h r o u g h i n s t r u m e n t s p l a c e d i n t h e s a t e l l i t e i t s e l f ( i i ) N a t i o n a l S c i e n c e F o u n d a t i o n F i s c a l r e s p o n s i b i l i t y f o r F e d e r a l f u n d s ( o t h e r t h a n t h o s e s u p p l i e d f o r the Department o f D e f e n s e ) a p p r o p r i a t e d f o r the U.S. program T h e s e funds were t o be g r a n t e d a f t e r s c i e n t i f i c e v a l u a t i o n o f t h e p r o p o s a l s by the P a n e l and on recommendation o f t h e USNC E x e c u t i v e Committee o f t h e N a t i o n a l Academy o f S c i e n c e s and a p p r o v a l o f the N a t i o n a l S c i e n c e B o a r d 554

EARTH SATELLITE ( i l l ) Department of Defense. (a) (b) (c) (d) (e) ( f ) (g) development and procurement of s a t e l l i t e launching v e h i c l e s , d e l i v e r y of the s a t e l l i t e i n o r b i t ; demonstration that an o r b i t had been a t t a i n e d , performance of at least one telemetric s c i e n t i f i c experiment using the s a t e l l i t e ; sundry l o g i s t i c s support needed f o r the operational success of the t o t a l e f f o r t i n c l u d i n g ground s t a t i o n s i t e s and necessary housing s t r u c t u r e s , deterxnining the engineering f e a s i b i l i t y of such s c i e n t i f i c instruments as were proposed by the National Academy of Sciences f o r i n c l u s i o n w i t h i n the s a t e l l i t e , and the r a dio t r a c k i n g and associated o r b i t computation program. 2. Organization of Working Groups. a. Tasks. The p r i n c i p a l tasks before the Panel at i t s i n c e p t i o n were: ( i ) to formulate a s c i e n t i f i c program to be c a r r i e d out by means of a r t i - f i c i a l s a t e l l i t e s as part of the U.S. program f o r the IGY, ( i i ) to e s t a b l i s h p o l i c i e s and formulate procedures r e l a t i n g to (a) conduct of the program, (b) budget, (c) release of information, and (d) i n s t i t u t i o n a l r e l a - t i o n s h i p s , ( i l l ) to coordinate the execution of the program. b. Working Groups. I n order to formulate the d e t a i l e d plans necessary f o r the execution of the program, the Panel i n i t i a l l y set up two working groups: ( i ) the Working Group on I n t e r n a l Instrumentation under the chairmanship of Dr. Van A l l e n , and ( i i ) the Working Group on Tracking and Computation under the chairmanship of Dr. W.H. Pickering I n November 1957, as a r e s u l t of the decision by the USNC Executive Committee at i t s 24th Meeting, October 1957, to place r e s p o n s i b i l i t y f o r ionospheric studies using s a t e l l i t e s I n the Technical Panel f o r the Earth S a t e l l i t e Program, the Working Group f o r Ionospheric Measurements was established. 3. Working Group on I n t e r n a l Instrumentation (1956). a. Members J.A. Van A l l e n (Chairman) L.R. Alldredge Michael Ference, Jr H. Friedman W.W. Kellogg H Odishaw Richard W Porter L Spitzer, J r . O.H. Schmitt (From 1957) b Meetings of the Working Group F i r s t Meeting Second Meeting Thir d Meeting Fourth Meeting F i f t h Meeting Six t h Meeting Seventh Meeting Eighth Meeting Ninth Meeting Tenth Meeting Operations Research O f f i c e , Johns Hopkins U n i v e r s i t y Ford Motor Company Naval Research Laboratory Rand Corporation National Academy of Sciences General E l e c t r i c Company Princeton U n i v e r s i t y U n i v e r s i t y of Minnesota March 6, 1956 June 4, 1956 October 11, 1956 January 23, 1957 February 6, 1957 A p r i l 30, 1957 October 21, 1957 November 5, 1957 February 11, 1958 May 26, 1958 555

EARTH SATELLITE c. Program of F l i g h t Experiments Using I n t e r n a l l y Instrumented S a t e l l i t e s . I t was agreed at the f i r s t meeting of the Working Group on I n t e r n a l Instrumentation held i n March 1956 that experiments should be selected from the proposals received on the basis of each of the f o l l o w i n g four aspects: ( i ) S c i e n t i f i c importance, ( i i ) Technical f e a s i b i l i t y ; ( i l l ) Competence of persons submitting the proposal; and ( i v ) Importance of a s a t e l l i t e to the proposed experiment. On the basis of ( i ) , the f o l l o w i n g were considered to deserve primary a t t e n t i o n - (a) I n v e s t i g a t i o n of environment of space at s a t e l l i t e a l t i t u d e , density, temperature, m e t e o r i t i c erosion. (b) Radiation measurements: solar u l t r a v i o l e t , X rays, cosmic. (c) Geomagnetic f i e l d measurements (d) Meteorological measurements: cloud cover, earth's energy balance. (e) Ionospheric measurements I n view of the large number of desirable experiments to be c a r r i e d out w i t h the use of earth s a t e l l i t e s , i t was agreed to consolidate them i n t o "packages" which could be c a r r i e d aboard a single v e h i c l e . These packages were set up as fol l o w s : Package I - Lyman-alpha and environmental Package I I - Cosmic-ray and m e t e o r i t i c detection Package I I I - Magnetometer and 30" i n f l a t a b l e sphere Package IVa - Energy balance Package IVb - Cloud cover Note: Both IVa and IVb were brought to f i n a l f e a s i b i l i t y , but since i t was planned to judge p r i o r i t y of these two on the basis of me- t e o r o l o g i c a l value, the meteorologists awarded p r i o r i t y to the IVa experiment. The Panel considered a large number of proposals on the basis of the above c r i t e r i a as a r e s u l t of which a selected program of p r i o r i t y f l i g h t experiments was agreed upon a t the lOth meeting held i n February 1957: Environmental measurements, Naval Research Laboratory (H.E. LaGow) Lyman-alpha and X r a d i a t i o n . Naval Research Laboratory (H. Friedman) Cosmic-ray observations, State U n i v e r s i t y of Iowa (J.A. Van Al l e n ) Measurements of i n t e r p l a n e t a r y matter. Geophysics Research D i r e c t o r a t e , AFCRL (Maurice Dubin) S a t e l l i t e geomagnetic measurements. Naval Research Laboratory (J.P. Heppner) Radiation balance of the earth. U n i v e r s i t y of Wisconsin (V.E. Suomi) Meteorological measurements, Evans Signal Laboratory, Signal Research & Development Laboratory (W.G. Stroud) The f o l l o w i n g experiments were funded f o r development and proof o f f e a s i b i l i t y : Extreme u l t r a v i o l e t solar r a d i a t i o n . Geophysics Research D i r e c t o r a t e , AFCRL (H. Hinteregger) 556

EARTH SATELLITE Flux of primary cosmic-ray n u c l e i , B a r t o l Research Foundation (Martin Pomerantz) and Research I n s t i t u t e of Advanced Studies (Gerhart Groetzinger) Measurement of cosmic l i g h t and r a d i a t i o n , Jet Propulsion Laboratory, C a l i f o r n i a I n s t i t u t e of Technology (W.H. Pickering) Meteoric erosion and e l e c t r i c charge, U n i v e r s i t y of Maryland (S.F. Singer) The Panel endorsed the recommendation of the Working Group on I n t e r n a l I n s t r u - mentation that experiments be attempted i n two successive t r i e s before r e l i n q u i s h i n g t h e i r place to other experiments i n the schedule of launching attempts. At the 14th meeting i n November 1957, the Panel decided to withdraw the Van A l l e n cosmic-ray experiment (Package I I ) from the Vanguard launching v e h i c l e and to place I t i n the Jupiter-C v e h i c l e which the Department of Defense had made av a i l a b l e to the USNC-IGY earth s a t e l l i t e program. The cloud cover experiment (Package IVb) was then t r a n s f e r r e d to the Vanguard s a t e l l i t e i n i t s place. Early i n 1958, the Panel expressed to the Department of Defense i t s desire to include i n the program an i n f l a t a b l e sphere. This was subsequently developed by the NACA w i t h I t s own funds f o r f l i g h t w i t h a Jupiter-C v e h i c l e . When the preliminary r e s u l t s of the Van A l l e n cosmic-ray experiments from 1958 alpha and 1958 gamma (Explorers I and I I I ) became a v a i l a b l e , i t was apparent that an a d d i t i o n a l s a t e l l i t e experiment, s u i t a b l y instrumented, should be flown immediately. I t was agreed, t h e r e f o r e , to defer the experiment assigned to the next Explorer ve- h i c l e , thus p e r m i t t i n g a f u r t h e r IGY r a d i a t i o n experiment of improved design to f l y . The Department of Defense agreed to make ava i l a b l e an a d d i t i o n a l v e h i c l e at a l a t e r date f o r the deferred NACA i n f l a t a b l e sphere air d r a g experiment. 4. Working Group on Tracking and Computation (1956). Members W.H. Pickering (Chairman) G.M. Clemence W.A. Heiskanen J.T. Mengel J.A. O'Keefe J.E. Steakley (From 1957) F.L. Whipple U.S. Naval Observatory Ohio State U n i v e r s i t y Naval Research Laboratory Army Map Service Aeronautical Chart and Information Center Smithsonian Astrophysical Observatory Meetings of the Working Group F i r s t Meeting Second Meeting T h i r d Meeting Fourth Meeting F i f t h Meeting S i x t h Meeting Seventh Meeting E i g h t h Meeting Ninth Meeting A p r i l 21, 1956 June 7, 1956 October 6, 1956 December 3, 1956 February 6, 1957 A p r i l 30. 1957 August 1, 1957 October 21, 1957 January 6, 1958 c. T r a c k i n g Program. The development and establishment of a d e f i n i t i v e s a t e l l i t e o r b i t of highest p o s s i b l e p r e c i s i o n was considered necessary to enable meaningful and accurate a n a l y s i s to be made of s c i e n t i f i c data from instrumentation c a r r i e d i n the s a t e l l i t e , and to d e r i v e other s c i e n t i f i c information, f or example, a i r d e n s i t i e s and geodetic determinations. 557

EARTH SATELLITE Once placed i n o r b i t , the s a t e l l i t e becomes m e f f e c t a c e l e s t i a l body and as such the f i r s t problem i s i t s a c q u i s i t i o n by i n i t i a l observations not only to e s t a b l i s h I t s c e l e s t i a l existence, but to provide data f o r p r e l i m i n a r y c a l c u l a t i o n s of i t s or- b i t i n order that ephemerides may be made. These p r e d i c t i o n s would permit the f u l l concentration of ground s t a t i o n s on a c q u i s i t i o n of the s a t e l l i t e and more precise or- b i t a l determinations, and the subsequent a c q u i s i t i o n of more extensive data on the basis of which the above studies can be conducted. ( i ) O p t i c a l Tracking. The o p t i c a l observation system has c e r t a i n inherent l i m i t a t i o n s : the path of the s a t e l l i t e must be known i n i t i a l l y to a p r e c i s i o n of 3 degrees so that preliminary s i g h t i n g p o s i t i o n s can be established f o r i n s u r i n g photo- graphic a c q u i s i t i o n , o p t i c a l observations are r e s t r i c t e d to b r i e f t w i l i g h t periods free of i n t e r f e r i n g cloud cover. The p r e c i s i o n o p t i c a l t r a c k i n g network was therefore planned by the Working Group on Tracking and Computation to include twelve s t a t i o n s located through- out the world. R e s p o n s i b i l i t y f o r establishment and operation of the network, i n - cluding development and construction of the telescopic camera equipment, was assigned to the Smithsonian Astrophysical Observatory. Arrangements f o r the s t a t i o n s were made by the Smithsonisin I n s t i t u t i o n through the IGY P a r t i c i p a t i n g Committees of the respec- t i v e countries, i n coordination w i t h the U.S. IGY Committee. ( l i ) Moonwatch. The organization e a r l y i n 1956 of amateur astronomers i n t o s a t e l l i t e observation teams was termed "Project Moonwatch." This program was set up by the Smithsonian Astrophysical Observatory u t i l i z i n g such t r a i n e d groups as the Society f o r Volunteer Star Watchers (SVSW). There were over one hundred "Moonwatch" teams scattered over the United States and teams were also formed i n twenty-seven other countries favorably located f o r s a t e l l i t e observations. A f t e r the launching of the Soviet s a t e l l i t e s , i t was decided to expand the Moonwatch program, as a r e s u l t of which there were i n 1959, 230 r e g i s t e r e d s t a t i o n s throughout the 27 countries taking part i n t h i s program, i n c l u d i n g 126 s t a t i o n s i n the USA. ( l i i ) Radio Tracking. I n November 1955, the Department of Defense agreed to cover the cost of developing and t e s t i n g a system of radio t r a c k i n g and recording of telemetry signals from s a t e l l i t e s based on ten s t a t i o n s , eight of which were to be arranged i n a picket-fence along the 75th meridian. Each s t a t i o n was i n i t i a l l y pro- vided w i t h equipment f o r t r a c k i n g a 108 MC radio s i g n a l from the s a t e l l i t e u t i l i z i n g a radio interferometer w i t h a c a l i b r a t e d antenna array f o r obtaining precise l o c a t i o n s . These s t a t i o n s were also designed to include f a c i l i t i e s f o r reception and recording of s a t e l l i t e telemetry signals. The development of the e l e c t r o n i c equipment, which occupies one large t r a i l e r van f o r each s t a t i o n , was c a r r i e d out by the Naval Research Laboratory w i t h the support of IGY funds, while operation and communication services f o r the network were provided by the Department of Defense. Five of the s t a t i o n s were modified a f t e r the launching of the Soviet s a t e l l i t e s w i t h a l t e r n a t e operation at AO Mc to permit radio t r a c k i n g of these s a t e l l i t e s , and personnel at the s t a t i o n s was increased to allow f o r a t h r e e - s h i f t operation. ( i v ) Minitrack-Mark I . The Naval Research Laboratory undertook r e s p o n s i b i l i t y f o r a system of p r e c i s i o n radio t r a c k i n g . This included development and design of the equipment, establishment and operation of t r a c k i n g s t a t i o n s and computation of o r b i t a l data. M i n i t r a c k s t a t i o n s were selected by a team c o n s i s t i n g of representatives of the Army Engineers, Signal Corps and Naval Research Laboratory and were established at Santiago, Chile; Antofagasta, Chile; Lima, Peru; Quito, Ecuador, Panama; Antigua, B r i t i s h West I n d i e s , Havana, Cuba, Jacksonville, F l o r i d a ; Blossom Point, Maryland; Fort Stewart, Georgia; San Diego, C a l i f o r n i a . I n December 1956, the Panel endorsed the recommendation of the Naval Research Laboratory to t r a n s f e r the M i n i t r a c k Mark I s t a t i o n planned f o r Panama t o A u s t r a l i a . This t r a n s f e r was l a t e r made. 558

EARTH SATELLITE The Department of the Army established and operated the s t a t i o n s i n Georgia, USA, Ecuador, Peru, Cuba and two st a t i o n s i n Chile, providing teams to operate the M i n i t r a c k and telemetering equipment plus the communications equipment. The Inter-American Geodetic Survey assisted i n the operation of the s t a t i o n s i n most of the L a t i n American countries. I n order to rel a y communications, the Army u t i l i z e d i t s r e l a y center f o r the Caribbean area i n Panama. (v) M i n i t r a c k Mark I I . A second M i n i t r a c k system ( M i n i t r a c k Mark I I ) was l a t e r established to support the primary network ( M i n i t r a c k Mark I ) by means of addi- t i o n a l ground s t a t i o n s of a s i m p l i f i e d type, also based on the interferometer p r i n - c i p l e . This system, which could be b u i l t by amateur groups at lower cost, was planned to permit amateur p a r t i c i p a t i o n . ( v i ) Microlock. The Microlock system of radio t r a c k i n g was established by the Jet Propulsion Laboratory of the C a l i f o r n i a I n s t i t u t e of Technology to trac k and receive telemetry from minimum-power devices at extreme l i n e - o f - s i g h t ranges. This system used a narrow radio-frequency bandwidth. A s i m p l i f i e d version f o r use by ad- vanced amateurs used two radio-frequency channels. ( v i i ) Moonbeam. The Panel l a t e r decided to e s t a b l i s h a system of volunteer r a d i o - t r a c k i n g and telemetry, l a r g e l y to stimulate and recognize i n t e r e s t i n the IGY s a t e l l i t e program by t e c h n i c a l a u x i l i a r y groups such as the American Radio Relay League, etc. This program, which has become known as Project MOONBEAM, m a t e r i a l l y assisted the primary networks by provid i n g a d d i t i o n a l data. The o v e r - a l l program was di r e c t e d by the Naval Research Laboratory ( l a t e r NASA) while the Jet Propulsion Laboratory assisted and maintained a Moonbeam informa- t i o n and te c h n i c a l assistance o f f i c e f o r the Western United States. d. O r b i t Computation and Data Analysis. U.S. coiiq)utation centers were planned i n connection w i t h the o p t i c a l and radio t r a c k i n g networks to carry out s c i e n t i f i c computations and analysis of s a t e l l i t e o r b i t s , as w e l l as to e s t a b l i s h search ephem- erides to permit observations of s a t e l l i t e s by s c i e n t i s t s throughout the world. Such centers were established by the Smithsonian Astrophysical Observatory and the Naval Research Laboratory. A f t e r the launching of the Soviet s a t e l l i t e s , i t was agreed to expand the o r i g i n a l computation program i n order to derive f u l l s c i e n t i f i c value from a study of a l l s a t e l l i t e s launched during the IGY program. The Smithsonian Astrophysical Observatory accepted r e s p o n s i b i l i t y f o r s a t e l - l i t e data only when o p t i c a l observations could be made and f o r any s a t e l l i t e s or sa- t e l l i t e vehicles i n o r b i t not c a r r y i n g an operational radio t r a n s m i t t e r . I n a d d i t i o n , f o r a l l U.S. s a t e l l i t e s c i t e d above, the Smithsonian Astrophysical Observatory was also assigned r e s p o n s i b i l i t y f o r the c a l c u l a t i o n of f i n a l p r e c i s i o n o r b i t s of a l l IGY s a t e l l i t e s . The SAO program was divided i n t o four main sections: o r b i t deter- mination, o r b i t c o r r e c t i o n , ephemerides or pr e d i c t i o n s and analysis. 5. Working Group on S a t e l l i t e Ionospheric Measurements (1957). Members A.H. Shapley (Chairman) W.W. Berning G. Grammer C.G. L i t t l e W. P f i s t e r G.C. Reid (From 1958) J.C. Sedden R.J. Slutz (Resigned 1958) Central Radio Propagation Laboratory B a l l i s t i c Research Laboratory Amateur Radio Relay League National Bureau of Standards, Central Radio Propagation Laboratory A i r Force Cambridge Research Laboratories U n i v e r s i t y of Alaska Naval Research Laboratory, NASA National Bureau of Standards 559

EARTH SATELLITE G. W. Swenson, J r . Ohio State U n i v e r s i t y O.G. V i l l a r d , J r . Stanford U n i v e r s i t y A.H. Waynick Pennsylvania State U n i v e r s i t y H. W. Wells Carnegie I n s t i t u t i o n of Washington b. Meetings of the Working Group F i r s t Meeting January 6, 1958 Second Meeting May 26, 1958 Third Meeting September 30, 1958 c. S a t e l l i t e Ionospheric Measurements Program. An unique opportunity f o r radio propagation studies and ionospheric research was afforded by the a v a i l a b i l i t y of the Soviet earth s a t e l l i t e s w i t h t h e i r 20-40 Mc radio transmissions, which are markedly af f e c t e d by the ionosphere. The value of these experiments f o r providing new data on upper-atmosphere ion d i s t r i b u t i o n and radio propagation c h a r a c t e r i s t i c s and various s o l a r - t e r r e s t r i a l r e l a t i o n s h i p s became very evident from observations made w i t h the aid of the Soviet s a t e l l i t e s . Weight considerations and the prosecution of other h i g h - p r i o r i t y experiments had precluded the e a r l i e r i n c l u s i o n of frequencies lower than 108 Mc f o r the f i r s t U.S. s a t e l l i t e s , but since the con t i n u a t i o n by the Soviets of 20-40 Mc t r a n s m i t t i n g equipment i n f u t u r e s a t e l l i t e s was a n t i c i p a t e d , and i n view of US-IGY plans to develop lower frequency t r a n s m i t t e r s f o r the U.S. s a t e l l i t e s , i t was decided to provide f o r f u l l p a r t i c i p a t i o n by U.S. s c i e n t i s t s i n s a t e l l i t e iono- spheric studies. A number of experiments were considered by the Working Group f o r S a t e l l i t e Ionospheric Measurements and were endorsed by the Technical Panel f o r the Earth Sa- t e l l i t e Program as follows: ( i ) Ionospheric e l e c t r o n density. B a l l i s t i c Research Laboratory, (Norman W. Arnold) ( i i ) Radio i n t e r f e r o m e t r y and data analysis. U n i v e r s i t y of I l l i n o i s (G.W. Swenson, Jr . ) ( i l l ) Auroral ionospheric studies i n v o l v i n g s a t e l l i t e radio transmissions. U n i v e r s i t y of Alaska (C.T. Elvey) ( i v ) Electron density and radio propagation studies u t i l i z i n g s a t e l l i t e t r ans- missions, Stanford U n i v e r s i t y (O.G. V i l l a r d , J r . , R.H. Bracewell and A.M. Peterson) (v) Doppler measurements from spaced lo c a t i o n s , Pennsylvania State Univer- s i t y (A.H. Waynick) ( v i ) Absolute s i g n a l strength and frequency measurements, L i n f i e l d Research I n s t i t u t e (W.P. Dyke) ( v i i ) True-height e l e c t r o n density p r o f i l e s , CRPL, National Bureau of Standards (R.J. Slutz) ( v i i i ) Polar propagation measurements, Geophysics Research D i r e c t o r a t e , AFCRL (Wolfgang P f i s t e r ) Provision was made f o r the cost of these experiments i n the 1958 IGY supple- mental Congressional a p p r o p r i a t i o n . I t was hoped that from observations from d i f f e r e n t longitudes and from successive passages of the s a t e l l i t e , i t would be posssible to p l o t a map of ionospheric conditions f o r the e n t i r e United States. 560

EARTH SATELLITE 6. Budget. R e s p o n s i b i l i t y f o r the i n i t i a l development of a budget that was to pro- vide f o r a broad s c i e n t i f i c program i n c l u d i n g ground observations and s a t e l l i t e - b o r n e experiments was assigned at the f i r s t meeting, October 1955, to an ad hoc Budget Panel under the d i r e c t i o n of Dr. Homer E. Newell, J r . I t was agreed that up to $20,000,000 would be recommended to the U.S. National Committee to cover t h i s program which was to be c a r r i e d out i n conjunction w i t h twelve launching attempts to be provided by the Department of Defense. The National Science Foundation, which provided the channel f o r obtaining f i s c a l support f o r a l l other aspects of the US-IGY s p e c i a l l y funded program, also undertook to obtain funds f o r the US-IGY s a t e l l i t e program. Accordingly, the Foundation i n - cluded $19,262,000 i n i t s 1956 IGY budget request f o r support of the IGY earth s a t e l - l i t e program. Following approval of the appropriation by the Congress, an amount of $18,362,000 was a l l o c a t e d f o r t h i s purpose by the U.S. National Committee. Late i n 1957, a f t e r the launching of the f i r s t Soviet s a t e l l i t e s , the US-IGY Na- t i o n a l Committee caused a thorough re-evaluation to be made of the US-IGY ea r t h sa- t e l l i t e program by the Technical Panel f o r the Earth S a t e l l i t e Program and other i n t e r e s t e d t e c h n i c a l panels of the Committee. I n the l i g h t of t h i s r e-evaluation, several changes i n the time schedule and content of the program appeared to be de- s i r a b l e to c a p i t a l i z e f u l l y on the s c i e n t i f i c o p p o r t u n i t i e s presented by the Soviet s a t e l l i t e s ; to improve the p o t e n t i a l value of experimental data expected from U.S. s a t e l l i t e s , and to adapt the s c i e n t i f i c program to an accelerated schedule f o r placing a U.S. s a t e l l i t e i n o r b i t . The f i n a l estimated cost of t h i s expanded and accelerated program t o support ad- d i t i o n a l s a t e l l i t e launchings was $2,100,000. Subsequently, i n January 1958, an appropriation of $2,000,000 was approved b r i n g i n g to $20,362,000 the t o t a l amount of funds a v a i l a b l e f o r the ea r t h s a t e l l i t e program. Further adjustments i n the US- IGY s a t e l l i t e program were made by the U.S. National Committee and the t o t a l approved a l l o c a t i o n s amounted to $20,067,666. 7. Engineering Program. a. Launching Vehicles. ( i ) Vanguard. The r e s p o n s i b i l i t y of the Department of Defense f o r the de- velopment of s a t e l l i t e rocket vehicles has already been r e f e r r e d t o . I n order to f u l f i l l t h i s r e s p o n s i b i l i t y , the Department of Defense established Project Vanguard under the management of the Naval Research Laboratory w i t h the f o l l o w i n g responsi- b i l i t i e s : (1) p r o v i s i o n of design s p e c i f i c a t i o n s and the f i n a l engineering of the instrumented payloads, (2) environmental t e s t i n g f o r a l l s a t e l l i t e s to be launched w i t h Vanguard v e h i c l e s , and (3) a radio telemetry system compatible w i t h radio beacon t r a n s m i t t e r s . The Naval Research Laboratory therefore agreed to proceed w i t h a m i n i - mum version c o n s i s t i n g of a v e h i c l e plus m i n i t r a c k , a 20-inch sphere w i t h m i n i t r a c k i n c o r p o r a t i n g the Lyman-alpha experiment and environmental studies such as tempera- t u r e , pressure and surface erosion using both spherical and c y l i n d r i c a l shaped s a t e l - l i t e s . For d e t a i l s of the Vanguard v e h i c l e see p r o j e c t 31.1. ( i i ) Jupiter-C. I n November 1957, the Department of Defense announced that the s c i e n t i f i c e arth s a t e l l i t e program f o r the IGY would include two supplementary launchings, making use of the Jupiter-C v e h i c l e of the U.S. Army. R e s p o n s i b i l i t y f o r development of the payload f o r the Explorer series of s a t e l l i t e s was assigned by the Department of Defense to the Jet Propulsion Laboratory of the C a l i f o r n i a I n s t i t u t e of Technology. The Jupiter-C was a four-stage rocket developed by the U.S. Army and the Jet Propulsion Laboratory w i t h an o v e r - a l l length of approximately 68-1/2 f e e t . The 561

EARTH SATELLITE f i r s t stage was a modified Redstone l i q u i d p r o pellant rocket approximately 56 feet long and 5 feet i n diameter. The nose-section assembly, separable from the c a r r i e r v e h i c l e , was 12-5/12 feet i n length. The f i r s t stage of the vehicle provided a l l the energy to l i f t the payload to the prescribed distance from the earth. A l l other stages increased the speed, but d i d not immediately carry the s a t e l l i t e to a greater height. I n March 1958, an improved Jupiter-C v e h i c l e was off e r e d by the Depart- ment of Defense (Juno I I ) to carry a payload weight of about 100 lbs . Shortly a f t e r - wards, the Panel was advised of the m o d i f i c a t i o n of the l a s t Vanguard t e s t by the ad d i t i o n of an Allegheny B a l l i s t i c s Laboratory improved t h i r d stage to launch a pay- load of about 50 lbs . ( i l l ) Lunar Probes. Early i n 1958, the Department of Defense informed the U.S. National Committee of i t s f i v e proposed lunar probe experiments and suggested that these might be included i n the IGY s a t e l l i t e program, the cost being borne by the Department of Defense. The USNC-IGY endorsed t h i s suggestion on the understanding that USNC p o l i c i e s and procedures w i t h respect to IGY pr o j e c t s would be adhered to such as s c i e n t i f i c cognizance of the proposed experiment, a v a i l a b i l i t y of a l l ex p e r i - mental data f o r interchange i n accordance w i t h CSAGI i n t e r n a t i o n a l agreements, and handling by the Academy of dissemination of information r e l a t i n g to t h i s e f f o r t . b. Launchmgs. At the outset, i t was decided t o launch a l l IGY s a t e l l i t e s from P a t r i c k A i r Force Base, Cape Canaveral, F l o r i d a , at a planned o r b i t a l i n c l i n a t i o n of 40° to the geographic equator. At a l a t e r date, the i n c l i n a t i o n of the o r b i t was r e - duced from 40° to about 32° f o r reasons of range safety. Subsequently, w i t h the Jupiter-C v e h i c l e , i t was fe a s i b l e to achieve o r b i t a l i n c l i n a t i o n s as high as 52°. c. Nomenclature. The suggestion by the Smithsonian Astrophysical Observatory and Harvard Observatory f o r an i d e n t i f i c a t i o n system f o r the a r t i f i c i a l s a t e l l i t e s was adopted as follows: i d e n t i f i c a t i o n by year, a l e t t e r of the Greek alphabet and a ninnber corresponding to the objects which were placed i n o r b i t at the same time, w i t h No. 1 being the b r i g h t e s t . No. 2 the second b r i g h t e s t , and so on. A l i s t of a l l launchings i s given i n part B o f t h i s chapter, preceeding the de s c r i p t i o n of the i n d i v i d u a l s a t e l l i t e p r o j e c t s . 8. Telemetry. The Panel decided at an e a r l y date that telemetry should not i n gen- e r a l be continuous, that data storage should be provided i n the s a t e l l i t e to permit read-out on command so that data f o r an e n t i r e o r b i t could be received and recorded by one of the M i n i t r a c k s t a t i o n s during a s a t e l l i t e over-pass. This group of s a t e l - l i t e s employed tape recorders to obtain complete synoptic data. However, a second group of s a t e l l i t e s designed to measure the i n t e n s i t y of solar r a d i a t i o n i n the Lyman-alpha region of the hydrogen spectrum, the i n t e n s i t y of primary cosmic rays and environmental conditions, had no p r o v i s i o n f o r storage and command read-out, but provided continuous transmission of telemetered s c i e n t i f i c i n formation e a s i l y received by i n t e r e s t e d radio amateurs or s c i e n t i f i c organizations. Two special telemetry s t a t i o n s located i n Singapore and Nigeri a were equipped w i t h instrumentation designed by the Jet Propulsion Laboratory to receive e i t h e r low-powered, narrow-band, phase-modulated 108 Mc si g n a l from horizon to horizon or a high-powered, wider-band, amplitude-modulated 108 Mc si g n a l from somewhat shorter distances. Three other s t a t i o n s , P a t r i c k A i r Force Base, Earthquake Valley and Pasadena, established by JPL, received low-powered 108 Mc si g n a l phase-modulated w i t h telemetered data, and were capable of receiving both telemetry and tr a c k i n g data. 9. Release and Pu b l i c a t i o n of Data. The Panel since i t s i n c e p t i o n gave considerable thought to the dissemination of s a t e l l i t e data. At an e a r l y stage i t was agreed t h a t a l l s a t e l l i t e data should be released as soon as i t became a v a i l a b l e ; t h e r e a f t e r , 562

EARTH SATELLITE w i t h an i n i t i a l release i n January 1956 on the f i r s t proposed U.S. s a t e l l i t e launching, s a t e l l i t e i n formation has from time to time been generally released to the press and s c i e n t i f i c p u b l i c by the USNC-IGY. A series of reports on s a t e l l i t e observations and i n t e r n a l instrumentation were made ava i l a b l e to a l l IGY p a r t i c i p a t i n g countries as w e l l as to the IGY World Data Centers. These reports incorporated the o p t i c a l obser- vations prepared by the Smithsonian Astrophysical Observatory as w e l l as preliminary reports on experiments m s a t e l l i t e s 1958 alpha and 1958 gamma. S a t e l l i t e reports were also widely d i s t r i b u t e d by the Smithsonian Astrophysical Observatory as w e l l as by Harvard College Observatory through announcement cards on o r b i t p r e d i c t i o n s . Procedures which were l a i d down by CSAGI i n conjunction w i t h the countries con- cerned f o r c o l l e c t i o n and exchange of s a t e l l i t e data are contained i n Volume V I I , Part I I , Section X I , of the Annals of the IGY. Considerable exchange of o r b i t a l data has taken place and some preliminary information on r e s u l t s of s a t e l l i t e experiments has been made av a i l a b l e by means of reports and p u b l i c a t i o n s i n s c i e n t i f i c j o u r n a l s . 10. Future Programs of Space Science. A report which recommended that the United States should undertake a continuous program i n space science was prepared by members of the Panel and subsequently endorsed by the USNC Executive Committee i n January 1958. This report was subsequently published i n the A p r i l 11, 1958 issue of Science. a. The proposed s c i e n t i f i c program was formulated on the assumption t h a t . ( i ) Technology i n support of f u r t h e r space science e x p l o r a t i o n w i l l probably develop gradually. Therefore, the payloads and distances traveled w i l l be r e l a t i v e l y small at f i r s t , and the s c i e n t i f i c experiments and observations w i l l be correspondingly modest i n the e a r l y stages. ( i i ) The s c i e n t i f i c program should be designed to give information at each stage which w i l l help i n the planning of l a t e r f l i g h t s . ( i l l ) Manned space f l i g h t w i l l occur i n the course, of the program, but before t h i s can take place, c e r t a i n c r u c i a l experiments, aimed s p e c i f i c a l l y at the design of a manned v e h i c l e , must be performed. ( i v ) I n the e x p l o r a t i o n of outer space, s c i e n t i s t s must not lose sight of the tremendous i m p l i c a t i o n s involved f o r l i f e on earth. b. This report recommended the f o l l o w i n g s e l e c t i o n of s a t e l l i t e and space probe experiments framed m order of projected v e h i c l e c a p a b i l i t y : ( i ) Light-weiRht S a t e l l i t e Experiments. (a: (b (c (d (e ( f (8 (h (1 (J (K ( 1 (n.: (n Creation of v i s i b l e objects T o t a l atmospheric thermal and v i s i b l e r a d i a t i o n measurements Mapping of the cloud cover Mapping of the night airglow and aurora Time f l u c t u a t i o n s of solar u l t r a v i o l e t and X r a d i a t i o n D i s t r i b u t i o n of hydrogen i n space Survey of c e l e s t i a l sources i n the f a r u l t r a v i o l e t E x t r a g a l a c t i c l i g h t Cosmic-ray observations Primary auroral p a r t i c l e s Micrometeorites Magnetic f i e l d Ionospheric observations B i o l o g i c a l experiments 563

EARTH SATELLITE ( i i ) Advanced S a t e l l i t e Experiments. (a) Selective and d i r e c t i o n a l thermal r a d i a t i o n measurements (b) Selective and d i r e c t i o n a l u l t r a v i o l e t and X-ray measurements (c) U l t r a v i o l e t photographs of the sun (d) Planetary spectrograms (e) An experimental t e s t of the general theory of r e l a t i v i t y ( f ) Solar (cosmic) radio noise i n the high frequency and low frequency spectrum (g) C o l l e c t i o n of micrometeoritic samples (h) Manned s a t e l l i t e s ( i l l ) Lunar I n v e s t i g a t i o n s . (a) Measurements of lunar mass and g r a v i t y (b) Direct measurement of the lunar magnetic f i e l d (c) Mass spectrographic measurements of the lunar atmosphere (d) Pressure and density of the lunar atmosphere (e) Seismic and microseismic observations of the lunar crust ( f ) Observations at the point of impact ( i v ) Planetary and I n t e r p l a n e t a r y I n v e s t i g a t i o n s . (a) Determination of the Astronomical Unit (b) Determination of the planetary masses (c) Entry i n t o planetary atmosphere (d) Landing on the planets (v) Manned Space F l i g h t . ( D e t a i l s of these proposed experiments are set out i n the a r t i c l e e n t i t l e d "Re- search i n Outer Space," Science, A p r i l 11, 1958, Volume 127, No. 3302.) 11. Space Science Board. I n June 1958, the National Academy of Sciences established the Space Science Board to consider and survey broadly the s c i e n t i f i c problems, op- p o r t u n i t i e s and im p l i c a t i o n s of man's advance i n t o space, and i n the Academy t r a d i t i o n , to o f f e r advice and assistance to the Government and the n a t i o n a l s c i e n t i f i c community i n t h i s r a p i d l y developing program. More s p e c i f i c a l l y , the Board has developed a series of s p e c i f i c reconmendations f o r experiments important i n the U.S. program f o r the immediate f u t u r e , and gave much serious thought and a t t e n t i o n to the longer range progreim objectives. Membership of the Board as of June 1958 included: L.V. Berkner (Chairman), H.S. Brown, Leo Goldberg, H.K. H a r t l i n e , D.F. Hornig, W.A. Noyes, Hugh Odishaw (Exec. D i r e c t o r ) , R.W. Porter, B.B. Rossi, A.H. Shapley, J.A. Simpson, S.S. Stevens, H.C. Urey, J.A. Van A l l e n , O.G. V i l l a r d , Harry Wexler, G.P. Woollard. 12. COSFAR. At I t s General Assembly i n October 1958, the I n t e r n a t i o n a l Council of S c i e n t i f i c Unions established an i n t e r n a t i o n a l committee on space research (COSPAR) which convened i t s f i r s t meeting i n London i n November 1958, w i t h representatives from s c i e n t i f i c i n s t i t u t i o n s of the countries engaged i n s a t e l l i t e or rocket research, as w e l l as from i n t e r e s t e d s c i e n t i f i c unions. The main purpose of t h i s Committee i s to f u r t h e r on an i n t e r n a t i o n a l scale the progress of a l l kinds of s c i e n t i f i c i n v e s t i - gations that are c a r r i e d out by means of rockets or rocket-propelled v e h i c l e s . I t w i l l deal only w i t h fundamental research and not technological development. The Space Science Board provides o f f i c i a l Academy representation to the COSPAR and serves as the l i n k f o r coordination of COSPAR plans and recommendations w i t h the continuing space research program of the United States. 564

EARTH SATELLITE C. Project Objectives and Results 1. Summary of Proje c t s . The tables below of space probe and s a t e l l i t e launchings i d e n t i f y payloads experiments w i t h c e r t a i n numbered p r o j e c t s contained i n the f o l l o w - ing section. These p r o j e c t s covered design of on-board instrumentation and analysis of the r e s u l t s . Other s a t e l l i t e p r o j e c t s necessary f o r the successful organization of the s a t e l l i t e program, such as those concerning p r e c i s i o n o p t i c a l and radio track- i n g , and f o r procurement of launching vehicles were also established. 2. Order of Project Description. The pr o j e c t s t h a t are described i n the f o l l o w i n g pages are i n numerical order to correspond w i t h the o r i g i n a l formulation of the pro- gram. For convenience, the p r o j e c t s are grouped below to r e f l e c t s i m i l a r i t y of purpose. Visual and O p t i c a l Tracking 30.3, 30.5, 30.6, 30.8 to 30.10, 30.12, 30.20, 30.21 31.1 32.1 to 32.12, 32.40 to 32.44, 32.46 to 32.48 Equipment and Engineering Services 32.30, 32.31 Radio Tracking 33.1, 33.2 Telemetry 34.1, 34.2 Procurement of Launching Vehicles S c i e n t i f i c Experiments 3. Cancelled Projects. Former p r o j e c t s bearing the f o l l o w i n g numbers were eliminated from the program or combined w i t h other p r o j e c t s : 30.1, 30.2, 30.4, 30.7, 30.11, 30.13 to 30.19, 32.13 to 32.29 and 32.45. Table I - IGY Space Probes Name Thor Able I Experiments Micrometeorite (32.4) Magnet, f i e l d Payload temp. Lunar surface Launching Date Aug. 17, 1958 Comments Failed Pioneer I (Thor Able 2) Same as above w i t h ion chamber (32.1) Oct. 11, 1958 Attained a l t i t u d e of 115,000 km. re-entered earth's atmosphere Pioneer I I (Thor Able 3) Ion chamber Magnetometer Te l e v i s i o n camera Micrometeorite Temperature Cosmic rays Oct. 23, 1958 Attained a l t i t u d e of 15,300 km Pioneer I I I (Juno I I ) Cosmic rays (32.1) Dec. 6, 1958 Attained a l t i t u d e of 102,000 km Pioneer IV (Juno I I ) Same as Pioneer I I I Cosmic rays (32.1) March 3, 1959 He l i o c e n t r i c o r b i t ( p e r i h e l i o n 148,000,000 km aphelion 170,000,000 km) 565

EARTH SATELLITE Table I I - IGY S a t e l l i t e s Name Explorer I 1958 Alpha Experiments Cosmic rays (32.1) L i f e t i m e Jan 31, 1958- Met. erosion (32.4) May 23, 1958 Temperatures Orbi t 33° I n i t i a l Perigee 360 km I n i t i a l Apogee** 2500 km Explorer I I Meteoric dust Meteorites Temperatures Cosmic rays Mar 5, 1958 Failed to o r b i t Vanguard I # 1958 Beta Temperature Mar 17, 1958 present 34° 650 km 4000 km Explorer I I I Cosmic rays (32.1) Mar 26, 1958 33° 190 km 2800 km 1958 Gamma Met. erosion (32.4) Jun 1958 Temperatures Vanguard Solar X rays Apr 28, 1958 Failed to o r b i t Test Vehicle 5 Environmental Vanguard - Sat. Lyman-alpha May 27, 1958 Failed to o r b i t Launch, Vehicle 1 Environmental Vanguard Solar X rays Jun 26, 1958 Failed to o r b i t SLV-2 Environmental Explorer IV Trapped r a d i a t i o n J u l 26, 1958- 50° 260 km 2200 km 1958 Epsilon (32 1) Oct 6, 1958 Explorer V Trapped r a d i a t i o n Aug 24, 1958 Failed to o r b i t Vanguard SLV-•3 Cloud cover Sept 26, 1958 Failed to o r b i t Explorer V I * 12 - f t . i n f l a t a b l e Oct 22, 1958 Failed to o r b i t sphere Vanguard I I Cloud cover (32.5) Feb 17, 1959- 33° 560 km 3300 km 1959 Alpha I n t . temp. (32.7) Mar 17, 1959 Vanguard 30-in. i n f l . sphere Apr 13, 1959 Failed to o r b i t SLV-5 Magnetometer Vanguard SLV-•6 Earth energy b a l . Jun 22, 1959 Failed to o r b i t Vanguard I I I Magnetometer (32.9) Sept 18, 1959- 33° 520 km 3700 km 1959 Eta Solar X ray (32.8) Dec 11, 1959 Lyman-alpha (32.8) Environmental (32.7) Explorer V I I Micromet. (32.32) Oct 13, 1959- 50.3° 550 km 10,900 km 1959 I o t a Cosmic rays (32.1) present Heavy n u c l e i (32 12) Earth energy b a l . (32.11) Solar X ray (32.8) Lyman-alpha (32.8) Radio signals Ground studies A subsequent successful f l i g h t of another payload was named Explorer VI also, t h i s was a post-IGY experiment. ** Orbit f i g u r e s are approximate. # F i r s t use of solar c e l l s to supply power f o r s a t e l l i t e instruments. 566

EARTH SATELLITE Project 30.3 - I n i t i a l Development of O p t i c a l Tracking System 1. Objectives. This p r o j e c t , undertaken at the Astrophysical Observatory, Smithsonian I n s t i t u t i o n ( h e r e i n a f t e r r e f e r r e d to as SAO), provided f o r the preliminary engineering and s c i e n t i f i c planning to prepare f o r the establishment of a high-precision o p t i c a l t r a c k i n g system f o r a r t i f i c i a l s a t e l l i t e s . 2. Operations. A d m i n i s t r a t i v e , engineering and s c i e n t i f i c problems studied included: a. S t a t i o n operations - equipment, method of observation, s i t e l o c a t i o n , i n s t a l - l a t i o n of equipment, and communications between observing s i t e s and SAO headquarters. The basic equipment at each s t a t i o n was to consist of a super-Schmidt camera and a c r y s t a l clock (see p r o j e c t 30.5). Twelve s t a t i o n s were to be located at appropriate s i t e s around the world (see p r o j e c t 30.6). b. Administrative headquarters of SAO f o r coordinating a c t i v i t i e s , maintaining communications, computing o r b i t s . c. Study of requirements f o r geographical coverage of t r a c k i n g s t a t i o n s and pre- l i m i n a r y negotiations f o r c o l l a b o r a t i o n w i t h s c i e n t i s t s around the world i n the t r a c k i n g program. d. Contracting f o r engineering design of the cameras and supplies, and i n i t i a t i n g procurement of e s s e n t i a l equipment w i t h long lead-time requirements. e. Coordination w i t h other elements of the s a t e l l i t e program, p r i n c i p a l l y Project Vanguard at the Naval Research Laboratory. 3. Personnel. F.L. Whipple was the p r o j e c t d i r e c t o r of t h i s study, J.A. Hynek was the p r i n c i p a l s c i e n t i s t associated w i t h him. 4. Results. This work resulted m the establishment of the t e c h n i c a l s p e c i f i c a t i o n s f o r the equipment and provided the basis f o r the establishment of the o p t i c a l t r a c k i n g program, which i s discussed m more d e t a i l i n the f o l l o w i n g p r o j e c t s . 567

EARTH SATELLITE Project 30.5 - O p t i c a l Tracking System, I n i t i a t i o n 1. Objectives. This p r o j e c t at SAO provided f o r the completion of the engineering design and f o r the purchase and construction of parts and components f o r two prototype cameras, the s e l e c t i o n of s t a t i o n s i t e s , and the completion of instrumental r e q u i r e - ments to enable the s t a t i o n s to operate properly, 2. Operations. The super-Schmidt meteor cameras used by SAO i n e a r l i e r work served as a point of departure f o r the s a t e l l i t e cameras. A set of assumptions was made r e - garding the probable o r b i t s ( i n c l i n a t i o n , apogee and perigee), the size, shape and r e f l e c t i v i t y of s a t e l l i t e v e h i c l e s , and the probable accuracy of preliminary o r b i t p r e d i c t i o n s to allow the p r e c i s i o n cameras to be set at the proper o r i e n t a t i o n to acquire a given s a t e l l i t e . The design that f i n a l l y evolved extended the operational range to include the p o s s i b i l i t y of t r a c k i n g an object the equivalent of a f i f t e e n - inch diameter sphere at a distance of at least 1000 miles, the brightness of such an object would correspond to a s t e l l a r magnitude of from ten to eleven. I t was assumed that predicted s i g h t i n g p o s i t i o n s could be r e l i a b l e to w i t h i n 3°. The camera consisted of an fl.O Schmidt-type system, of 20-inch aperture and w i t h a m i r r o r of 30-inch diameter. F i e l d f l a t t e n e r s of special glass were designed to be supplied by the Schott glassworks, Mainz, Germany. Aspheric back-up plates were pro- vided against which the f i l m s t r i p s (55 mm x 250 mm) would be tensioned so as to l i e i n the f o c a l surface. This system was expected to provide good image q u a l i t y over an area 30° i n diameter, and to enable f i l m to be changed reasonably r a p i d l y , e s p e c i a l l y during t w i l i g h t conditions when i t might be possible to make several exposures during a t r a n s i t . For t r a c k i n g the s a t e l l i t e s , a t r i - a x i a l support was designed so that the f i l m could be oriented m any d i r e c t i o n p a r a l l e l to any given s a t e l l i t e o r b i t . A s i d e r e a l trac k i n g r a t e was provided f o r so that the f i x e d stars could be used as reference p o i n t s . A v a r i a b l e r a t e was also provided f o r so that the s a t e l l i t e r a t e could be matched. Timing was accomplished by a r o t a t i n g shutter that chopped the image as the camera tracked. A c r y s t a l clock w i t h presentation arranged f o r photography was used to pro- vide time information t h a t was included on the frame at the i n s t a n t of shutter occul- t a t l o n . Consideration of the accuracy of star p o s i t i o n s , f i l m d i s t o r t i o n i n processing, and timekeeping e r r o r s of the clocks, i n d i c a t e d that the s a t e l l i t e p o s i t i o n could be determined to w i t h i n two seconds of arc transverse to the o r b i t and f i v e seconds of arc along the o r b i t . 3. Personnel. F.L. Whipple was p r o j e c t d i r e c t o r ; J.A. Hynek was the p r i n c i p a l SAO s c i e n t i s t associated w i t h him f o r t h i s work. The o p t i c a l design was c a r r i e d out by Dr. James G. Baker. Mr. Joseph Nunn designed the mechanical system. The c r y s t a l clocks were designed and constructed by Ernst Norrman. 4. Results. Just as the f i r s t prototype o p t i c a l instrument was completed, the f i r s t s a t e l l i t e of the IGY was launched by the USSR. This r e s u l t e d i n a speed-up of the program and a change i n the a l l o c a t i o n of instruments. I n e f f e c t , the f i r s t two t r a c k i n g cameras ceased to be prototypes and were put i n t o r o u t i n e operation at White Sands, New Mexico and O l i f a n t s f o n t e i n , South A f r i c a as soon as possible, w i t h the r e - maining ten instruments accelerated i n production. The camera performance exceeded expectations: f o r example, i t proved possible to photograph Vanguard I (1958 Beta) at an equivalent magnitude of about 13. 568

EARTH SATELLITE Project 30.6, 30.8 - Establishment and Operation of O p t i c a l Tracking Stations 1. Objectives. These p r o j e c t s at SAO provided f o r the establishment of twelve sa- t e l l i t e t r a c k i n g s t a t i o n s throughout the world. The reduced data obtained from the o p t i c a l s t a t i o n s would permit the c a l c u l a t i o n of d e f i n i t i v e o r b i t s f o r use i n corre- l a t i n g w i t h on-board and ground-based experiments and provide the valuable data f o r s c i e n t i f i c research. I n a d d i t i o n , quick-look, or field-reduced data would be valuable f o r c e r t a i n geophysical research by s a t e l l i t e s , as w e l l as serving as the basis f o r continued p r e d i c t i o n s f o r the tra c k i n g network i t s e l f . 2. Operations. S t a f f members of SAO undertook a study e a r l y i n the planning period to develop a l i s t of possible locations f o r the t r a c k i n g s t a t i o n s . Dr. Hynek and other SAO s c i e n t i s t s v i s i t e d many of the countries having s u i t a b l e l ocations and d i s - cussed w i t h l o c a l s c i e n t i s t s and government representatives methods of c o l l a b o r a t i n g i n e s t a b l i s h i n g and operating the s t a t i o n s as w e l l as f u r n i s h i n g power and l i v i n g f a c i l i t i e s at the s i t e . The locations were chosen to have as broad a geographical d i s t r i b u t i o n as possible, mostly m two b e l t s , of l a t i t u d e s approximately equal to the expected northern and southern l i m i t s of the o r b i t excursions, w i t h consideration of l o c a l meteorological conditions a f f e c t i n g seeing. The s t a t i o n locations were: S t a t i o n Latitude Longitude Obs. Began Organ Pass, N. Mex., USA 32°25 26V 7 253°26 5IV 8 Nov. 1957 O l i f a n t s f o n t e i n , U. So. A f r i c a -25 57 34.7 28 14 51.1 Feb. 1958 Woomera, A u s t r a l i a -31 06 06.7 136 46 54.9 Feb. 1958 Cadiz, Spain 36 27 49.8 353 47 41.5 June 1958 Mitaka, Japan 35 40 23.6 139 32 06.9 A p r i l 1958 Naini T a l , I n d i a 29 21 32.5 79 27 25.3 June 1958 Arequipa, Peru -16 27 52.8 288 30 20.6 June 1958 Shiraz, I r a n 29 38 15.6 52 31 08.3 July 1958 Curacao, Netherlands W.I. 12 05 27.9 291 09 41.3 May 1958 J u p i t e r , Fla., USA 27 01 16.6 279 53 11.8 May 1958 V i l l a Dolores, Argentina -31 56 36.5 294 53 23.5 June 1958 Haleakala,, Maui, Hawaii 20 42 36.1 203 44 31.7 June 1958 Measured i n degrees east of the Greenwich Meridian U.S. personnel r e c r u i t e d by SAO were t r a i n e d at the New Mexico s t a t i o n . I n addi- t i o n , s c i e n t i f i c and t e c h n i c a l personnel of the various countries where s t a t i o n s were located, p a r t i c i p a t e d i n the observing program. The- cooperation of the IGY committees of the various countries helped reduce to a minimum the customs delays i n shipping the equipment and supplies and helped i n making the numerous l o c a l arrangements. 3. Personnel. F.L. Whipple was the p r o j e c t d i r e c t o r f o r t h i s work; p r i n c i p a l SAO s c i e n t i s t s associated were J.A. Hynek, K.G. Henize, and G.F. S c h i l l i n g . 4. Results. The p r e c i s i o n s a t e l l i t e t r a c k i n g cameras performed as expected and pro- duced a c o l l e c t i o n of a large number of observations. For example, during the month of A p r i l , 1959, 126 observations were made at Woomera, A u s t r a l i a , at t h i s s t a t i o n , 414 observations were made from the s t a r t of observations t o May 1959. The average monthly number of observations, as of May 1959, ranged from 52 at Woomera to 16 at Shiraz, I r a n and J u p i t e r , F l o r i d a . V a r i a t i o n s m the geometrical p o s i t i o n s of the s a t e l l i t e o r b i t s and i n l o c a l meteorological conditions undoubtedly accounted f o r 569

EARTH SATELLITE the wide range. The i n d i v i d u a l observations were c o l l e c t e d at SAO and formed the basis f o r the computation of o r b i t a l elements, from which s t a t i o n p r e d i c t i o n s could r e a d i l y be derived, and f o r p r e c i s i o n o r b i t s used i n basic research such as the d e r i - v a t i o n of atmospheric properties and other geophysical r e s u l t s (see p r o j e c t 30.10 f o r f u r t h e r d e t a i l s ) . 570

EARTH SATELLITE Project 30.9 - Visual Observing Program - Moonwatch 1. Objectives. This p r o j e c t , organized by SAO, was designed to provide s a t e l l i t e s i g h t i n g i n formation i n the e a r l y phase of a s a t e l l i t e ' s l i f e t i m e i n order to obtain a preliminary ephemeris f o r the use of the p r e c i s i o n o p t i c a l network. I n a d d i t i o n , the v i s u a l observers could hope to re-acquire " l o s t " s a t e l l i t e s and to secure i n f o r - mation m the l a t e phases of a s a t e l l i t e o r b i t , as the s a t e l l i t e approached nearer to earth and i t s o r b i t became e r r a t i c . F i n a l l y , the v i s u a l program complemented the radio t r a c k i n g networks (see p r o j e c t 33.1) f o r many s a t e l l i t e s and served as the major preliminary t r a c k i n g service f o r s a t e l l i t e s whose telemetry f a i l e d and f o r parts of the rocket which stayed m o r b i t . 2. Operations. The v i s u a l program, developed by SAO a f t e r a period of c o n s u l t a t i o n and t r i a l s w i t h a i r c r a f t and other simulated s a t e l l i t e passes, comprised teams of volunteers from u n i v e r s i t i e s , high schools, government agencies, commercial organiza- t i o n s , p r i v a t e science clubs, and groups of i n t e r e s t e d laymen, under the d i r e c t i o n of a leader w i t h some astronomical or s c i e n t i f i c experience. Small telescopes were spe- c i a l l y designed and were used, f i x e d m an array so as to give complete coverage along a large p o r t i o n of a c e l e s t i a l arc. The o r i e n t a t i o n could be adjusted f o r any p a r t i - cular s a t e l l i t e . Timing was usually provided by recording on a tape recorder signals from WWV, WWVH, or other s i m i l a r time-frequency s t a t i o n s . As the s a t e l l i t e crossed the l i n e at which the telescopes were pointed, i t would come i n the f i e l d of view of one of the observers who would signal the f i r s t s i g h t i n g and signal the moment when the s a t e l l i t e crossed a l i n e of reference (e.g., a meridian). The time of crossing and the p o s i t i o n w i t h respect to the f i x e d stars i n the f i e l d of view were noted and forwarded to SAO. For some teams that proved to be very successful, some special timing and o p t i c a l equipment was supplied, but f o r the most p a r t , the i n d i v i d u a l teams organized and equipped themselves, Moonwatch pub l i c a t i o n s were prepared at SAO to provide the teams w i t h t e c h n i c a l information and new items of general i n t e r e s t . As of June 30, 1959 t h i r t y - f i v e Spe- c i a l B u l l e t i n s and f i f t e e n Observing Status L i s t s had been issued, along w i t h a large number of Newsletters, issued approximately every week. 3. Personnel. F.L. Whipple was p r o j e c t d i r e c t o r of t h i s work, J.A. Hynek was the senior s c i e n t i s t i n charge of the v i s u a l program. Leon Campbell, J r . , was c h i e f of the Moonwatch D i v i s i o n , Armand Spitz helped w i t h the e a r l y stages of the organization of the program. A National Advisory Committee assisted w i t h the planning of observing techniques, instrumentation, and recruitment of teams. 4. Results. As of June, 1959, approximately 8000 volunteers had p a r t i c i p a t e d i n Moonwatch, comprising a t o t a l of some 250 teams, of which 193 supplied observations to SAO. Achievement c e r t i f i c a t e s were recommended f o r 50 teams and awards to 205 i n d i v i d u a l p a r t i c i p a n t s f o r meritorious c o n t r i b u t i o n s to the program. The teams were located i n North and South America, A f r i c a , Europe, Asia, the Middle East, as w e l l as i n the A r c t i c Basin on S t a t i o n C and Ice Island T-3. Moonwatch teams were a l e r t e d for each U.S. s a t e l l i t e launch, p a r t i c u l a r l y f o r ex- periments such as the i n f l a t a b l e sphere f o r which no radio tra c k i n g was possible of some of the elements placed i n t o o r b i t . From the beginning of the Moonwatch operation i n October, 1957, through June, 1959, nearly 10,000 observations were sent to SAO. The Moonwatch program continued a f t e r the IGY period and teams are s t i l l c o n t r i b u t i n g importantly to the s a t e l l i t e t r a c k i n g program. As an example of the f u n c t i o n of Moonwatch during special s i t u a t i o n s , a search plan was i n i t i a t e d during 1959 f o r S a t e l l i t e 1958 Beta 1 (the non-broadcasting element 571

EARTH SATELLITE of Vanguard I ) which had been " l o s t . " Using an observation made May 6 by the two Albuquerque, N.M. teams a t a j o i n t s e s s i o n , Arthur S. Leonard, leader of a Sacramento, C a l i f o r n i a team, modified the o r b i t a l elements of 1958 Beta 2 (Vanguard I ) ; u s i n g t h i s p r e d i c t i o n , h i s team observed Beta 1 on May 10, allowing f o r f u r t h e r r e v i s i o n s to the o r b i t a l p r e d i c t i o n s . S e v e r a l C a l i f o r n i a s t a t i o n s as w e l l as the Albuquerque s t a t i o n sighted Beta 1 the next evening. These Moonwatch s i g h t i n g s allowed o r b i t a l p r e d i c - t i o n s to be improved so that p r e c i s i o n o p t i c a l observations began on May 12. During the period May 23-June 9, only three observations were made of 1958 E p s i l o n ( E x p l o r e r IV) and Moonwatch concentrated on t h i s o b j e c t . F i f t e e n teams were given a s p e c i a l assignment and a number of observations were made, leading to the a c t u a l r e - l o c a t i o n of 1958 E p s i l o n . A number of s p e c i a l r e p o r t s on Moonwatch observations were i s s u e d by SAO. ?40 360 0 300 200 100 Satellite 1958 J 1 Orbital aLCeleration o < 10 Satellite 1958 0 2 dp Solar flux at 10 7 cm wavelength F i g u r e 1. Sec u l a r A c c e l e r a t i o n s of S a t e l l i t e s 1958 D e l t a and 1958 Beta compared with 10.7-cm s o l a r f l u x . Two l a r g e geomagnetic d i s t u r b a n c e s a r e i n d i c a t e d by the arrows I n the upper s e c t i o n a t J u l y 8-9, September 4. A c c e l e r a t i o n s were computed a t i n t e r v a l s of 25 r e v o l u t i o n s . 572

EARTH SATELLITE Project 30.10 - O p t i c a l Tracking Data Reduction, Analysis and Headquarters Operation 1. Obiectives. This p r o j e c t at SAO provided f o r a headquarters and s c i e n t i f i c center to u t i l i z e the v i s u a l and o p t i c a l data secured through p r o j e c t s 30.8 and 30.9, as w e l l as M i n i t r a c k and radar observations a v a i l a b l e from other agencies. A computations center was established to as s i s t i n the numerical reduction and analysis of s a t e l l i t e data, a photoreduction d i v i s i o n was s t a f f e d and equipped to provide precise measure- ments of s a t e l l i t e p o s i t i o n s and times, using Baker-Nunn camera f i l m s received from the f i e l d s t a t i o n s , and a communications center was established to e f f e c t coordination between SAO and i t s f i e l d s t a t i o n s , as w e l l as w i t h the Vanguard system and other trac k i n g agencies. These components coordinated c l o s e l y w i t h the f i e l d u n i t s and the research and analysis s t a f f to c o l l e c t and analyze data leading to new information about such geophysical parameters as a i r density and the geopotential f i e l d . 2. Operations. Several teletype machines were i n s t a l l e d , l i nked w i t h AT and T, M i l i - t a r y , and Western Union networks. Computing programs were prepared f o r obtaining or- b i t s and o r b i t a l elements from the t r a c k i n g data. I n the beginning of the program, SAO had access to the IBM 704 computer at Massachusetts I n s t i t u t e of Technology, and l a t e r secured i t s own computer f a c i l i t i e s . Routines were worked out to permit rapid processing of data and techniques developed for u t i l i z i n g the observations from the Moonwatch program, where conventional i n t e r p o l a t i o n methods proved inadequate owing to the closeness of the observations. The computing programs as f i n a l l y developed took i n t o account the changes m the o r b i t s induced by several e f f e c t s and allowed refinement of p r e d i c t i o n s (e.g., i n s e r t i o n of new information on s a t e l l i t e e l e v a t i o n s ) . The o r b i t a l elements were obtainable from the computations, these elements describe the o r b i t by g i v i n g c e r t a i n geometrical and timing information w i t h respect t o a con- venient reference frame. Baker-Nunn photographs were analyzed beginning i n June 1958, by use of the Van Briesbroeck t h e o d o l i t e and the Mann two-screw measuring engine. The two devices proved about comparable i n e f f i c i e n c y o f operation, an experienced operator could measure four to S I X s a t e l l i t e images per day. The Mann engine, however, proved to have greater p r e c i s i o n , the probable e r r o r ranging from one to two seconds of arc. Random f i l m d i s t o r t i o n was shown to introduce e r r o r s no greater than one or two seconds of arc as long as reference stars were chosen w i t h i n a two-degree radius of the s a t e l l i t e image. 3. Personnel. F.L. Whipple was the pr o j e c t d i r e c t o r , J. A l l e n Hynek, L u i g i Jacchia, G.F. S c h i l l i n g , T.E. Sterne, George Veis, J.W, Slowey, P.E. Zadunaisky, Y. Kozai, Don Lautman, R.E. McCrosky, and C.A. Whitney were the p r i n c i p a l s c i e n t i s t s associated w i t h the p r o j e c t . 4. Data. S a t e l l i t e o r b i t a l observations and computed o r b i t s were published as Smith- sonian Special Reports and selected information was also published i n the World Data Center A S a t e l l i t e Report Series. O r b i t a l elements were published on Harvard Announce- ment Cards and were given wide d i s t r i b u t i o n not only to tr a c k i n g i n s t a l l a t i o n s but to in t e r e s t e d s c i e n t i s t s and the p u b l i c . 5. Results. This work produced three q u i t e d i f f e r e n t kinds of r e s u l t s : o r b i t a l pre- d i c t i o n s f o r a c q u i s i t i o n purposes, o r b i t s of s u f f i c i e n t p r e c i s i o n f o r use w i t h t e l e - metered data, d e t a i l s of o r b i t a l dynamics that could be used to i n f e r departures from the c e n t r a l g r a v i t a t i o n a l f i e l d as w e l l as atmospheric and other perturbations. a. O r b i t Predictions. The success of the Moonwatch programs and the pr e c i s i o n observations o f the o p t i c a l network are a d i r e c t r e s u l t of the computing program f o r preparing t r a c k i n g p r e d i c t i o n s . Information was also released to the public communi- cations media f o r newspaper and r a d i o / t e l e v i s i o n release, as there was wide public i n t e r e s t i n s i g h t i n g the various s a t e l l i t e s and components i n o r b i t . 573

EARTH SATELLITE b. P r e c i s e O r b i t s . Measurements o f the f i l m s f r o m the p r e c i s i o n o p t i c a l network p e r m i t t e d the d e r i v a t i o n o f o r b i t s t h a t were l e s s p r e c i s e t h a n t h e o b s e r v a t i o n a l d a t a and not c o m p l e t e l y r e c o n c i l a b l e w i t h r e s u l t s o f o t h e r o b s e r v i n g and o r b i t a l programs ( e . g . , M i n i t r a c k ) , the d i f f i c u l t i e s i n v o l v e d stemmed f r o m p e r t u r b a t i o n s t h a t were n o t w e l l u n d e r s t o o d , such as t h o s e r e s u l t i n g f r o m t h e i m p e r f e c t l y known g r a v i t a t i o n a l f i e l d , atmospheric d r a g , e l e c t r i c and magnetic e f f e c t s , and the s o l a r r a d i a t i o n p r e s - s u r e . Atmospheric drag i t s e l f i s a complex s u b j e c t , m w h i c h many f a c t o r s p l a y a r o l e (see 'c' b e l o w ) . D e f i n i t i v e o r b i t s were produced f o r v a r i o u s s a t e l l i t e s f o r use i n c o n j u n c t i o n w i t h on-board e x p e r i m e n t s so t h a t t h e e x p e r i m e n t e r c o u l d r e l a t e h i s d a t a t o a c o o r d i n a t e system ( l a t i t u d e , l o n g i t u d e , a l t i t u d e , t i m e ) w i t h r e s p e c t t o the e a r t h . F u r t h e r r e f i n e m e n t s were c o n t i n u o u s l y a p p l i e d i n i m p r o v i n g t h e p r e c i s i o n o f o r b i t s . c. O r b i t s as S c i e n t i f i c Data. The f i r s t s a t e l l i t e o r b i t s were o f s u f f i c i e n t l y low a l t i t u d e t h a t the e f f e c t o f atmospheric drag c o u l d be observed i n a r a t h e r s h o r t t i m e . I t p r o v e d p o s s i b l e t o e s t i m a t e t h e aerodynamic c h a r a c t e r i s t i c s o f t h e o b j e c t s i n o r b i t and, u s i n g i n f o r m a t i o n on the decay o f the o r b i t s , t o e s t i m a t e atmospheric d e n s i t i e s a t o r b i t a l a l t i t u d e s near p e r i g e e , a r e g i o n o f the atmosphere where d i r e c t measurements had n o t been made. Improved models o f atmospheric s t r u c t u r e above the l e v e l s a t t a i n e d by sounding r o c k e t s were proposed, w i t h the g e n e r a l c o n c l u s i o n t h a t d e n s i t i e s were much h i g h e r t h a n had been expected by e x t r a p o l a t i n g f r o m r o c k e t meas- urements. Not many o f the s a t e l l i t e s and s a t e l l i t e components i n o r b i t , however, were o f simple aerodynamic shape and the m o t i o n i n o r b i t was complex, many o f t h e o b j e c t s tumbled o r developed p r o p e l l o r - l i k e m o t i o n s . O b s e r v a t i o n s and t h e o r y combined t o p r o v i d e more u n d e r s t a n d i n g o f these i n t e r e s t i n g phenomena. The h i g h e r o r b i t s o f some s a t e l l i t e s . Vanguard 1 (1958 Beta) f o r example, made i t p o s s i b l e t o observe a g r e a t number o f r e v o l u t i o n s w i t h the p r e c i s i o n o p t i c a l network and thus o b t a i n d e t a i l e d i n f o r m a t i o n on o r b i t a l v a r i a t i o n s . The a c c e l e r a - t i o n s o f 1958 Beta 2 (see F i g . 1) c o r r e l a t e v e r y w e l l w i t h t he o c c u r r e n c e o f s o l a r f l a r e s and the r a d i o e m i s s i o n f r o m the sun, and a l s o show the 27-day s o l a r c y c l e . T h i s c o r r e l a t i o n , d i s c o v e r e d by J a c c h i a , i s i n t e r p r e t e d as a r i s i n g f r o m the h e a t i n g o f the atmosphere by s o l a r r a d i a t i o n , c a u s i n g the atmosphere t o expand, thus i n c r e a s i n g the d e n s i t y a t h i g h a l t i t u d e s , J a c c h i a a l s o d i s c o v e r e d a b u l g i n g o f the atmosphere, a p p a r e n t l y f r o m r a d i a t i o n h e a t i n g , w h e r e i n t h e 600-km d e n s i t y l e v e l r i s e s t o about 950 km. The bulge f o l l o w s t h e s u b - s o l a r p o i n t by a p p r o x i m a t e l y two h o u r s . The s a t e l l i t e o r b i t i n f o r m a t i o n has a l s o been used t o c a l c u l a t e the c o e f f i - c i e n t s o f the s e v e r a l s p h e r i c a l - h a r m o n i c s expansion o f the e a r t h ' s g r a v i t a t i o n a l f i e l d , p e r m i t t i n g a r e f i n e m e n t o f the second-order c o e f f i c i e n t ( t h e p o l a r f l a t t e n i n g ) , the d e r i v a t i o n o f the t h i r d - o r d e r c o e f f i c i e n t ( g i v i n g r i s e t o the t e r m "pear-shaped e a r t h " ) , and h i g h e r harmonics t o the f i f t h . T h i s b r i e f summary cannot cover i n d e t a i l a l l the r a m i f i c a t i o n s o f the uses o f p r e c i s i o n o r b i t s and w o r k e r s a t many o t h e r i n s t i t u t i o n s b esides the S m i t h s o n i a n have d e r i v e d s c i e n t i f i c i n f o r m a t i o n f r o m o r b i t a l d a t a and p u b l i s h e d t h e i r f i n d i n g s m the l i t e r a t u r e . The b i b l i o g r a p h y c i t e d below i s l i m i t e d t o S m i t h s o n i a n c o n t r i - b u t i o n s . 6. B i b l i o g r a p h y . a. Papers Pr e s e n t e d a t M e e t i n g s . L. Campbell, J r . and A.N. S p i t z - "Report on Moonwatch Program." American A s t r o n o m i c a l S o c i e t y M e e t i n g , Madison, W i s c o n s i n , J u l y 1958. L.E. Cunningham; "The M o t i o n o f a Nearby S a t e l l i t e W i t h H i g h l y I n c l i n e d O r b i t . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , B e r k e l e y , C a l i f o r n i a , August 1956. 574

EARTH SATELLITE K.G. Henize, J.A. Hynek. and F.L. Whipple- "Report on the IGY Ph o t o g r a p h i c Program o f S a t e l l i t e T r a c k i n g . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , Madison, W i s c o n s i n , J u l y 1958. "Report on the P r e c i s i o n O p t i c a l T r a c k i n g Program f o r A r t i f i c i a l E a r t h S a t e l l i t e s . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , G a i n e s v i l l e , F l o r i d a , December 1958. J.A. Hynek and F.L. Whipple " I n s t r u m e n t a t i o n f o r the O b s e r v a t i o n o f the IGY S a t e l l i t e s . " American M e t e o r o l o g i c a l S o c i e t y - American G e o p h y s i c a l Union M e e t i n g , Washington, D.C., May 1957. L. J a c c h i a , F.L. Whipple, C.A. Whitney, T.E. S t e r n e , R.E. McCrosky: " A i r D e n s i t i e s f r o m the M o t i o n o f S a t e l l i t e 1957 Al p h a . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , I n d i a n a p o l i s , I n d . , December 1957. L.G. J a c c h i a "Atmospheric F l u c t u a t i o n s o f S o l a r O r i g i n Revealed by A r t i - f i c i a l S a t e l l i t e s . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , Rochester, N.Y., March 1959. R.E. McCrosky and G.F. S c h i l l i n g . "Luminous I n t e n s i t i e s f r o m IGY S a t e l l i t e s D u r i n g the L a s t F l i g h t Stages." American M e t e o r o l o g i c a l S o c i e t y - American G e o p h y s i c a l Union Meeting, Washington, D.C., May 1957. J.W. Slowey and R.E. B r i g g s , : "An E l e c t r o n i c Computer Method o f O r b i t D e t e r m i n a t i o n f r o m Three O b s e r v a t i o n s o f a Nearby S a t e l l i t e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , I n d i a n a p o l i s , I n d i a n a , December 1957. A. S p i t z : " P r o f e s s i o n a l C o o p e r a t i o n w i t h t he V i s u a l S a t e l l i t e O b s e r v i n g Program." American A s t r o n o m i c a l S o c i e t y M e e t i n g , B e r k e l e y , C a l i f o r n i a , August 1956. A. S p i t z " I n c r e a s i n g the O b s e r v a b i l i t y o f the S a t e l l i t e by S t r u c t u r a l Changes i n t h e Specular S u r f a c e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , Urbana, I l l i n o i s , August 1957. T.E. Sterne- "A Suggested A n a l y t i c a l Treatment o f the O r b i t o f a Close S a t e l l i t e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , B e r k e l e y , C a l i f o r n i a , August 1956. " A n a l y t i c a l O r b i t s o f Close S a t e l l i t e s o f O b l a t e P l a n e t s . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , New York, N.Y., December 1956. "An Atmospheric Model and Some Remarks on the I n f e r e n c e o f D e n s i t y f r o m the O r b i t o f a Close E a r t h S a t e l l i t e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , Cambridge, Massachusetts, May 1957. "Suggestions f o r F i n d i n g Ephemeris o f an Atmospheric E a r t h S a t e l l i t e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , I n d i a n a p o l i s , I n d i a n a , December 1957. "The E f f e c t o f R o t a t i o n o f a P l a n e t a r y Atmosphere upon the O r b i t o f a Close S a t e l l i t e . " American A s t r o n o m i c a l S o c i e t y M e e t i n g , G a i n e s v i l l e , F l o r i d a , December 1958. G. Veis- "Geodetic Connections w i t h A r t i f i c i a l S a t e l l i t e s . " American G e o p h y s i c a l Union M e e t i n g , May 1959. 575

EARTH SATELLITE C.A. Whitney and G.F. S c h i l l i n g "Atmospheric C o n d i t i o n s a t High A l t i t u d e s f r o m S a t e l l i t e O b s e r v a t i o n s . " American M e t e o r o l o g i c a l S o c i e t y M e e t i n g , March 1959. C.A. W h i t n e y " O r b i t a l Dynamics and the I n t e r p r e t a t i o n o f O r b i t a l Data " P r o j e c t RAND Symposium on the Aerodynamics o f the Upper Atmosphere, June 1959. "General Survey o f the F i e l d . " A.R.P.A. Space T r a j e c t o r y Symposium, Orlando, F l o r i d a , December 1959. F. L. Whipple and G.F. S c h i l l i n g - "Upper Atmosphere Data Expected f r o m the IGY S a t e l l i t e T r a c k i n g Program." American M e t e o r o l o g i c a l S o c i e t y - American Ge o p h y s i c a l Union M e e t i n g , Washington, D.C., May 1957. b. P u b l i s h e d Papers. A.V. Baez: " G r a p h i c a l D e r i v a t i o n o f the I n v e r s e Square Law o f G r a v i t a t i o n f r o m an E l l i p t i c a l O r b i t and K e p l e r ' s Law o f Areas." Amer J o u r n . Phys., v o l . 28, 1960, p 254. G. Colombo " I n s t a b i l i t y o f M o t i o n a t the L a g r a n g i a n T r i a n g u l a r P o i n t i n the Earth-Moon System." N a t u r e , v o l . 198, 1962, p. 1063. G. Colombo "The Magnetic Torque A c t i n g on A r t i f i c i a l S a t e l l i t e s . " i n Proceedings o f Conference on Gyrodynamics, lUTAM, C e l e r i n a , 1963. R.J. D a v i s , R.E. McCrosky, F.L. Whipple and C.A. Whitney "A P l a n f o r O p e r a t i n g an A s t r o n o m i c a l Telescope m an E a r t h S a t e l l i t e . " A s t r o n . J o u r n a l , v o l . 64, 1959, p. 50. R.J. D a v i s , R.C. Welles and F.L. Whipple "On D e t e r m i n i n g the O r i e n t a t i o n o f a C y l i n d r i c a l A r t i f i c i a l E a r t h S a t e l l i t e . " A s t r o n a u t i c a A c t a , v o l . 3, 1957, p. 231. R.J. D a v i s , F.L. Whipple and C.A. Whitney "An A s t r o n o m i c a l Telescope i n Space." A s t r o n a u t . S c i . Rev., v o l . 1, 1959, p. 9 e t seq. K.H. Debus, W.G. Johnson, R.V. Hembree and C.A. L u n d q u i s f "A P r e l i m i n a r y Review o f the Upper Atmosphere O b s e r v a t i o n s Made D u r i n g the S a t u r n H i g h Water Experiment." Proc. 1 3 t h I n t . A s t r o n a u t . Congress, S p r i n g e r - V e r l a g , 1964. Y. Hagihara "On the M o t i o n o f S a t e l l i t e s w i t h C r i t i c a l I n c l i n a t i o n . " S m i t h s o n i a n C o n t r . A s t r o p h y s . , v o l . 5, no. 5, 1961. Y. Hagihara- " R o t a t i o n o f an E a r t h S a t e l l i t e i n F l i g h t Along i t s O r b i t . " S m i t h s o n i a n C o n t r . A s t r o p h y s . , v o l . 5, no. 9, 1961. K.G. Henize "The Baker-Nunn S a t e l l i t e - t r a c k i n g Camera." Sky and Telescope, v o l . 16, 1957, p. 108. K.G. Henize " T r a c k i n g A r t i f i c i a l S a t e l l i t e s and Space V e h i c l e s . " Advances i n Space Science, Academic Press, 1960, p. 117. J.A. Hynek, K.G. Henize and F.L. Whipple: "Report on the P r e c i s i o n O p t i c a l T r a c k i n g Program f o r A r t i f i c i a l E a r t h S a t e l l i t e s . " A s t r o n . J o u r n a l , v o l . 64, 1959, p. 52. 576

EARTH SATELLITE I.G. I z s a k - " P e r i o d i c Drag P e r t u r b a t i o n s o f A r t i f i c i a l S a t e l l i t e s . " A s t r o n . J o u r n a l , v o l . 65, 1960, p. 355. I.G. I z s a k : "On S a t e l l i t e O r b i t s w i t h Very Small E c c e n t r i c i t i e s . " A s t r o n . J o u r n a l , v o l . 66, 1961, p. 129. I.G. I z s a k : "A D e t e r m i n a t i o n o f the E l l i p t i c i t y o f the E a r t h ' s Equator f r o m t h e M o t i o n o f Two S a t e l l i t e s . " A s t r o n . J o u r n a l , v o l . 66, 1961, p. 225. I.G. I z s a k . "A D e t e r m i n a t i o n o f the E l l i p t i c i t y o f the E a r t h ' s Equator f r o m the M o t i o n o f Two S a t e l l i t e s . " Space Research I I , N o r t h - H o l l a n d P u b l . Co., Amsterdam, 1961, p 352. I.G. I z s a k and Y. Kozai- " E q u i p o t e n t i a l Surfaces o f the E a r t h as O b t a i n e d f r o m S a t e l l i t e M o t i o n s ( A b s t r a c t ) . " J o u r n . Geophys. Res., v o l . 66, 1961, p. 2538. I.G. I z s a k . "The Odd Harmonic E f f e c t i n the M o t i o n o f the S a t e l l i t e s 1960 B e t a 2 and I960 I o t a 2." Proc. o f the F i r s t I n t e r n a t i o n a l Symposium on the Use o f A r t i f i c i a l S a t e l l i t e s f o r Geodesy, N o r t h - H o l l a n d P u b l . , Amsterdam, 1963, p. 329. I.G. I z s a k . "On the C r i t i c a l I n c l i n a t i o n i n S a t e l l i t e Theory." Proc. o f the F i r s t I n t e r n a t i o n a l Symposium on t h e Use o f A r t i f i c i a l S a t e l l i t e s f o r Geodesy, N o r t h - H o l l a n d P u b l . , Amsterdam, 1963, p. 117. I.G. I z s a k . "A Note on P e r t u r b a t i o n Theory." A s t r o n . J o u r n . , v o l . 68, 1963, pp. 59-61. I.G. I z s a k : " T e s s e r a l Harmonics i n the G e o p o t e n t i a l . " N a t u r e , v o l . 199, 1963, pp. 137-139. I.G. I z s a k . " T e s s e r a l Harmonics o f the G e o p o t e n t i a l and C o r r e c t i o n s t o S t a t i o n C o o r d i n a t e s . " J o u r n . Geophys. Res., v o l , 69, 1964, pp. 2621-2630. L.G. J a c c h i a . "The F i n a l Moments o f S p u t n i k I I . " Sky and Telescope, v o l . 17, 1958, pp. 561-562. L.G. J a c c h i a : "Two Atmospheric E f f e c t s i n the O r b i t a l A c c e l e r a t i o n o f A r t i f i c i a l S a t e l l i t e s . " N a t u r e , v o l . 183, 1959, p. 1662. L.G. J a c c h i a : " C o r p u s c u l a r R a d i a t i o n and the S e c u l a r A c c e l e r a t i o n o f S a t e l l i t e s ( A b s t r a c t ) . " A s t r o n . J o u r n . . v o l . 64, 1959, p. 335. L.G. J a c c h i a - " I n d i v i d u a l C h a r a c t e r i s t i c s o f Meteor F a m i l i e s ( A b s t r a c t ) . " A s t r o n . J o u r n . , v o l . 65, 1960, p. 53. L.G. J a c c h i a " A r t i f i c i a l E a r t h S a t e l l i t e s . " S c i e n t i a , s er. 6, v o l . 54, 1960. L.G. J a c c h i a - "A V a r i a b l e A t m o s p h e r i c - d e n s i t y Model f r o m S a t e l l i t e A c c e l e r a t i o n s . " J o u r n . Geophys. Res., v o l . 65, 1960, pp. 2275-2782. L.G. J a c c h i a and F.L. Whipple " P r e c i s i o n O r b i t s o f 413 P h o t o g r a p h i c Meteors." S m i t h s o n i a n C o n t r . A s t r o p h y s , v o l . 4, no. 4, 1961. L.G. J a c c h i a : " I r r e g u l a r i t i e s i n Atmospheric D e n s i t i e s Deduced f r o m S a t e l l i t e O b s e r v a t i o n s . " Ann. Geophys.. v o l . 17, 1961, pp. 52-55. 577

EARTH SATELLITE L.G. J a c c h i a - "A Working Model f o r the Upper Atmosphere." N a t u r e , v o l . 192, 1961, pp. 1147-1148. L.G. J a c c h i a . " S a t e l l i t e Drag D u r i n g the Events o f November 1960." Space Research I I . H.C. van de H u l s t , C. de Jager and A.F. Moore, ed., N o r t h - H o l l a n d P u b l . Co., Amsterdam, 1961, pp. 747-750. L.G. J a c c h i a : " I n t e r p l a n e t a r y M a t t e r . " Handbook o f A s t r o n o m i c a l E n g i n e e r i n g . H.H. K o e l l e , ed., McGraw-Hill Book Co., New York, 1961, pp. 2.57-2,64. L.G. J a c c h i a : "Comment on Paper by D.G. Parkyn." S a t e l l i t e 1958 D e l t a 2 Data A n a l y s i s . J o u r n . Geophys. Res., v o l . 67, 1962, p. 2989. L.G. J a c c h i a : "The D e t e r m i n a t i o n o f Atmospheric Drag on A r t i f i c i a l S a t e l - l i t e s . " Dynamics o f S a t e l l i t e s . lUTAM Symposium. P a n s , pp. 136-142, S p r i n g e r - V e r l a g , B e r l i n , 1963. L.G. J a c c h i a : " E l e c t r o m a g n e t i c and C o r p u s c u l a r H e a t i n g o f the Upper Atmos- phere." Space Research I I I . N o r t h - H o l l a n d P u b l . , Amsterdam, 1963. L.G. J a c c h i a : " S a t e l l i t e S t u d i e s o f t h e Upper Atmosphere." Tr a n s . Amer. Geophys. Union, v o l . 44, 1963, p. 436. L.G. J a c c h i a and J. Slowey: "Atmospheric H e a t i n g i n the A u r o r a l Zones f r o m the Drag A n a l y s i s o f the I n j u n I I I S a t e l l i t e . " A s t r o n . J o u r n . . v o l . 68, 1963, pp. 538-539. L.G. J a c c h i a : " V a r i a t i o n s i n the E a r t h ' s Upper Atmosphere as Revealed by S a t e l l i t e Drag." Rev. Mod. Phys.. v o l . 35, 1963, pp. 973-991. L.G. J a c c h i a : " I n f l u e n c e o f S o l a r A c t i v i t y on the E a r t h ' s Upper Atmosphere." P l a n e t . Space S c i . . v o l . 12, 1964, pp. 355-378. L.G. J a c c h i a and J. Slowey: "An A n a l y s i s o f t h e Atmospheric Drag o f t h e E x p l o r e r I X S a t e l l i t e f r o m P r e c i s e l y Reduced P h o t o g r a p h i c O b s e r v a t i o n s . " Space Research IV. P. M u l l e r , ed., N o r t h - H o l l a n d P u b l . , Amsterdam, 1964, pp. 257-270. L.G. J a c c h i a and J. Slowey- "Atmospheric H e a t i n g i n the A u r o r a l Zones: A P r e l i m i n a r y A n a l y s i s o f the Drag o f the I n j u n I I I S a t e l l i t e . " J o u r n . Geophys. Res., v o l . 69, 1964, pp. 905-910. Y. K o z a i "On t h e M o t i o n o f a Close E a r t h S a t e l l i t e ( A b s t r a c t ) . " A s t r o n . J o u r n . . v o l . 64, 1959, p. 337. Y. K o z a i : "The M o t i o n o f a Close E a r t h S a t e l l i t e . " A s t r o n . J o u r n . . v o l . 64, 1959, pp. 367-377. Y. K o z a i . " E f f e c t o f P r e c e s s i o n and N u t a t i o n on t h e O r b i t a l Elements o f a Close E a r t h S a t e l l i t e . " A s t r o n . J o u r n . , v o l . 65, 1960, pp. 621-623. Y. K o z a i : "Note on the M o t i o n o f a Close E a r t h S a t e l l i t e w i t h a Small E c c e n t r i c i t y . " A s t r o n . J o u r n . . v o l . 66, 1961, pp. 132-134. Y. K o z a i : "The G r a v i t a t i o n a l F i e l d o f the E a r t h D e r i v e d f r o m M o t i o n s o f Three S a t e l l i t e s . " A s t r o n . J o u r n . . v o l . 66, 1961, pp. 8-10. Y. Kozai- " T e s s e r a l Harmonics o f the G r a v i t a t i o n a l P o t e n t i a l o f t h e E a r t h as D e r i v e d f r o m S a t e l l i t e M o t i o n s . " A s t r o n . J o u r n . , v o l . 66, 1961, pp. 355-358. 578

EARTH SATELLITE Y. K o z a i : " P o t e n t i a l F i e l d o f the E a r t h D e r i v e d f r o m M o t i o n s o f A r t i f i c i a l S a t e l l i t e s . " Proc. Symposium o f Geodesy i n t h e Space Age, S.H. L a u r i l a and W.A. Heiskanen, ed., pp. 174-176, Ohio S t a t e U n i v e r s i t y , I n s t . Geodesy, Photogrammetry, and C a r t o g r a p h y , P u b l . No. 15, 1961. Y. Kozai "Mean Values o f Cosine F u n c t i o n i n an E l l i p t i c M o t i o n . " A s t r o n . J o u r n . , v o l . 67, 1962, p. 311. Y. K o z a i : "Second-order S o l u t i o n o f A r t i f i c i a l S a t e l l i t e Theory W i t h o u t A i r d r a g . " A s t r o n . J o u r n . . v o l . 67, 1962, p. 446. Y. Kozai- " S e c u l a r P e r t u r b a t i o n s o f A s t e r o i d s w i t h H i g h I n c l i n a t i o n and E c c e n t r i c i t y . " A s t r o n . J o u r n . , v o l . 67, 1962, pp. 591-598. Y. Kozai- " N u m e r i c a l R e s u l t s on the G r a v i t a t i o n a l P o t e n t i a l o f t h e E a r t h . " Proc. o f the F i r s t I n t e r n a t i o n a l Symposium on the Use o f A r t i f i c i a l S a t e l - l i t e s f o r Geodesy, N o r t h - H o l l a n d P u b l . , Amsterdam, 1963, p. 305. Y. K o z a i : " P o t e n t i a l o f the E a r t h D e r i v e d f r o m S a t e l l i t e M o t i o n . " Dynamics o f S a t e l l i t e s , M. Roy, ed., S p r i n g e r - V e r l a g , B e r l i n , 1963. K. Lassovszky: "On the Accuracy o f the Measurements Made Upon F i l m s Photo- graphed by Baker-Nunn S a t e l l i t e T r a c k i n g Cameras ( A b s t r a c t ) . " A s t r o n . J o u r n . , v o l . 124, 1961, pp. 940-944. B. L o v e l l , F.L. Whipple and L. Solomon: "Radio E m i s s i o n f r o m F l a r e S t a r s . " N a t u r e , v o l . 198, 1963, pp. 228-230. B. L o v e l l , F.L. Whipple and L.H. Solomon: " O b s e r v a t i o n o f a S o l a r Type Radio B u r s t f r o m a F l a r e S t a r . " N a t u r e , v o l . 201, 1964, pp. 1013-1014. B. L o v e l l , F.L. Whipple and L. Solomon: " R e l a t i v e V e l o c i t y o f L i g h t and Radio Waves i n Space." N a t u r e , v o l . 202, 1964, p. 377. C. A. L u n d q u i s t , R.J. Naumann and A.H. Weber: " D i r e c t i o n a l F l u x D e n s i t i e s and M i r r o r P o i n t D i s t r i b u t i o n s o f Trapped P a r t i c l e s f r o m S a t e l l i t e 1958 E p s i I o n Measurements." J o u r n . Geophys. Res., v o l . 67, 1962, p. 4125. D. M a l a i s e : " P h o t o g r a p h i c O b s e r v a t i o n s o f the T a i l A c t i v i t y o f Comet Burnham 1960 I I . " A s t r o n . J o u r n . . v o l . 68, 1963, pp. 561-565. R.C. Nigam: "S e c u l a r Decrease i n the I n c l i n a t i o n o f A r t i f i c i a l S a t e l l i t e s . " AIAA J o u r n . . June 1963, p. 1455. J.S. R i n e h a r t : " O p t i c a l T r a c k i n g o f E a r t h S a t e l l i t e s . " B u l l . Amer. Phys. S o c , s e r . 2, v o l . 3, 1958, p. 290. G.F. S c h i l l i n g and T.E. S t e r n e : " D e n s i t i e s and Temperatures o f the Upper Atmosphere I n f e r r e d f r o m S a t e l l i t e O b s e r v a t i o n s . " J o u r n . Geophys. Res., v o l . 64, 1959, pp. 1-4. G.F. S c h i l l i n g and C.A. Whitney: " D e r i v a t i o n and A n a l y s i s o f Atmospheric D e n s i t y f r o m O b s e r v a t i o n s o f S a t e l l i t e 1958 E p s i l o n . " P l a n e t a r y and Space S c i . , v o l . 1, 1959, pp. 136-145. T.E. S t e r n e : "A Suggested A n a l y t i c a l Treatment o f the O r b i t o f a Close S a t e l l i t e . " A s t r o n . J o u r n . . v o l . 62, 1957, p. 33. 579

EARTH SATELLITE T.E. Ste r n e " A n a l y t i c a l O r b i t s o f Close S a t e l l i t e s o f O b l a t e P l a n e t s . " A s t r o n . J o u r n . , v o l . 62, 1957, p. 96. T.E. Sterne " C e l e s t i a l Mechanics o f A r t i f i c i a l S a t e l l i t e s . " Sky and Telescope, v o l . 17, 1957, p. 66. T.E. S t e r n e : "The G r a v i t a t i o n a l O r b i t o f a S a t e l l i t e o f an O b l a t e P l a n e t . " A s t r o n . J o u r n . . v o l . 63, 1958, p. 28. T.E. S t e r n e : " D e n s i t y o f t h e Upper Atmosphere." Science, v o l . 128, 1958, p. 420. T.E. S t e r n e : "Formula f o r I n f e r r i n g Atmospheric D e n s i t y f r o m t h e M o t i o n o f an A r t i f i c i a l E a r t h S a t e l l i t e . " Science, v o l . 127, 1958, p. 1245. T.E. S t e r n e : "The E f f e c t o f the R o t a t i o n o f a P l a n e t a r y Atmosphere upon t h e O r b i t o f a Close S a t e l l i t e . " A s t r o n . J o u r n . . v o l . 64, 1959, p. 64. T.E. S t e r n e : Note on R.R. Newton's paper, " M o t i o n o f a S a t e l l i t e Around an Unsymmetrical C e n t r a l Body." J o u r n a l A p p l . Phys., v o l . 30, 1959, p. 270. T.E. S t e r n e : " E f f e c t o f the R o t a t i o n o f a P l a n e t a r y Atmosphere upon t he O r b i t o f a Close S a t e l l i t e . " J o u r n . Amer. Rocket S o c , v o l . 29, 1959, pp. 777-782. G. V e i s : "Geodetic Uses o f A r t i f i c i a l S a t e l l i t e s . " S m i t h s o n i a n C o n t r . A s t r o p h y s . . v o l . 3, 1960, pp. 95-161. G. V e i s and F.L. Whipple: "Experience i n P r e c i s i o n O p t i c a l T r a c k i n g o f S a t e l l i t e s f o r Geodesy." Space Research I I . H.C. van de H u l s t , C. de Jager, and A.F. Moore, ed., N o r t h - H o l l a n d P u b l . Co., Amsterdam, 1961, pp. 17-33. G. V e i s : " O p t i c a l T r a c k i n g o f A r t i f i c i a l S a t e l l i t e s . " Space Science Reviews, v o l . I I , 1963, pp. 250-296. C.Y. Wang: "On the C o r r e l a t i o n Between the F l u c t u a t i o n s o f Heat Flow and G r a v i t a t i o n a l P o t e n t i a l o f the E a r t h ( A b s t r a c t ) . " Trans. Amer. Geophys. Union, v o l . 45, 1964, p. 36. C.Y. Wang: " F i g u r e o f the E a r t h as Obtain e d f r o m S a t e l l i t e Data and i t s G e o p h y s i c a l I m p l i c a t i o n s . " D i s s e r t a t i o n , H a r v a r d U n i v e r s i t y , 1964. F.L. Whipple: "The S c i e n t i f i c Values o f A r t i f i c i a l S a t e l l i t e s . " J o u r n . F r a n k l i n I n s t . . v o l . 262, 1956, pp. 95-109. F.L. Whipple: " O r b i t Accuracy and Ranges f o r Ground-based O p t i c a l T r a c k i n g . " V i s t a s i n A s t r o n a u t i c s , Pergamon Press, 1957, p. 258. F.L. Whipple: " O b s e r v a t i o n s o f S a t e l l i t e I . " S c i . American, v o l . 197, 1957, p. 37. F.L. Whipple: " O p t i c a l T r a c k i n g o f A r t i f i c i a l E a r t h S a t e l l i t e s . " Proc. Amer. P h i l o s . S o c . v o l . 103, 1958, p. 215. F.L. Whipple: " O p t i c a l T r a c k i n g o f A r t i f i c i a l S a t e l l i t e s . " S c ience, v o l . 128, 1958, pp. 124-129. F.L. Whipple, R.J. Davis and J.B. Z i r k e r : "The O r b i t o f a Small E a r t h S a t e l l i t e . " S c i e n t i f i c Uses o f E a r t h S a t e l l i t e s . U n i v e r s i t y o f M i c h i g a n Press, 1956, pp. 1-22. 580

EARTH SATELLITE F.L. Whipple, R.J. Davis and J.B. Z i r k e r : "Time A v a i l a b l e f o r the O p t i c a l O b s e r v a t i o n o f an E a r t h S a t e l l i t e . " I b i d . , pp. 23-28. F.L. Whipple and J.A. Hynek: "The IGY S a t e l l i t e T r a c k i n g Program as a Source o f Geodetic I n f o r m a t i o n . " Ann. Geophys., v o l . 14, 1958, pp. 326-328. F.L. Whipple and J.A. Hynek: "The IGY S a t e l l i t e T r a c k i n g Program as a Source o f Geodetic I n f o r m a t i o n . " B u l l . Geod., no. 49, 1958, pp. 50-52. F.L. Whipple: " S o l i d P a r t i c l e s i n the S o l a r System." J o u r n . Geophys. Res., v o l . 64, 1959, pp. 1653-1654. F.L. Whipple. "Fundamental Problems i n P r e d i c t i n g P o s i t i o n s o f A r t i f i c i a l S a t e l l i t e s . " Proc. Symp. A p p l i e d Math., v o l . 9, 1959, pp. 36-47. F.L. Whipple: " M e t e o r i t i c M a t e r i a l m Space." P h y s i c s and M e d i c i n e o f the Atmosphere and Space." 0.0. Benson, J r . and H. S t r u g h o l d , ed., 1960, pp. 48-59. F.L. Whipple; Sub-commission 22a, Report on M e t e o r i t e s , T r a n s . I n t e r n . A s t r . Union, v o l . 10, 1960, pp. 345-353. F.L. Whipple; "Notes on the Immediate F e a s i b i l i t y o f an O r b i t i n g A s t r o - n o m i c a l Telescope." I X I n t e r n a t i o n a l A s t r o n a u t i c a l Congress, 1958, S p r i n g e r - V e r l a g , pp. 92-95. F.L. Whipple and R.J. D a v i s : "Proposed S t e l l a r and I n t e r s t e l l a r Survey." A s t r o n . J o u r n . . v o l . 65, 1960, pp. 285-290. C.A. Whitney: " D e t e r m i n a t i o n o f Atmospheric D e n s i t i e s f r o m S a t e l l i t e O b s e r v a t i o n s . " Ann. Geophys., v o l . 17, 1961, pp. 237-244. P,E. Zadunaisky, I . I . S h a p i r o and H.M. Jones. " S o l a r R a d i a t i o n P ressure E f f e c t s , Gas Leakage Rates, and A i r D e n s i t i e s I n f e r r e d f r o m t h e O r b i t o f Echo I . " Space Research I I , H.C. van de H u l s t , C. de Jager and A.F. Moore, ed., N o r t h - H o l l a n d P u b l . Co., Amsterdam, 1961, pp. 339-351. S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y S p e c i a l Reports R.M. Adams: "Improvements i n t h e P r e d i c t i o n Program f o r C r o s s i n g s o f Given L a t i t u d e P a r a l l e l s " - - 1 2 ( 3 4 ) . "Use and D i s t r i b u t i o n o f S a t e l l i t e P r e d i c t i o n s " - - l l ( 1 7 ) . R.M. Adams and R.G. A l b e r t "Catalogues o f S a t e l l i t e O b servations"--24,26. R.M. Adams, R.E. B r i g g s and E.K.L. Upton. " P o s i t i o n s o f S a t e l l i t e 1957 Beta 1 D u r i n g the F i r s t 100 R e v o l u t i o n s " - - 1 6 . R.M. Adams, N. McCumber and M. Brinkman; "Processed O b s e r v a t i o n a l Data f o r USSR S a t e l l i t e s 1957 Alpha and 1957 Beta"--SCA 2-10 ( 2 8 7 ) . R.G. A l b e r t "Catalogues o f S a t e l l i t e Observations"--24,26,28,28A,31,32,34, 35,36,37,39. J. Ashbrook, G.F. S c h i l l i n g and T.E. S t e r n e : " G l o s s a r y o f A s t r o n a u t i c a l Terms f o r the D e s c r i p t i o n o f S a t e l l i t e Orbits"--SCA 2-10 ( 2 1 1 ) . 581

EARTH SATELLITE R.E. B r i g g s - "Program o f Spot P r e d i c t i o n s f o r S p e c i f i c O b s e r v i n g S i t e s , APO Ephemeris T h r e e " - - l l ( 2 3 ) . R.E. B r i g g s : "A Table o f the Times o f P e r i g e e Passage f o r S a t e l l i t e 1958 Beta 2 " - - 3 0 ( 9 ) . R.E. B r i g g s , R.M. Adams and E.K.L. Upton: " P o s i t i o n s o f S a t e l l i t e 1957 Beta 1 D u r i n g t h e F i r s t 100 R e v o l u t i o n s " - - 1 6 . R.E. B r i g g s and L.G. J a c c h i a : " O r b i t a l A c c e l e r a t i o n o f S a t e l l i t e 1958 Beta 2 " - - 1 8 ( 9 ) . R.E, B r i g g s and J.W. Slowey: "An I t e r a t i v e Method o f O r b i t D e t e r m i n a t i o n f r o m Three O b s e r v a t i o n s o f a Nearby S a t e l l i t e " - - 2 7 ^ ( 1 ) . M. Brinkman, R.M. Mams and N. McCumber: "Processed O b s e r v a t i o n a l Data f o r USSR S a t e l l i t e s 1957 Alpha and 1957 Beta"--SCA 2-10 ( 2 8 7 ) . E. B u l l i s : " E x p l a n a t i o n o f Codes Used i n C a t a l o g u e " - - 4 1 ( 6 ) . "Moonwatch Catalogue, October, November, and December, 1958"--28(13). J.R. Cherniack and E.M. Gaposchkin: " S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y Program W r i t e u p (SCR0GE)"--121. R. C i t r o n and L.H. Solomon "Baker-Nunn Photography o f the Syncom I I F o u r t h - s t a g e I g n i t i o n " - - 1 5 6 . G. Colombo: "The M o t i o n o f S a t e l l i t e 1958 E p s i l o n Around i t s Center o f Mass"--70. R.J. Davis, S.E. Strom and K.M. Strom "A Method o f A n a l y s i s f o r Lens and M i r r o r Systems"--56. R.H. Giese: " A l t i t u d e D e t e r m i n a t i o n f r o m Specular and D i f f u s e R e f l e c t i o n by C y l i n d r i c a l A r t i f i c i a l S a t e l l i t e s " - - 1 2 7 . G.S, Hawkins and S.K. R o s e n t h a l "The T r a j e c t o r y o f T e k t i t e " - - 1 0 5 . I.G. I z s a k . " S a t e l l i t e O r b i t a l Data, No. E-3"--141. " S a t e l l i t e O r b i t a l Data"--142. "Laplace C o e f f i c i e n t s and T h e i r Newcomb D e r i v a t i v e s " - - 1 2 9 . " S a t e l l i t e O r b i t a l Data"--126. " D i f f e r e n t i a l O r b i t Improvement w i t h the Use o f Rot a t e d Residuals"--72- " S a t e l l i t e O r b i t a l Data"--103. I.G, I z s a k - " S a t e l l i t e O r b i t a l Data"--113. " S a t e l l i t e O r b i t a l Data"--119. " S a t e l l i t e O r b i t a l Data"--117. " S a t e l l i t e O r b i t a l Data"--120. 582

EARTH SATELLITE "A Theory o f S a t e l l i t e M o t i o n About an Obl a t e P l a n e t I . A Second-order S o l u t i o n o f V i n t i ' s Dynamic Problem"--SCA 6 (81) 52. "A D e t e r m i n a t i o n o f the E l l i p t i c i t y o f the E a r t h ' s Equator f r o m t h e M o t i o n o f Two S a t e l l i t e s " - - 5 7 . I.G. I z s a k , J.M. Gerard, R. Efimba and M.P. B a r n e t f " C o n s t r u c t i o n o f Newcomb O p e r a t o r s on a D i g i t a l Computer"--140. L.G. J a c c h i a : "The Atmospheric Drag o f A r t i f i c i a l S a t e l l i t e s D u r i n g t h e October 1960 and November 1960 Events"--62. L.G. J a c c h i a and J. Slowey: "Formulae and Tables f o r t h e Computation L i f e t i m e s o f A r t i f i c i a l S a t e l l i t e s " - - 1 3 5 . "Atmospheric H e a t i n g i n the A u r o r a l Zones: A P r e l i m i n a r y A n a l y s i s o f t h e Atmospheric Drag o f the I n j u n I I I S a t e l l i t e " - - J J 6 . "Temperature V a r i a t i o n s i n t h e Upper Atmosphere D u r i n g G e o m a g n e t i c a l l y Q u i e t I n t e r v a l s " - - 1 5 2 . " A c c u r a t e Drag D e t e r m i n a t i o n s f o r E i g h t A r t i f i c i a l S a t e l l i t e s , Atmospheric D e n s i t i e s and Temperatures"--100. "An A n a l y s i s o f t h e Atmospheric Drag o f the E x p l o r e r I X S a t e l l i t e f r o m P r e c i s e l y Reduced P h o t o g r a p h i c O b s e r v a t i o n s " - - 1 2 5 . W. KtJhnlein: "Geodesies on an E q u i p o t e n t i a l S urface o f R e v o l u t i o n " - - 1 4 4 . Y. Kozai " T e s s e r a l Harmonics o f the P o t e n t i a l o f t h e E a r t h as D e r i v e d f r o m S a t e l l i t e M o t ions"--72. Y. Kozai- " E f f e c t s o f S o l a r R a d i a t i o n Pressure on t h e M o t i o n o f an A r t i f i c i a l S a t e l l i t e " - - S C A 6 (109) 57. Y. K o z a i : "Numerical R e s u l t s f r o m O r b i t s " - - 1 0 1 . K. L a s s o v s z k y "On t h e Accuracy o f Measurements Made upon F i l m s Photographed by Baker-Nunn S a t e l l i t e T r a c k i n g Cameras"--74. C. A. L u n d q u i s t , R.C. Vanderburgh, W.A. Munn, D. T i l l e s , E.L. Fireman and J. D e F e l i c e : "Re-entry and Recovery o f Fragments o f S a t e l l i t e 1960 E p s i l o n 1"--109. J.E. MacDonald: " C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , No. P-6"--104. J.E. MacDonald and K. Haramundanis: " C a t a l o g o f P r e c i s e l y Reduced Obser- v a t i o n s No. P-5"--102. D. V. Mechau- "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-16"--54. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-19"--55. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-20"--57. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-21"--58. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-22"--66. 583

EARTH SATELLITE "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-23"--67. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-24"--68. " L i s t o f C o o r d i n a t e s o f S t a t i o n s Engaged m t h e O b s e r v a t i o n o f A r t i f i c i a l E a r t h S a t e l l i t e s " - - 6 9 . B. M i l l e r : "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-31"--114. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-32"--115. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-33"--116. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-34"--130. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-35"--131. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s , No. C-36"--132. "Catalogue o f S a t e l l i t e O b s e r v a t i o n s " - - 1 5 3 . "Catalogue o f S a t e l l i t e O b s ervations"--155. B. M i l l e r and Y. K o z a i : " O r b i t a l Elements f o r the P e r i o d September 1959 t h r o u g h A p r i l , 1960"--51. M. N i c o l e t : " D e n s i t y o f the Heterosphere R e l a t e d t o Temperature"--25. N.C. Nigam: "On t h e S e c u l a r Decrease i n the I n c l i n a t i o n o f A r t i f i c i a l S a t e l l i t e s " - - 1 1 2 . "The O r b i t s and the A c c e l e r a t i o n s o f S a t e l l i t e s 1959 1 and 1959 2"--53. "The Revised O r b i t o f S a t e l l i t e 1958 Zeta"--64. L.H. Solomon- " T r a c k i n g o f Centaur (AC-2)"--156. S t a f f o f the S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y : " I n t r o d u c t i o n t o a C a t a l o g o f P o s i t i o n s and Proper M o t i o n s o f 258 997 S t a r s f o r t h e Epoch and Equinox o f 1950.0"--151. P. S t e r n : " C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , P-9"--137. P. S t e r n : " C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , P-10"--138. "C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , No. P - l l " - - 1 4 7 . " C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , No. P-12"--148. "C a t a l o g o f P r e c i s e l y Reduced Obs e r v a t i o n s " - - 1 1 8 . " C a t a l o g o f P r e c i s e l y Reduced O b s e r v a t i o n s , No. P-7"--106. "Ca t a l o g o f S a t e l l i t e O b s e r v a t i o n s " - - 1 5 4 . R.C. Vanderburgh: "On t h e V i s u a l T r a c k i n g o f Two B r i g h t S a t e l l i t e s f r o m C-130-type A i r c r a f t " - - 1 4 6 . 584

EARTH SATELLITE G. V e i s : "The D e t e r m i n a t i o n o f A b s o l u t e D i r e c t i o n s m Space w i t h A r t i f i c i a l S a t e l l i t e s " - - 1 3 3 . " P r e c i s e Aspects o f T e r r e s t r i a l and C e l e s t i a l Reference Frames"--123. "The P o s i t i o n s o f t h e Baker-Nunn Camera S t a t i o n s " - - 5 9 . C.Y. Wang; "Inhomogeneous D i s t r i b u t i o n o f the R a d i o a c t i v e Heat Sources"--143. "On the D i s t r i b u t i o n o f Surface Heat Flows and the Second Order V a r i a t i o n s i n t h e E x t e r n a l G r a v i t a t i o n a l F i e l d " - - 1 3 4 . S,P. Wyatt; " E f f e c t o f t h e D i u r n a l Atmospheric Bulge on S a t e l l i t e A c c e l e r a - t i o n s " --63. "The E f f e c t o f R a d i a t i o n P ressure on the S e c u l a r A c c e l e r a t i o n o f S a t e l l i t e s " --60. P.E, Zadunaisky and B. M i l l e r "Elements o f the O r b i t o f the S a t e l l i t e 1959 E t a (Vanguard I I I ) D u r i n g the F i r s t Year A f t e r Launching"--TjL. P.E. Zadunaisky, I . I . S h a p i r o and H.M. Jones: " E x p e r i m e n t a l and T h e o r e t i c a l R e s u l t s on t h e O r b i t o f Echo I " - - 6 1 . 585

EARTH SATELLITE P r o j e c t 30.12 - A d m i n i s t r a t i v e Costs o f O p t i c a l T r a c k i n g Program 1. O b j e c t i v e s . T h i s p r o j e c t a t t h e SAO covered the d i r e c t a d m i n i s t r a t i v e s t a f f and f a c i l i t i e s r e q u i r e d f o r a d m i n i s t r a t i o n and management o f P r o j e c t s 30.6, 30.8 and 30.9, i n c l u d i n g r e c r u i t m e n t , f i s c a l , s u p p l y and s i m i l a r s e r v i c e s . 2. P e r s o n n e l . F.L. Whipple, SAO, was p r o j e c t d i r e c t o r o f t h i s work; J.L. Keddy, S m i t h s o n i a n I n s t i t u t i o n , Washington, D.C., was c o g n i z a n t f o r t h e a d m i n i s t r a t i v e s t a f f i n Washington. P r o j e c t 30.20 - I n t e r i m O p t i c a l S a t e l l i t e T r a c k i n g Network 1. O b j e c t i v e s . T h i s p r o j e c t , a t t h e U.S. Army B a l l i s t i c Research L a b o r a t o r i e s , Aberdeen P r o v i n g Ground, was u n d e r t a k e n t o p r o v i d e p r e c i s i o n o p t i c a l systems capable o f p h o t o g r a p h i n g f a i n t o b j e c t s a g a i n s t s t a r s , a l o n g w i t h t e c h n i c a l s u p p o r t f o r t h e t r a c k i n g o f the f i r s t USSR and U.S. s a t e l l i t e s p l a c e d i n t o o r b i t , inasmuch as t h e p r o d u c t i o n , t e s t i n g and c a l i b r a t i o n o f the f u l l complement o f Baker-Nunn p r e c i s i o n cameras (see p r o j e c t 30.6/8) were n o t completed u n t i l mid-1958 and o n l y a few u n i t s were a v a i l a b l e i n l a t e 1957. 2. O p e r a t i o n s . Through c o o p e r a t i v e arrangements between BRL and t h e S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y , equipment was i n s t a l l e d f o r i n t e r i m o p e r a t i o n a t t h e p r e - c i s i o n o p t i c a l t r a c k i n g s t a t i o n s e s t a b l i s h e d by SAO f o r the Baker-Nunn p r e c i s i o n cam- e r a network. As t h e p r e c i s i o n s a t e l l i t e cameras became a v a i l a b l e , t h e y were i n s t a l l e d a t the s i t e s , r e p l a c i n g t h e i n t e r i m equipment. The i n t e r i m n e t w o r k was f u l l y r e p l a c e d by the permanent network by about mid-1958. 3. P e r s o n n e l . T h i s work was under the s u p e r v i s i o n o f Dr. L.A. Delsasso, BRL, o t h e r p r i n c i p a l s c i e n t i f i c p e r s o n n e l a s s o c i a t e d w i t h t h e p r o j e c t were Dr. D i r k Reuyl and Mr. W a l t e r J. C a r r i o n . 586

EARTH SATELLITE P r o j e c t 30.21 - V o l u n t e e r S a t e l l i t e T r a c k i n g Programs: P h o t o t r a c k and Moonbeam 1. O b i e c t i v e s . T h i s p r o j e c t , conducted under t h e auspices o f t h e S o c i e t y o f Photo- g r a p h i c S c i e n t i s t s and Engineers (SPSE), p r o v i d e d c o o r d i n a t i o n o f v o l u n t e e r e f f o r t as backup t o t h e p r e c i s i o n o p t i c a l and r a d i o networks engaged i n s a t e l l i t e t r a c k i n g . P a r t i c u l a r emphasis was p l a c e d on t h e i n i t i a l and t e r m i n a l phases o f o r b i t where ad- vantages o f t h e g r e a t e r g e o g r a p h i c d i s t r i b u t i o n o f v o l u n t e e r o b s e r v e r s c o u l d be r e a l - i z e d . E f f o r t s were a l s o made t o c o o r d i n a t e t h e a c t i v i t i e s o f r a d i o amateurs i n r e c o r d i n g t e l e m e t e r s i g n a l s so as t o o b t a i n tape r e c o r d i n g s o f s c i e n t i f i c v a l u e t o groups who had s u p p l i e d t h e onboard i n s t r u m e n t a t i o n and who were concerned w i t h a n a l - y s i s o f i o n o s p h e r i c e f f e c t s . 2. O p e r a t i o n s . As a p r e r e q u i s i t e t o s a t i s f a c t o r y v o l u n t e e r p h o t o g r a p h i c and r a d i o o b s e r v a t i o n a l s u p p o r t , means were developed f o r communicating mean o r b i t a l elements w i t h r e a s o n a b l e t i m e d e l a y s , and methods were made a v a i l a b l e whereby s a t i s f a c t o r y l o o k - a n g l e p r e d i c t i o n s o r p r e d i c t i o n s o f D o p p l e r i n f l e c t i o n t i m e s , as t h e case may be, c o u l d be r e a l i z e d . S h o r t l y a f t e r t h e l a u n c h i n g o f t h e f i r s t S o v i e t s a t e l l i t e s , an i n t e r i m program o f b r o a d c a s t i n g p r e d i c t i o n s o f c r o s s i n g s o f t h e 4 0 t h P a r a l l e l N o r t h o ver t h e c o n t i n e n t a l U n i t e d S t a t e s was i n i t i a t e d t h r o u g h t h e c o o p e r a t i o n o f t h e C i v i l A i r P a t r o l . As soon as s a t i s f a c t o r y methods f o r l o c a l c o m p u t a t i o n o f t h e same i n f o r - m a t i o n f r o m mean o r b i t a l elements were a v a i l a b l e f o r f i e l d d i s t r i b u t i o n ( S a t e l l i t e R eport No. 7 ) , arrangements were e f f e c t e d f o r a i r m a i l d i s t r i b u t i o n o f mean o r b i t a l elements i n p o s t c a r d form. U n t i l t h e d i s t r i b u t i o n l i s t f o r i n t e r e s t e d o b s e r v e r s was completed, t h e C i v i l A i r P a t r o l u n d e r t o o k i n t e r i m d i s s e m i n a t i o n o f m o d i f i e d o r b i t a l elements t h r o u g h i t s r a d i o n e t w o r k s . Since t h i s t i m e , m o d i f i e d o r b i t a l elements have been communicated d i r e c t l y by a i r m a i l p o s t c a r d . S i m u l t a n e o u s l y w i t h t h e development o f t h e p r e d i c t i o n manual ( S a t e l l i t e Report No. 7 ) , arrangements were made f o r communi- c a t i n g m o d i f i e d o r b i t a l elements over t h e AGIWARN network i n code form. The system f o r t r a n s m i t t i n g mean elements by a i r m a i l p o s t c a r d s and over t h e w o r l d - w i d e r a d i o w a r n i n g networks i n SATOR code has been c o n t i n u e d i n t o t h e post-IGY p e r i o d . The SATOR code, which was developed as p a r t o f the V o l u n t e e r S a t e l l i t e T r a c k i n g Program, was approved f o r c o n t i n u a t i o n a t the COSPAR Conference i n 1961. a. P h o t o t r a c k . T h i s program was designed t o take advantage o f t h e p o s s i b i l i t y o f r e c o r d i n g t r a c e s o f t h e b r i g h t e r s a t e l l i t e s when photographed by f i x e d cameras. I n o r d e r t h a t t h e r e s u l t i n g o b s e r v a t i o n s would be t o a s c a l e p r a c t i c a l f o r measurement, a minimum n e g a t i v e s i z e o f 4" x 5" was recommended as w e l l as a minimum f o c a l l e n g t h o f 5" w i t h r e a s o n a b l y f a s t a p e r t u r e r a t i o s . The o b j e c t i n making o b s e r v a t i o n s o f t h i s t y p e was the show p o i n t s a l o n g t h e s a t e l l i t e t r a c e a c r o s s t h e f i x e d - s t a r background whose r e l a t e d event t i m e s were d e t e r m i n a b l e t o 0.1 second ( r e f e r a b l e t o U n i v e r s a l T i m e ) . The f a s t e s t c o m m e r c i a l l y - a v a i l a b l e emulsions were recommended w i t h f o r c e d de- velopment f o r r e c o r d i n g o b j e c t s r a n g i n g i n b r i g h t n e s s down t o those near t h e t h r e s h o l d o f v i s i b i l i t y o f the human eye. D e t a i l e d i n s t r u c t i o n s i n the form o f b u l l e t i n s were m a i l e d by the V o l u n t e e r S a t e l l i t e T r a c k i n g Program o f SPSE t o i n t e r e s t e d o b s e r v e r s . They i n c l u d e d recommenda- t i o n s f o r p r e c i s i o n t i m i n g , mounting cameras, e l i m i n a t i n g v i b r a t i o n , s e c u r i n g adequate f o c u s , as w e l l as programming t h e a c t u a l exposure d u r i n g s a t e l l i t e pass. C o n t r o l l e d d i s c o n t i n u i t i e s o f the s a t e l l i t e t r a c e exposure were emphasized as t h e key t o s e c u r i n g ( i ) t i m e d p o s i t i o n s a l o n g t h e s a t e l l i t e t r a c e , and ( i i ) t i m e d p o s i t i o n s a l o n g t h e s t a r t r a c e . Recommendations developed d u r i n g t h e IGY f o r t h e s i m p l e s t t i m i n g procedures i n v o l v e d s w i n g i n g a d a r k s l i d e o r paddle b e f o r e t h e l e n s s y n c h r o n i z e d t o r a d i o t i m e t i c k s r e c e i v e d on short-wave r a d i o s . S y n c h r o n i z a t i o n a c c u r a t e t o ± 0.05 seconds c o u l d be r e a l i z e d by those p r a c t i c i n g t h i s t e c h n i q u e . A d d i t i o n a l l o n g e r exposure i n - t e r r u p t i o n s d u r i n g t h e s a t e l l i t e passage t h r o u g h t h e camera f i e l d were recommended so as t o leave c o r r e s p o n d i n g gaps b o t h i n the s a t e l l i t e and i n the s t a r t r a c e s . T h i s 587

EARTH SATELLITE s i m p l e s t manual t e c h n i q u e c o n t i n u e s today t o be the one recommended f o r f i x e d - c a m e r a o b s e r v a t i o n s w i t h lenses o f 7" f o c a l l e n g t h o r l e s s . D u r i n g t h e IGY v a r i o u s forms o f i n s t r u m e n t a t i o n f o r more e l a b o r a t e f i x e d cameras, such as the 12" f/2.5 and the 36" f/6.3 were developed and d i s s e m i n a t e d i n b u l l e t i n form. As a means f o r f i e l d r e d u c t i o n , recommendations f o r s c a l i n g s t a r p o s i t i o n s f r o m the n e g a t i v e s and t r a n s f e r r i n g them t o s t a r c h a r t s were d i s s e m i n a t e d t h a t p e r m i t t e d f i e l d r e d u c t i o n t o an accuracy o f 0.1° o f a r c . Accuracy o f t h i s o r d e r was s u b s t a n t i a l l y g r e a t e r t h a n was b e i n g r e a l i z e d f r o m Moonwatch o p e r a t i o n s a t the t i m e . I n o r d e r t o f a c i l i t a t e t h e a p p l i c a t i o n o f P h o t o t r a c k f i x e s , s p e c i a l s t a t i o n numbers were as s i g n e d by t h e Smi t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y t o p a r t i c i p a t i n g P h o t o t r a c k s i t e s . Co- o r d i n a t e s f o r such s i t e s were d e t e r m i n e d t h r o u g h t h e i r l o c a t i o n on 7-1/2 mi n u t e U n i t e d S t a t e s G e o l o g i c a l Survey s h e e t s , o r o t h e r a p p r o p r i a t e survey methods. b. Moonbeam. P r i o r t o t h e i n i t i a t i o n o f t h e V o l u n t e e r S a t e l l i t e T r a c k i n g Program, a number o f a r t i c l e s had appeared i n v a r i o u s amateur r a d i o p u b l i c a t i o n s d e s c r i b i n g t h e k i n d o f t e l e m e t r y s i g n a l s proposed f o r a r t i f i c i a l e a r t h s a t e l l i t e s and the two p r i n c i - p a l t r a c k i n g t e c h n i q u e s a p p r o p r i a t e t o measurement o f p o s i t i o n . D o p p l e r t r a c k i n g , i n I t s s i m p l e s t form, d i d n o t i n v o l v e e l a b o r a t e equipment, a l t h o u g h i n i t s more s o p h i s - t i c a t e d forms I t c o u l d become h i g h l y complex, as i n t h e M i c r o l o c k System developed a t the J e t P r o p u l s i o n L a b o r a t o r y . By comparison, t h e i n t e r f e r o m e t e r t e c h n i q u e s p a t t e r n e d a f t e r the Prime M i n i t r a c k network (see P r o j e c t 33.1) were s u b s t a n t i a l l y more demanding i n terms o f antenna c o n s t r u c t i o n , l o c a t i o n , and o r i e n t a t i o n but promised h i g h e r p o s i - t i o n a l accuracy. M o n i t o r i n g t r a n s m i t t e d r a d i o mesoages (as opposed t o t r a c k i n g ) was a v a i l a b l e t o any ob s e r v e r i n t e r e s t e d enough t o b u i l d a si m p l e c o n v e r t e r . One o f t h e immediate r e s u l t s o f the use o f r a d i o s i g n a l s f o r t e l e m e t r y purposes on a c o n t i n u o u s - t i m e b a s i s was t o encourage v o l u n t e e r o b s e r v e r s t o b u i l d a p p r o p r i a t e c o n v e r t e r s on t h e i r own i n i - t i a t i v e , and t o r e c o r d t h e s i g n a l s on magnetic tape. Soon a f t e r t h e f i r s t S p u t n i k , v o l u n t e e r o b s e r v a t i o n s m t h e f o r m o f unreduced magnetic tapes began t o f l o w i n t o the computing c e n t e r s . Since t h e r a d i o o b s e r v e r was c o n f r o n t e d w i t h t h e same r e q u i r e m e n t f o r p r e d i c - t i o n s e r v i c e s as the v o l u n t e e r P h o t o t r a c k o b s e r v e r , t h e SPSE o f f e r e d as p a r t o f i t s program t o supply a p p r o p r i a t e p r e d i c t i o n s e r v i c e s t o encourage t h e c o m p l e t i o n o f ap- p r o p r i a t e t r a c k i n g i n s t r u m e n t a t i o n and t o c o n t r o l t h e f l o w o f v o l u n t e e r t e l e m e t r y d a t a i n such a way t h a t r a d i o amateur enthusiasm c o u l d be channeled i n t o r e w a r d i n g a c t i v i t y . A f t e r the V o l u n t e e r S a t e l l i t e T r a c k i n g Program was implemented, a f o u r t h t y p e o f r a d i o o b s e r v a t i o n was urged. I t was f e l t t h a t s i n c e beacon s i g n a l s on d i f f e r e n t r a d i o f r e q u e n c i e s were b e i n g employed, and s i n c e the p e r i o d d u r i n g w h i c h a g i v e n pass c o u l d be observed a t a s t a t i o n was a f u n c t i o n o f i o n o s p h e r i c c o n d i t i o n s , as w e l l as s i g n a l f r e q u e n c i e s and the geometry o f the pass, sample s i g n a l s t r e n g t h r e p o r t s might be o f v a l u e . A program f o r r e p o r t i n g v a r i a t i o n s i n s i g n a l s t r e n g t h as a f u n c t i o n o f t i m e was a c c o r d i n g l y implemented. c. M i n i t r a c k Mark I I . T h i s system, i n i t s s i m p l e s t f o r m ( F i g . 2) c o n s i s t e d o f two matched antennas m an extended base a r r a y , a r e c e i v e r and o s c i l l o g r a p h . Passage o f an a r t i f i c i a l e a r t h s a t e l l i t e would produce a p a t t e r n o f r e i n f o r c e m e n t and c a n c e l - l a t i o n s u c c e s s i v e l y o f the s i g n a l s r e c e i v e d a t each antenna, w h i c h c o u l d be r e c o r d e d as a p a t t e r n o f peaks and n u l l s . One o f the d i f f i c u l t i e s i n i n t e r p r e t i n g r e c o r d s o f t h i s t y p e , even where v e r y s a t i s f a c t o r y t i m e s i g n a l s were r e c o r d e d as i n an a u x i l i a r y c h a n n e l , was i n i n t e r p r e t i n g w hich n u l l corresponded t o the time o f the passage o f the s a t e l l i t e t h r o u g h the p r i n c i p a l p l a n e o f the antenna a r r a y . One method o f r e - s o l v i n g a m b i g u i t y o f t h i s type would have been t o use si m u l t a n e o u s i n t e r f e r o m e t e r r e - c o r d i n g s o f two or more c o n c e n t r i c base l i n e s o f d i f f e r e n t l e n g t h . I n g e n e r a l , t h e 588

EARTH SATELLITE ICONVERTERI COMMUNICATIONS RECEIVER r L METER Simple Mark I I Advanced Mark I I F i g u r e 2. Mark I I M i n i t r a c k Systems TWO- ANTENNA INTEHfETOMETER ilTELEMETERINGI | I. I .1 I I MISSILE "TRANSMITTER INTERFEROMETER PHASE LOCKED RECEIVER RECEIVER t 1 PHASE COHERENT REFERENCE SIGNALS TELEMETERING DISCRIMINATORS X wwv RECEIVER ANGLE OF FREQUENCY AND , ARRIVAL SIGNAL STRENGTH TELEMETERED FREQUENCY AND DATA TIME . STANDARDS RECORDED DATA OUTPUTS 90deg SIGNAL + NOISE PHASE LOOP F I L T E R D E T E C T O R (low P038) VOLTAGE - C O N T R O L L E D OSCILLATOR (VCO) PHASE D E T E C T O R S IGNAL AMPLITUDE Block Diagram of Microlock Basic Phase-Locked Loop f\ f\f\f\f \y \J\j\j\] TIME Interferometer Signal F i g u r e 3. M i c r o l o c k T r a c k i n g System 589

EARTH SATELLITE ambiguities associated w i t h volunteer observations made w i t h M i n i t r a c k Mark I I systems were considered to be resolvable by the s a t e l l i t e computing centers by reference to prime M i n i t r a c k data. Some volunteer s t a t i o n s advanced to dual base-line experiments, although none attempted the advanced setup ( i n Fig. 2) r e q u i r i n g three 1000-ft base lin e s and three sets of antenna arrays. Another d i f f i c u l t y i n p r a c t i c a l a p p l i c a t i o n of volunteer M i n i t r a c k observations lay i n the e f f e c t s of o r i e n t a t i o n and c o l l i m a t i o n e r r o r s . The e f f o r t required to secure photographic c a l i b r a t i o n data w i t h an airborne simulated s a t e l l i t e s i g n a l generator and e l e c t r o n i c f l a s h , such as was used i n the prime interferometer s t a t i o n s , proved to be beyond the resources of nearly a l l Mark I I Minitrack groups. The p r i n c i p a l use to which volunteer interferometer s t a t i o n s were put was i n providing confirmation of achievement of o r b i t during the period immediately a f t e r launch. d. The Jet Propulsion Laboratory Microlock System. As developed by amateurs from the Jet Propulsion Laboratory, the JPL Microlock System contained a number of impor- ta n t features. One was use of p a i r s of antennas which could be arranged f o r any par- t i c u l a r s a t e l l i t e track (Fig. 3) and employing two h i g h l y stable communication receivers w i t h several a u x i l i a r y c i r c u i t s , as w e l l as a p r e c i s i o n - t i m i n g source and a c a l i b r a t i o n o s c i l l a t o r . The feature of greatest i n t e r e s t to other volunteer observers proved to be a phase-locked system ( F i g . 3) which s h i f t e d the 10-cycle bandwidth receiver auto- m a t i c a l l y to f o l l o w changes i n frequency caused by Doppler s h i f t and/or t r a n s m i t t e r - frequency d r i f t . As a byproduct, the JPL Microlock System provided means f o r automatic recording of Doppler data ( F i g . 3). The phase-locked feature and narrow band width made the Microlock receiver extremely s e n s i t i v e , p e r m i t t i n g operation at what would otherwise have been unfavorable signal-to-noise r a t i o s . I t was calculated t h a t the t r a c k i n g c a p a b i l i t y was such that a device r a d i a t i n g one m i l l i w a t t a t 1.08 Mc could be tracked to about 3000 miles. The Microlock system was adapted to record the 40 Mc signals emitted by USSR s a t e l l i t e s and l a t e r to the higher frequencies adapted f o r U.S. s a t e l l i t e beacons. 3. Personnel. The Phototrack Program was administered and coordinated by the Society of Photographic S c i e n t i s t s and Engineers under the supervision of Norton Goodwin, SPSE. The M i n i t r a c k and Microlock Programs were coordinated under the same p r o j e c t and super- vised t e c h n i c a l l y by personnel of the Naval Research Laboratory and the Jet Propulsion Laboratory. 4. Results. Observations made of various s a t e l l i t e s under t h i s program were processed and combined w i t h other observations at the s a t e l l i t e - c o m p u t i n g centers of NRL ( r a d i o ) and the Smithsonian Astrophysical Observatory ( o p t i c a l ) , where p r e d i c t i o n ephemerides were being generated and modified, and where p r e c i s i o n o r b i t s were f i n a l l y computed. At the end of the I n t e r n a t i o n a l Geophysical Year, sponsorship of the Phototrack Pro- gram was undertaken by the National Aeronautics and Space Adm i n i s t r a t i o n . 5. Bibliography. L.N. Cormier, N. Goodwin* " S i m p l i f i e d S a t e l l i t e P r e d i c t i o n from Modified O r b i t a l Elements." WDC-A S a t e l l i t e Report Series, No. 7, January 1, 1959, NAS, Washington, D.C. V.R. Simas, G.C. Kronmiller: "Minitrack Report No. 7, C a l i b r a t i n g the Mark I I M i n i t r a c k System w i t h Radio Stars as Signal Sources." NRL Report 5215, October 17, 1958. E.R. Dyer, Jr. "Simple Method f o r Obtaining a S a t e l l i t e F i x and Trans- m i t t i n g Information to Computing Centers Withm 24 Hours." Volunteer IGY S a t e l l i t e Tracking Program B u l l e t i n , 14 Oct. 1958. H.L. Richter, J r . , W.F. Sampson, R. Stevens "Microlock. A Minimum-Weight Radio Instrumentation System for a S a t e l l i t e . " Jet Propulsion Laboratory P u b l i c a t i o n No. 376, A p r i l 17, 1958. 590

EARTH SATELLITE "Minit r a c k S t a t i o n of the Sohio Moonbeam Group." QST. v o l . 42, no. 4, A p r i l 1958, pp. 48-9. C. T. B u t l e r , H.L. Richter, Jr.* "Amateur Microlock Handbook." San Gabriel ( C a l i f . ) Radio Club. D. G. King-Hele and R.H. Merson: " S a t e l l i t e O r b i t s i n Theory and Pra c t i c e . " Journal of the B r i t i s h I n t e r p l a n e t a r y Society, v o l . 16, July-August 1958, pp. 446-471. W. Matthews and G.H. Ludwig- " S c i e n t i f i c Telemetry f o r USNC-IGY." QST, v o l . 42, January 1958, pp. 41-46. W.D. Kahn: " C a l i b r a t i o n of M i n i t r a c k Mark I I . " Ast. Journal, v o l . 62, no. 10, December 1957, pp. 396-399. W.H. Pickering: "Project Moonbeam: The Radio Amateur and the IGY S a t e l l i t e . " QST. v o l . 41, no. 11, Nov. 1957, p. 15. V.R. Simas, W.B. Moriarty: "Tape Recording the Mark I I M i n i t r a c k Signals* An Inexpensive Recording Method f o r Amateur Tracking Stations." QST, v o l . 41, no. 11, Nov. 1957, pp. 42-5. R.L. Easton: "Mark I I M i n i t r a c k Base-Lme Components." QST. v o l . 41, no. 9, Sept. 1957, pp. 30-41. R.L. Easton: " C a l i b r a t i o n of the Mark I I M i n i t r a c k . " QST, v o l . 41, no. 4, A p r i l 1957, pp. 42-44. R.L. Easton: "Radio Tracking of IGY S a t e l l i t e s : The Mark I I M i n i t r a c k System." Journal of Astronautics, v o l . 4, no. 2, 1957, pp. 31-2. V.R. Simas: "A Low-Noise Preamplifier f o r S a t e l l i t e Tracking." QST. v o l . 40, no. 12, Dec. 1956, pp. 42-3. H.L. Richter, J r . : "Microlock." QST, v o l . 41, no. 12, Dec. 1957, pp. 20-26. 591

EARTH SATELLITE Project 31.1 - Procurement of S a t e l l i t e Launching Vehicles 1. Ob.iectives. The r e s p o n s i b i l i t y of development and procurement of s a t e l l i t e launching vehicles (Vanguard) was assigned by the Department of Defense to the Naval Research Laboratory I n order to help defray some of the cost of t h i s program, t h i s p r o j e c t was set up f o r the t r a n s f e r of funds to NRL. 2. Operations. The program was planned to include a series of t e s t launchings f o l - lowed by f u l l - p a y l o a d launchings. Of the three te s t launching t r i e s , each w i t h a small payload equipped only w i t h temperature sensors f o r environmental measurements and small t r a n s m i t t e r s f o r tra c k i n g purposes, only one was successful. This v e h i c l e c a r r i e d Vanguard I i n t o what turned out to be a h i g h l y useful o r b i t apogee - 650 km, perigee - 3970 km, i n c l i n a t i o n 34.25°, l i f e t i m e - i n d e f i n i t e . P recision observations of the o r b i t of Vanguard I have resulted i n a great deal of useful information on the density of the outer atmosphere, solar e f f e c t s on atmospheric density, and the geo- g r a v i t a t i o n a l f i e l d . The eight launching attempts w i t h f u l l payload r e s u l t e d i n two successful o r b i t s Vanguard I I - described i n p r o j e c t 32.5 and Vanguard I I I - described i n p r o j e c t 32.9. 3. Personnel. The development and procurement of Vanguard launch vehicles were under the supervision of J.P. Hagen, NRL. 592

EARTH SATELLITE Project 32.1 - Cosnac-Ray Observations 1. Obiectives. This p r o j e c t at the Department of Physics, State U n i v e r s i t y of Iowa, was designed to make comprehensive measurements of the t o t a l i n t e n s i t y of cosmic r a - d i a t i o n as a f u n c t i o n of time, l a t i t u d e , longitude, and a l t i t u d e . As a r e s u l t of the f i r s t experiment, when i t was discovered that at a c e r t a i n a l t i t u d e the r a d i a t i o n l e v e l increased sharply to f a r beyond normal cosmic-ray l e v e l s , the program was re- oriented to i n v e s t i g a t e i n d e t a i l the s t r u c t u r e of t h i s zone of intense r a d i a t i o n . 2. Operations. SUI s c i e n t i s t s developed instrument packages containing r a d i a t i o n detectors and telemetry c i r c u i t s f o r use i n Vanguard vehicles. A tape recorder was also developed that stored information and played i t back at high speed upon i n t e r r o - gation of the s a t e l l i t e . The instrument assemblies were modified f o r the Explorer nose-cones and l a t e r f o r the Pioneer space probe rockets. Successful launchings were obtained w i t h Explorers I , I I I , IV, V I I and Pioneer I , I I I and IV. For d e t a i l s of these launchings see tables, pp. 18-19. Telemetered information, recorded at tr a c k i n g s t a t i o n s on magnetic tapes, was analyzed at SUI using special tape reading equipment designed and constructed f o r t h i s work. The Geiger counter information was tabulated and p l o t t e d on pr o j e c t i o n s of the s a t e l l i t e o r b i t w i t h the geomagnetic f i e l d as a reference frame. 3. Personnel. James A. Van A l l e n was pr o j e c t d i r e c t o r f o r t h i s work, other senior s c i e n t i s t s associated w i t h him at SUI were Carl Mcllwain, George Ludwig, E.G. Ray, and L Frank. Assistance was also given to t h i s work by personnel of the Jet Pro- pulsion Laboratory and Space Technology Laboratory. 4. Data. Reduced data from Explorer I has been published i n an SUI report and sub- mit t e d to the World Data Centers. I n a d d i t i o n , the counter data from Explorer IV are avai l a b l e along w i t h the precise o r b i t a l data and magnetic information B, the f i e l d strength, I , the magnetic i n v a r i a n t , and L, a parameter ch a r a c t e r i z i n g p a r t i c u l a r l i n e s of force of the geomagnetic f i e l d . 5. Results. The o r b i t of Explorer I (1958 Alpha) was eccentric, w i t h a perigee of about 360^ km and an apogee of about 2500 km, the i n c l i n a t i o n of the o r b i t was 33.5°. For much of the time, the counting rates seemed to be what was expected on the basis of e x t r a p o l a t i n g p l o t s of i n t e n s i t y vs. a l t i t u d e , as determined at lower a l t i t u d e s w i t h balloons and rockets. However, on some of the passes the counting rate apparently exceeded the c a p a b i l i t y of the detection and telemetering systems and the signal as received at the ground was i n t e r p r e t e d as i n d i c a t i n g operation of the detectors at counting rates above the overload l e v e l ( i . e . , greater than 35,000 counts per s e c ) . Spare assemblies were then tested at the SUI labo r a t o r i e s and c a l i b r a t e d up to satura- t i o n , hence some idea was gained of at least the lower l i m i t of intense r a d i a t i o n believed to have been encountered during the h i g h - a l t i t u d e portions of the o r b i t . The o r b i t of Explorer I I I (1958 Gamma) was s i m i l a r to that of Explorer I , the i n t e r n a l instrumentation was also s i m i l a r w i t h the a d d i t i o n of a tape recorder f o r storage of observations f o r rapid repeat to the ground telemeter receivers upon i n t e r r o g a t i o n . Analysis of the information obtained from these two s a t e l l i t e s showed that the " r a d i a - t i o n " consisted at least i n part of energetic p a r t i c l e s , presumed to be protons and electrons i n geomagnetically trapped o r b i t s . The o r b i t of Explorer IV was arranged to explore more of the r a d i a t i o n region, i t had an i n c l i n a t i o n of about 50° and an apogee of about 2200 km. Instrumentation i n - cluded a Geiger counter shielded w i t h lead and an unshielded counter w i t h a capacity some 1500 times the r a d i a t i o n i n t e n s i t y that saturated the counters i n Explorers I and I I I , two s c i n t i l l a t i o n counters were also employed, one to measure approximately the t o t a l energy and the other to count the incident corpuscular r a d i a t i o n . When the 593

EARTH SATELLITE counting rates were p l o t t e d w i t h reference to the geomagnetic f i e l d , i t was seen that a " r a d i a t i o n zone" was present, r e l a t e d to the l i n e s of force of the geomagnetic f i e l d . Figure 4 shows the observed and extrapolated contours. The s t r u c t u r e of the contours near 60-70° magnetic l a t i t u d e suggested to SUI s c i e n t i s t s a r e l a t i o n s h i p to s o f t r a - d i a t i o n above 50 km i n the auroral zone observed i n e a r l i e r SUI rocket experiments and also suggested that the s t r u c t u r e of the " r a d i a t i o n zone" might be more complex than i n d i c a t e d by the f i r s t r e s u l t s . The p o s s i b i l i t i e s of t h i s l a t t e r point were d i s - cussed at SUI and instrumentation was prepared f o r f u r t h e r measurements. To f u r t h e r the probing of t h i s newly-discovered feature of the earth's outer a t - mosphere, instrumentation was placed on deep space probes, Pioneer I and I I I , which provided observations out to about f i f t e e n earth r a d i i , and Pioneer IV, which reached to w i t h i n about 100,000 km of the moon. The counting-rate data showed the existence of two d i s t i n c t , widely-separated zones, as shown i n Figure 5. A high of 16,700 counts per second i n the inner region and a high of 25,600 counts per second i n the outer region were observed during the Pioneer I I I measurements. Pioneer IV traversed the f a r reaches of the outer zone and i t was observed that r a d i a t i o n i n t e n s i t y d i d not f a l l back to normal cosmic-ray le v e l s u n t i l at least 10 earth r a d i i or so, f l u c t u a t i o n s i n the counting rate at the l i m i t of the outer zone were also observed. I t should be noted that the schematic representation as shown i n Figure 5 i s g r e a t l y s i m p l i f i e d , as the regions of intense r a d i a t i o n show wide s p a t i a l and temporal f l u c t u a t i o n s . The f i n a l IGY s a t e l l i t e experiment of the SUI group was c a r r i e d on Explorer V I I (1959 I o t a ) which had an i n c l i n a t i o n of about 50°, a perigee of about 550 km and an apogee of about 1100 km. Two Geiger counters, one shielded, the other unshielded, were used f o r detection of cosmic rays and lower energy p a r t i c l e s . A number of solar- t e r r e s t r i a l coupled events were observed during the l i f e t i m e of Explorer V I I i n c l u d i n g the observation of the a r r i v a l of solar protons f o l l o w i n g t h e i r a c c e l e r a t i o n i n a so- l a r f l a r e , at the same time a polar cap event -- increased ionospheric absorption i n - side the auroral zone -- was noted. During a severe geomagnetic storm on November 28, 1959, the r a d i a t i o n detectors aboard Explorer V I I showed anomalous counts, while at the same time active v i s u a l auroras and a subvisual monochromatic red arc were observed over Northern United States. I t i s hypothesized that when solar plasma encounters the earth's magnetosphere, the magnetic f i e l d i s d i s t o r t e d i n such a way that p a r t i c l e s normally trapped i n the outer r a d i a t i o n b e l t are "dumped" out of the b e l t to i n t e r a c t w i t h the atmosphere at a l t i t u d e s lower than the m i r r o r points and spread to lower l a - t i t u d e s . The d i r e c t c o r r e l a t i o n observed by Explorer V I I between occurrences i n the r a d i a t i o n b e l t s and auroral a c t i v i t y i n the high atmosphere was the f i r s t experimental evidence of the "dumping" hypothesis. The discovery and d e l i n e a t i o n of zones of geomagnetically trapped, high energy charged p a r t i c l e s -- the t h e o r e t i c a l basis of which was l a i d i n e a r l y mathematical work of Poincare and p a r t i c u l a r l y SttJrmer -- gave a great impetus to exploring the magneto- sphere of the earth. Many other experiments of other groups and t h e o r e t i c a l work around the world added new d e t a i l s to knowledge and understanding of the Van A l l e n Radiation B e l t s , as t h i s phenomenon came to be known, p a r t i c u l a r l y a) w i t h respect to the population i d e n t i t y , and energy spectrum of the trapped p a r t i c l e s , b) the mecha- nisms of trapping and, possibly, acceleration of p a r t i c l e s , c) the behavior of the b e l t s during solar and i n t e r p l a n e t a r y disturbances, and d) the r e l a t i o n s h i p s between t e r r e s t r i a l manifestations of solar disturbances and a c t i v i t y i n the b e l t s . This i s by no means to say that a f u l l understanding or even d e s c r i p t i o n of the b e l t s i s at hand, but a considerable s t a r t has been made i n understanding t h e i r nature and r o l e i n the i n t e r r e l a t e d e l e c t r i c and magnetic phenomena of the earth's outer atmosphere. 594

EARTH SATELLITE UWNETIC / , MIS '• - I I 10.000 1000 V 100 8 I / ; / / I I I I I Figure 4. Radiation Contours Derived from Explorers I , I I I , I v GEOMAGNETIC AXIS 100 100 Figure 5. Radiation Contours Derived from Explorer and Pioneer Data 595

EARTH SATELLITE 6. Bibliography. a. Papers Presented at Meetings. J.A. Van A l l e n , G.H. Ludwig, E.C. Ray, C.E. Mcllwain- "The Observations of High I n t e n s i t y Radiation by S a t e l l i t e s 1958 Alpha and Gamma." Rocket and S a t e l l i t e Symposium, 6th Gen. Assembly CSAGI, Moscow, 1958. (Publ. i n IGY S a t e l l i t e Report Series No. 3, N a t l . Academy of Sciences, Washington 25, D.C.). J.A. Van Al l e n : "Remarks on Observations of High I n t e n s i t y Radiation by S a t e l l i t e s 1958 Alpha and 1958 Gamma." Special Meeting f o r Members National Academy of Sciences, American Physical Society, May 1, 1958, Washington, D.C. (Published m IGY S a t e l l i t e Report Series No. 3, National Academy of Sciences, Washington, D.C). J.A. Van A l l e n : "The Geomagnetically Trapped Corpuscular Radiation." Moscow Cosmic Ray Conference, 1959. (Published i n Proceedings of the Moscow Cosmic Ray Conference. Vol. I I , pp. 7-13, lUPAP, Moscow, 1960). J.A. Van A l l e n : " O r i g i n and Nature of the Geomagnetically Trapped Radiation." F i r s t I n t e r n a t i o n a l Space Science Symposium, Nice, 1960. (Published i n Space Research. H. Kallmann-Bij1, Ed., North-Holland Publishing Co., Amster- dam, 1960, pp. 749-750. C.E. Mcllwain, P. Rothwell: " S a t e l l i t e Observations of Time V a r i a t i o n s of Charged P a r t i c l e I n t e n s i t i e s at High L a t i t u d e s . " Meeting of American Physical Society. (Abs. Pub. i n B u l l e t i n . APS, Ser. I I , v o l . 4, no. 4, 1959, p. 238). J.A. Van Al l e n : "The Geomagnetically Trapped Corpuscular Radiation." Symposium on Problems m Space Exploration, National Academy of Sciences, A p r i l 1959, Washington, D.C. (Published i n Annals of the IGY. Vol. X I I , Part I I , pp. 753-59, Pergamon Press, London, and Journal of Geophysical Research, v o l . .64, no. 8, 1959, pp. 1683-89). C.E. Mcllwain, P. Rothwell: " S p a t i a l Dependence on the I n t e n s i t y of Charged P a r t i c l e s Trapped i n the Earth's F i e l d between 50°N and 50°S Geographic L a t i t u d e , and 300- to 2000-km A l t i t u d e . " F o r t y - F i r s t Annual Meetin, AGU, A p r i l 1960, Washington, D.C. (Abs. published i n Journal of Geophysical Research, v o l . 65, no. 8, 1960, pp. 2508-09). b. Published Papers. J.A. Van A l l e n , L.A. Frank: "Radiation Around the Earth to a Radial Distance of 107,400 Kilometers." Nature, v o l . 184, 1959, pp. 430-34. J.A. Van A l l e n , L.A. Frank: "Radiation Measurements to 658,000 Kilometers w i t h Pioneer IV/' Nature, v o l . 184, 1959, pp. 219-24. J.A. Van A l l e n , C.E. Mcllwain, G.H. Ludwig- "Radiation Observations w i t h S a t e l l i t e 1958 Epsilon." Journal of Geophysical Research, v o l . 64, 1959, pp. 271-86. A. Rosen, CP. Sonnett, P.J. Coleman, J r . , C.E. Mcllwain: " I o n i z i n g Ra- d i a t i o n at A l t i t u d e s of 3,500 to 36,000 km- Pioneer I . " Journal of Geophysical Research, v o l . 65, July 1959, pp. 709-12. P. Rothwell and CE. Mcllwain. " S a t e l l i t e Observations of Solar Cosmic Rays." Nature, v o l . 184, July 18, 1959, pp. 138-40. 596

EARTH SATELLITE G.H. Ludwig: "Cosmic Ray Instrumentation m the F i r s t U.S. Earth S a t e l l i t e . " Review of Sci. I n s t . . v o l . 30, 1959, pp. 223-29. G.H. Ludwig, W.A. Whelpley. "Corpuscular Radiation Experiment of S a t e l l i t e 1959 I o t a (Explorer V I I ) . " Journal of Geophysical Research, v o l . 65, 1960, pp. 1119-24. E.G. Ray: "On the Theory of Protons Trapped m the Earth's Magnetic F i e l d . " Journal of Geophysical Research, v o l . 65, I960, pp. 1125-34. B.J. O'Brian, J.A. Van A l l e n , F.E. Roach, C.W. Ga r t l e i n - " C o r r e l a t i o n of an Auroral Arc and a Subvisible Monochromatic 6300A Arc w i t h Outer-Zone Radiation on November 28, 1959." Journal of Geophysical Research, v o l . 65, 1960, pp. 2759-66. B.J. O'Brian, G.H. Ludwig: "Development of M u l t i p l e Radiation Zones on October 18, 1959." Journal of Geophysical Research, v o l . 65, 1960, pp. 2695-99. J.A. Van A l l e n , Wei Ching L i n : "Outer Radiation Belt and Solar Proton Observations w i t h Explorer V I I during March-April 1960." Journal of Geophysical Research, v o l . 65, 1960, pp. 2998-3003. P. Rothwell, C.E. Mcllwain "Magnetic Storms and the Van A l l e n Radiation Belts- Observations from S a t e l l i t e 1958 Epsilon (Explorer V I ) . " Journal of Geophysical Research, v o l . 65, March 1960, pp. 799-806. S. Yoshida, G.H. Ludwig, J.A. Van A l l e n : " D i s t r i b u t i o n of Trapped Radiation i n the Geomagnetic F i e l d . " Journal of Geophysical Research, v o l . 65, March 1960, pp. 807-813. 597

EARTH SATELLITE Project 32.2 - Meteoric Erosion and E l e c t r i c Charge of a S a t e l l i t e 1. Objectives. This p r o j e c t a t the Department of Physics, U n i v e r s i t y of Maryland, provided f o r the development and t e s t i n g of an a l t e r n a t e method of measuring erosion of the s a t e l l i t e skin by meteoric m a t e r i a l and to explore means of determining the e l e c t r o s t a t i c charge accumulated by a s a t e l l i t e . The determination of meteoric ero- sion would permit an estimate of the f l u x of meteoric m a t e r i a l , as a check against estimates derived from ground-based o p t i c a l and radio observations. The erosion e f f e c t s of such m a t e r i a l would play an important r o l e i n the design considerations of f u t u r e s a t e l l i t e s from the mechanical point of view, and would also be of impor- tance i n estimating the v i s i b i l i t y and thermal regimen of p a r t i c u l a r s a t e l l i t e s as affected by the conditions of the s k i n surface. The e l e c t r o s t a t i c charge would be of importance i n estimating i f there might be any e l e c t r i c forces important enough to cause o r b i t perturbations. 2. Operations. a. Radioactive meteor erosion gauge. Theoretical studies were c a r r i e d out i n order to estimate the range of the expected erosion and to provide a t h e o r e t i c a l basis f o r estimating the f l u x of meteoric m a t e r i a l from observation of erosion r a t e s . Some experiments were also designed conceptually, i n which charged dust p a r t i c l e s were accelerated e l e c t r o s t a t i c a l l y and dir e c t e d toward m e t a l l i c surfaces so that ero- sion e f f e c t s could be studied d i r e c t l y . The basis of the proposed experimental setup f o r erosion measurement was as foll o w s . Beta-emitting r a d i o a c t i v e m a t e r i a l would be deposited on the outside of a small area of the s a t e l l i t e s k i n i n one or possibly a l l of three ways ( i ) on the surface to measure the s u r f i c i a l erosion, ( i i ) throughout the volume of the s k i n to measure the volume erosion, and ( i i i ) i n a layer on the s k i n but shielded by a cov- eri n g layer to measure penetration of meteoric m a t e r i a l . A se n s i t i v e Geiger detector inside the s a t e l l i t e would monitor the counting r a t e , which would decrease as the radio a c t i v e m a t e r i a l was eroded away. Min i a t u r i z e d counters, scalers, a m p l i f i e r s and high voltage power supplies were developed w i t h a t o t a l gross weight of about 22 grams. The u n i t was designed to operate w i t h i n temperature ranges s p e c i f i e d m the design of Vanguard payloads, and to operate from a v a i l a b l e power supply voltages, w i t h a very low power d r a i n . b. S a t e l l i t e e l e c t r i c charge. Two methods were investigated t h e o r e t i c a l l y and experimentally. I n one proposed method an e l e c t r o n - e m i t t i n g probe would be supported e x t e r n a l to the s a t e l l i t e . The e l e c t r o n gun current as a f u n c t i o n of the p o t e n t i a l acquired by the probe would allow c a l c u l a t i o n of the p o t e n t i a l of the s a t e l l i t e i t s e l f w i t h respect to the p o t e n t i a l acquired by the cathode, i n t u r n equal to the p o t e n t i a l of the undisturbed plasma. The second method involved a conical volume m the s a t e l - l i t e w i t h a shutter arrangement to provide open i n t e r v a l s of some 1/10 second, very short as compared w i t h s a t e l l i t e r o t a t i o n period. A small insulated sphere constructed of a metal w i t h a known p h o t o e l e c t r i c property would be mounted behind the shutter and I t s p o t e n t i a l measured as i t was exposed t o s u n l i g h t , e l e c t r o n s , or ions, or various combinations of these. I t was thought t h a t the various curves of p o t e n t i a l - w i t h - t i m e f o r these i r r a d i a t i o n s would be d i f f e r e n t enough to permit s e l e c t i o n of the curve f o r sunlight alone. Since materials w i t h well-known properties would be used, and assum- ing adequate knowledge of the solar energy spectrum, i t was thought that the sphere p o t e n t i a l could be used as a known reference f o r the measurement of the p o t e n t i a l acquired by the s a t e l l i t e . Such a probe was a c t u a l l y b u i l t (under an A i r Force con- t r a c t ) and used to measure the p o t e n t i a l of a high a l t i t u d e sounding rocket. 598

EARTH SATELLITE 3. Personnel. This work was d i r e c t e d by S. F. Singer, other senior s c i e n t i s t s associ- ated w i t h Dr. Singer i n t h i s work were E. Bpik and M. J. Swetnick. 4. Results. These i n v e s t i g a t i o n s were supported as backup and al t e r n a t e s to other projects and an opportunity d i d not become ava i l a b l e to carry out the proposed measure- ments w i t h a s a t e l l i t e f l i g h t . 5. Bibliography. a. Papers Presented at Meetings. S. F. Singer: "The E f f e c t of Meteoric P a r t i c l e s on a S a t e l l i t e , " Semi-Annual Meeting, American Rocket Society, June 1958, Cleveland (Pub. i n Jet Propulsion, December 1956, pp. 1071-76). b. Published Papers. K. P. Chopra and S. F. Singer: "Drag of Sphere Moving i n a Conducting F l u i d i n the Presence of a Magnetic F i e l d , " 1958 Heat Transfer and F l u i d Mechanics I n s t i t u t e , Stanford Un i v e r s i t y Press. 599

EARTH SATELLITE Project 32.3 - Extreme U l t r a v i o l e t Solar Radiation 1. Ob.iectives. This p r o j e c t a t the Geophysics Research D i r e c t o r a t e , AFCRL, was under- taken to inv e s t i g a t e experimental p o s s i b i l i t i e s using p h o t o e l e c t r i c techniques f o r measuring extreme u l t r a v i o l e t solar r a d i a t i o n i n the range from about 1050 A to 500 A. This region of the spectrum i s p a r t i c u l a r l y d i f f i c u l t using conventional photon counter or i o n i z a t i o n chamber de t e c t i o n . 2. Operations. The main e f f o r t was concentrated upon the construction^ laboratory c a l i b r a t i o n , and rocket f l i g h t of two types of instruments, both w i t h telemetry of data- (a) monochromators w i t h p h o t o e l e c t r i c d e t e c t i o n , scanning e i t h e r the wave- length range 250 A - 1300 A, or the range 62 A - 325 A, tra i n e d on the sun i n f l i g h t by a b i - a x i a l p o i n t i n g c o n t r o l (described i n p u b l i c a t i o n l i s t e d below); and (b) re- ta r d i n g p o t e n t i a l analyzers i n plane p a r a l l e l geometry w i t h automatic r e t a r d i n g voltage sweep and automatic switching of operating parameters i n f l i g h t so as to measure photons, el e c t r o n s , and ions i n sequence. 3. Personnel. This work was under the d i r e c t i o n of H. E. Hmteregger, other senior s c i e n t i s t s associated w i t h Hmteregger were L. Heroux and L. A. H a l l . 4. Results. This exploratory p r o j e c t was intended as back-up to other experiments. Though i t d i d not prove possible to instrument an IGY s a t e l l i t e , several rocket experiments were conducted successfully providing f i r s t information on p h o t o e l e c t r i c emission from s o l i d s exposed to the u n f i l t e r e d solar extreme u l t r a v i o l e t r a d i a t i o n as w e l l as p h o t o e l e c t r i c measurements of solar extreme u l t r a v i o l e t photon fluxes i n the upper atmosphere. 5. Bibliography. H. E. Hmteregger. "Analysis of Pfiotoelectrons from Solar Extreme U l t r a v i o l e t " Journal of Geophysical Research, Vol. 64, No. 8, Aug. 1959 H. E. Hmteregger "Combined Retarding P o t e n t i a l Analysis of Photoelectrons and Environmental Charged P a r t i c l e s up to 234 km" Space Research, Proceedings of the F i r s t I n t e r n a t i o n a l Space Science Symposium, Nice, 1960. North-Holland Publishing Co. Amsterdam. H. E. Hmteregger, K. R. Damon, L. Heroux and L. A. H a l l : "Telemetering Mon- ochromator Measurements of Solar 304 A Radiation and i t s Attenuation i n the Upper Atmosphere" Space Research, Proceedings of the F i r s t I n t e r n a t i o n a l Space Science Symposium, Nice, 1960 p. 615-627, North-Holland Publishing Company, Amsterdam H. E. Hmteregger "Monochromator Measurements of Lyman Series Emissions of Solar H and He+" Tenth I n t e r n a t i o n a l Astrophysical Symposium, Liege, J u l y , 1960. Memoires Soc. R. Sc. Liege, cinquieme s e r i e , tome IV, fasc. unique. H. E. Hmteregger "Telemetering Monochromator Measurements of Extreme U l t r a - v i o l e t Radiation," Space Astrophysics, Ed., W i l l i a m L i l l e r , McGraw-Hill Book Co., New York (1961) Ch. 3 and 4 H. E. Hmteregger* "Preliminary Data on Solar Extreme U l t r a v i o l e t Radiation" Presented at COSPAR, Florence, I t a l y , A p r i l 1961, Journal of Geophysical Research, August 1961. 600

EARTH SATELLITE Project 32.4 - Measurement of I n t e r p l a n e t a r y Matter from Earth S a t e l l i t e s 1 Objectives. This work at the Geophysics Research D i r e c t o r a t e , AFCRL, involved the determination of the q u a n t i t y of the dust component of i n t e r p l a n e t a r y matter intercepted by the s a t e l l i t e s , the s p a t i a l d i s t r i b u t i o n of t h i s i n t e r p l a n e t a r y dust, and the e f f e c t of t h i s matter on s a t e l l i t e surfaces. 2. Operations. The basis of t h i s experiment was a s e n s i t i v e transducer to detect the impact of i n t e r p l a n e t a r y dust on the s a t e l l i t e surface. The preliminary work included the design, construction and c a l i b r a t i o n of a p i e z o e l e c t r i c transducer, t r a n s i s t o r i z e d a m p l i f i e r and storage device. The c a l i b r a t i o n of the accelerometer involved laboratory development of a system f o r impacting p a r t i c l e s on a surface, and the construction of p i e z o e l e c t r i c c r y s t a l u n i t s s e n s i t i v e i n the u l t r a s o n i c frequency range. Pulse height as produced by the transducer was p r o p o r t i o n a l to the momentum of the impacting p a r t i c l e , and since the p a r t i c l e v e l o c i t y and s e n s i t i v i t y of the equipment were w i t h i n known bounds, the mass of the p a r t i c l e could be determined. On-board instrumentation was designed and constructed to take i n t o account ex- pected temperature ranges, v i b r a t i o n and acceleration of the s a t e l l i t e . Equipment was flown on s a t e l l i t e s Explorer I and I I I and space probe Pioneer I . On Explorer I and I I I a series of twelve wire-wound g r i d detectors were mounted around the c y l i n - d r i c a l motor. These detectors, which should break upon impact by s o l i d p a r t i c l e s w i t h diameters greater than 6 microns, covered an area of one square centimeter each. Two grids indicated breaks on Explorer I I I a f t e r a combined exposure of four months f o r both s a t e l l i t e s . This rate of d e s t r u c t i o n of the grids was consistent w i t h the transducer data. 3. Personnel. This work was under the d i r e c t i o n of M. Dubin and E. R. Manring, other senior s c i e n t i s t s associated w i t h the work included Professor J. L. Bohn of Temple U n i v e r s i t y . 4. Data. The data from the several f l i g h t s have been included i n the tec h n i c a l papers l i s t e d under section 6, Bibliography. 5. Results. The data from Explorer I , as shown m Figure 6, covers about 12 days of operation of the equipment, during which time there were recorded 145 impacts f o r a mean impact r a t e of 8.0 x lO""^ impacts/m^sec. A d i u r n a l v a r i a t i o n of about three- to-one was noted. During f i v e successive s a t e l l i t e passes f o r a period of eight hours, the impact rate was s u b s t a n t i a l l y higher, as shown under the shaded p o r t i o n of the curve m Figure 6, between 16 and 24 hours. I t i s hypothesized that a "meteor shower" was encountered during t h i s period g i v i n g r i s e to the high rates. This hypothesis correlates w i t h ionospheric observations during the same time intense sporadic E was observed i n the ionosphere i n the v i c i n i t y of those s t a t i o n s r e p o r t i n g the maximum impact rate from the s a t e l l i t e . At White Sands, New Mexico, f o r example. Eg was recorded' w i t h a c r i t i c a l frequency of 7 Mc and seven m u l t i p l e r e f l e c t i o n s during the "shower." There are many suggestions i n ionospheric l i t e r a t u r e r e l a t i n g Eg to meteoric a c t i v i t y . F i n a l l y , the "shower" occurred during the time of day at which the meteor occurrence would normally be at a minimum. I n the Explorer I experiment, an area of 0.23 m̂ was exposed w i t h a threshold l e v e l of 2.5 X 10"-̂ g cm/sec, f o r an assumed average v e l o c i t v of 30 km/sec, the minimum mass that could be observed was, the r e f o r e , 8 x 10" gm. I t i s calculated that the mass i n f l u x upon the earth f o r t h i s component, i. e. greater than 8 x lO'-'-'̂ gm, would be approximately 1.3 x 1 0 " g / m sec or 6 x 10° kg/day over the earth's surface. The density of matter a t 1 A.U., assuming a v e l o c i t y of 30 km/sec, was calculated to be 5 X 10" gm/cm-̂ f o r t h i s component of cosmic matter. Extrapolating these c a l - culations and using the mass d i s t r i b u t i o n f u n c t i o n obtained through radio observations 601

EARTH SATELLITE of meteors, i t i s estimated that up to 10^ kg/day of cosmic matter may be accreted by the e n t i r e e a r t h , and the i n t e r p l a n e t a r y density may be of the order of 10'^^ gm/cm'. The experiment on Pioneer I c a r r i e d s i m i l a r equipment but w i t h an extra channel to detect larger p a r t i c l e s . The s e n s i t i v i t y was sixt e e n times higher than f o r the Explorer I experiment, but the counting rate was only h a l f . The e a r l i e r measurements had shown a d i u r n a l v a r i a t i o n of approximately three to one and that large sporadic v a r i a t i o n s could occur. Furthermore the o r b i t and spin axis of Pioneer I were such that the sensing element was exposed to matter m the plane of the e c l i p t i c only some 20 percent of the time, and there i s evidence from zodiacal l i g h t analysis t h a t i n t e r p l a n e t a r y matter may be concentrated m the plane of the e c l i p t i c . Thus, the lower counting rate observed on Pioneer I may be reconcilable w i t h the data from Explorer I and zodiacal l i g h t observations. The accretion of cosmic matter i n the high atmosphere of the e a r t h has geophysical imp l i c a t i o n s that touch on other d i s c i p l i n e s . The matter d i s i n t e g r a t e s by sp u t t e r i n g and a b l a t i o n . Assuming that the r e s u l t i n g atoms may be spread over a 10 km a l t i t u d e region and have holdup times of about three days, i t i s calculated t h a t some 10-̂ atoms of sodium per cm , and some other elements l i k e calcium, may be added to the atmo- sphere per day, assuming concentrations of about one percent of these elements i n the cosmic m a t e r i a l . This i n f l u x could e x p l a i n the source of sodium i n the observations of the sodium t w i l i g h t f l a s h and sodium airglow component, and the e f f e c t of minor constituents i n explaining the nocturnal E region. 6. Bibliography. a. Papers presented at Meetings M. Dubin- "Cosmic Debris of In t e r p l a n e t a r y Space," presented a t Second Astronautics Conference, A p r i l 1958, Denver. Published m Vistas of Astronautics. M, Dubin- "IGY Micrometeorite Measurements," F i r s t I n t e r n a t i o n a l Space Science Conf. Nice, Jan. 1960 (Pub. i n Space Research, H. Kallmann-Bijl, Ed., North-Holland Pub. Co., 1960) M. Dubin: " D i r e c t Measurement of Meteoric Dust using Rockets and S a t e l l i t e s , " Tenth General Assembly, lAU, August 1958, Moscow. b. Published Papers E. Manring, M. Dubin " S a t e l l i t e Micrometeorite Measurements," IGY S a t e l l i t e Report Series, No. 3, May 1958, National Academy of Sciences, Washington, D. C. E. Manring "Micrometeorite Measurements from 1958 Alpha and Gamma S a t e l l i t e s , " Planet. Space Science, Vol. 1, No. 1, p. 27, 1959 M. Dubin. " M e t e o r i t i c Dust Measured from Explorer I " Planetary and Space Science, v o l . 2, No. 2/3, 1960, pp. 121-129, Annals of the IGY. v o l . X I I , Part I I , pp. 472-483. M. Dubin "IGY Micrometeorite Measurements," (Pub. i n Space Research I , H. Kallmann-Bijl, Ed., North Holland Pub. Co., 1960) M. Dubin, W. M. Alexander and 0. E. Berg: "Cosmic Dust Showers by Dir e c t Measurements," presented a t Symposium on Astronomy and Physics of Meteors, Cambridge, Mass., August 28-September 1, 1961. (Pub. i n Smithsonian Contributions to Astrophysics, Vol. 7, p. 109-114) (GPO, Wash., D.C, 1963) M. Dubin and C. W. McCracken "Measurements of D i s t r i b u t i o n s of I n t e r p l a n e t - ary Dust," pub. m Astronomical Journal 67, p. 248-256, 1962. 602

EARTH SATELLITE FLUX WITHOUT "SHOWER" COMPONENT FLUX OF "SHOWER" COMPONENT S 4 6 8 10 12 14 16 18 20 22 24 TIME IN HOURS Figure 6. Diurnal Variation of Meteoritic Impacts on Alpha 1958 603

EARTH SATELLITE Project 32.5 Meteorological Measurements from an Earth S a t e l l i t e 1 Objectives. This p r o j e c t undertaken at the U. S. Army Signal Research and Development Laboratory, Fort Monmouth, provided f o r the development of instrumentation to observe t e r r e s t r i a l cloud cover and other "surface" features from an earth s a t e l l i t e . These observations would provide preliminary assessment of how s a t e l l i t e experiments could be used for meteorological purposes and were expected also to be of immediate importance to synoptic meteorological f o r e c a s t i n g . 2. Operations. An instrument package was developed u t i l i z i n g two photocells, each at the focus of an o p t i c a l telescope aimed i n opposite d i r e c t i o n s at an angle of 45° from the spin axis of the s a t e l l i t e . The c o n f i g u r a t i o n of the sensors and the s p i n , about 50 rpm, of the s a t e l l i t e were expected to make possible the determination of the d i r e c t i o n of the earth's horizon, as a reference, and a scan of the t e r r e s t r i a l albedo i n a band about 35-40° north and south of the equator. A tape recorder stored data from the sensors, to be played back r a p i d l y upon i n t e r r o g a t i o n from ground telemeter s t a t i o n s . An e l e c t r i c day and night switch a c t i v a t e d by solar c e l l s turned on the b a t t e r y operated recording instrumentation only when the s a t e l l i t e viewed sun- l i t areas. 3. Personnel. This work was under the supervision of W. G. Stroud (now at NASA), other senior s c i e n t i s t s associated w i t h Dr. Stroud i n t h i s work were Drs. Stampfl, Hanel and Nordberg ( a l l now at NASA), and Mr. L i c h t (now w i t h Lockheed El e c t r o n i c s Corp.) 4. Data. Data were received at the Evans Area of the U. S. Army Signal Research and Development Laboratory from the telemeter s t a t i o n s f o r analysis. The data were l a t e r t ransferred to NASA f o r continued analysis under Dr. Stroud. 5. Results. The equipment was flown on Vanguard I I (1959 Alpha) w i t h an o r b i t of 33° i n c l i n a t i o n , perigee of about 560 km and apogee of about 3300 km. Data were received f o r about four weeks from the time of launching, February 17, 1959. The good performance of the s a t e l l i t e sensor system indicated great d e t a i l i n the var- i a t i o n s of the r e f l e c t e d e arth r a d i a t i o n received by the s a t e l l i t e and i t was shown that these d e t a i l s corresponded to observations of meteorological systems scanned by the s a t e l l i t e . However, ac t u a l maps of cloud cover were never drawn from Vanguard I I because the s a t e l l i t e developed a precession that introduced great d i f f i c u l t y i n reducing the data. Because of t h i s , the data have not been f u l l y analyzed. The experiment showed, however, that the simple techniques employed were capable of y i e l d i n g information of s u f f i c i e n t r e s o l u t i o n to be u s e f u l , and the experience gained from t h i s f l i g h t was of high value i n designing and carrying out f u r t h e r meteorological s a t e l l i t e experiments. 6. Bibliography. a. Papers Presented at Meetings W. G. Stroud, R. Hanel, W. Nordberg, and R. Stampfl, U.S. Army Signal Engineering Laboratories. A paper delivered a t the CSAGI Rocket and S a t e l l i t e Conference, Washington, D.C., 30 September - 5 October 1957. b. Published Papers R. A. Hanel, J. L i c h t , W. Nordberg, R. A. Stampfl, and W. G. Stroud "The S a t e l l i t e Vanguard I I Cloud Cover Experiment". IRE Trans, on M i l . E l e c t . , Volume MIL-4, Numbers 2 and 3, A p r i l - J u l y , 1960. 604

I EARTH SATELLITE F. 0. Vonbun "Analysis of S a t e l l i t e Motion from Radio Reception," IRE Trans, on M i l . E l e c t . , Volume MIL-4, Numbers 2 and 3, A p r i l - J u l y , 1960. W. G. Stroud, R. Hanel, W. Nordberg, and R. A. Stampfl "Meteorological Measurements from an Earth S a t e l l i t e . " Annals of the IGY, v o l 6, p t . 2, pp. 340-345, 1958. R. Hanel and R. A. Stampfl "An Earth S a t e l l i t e Instrumentation f o r Cloud Measurements." 1958 IRE National Convention Record, p t . 5, pp. 136-141. R. Hanel, R. A. Stampfl, J. Cressey, J. L i c h t , and E. Rich "Tracking Earth's Weather w i t h Cloud Cover S a t e l l i t e , " E l e c t r o n i c s , v o l . 32, pp. 44-49, May 1959. W. G. Stroud and W. Nordberg S c i e n t i f i c Uses of Earth S a t e l l i t e s , p. 113, Univ. of Mich. Press, 1956. 605

EARTH SATELLITE Project 32.6 - Electron Densities i n the Atmosphere 1. Ob.iectives. This p r o j e c t at the U. S. Army B a l l i s t i c Research Laboratories provided f o r a study of a method f o r determining e l e c t r o n densities i n the ionosphere by analysis of radio signals from the s a t e l l i t e . 2. Operations. A study was made of the design of a small l i g h t - w e i g h t t r a n s m i t t e r to be c a r r i e d i n a s a t e l l i t e . Ground reception of t h i s s i g n a l and comparison of Doppler s h i f t s w i t h respect to a standard would give the apparent s a t e l l i t e v e l o c i t y and information as to i t s apparent p o s i t i o n . I t was planned to compare these determinations w i t h the a c t u a l s a t e l l i t e v e l o c i t i e s and positions as obtained w i t h precision o p t i c a l t r a c k i n g equipment. Such comparison would permit inference of ele c t r o n d e n s i t i e s i n the transmission path, which account f o r the d i f f e r e n c e between the radio and o p t i c a l information. A f u r t h e r study was made of the p o s s i b i l i t y of using the 108 Mc M i n i t r a c k trans- mission, intended f o r tra c k i n g and telemetry, f o r the deduction of e l e c t r o n d e n s i t i e s . I t was concluded that the accuracy required f o r good measurements could not be obtained using a single 108 Mc transmission. Since i t d i d not prove possible to include m the on-board experiments a tr a n s m i t t e r of the type contemplated, and m view of the conclusion reached concerning the 108 Mc M i n i t r a c k frequency, t h i s pro- j e c t was withdrawn. I n the o r i g i n a l proposal, the B a l l i s t i c Research Laboratories contemplated a CW beacon frequency of approximately 50 megacycles. The frequency suggested at a s l i g h t l y l a t e r date was 74 megacycles because numerous radio Doppler r e c e i v i n g s t a t i o n s were i n existence w i t h i n the U. S. which could, w i t h minor m o d i f i c a t i o n s , be used f o r obtain- ing Doppler t r a c k i n g information. When the f i r s t USSR s a t e l l i t e s were launched, the B a l l i s t i c Research Laboratories assembled appropriate receivers i n an attempt to ob t a i n ionospheric i n f o r m a t i o n from the 20- and 40-megacycle r a d i a t i o n s . However, the presence of telemetry modulation proved incompatible w i t h the track i n g f i l t e r s used m the receivers and use f u l data were not obtained. 3. Personnel. This work was under the supervision of N. W. Arnold, W. W. Berning was also associated w i t h the p r o j e c t . 4. Bibliography. "Summary of Electronic S a t e l l i t e Tracking Operations f o r Soviet S a t e l l i t e 1957 Alpha-2 and 1957 Beta," BRL Memo Report No. 1174, October 1958. 606

EARTH SATELLITE Project 32.7 S a t e l l i t e Environmental Measurements 1. Objectives. This p r o j e c t a t the Naval Research Laboratory provided f o r the measurement of i n t e r n a l temperatures and pressures inside the s a t e l l i t e assemblies, i n order to a s c e r t a i n the environmental conditions of the e l e c t r o n i c components, p a r t i c u l a r l y t r a n s i s t o r s which are temperature s e n s i t i v e . These measurements also provided a check on the means employed to c o n t r o l the temperature of the s a t e l l i t e , and to detect leakage of the pressure zones i n the s h e l l from f a i l u r e of welds or seals or a r i s i n g from m e t e o r i t i c puncture. I n order to provide information on the a b i l i t y of s h e l l materials to withstand long-time exposure to i n t e r p l a n e t a r y matter impacting a t high v e l o c i t y , micrometeorite impacts were measured, 2. Operations. a. Temperature Measurements. The Vanguard s a t e l l i t e s h e l l s were constructed w i t h an inner " i s l a n d " thermally i n s u l a t e d and supported to the s h e l l by s t r u t s . Thermistors were placed on the inner surface of the s h e l l and i n the " i s l a n d " to monitor temperature. b. Pressure Measurements. The instrumented spheres were equipped w i t h pressurized zones. Penetration of the s a t e l l i t e ' s 0.025-in. t h i c k magnesium s h e l l would have been detected by the loss of pressure from e i t h e r of two herm e t i c a l l y sealed zones on the s a t e l l i t e ' s s h e l l . Each zone comprised approximately 20 percent of the s a t e l l i t e surface. A miniature aneroid-type d i f f e r e n t i a l - p r e s s u r e gauge was connected between the two zones and would have changed i t s resistance w i t h any changes from the i n i t i a l pressure d i f f e r e n c e . c. Surface Erosion. Erosion measurements were made w i t h three chromium s t r i p s evaporated onto Pyrex glass and cemented to the outer surface of the s a t e l l i t e . P i t t i n g of these s t r i p s by micrometeorite impacts or by erosive s p u t t e r i n g of ions, atoms or molecules would have caused an increase i n the e l e c t r i c a l resistance of the s t r i p s . d. Micro-Meteorite Impacts. Micrometeorite impacts were counted d i r e c t l y w i t h p i e z o - e l e c t r i c microphones located on the s h e l l o f the s a t e l l i t e . Each impact up to 1000 from p a r t i c l e s of v i s u a l magnitude 20 or larger were stored i n saturable magnetic cores. During passage over a telemetering ground s t a t i o n , both the t o t a l counts and the instantaneous impact rate were determined. 3. Personnel. H. E. LaGow was p r o j e c t d i r e c t o r , other senior s c i e n t i s t s associated w i t h Mr. LaGow were: Mr. L. Secretan, W. M. Alexander and C. W. McCracken. 4. Data. Results of micrometeoritic impacts were published i n papers that included the data from t h i s experiment, see bibliography below. 5. Results. a. Temperature Data. ( i ) The temperature of S a t e l l i t e s TV-5, SLVl and SLV2 were monitored during t h e i r short f l i g h t . At no time d i d the temperature r i s e above room temperature except when SLV2 plunged from a high a l t i t u d e to the sea. Maximum recorded temperature was 50°C. ( i i ) The temperature of Vanguard I I I was monitored f o r a period of 70 days. The maximum temperature recorded was about 40° + 2°C and the minimum was -2°C f o r a short period i n the beginning of the f l i g h t . Average i n t e r n a l temperature was 20°C except i n the beginning of the f l i g h t when i t dropped to 7°C f o r a short period. 607

EARTH SATELLITE b. Pressure. The d i f f e r e n t i a l pressure between the two pressure zones d i d not vary by a readable amount, from which i t i s concluded t h a t no penetration took place. c. I n t e r p l a n e t a r y Matter. Data were obtained f o r 78 days on Vanguard I I I , launched 18 September 1959. Impacts on the 20-in. sphere w i t h momenta greater than 1 X 10"^ dyne sec corresponding to 3.3 x 10"^ gm a t 30 km/sec were stored i n counters and readout as the s a t e l l i t e passed over the telemetry s t a t i o n s . The mam features of the data are: ( i ) The impact ra t e was h i g h l y v a r i a b l e , impacts/hour averaged over periods 18 September-9 October, 10 November-20 November, and 16 November-18 November were 1.86, 14.6, 41.2 r e s p e c t i v e l y . ( i i ) I n t e r p l a n e t a r y dust p a r t i c l e s from the Leonid Meteor stream were probably responsible f o r the highest observed impact r a t e , 20 impacts were observed i n 6.3 minutes g i v i n g a r a t e of 1900/hour. ( i i i ) Preliminary analysis of average impact rates on Vanguard I I I gives an i n f l u x of 10^ tons/ day s t r i k i n g the earth. 6. Bibliography. a. Papers Presented a t Meetings H. E. LaGow, S. N, Schaeffer, J. C. Schaffert- "Micrometeorite Impact Measurements on a 20-in. Diameter Sphere a t 700-2500 km A l t i t u d e , " Vth General Assembly, CSAGI, Moscow, August 1958 (Pub. i n Annals of the IGY, Vol. X I I , part I I , pp. 465-71, Pergamon Press, 1961) H. E. LaGow, W. M. Alexander "Recent D i r e c t Measurements of Cosmic Dust i n the V i c i n i t y of the Earth Using S a t e l l i t e s , " F i r s t I n t e r n a t i o n a l Space Science Symposium COSPAR, Nice, January 1960 (Pub. i n Space Research, H. K a l l m a n - B i j l , Ed., North-Holland Pub. Co. 1960) W. M. Alexander, C. W. McCracken, H. E. LaGow. " I n t e r p l a n e t a r y Dust P a r t i c l e s of Micron-Size Probably Associated w i t h the Leonid Meteor Stram," 108th meeting of the American Astronomical Society, Nantucket, Mass. June 1961 (Pub. i n Journal of Geophysical Research, v o l . 66, No. 11, pp. 3970-73, Nov. 1961) 608

EARTH SATELLITE Project 32.8 - Lyman-Alpha and X rays 1. Obiectives. This p r o j e c t a t the Naval Research Laboratory provided f o r develop- ment of instrumentation to monitor solar r a d i a t i o n i n the u l t r a v i o l e t and X-ray p o r t i o n of the spectrum, which i s not a v a i l a b l e f o r study below the absorptive layers of the atmosphere. I n the u l t r a v i o l e t range, an important wavelength i s the Lyman-alpha r a d i a t i o n of hydrogen a t 1216 A. This experiment was designed to give more complete information concerning the h i s t o r y of Lyman-alpha and X-ray emission from solar f l a r e s , work that had been begun using rocket techniques. The rocket technique, however, could catch the f i r s t f l a r e r a d i a t i o n s only by accident; the rockets were usually f i r e d when a c t i v i t y had already been noted, and so missed the onset of enhanced energetic r a d i a t i o n . 2. Operations. Equipment f o r observing solar X rays was designed f o r Vanguard I I I (1959 E t a ) , Two i d e n t i c a l i o n i z a t i o n chambers s e n s i t i v e i n the wavelength region 1-10 A were i n s t a l l e d about 120° i n the s a t e l l i t e ' s e q u a t o r i a l plane. The instrument- a t i o n was to measure the solar X-ray f l u x and the peak i n t e n s i t y , the l a t t e r by means of a peak-reading memory device. A more elaborate experiment was designed f o r Explorer V I I (1959 I o t a ) . A photo- s e n s i t i v e c y l i n d r i c a l i on chamber was provided, f i t t e d w i t h a l i t h i u m f l u o r i d e window. The instrument was s e n s i t i v e i n the range 1040° to 1340°, the only important r a d i a t i o n i n t h i s s p e c t r a l region i s the hydrogen Lyraan-alpha a t 1216 A. The X-ray instrument, s i m i l a r i n shape and design to the u l t r a v i o l e t detector, was f i l l e d w i t h argon and f i t t e d w i t h a b e r y l l i u m window, i t was s e n s i t i v e i n the range 2-8 A, 3. Personnel. Herbert Friedman was p r o j e c t d i r e c t o r , other senior s c i e n t i s t s associa- ted w i t h Dr. Friedman were Talbot Chubb, Robert W. K r e p l i n and W i l l i a m A. Nichols. 4. Results. The experiment incorporated i n Vanguard I I I f a i l e d to produce u s e f u l data as the instrumentation was swamped by Van A l l e n b e l t electrons whose energies were greater than 150 Kev. The instrumentation i n Explorer V I I produced data which were compromised i n the same way. However, i n t h i s case i t was possible to e x t r a c t some use f u l information by p l o t t i n g the l a t i t u d e , longitude, and a l t i t u d e of the points a t which the ion chambers became saturated by these electrons. I t has been determined that these t r a n s i t i o n s occur c h a r a c t e r i s t i c a l l y w i t h a harder r a d i a t i o n spectrum (as determined from the Explorer V I I Geiger counters) than has been in d i c a t e d f o r the i n t e r i o r of the outer zone. The p o s i t i o n of these t r a n s i t i o n s and t h e i r c y c l i c a l occurrence i s evidence t h a t they are caused by the trapped r a d i a t i o n . The experience gained from these two experiments was useful i n planning a series of continuing experiments a f t e r the IGY period. The "Sunray" s a t e l l i t e , launched m June 1960, provided f o r the f i r s t time coverage of the u l t r a v i o l e t and X r a d i a t i o n from a solar f l a r e during the onset and development phase. While t h i s was not an IGY experiment, the case h i s t o r y of a f l a r e was one of the goals of the IGY program and I S described here as an i n d i r e c t r e s u l t of the IGY program. On August 6, 1960, data were received during a pass by 1960 Eta I I over Blossom Point, Maryland, simultaneously w i t h a Class 1 solar f l a r e that lasted 18 minutes. The f l a r e began j u s t as the s a t e l l i t e came w i t h i n range of the s t a t i o n , and s i x minutes of clear s i g n a l reception showed the h i s t o r y of development of u l t r a v i o l e t and X-ray emission i n r e l a t i o n to ionospheric behavior and to so l a r - r a d i o noise. One minute a f t e r the s t a r t of the v i s i b l e f l a r e , short-wave radio signals began to fade, two minutes l a t e r , cosmic radio noise began to fade. At t h i s p o i n t , the 609

EARTH SATELLITE s a t e l l i t e signals c l e a r l y showed an increase i n the i n t e n s i t y of solar X rays. One minute l a t e r , the sun began to emit a strong radio-noise burst at 2800 Mc. The noise burst persisted f o r two minutes, during which the X-ray f l u x rose to a very high l e v e l and remained intense even a f t e r the radio-noise burst had disappeared. When the s a t e l l i t e passed out of reception range, the X-ray f l u x was s t i l l strong, but on the s a t e l l i t e ' s next t r a n s i t , two hours l a t e r , the sun was again completely calm and there was no i n d i c a t i o n of abnormal X-ray emission. Throughout t h i s sequence of events the sun's u l t r a v i o l e t r a d i a t i o n remained completely unchanged. 6. Bibliography. S. Russack: "Measurements of the D i s t r i b u t i o n of Electrons i n the Outer Radiation Zone", F i n a l Report Contract Nonr-3270(oo) (X) ER 11688, February 28, 1961, The Martin Company. I I o«swv*t,o<tl VANGUARD m DISTRIBUTION OF MAGNETIC DATA SEPT. IS - Dec 12, W59 Figure 7. Geomagnetic Data from Vanguard I I I . 610

EARTH SATELLITE Project 32.9 - S a t e l l i t e Geomagnetic Measurements 1. Objectives. This p r o j e c t a t the Naval Research Laboratory ( l a t e r t r a n s f e r r e d to the Goddard Space F l i g h t Center, NASA) provided f o r measuring the scalar i n t e n s i t y of the magnetic f i e l d w i t h a proton precession magnetometer i n order to survey the main geomagnetic f i e l d and i t s changes during magnetic storms and other events occurring i n the v i c i n i t y of the earth f o l l o w i n g solar disturbances. 2. Operations. A completely t r a n s i s t o r i z e d proton magnetometer was constructed f o r t h i s p r o j e c t at Varian Associates, Palo A l t o , f o r i n s t a l l a t i o n i n Vanguard I I I ( S a t e l l i t e 1959 E t a ) . The magnetometer transmitted a two-second sample of the magnetic f i e l d on r e c e i p t of a command si g n a l from a Mi n i t r a c k s t a t i o n . The frequence trans- mitted along w i t h coded time signals and a reference frequency were recorded a t the trac k i n g s t a t i o n s and returned to NASA f o r analysis. Also, vector proton magneto- meters were i n s t a l l e d at each M i n i t r a c k s t a t i o n and operated f o r the period of the s a t e l l i t e l i f e . 3. Personnel. J. P. Heppner was p r o j e c t d i r e c t o r , other senior s c i e n t i s t s associated w i t h t h i s work were J. C. Cain, I . R. Shapiro and J. D. S t o l a r i k . 4. Data. The geographic d i s t r i b u t i o n of r e l i a b l e data i s i l l u s t r a t e d i n Figure 7. The shaded area i n t h i s f i g u r e i s s l i g h t l y less than 3% of tha t of the earth. For reasons of antenna s e n s i t i v i t y and of obtaining maximum data from the a v a i l a b l e power supply, the magnetometer was interrogated p r i m a r i l y near the meridian of each Min i t r a c k s t a t i o n . The few points obtained over South A f r i c a was the r e s u l t of mak- ing the i n s t a l l a t i o n of the Johannesburg s t a t i o n a f t e r the s a t e l l i t e launch. The d i s t r i b u t i o n of data f o r a l l s t a t i o n s w i t h a l t i t u d e i s given i n Table I I I . The data have been published. TABLE I I I D i s t r i b u t i o n of Vanguard Data from a l l s t a t i o n s w i t h a l t i t u d e t i t u d e Range (Km) Data A l t i t u d e Range (Km) Data 500 799 633 2300 - 2599 245 800 1099 342 2600 - 2899 238 1100 1399 441 2900 - 3199 192 1400 1699 302 3200 - 3499 157 1700 1999 316 3500 - 3799 212 2000 2299 292 3800 0 5. Results. The Vanguard I I I s a t e l l i t e operated successfully from launch, September 18, 1959, u n t i l i t s power supply f a i l e d December 12, a period of 84 days. The o r b i t was a t an i n c l i n a t i o n of 33.5° geocentric w i t h an apogee of 3750 km and 611

EARTH SATELLITE perigee of 510 km. The geomagnetic l a t i t u d e range covered was + 45°. During the period of transmission the ten receiving s t a t i o n s monitored a t o t a l of about 2450 s a t e l l i t e passes to receive over 4200 magnetometer signals. A set of 2872 of these signals has been designated as a prime data set on the basis of s i g n a l q u a l i t y and freedom from possible coded time e r r o r s . The remaining signals have been c l a s s i f i e d m secondary sets of lesser r e l i a b i l i t y . Since some of the Min i t r a c k s t a t i o n s were r e l a t i v e l y closely spaced i t was oft e n possible to receive the magnetometer signals at more than one receiver. A comparison of the differences between the approximately 500 duplicate signals recorded was made i n an e f f o r t to estimate the l i m i t s of accuracy of the experiment. Taking the best of these signals as reference, the differences formed a roughly Gaussian d i s t r i b u t i o n w i t h a sigma of 3 gamma. I t i s f e l t that t h i s p r e c i s i o n i s representative of the accuracy of the data since the other known sources of er r o r are small. I n a d d i t i o n to providing magnetic f i e l d data, the proton magnetometer also acted as a receiver f o r w h i s t l e r (VLF) signals i n the 0.4 to 10 kc range. Observed were not only the dispersed, lightning-produced atmospherics, but also a few " r i s e r s " or signals that other workers have i n t e r p r e t e d as r a d i a t i o n from trapped p a r t i c l e s . These unexpected data have been analyzed to check the adequacy of theories on w h i s t l e r propagation, to estimate e l e c t r o n d e n s i t i e s above the F-peak, and to study the conditions allowing the propagation of VLF signals from the troposphere t o the s a t e l l i t e i n the w h i s t l e r mode. a. Analysis I n order to make meaningful i n t e r p r e t a t i o n s of the geomagnetic measurements from the Vanguard I I I s a t e l l i t e i t was necessary to obtain f i r s t a r e l i a b l e reference f i e l d from which time f l u c t u a t i o n s could be studied. The gener- a t i o n of a r e l i a b l e reference f i e l d was f i r s t attacked by e x t r a p o l a t i o n of the ground measured f i e l d as synthesized from harmonic expansions. Sets of spherical harmonic c o e f f i c i e n t s used included those by Finch and Leaton (1957) and by Jensen and Whitaker (1960). (See NASA Report G-696, pages 12 and 13). A sample p l o t of the f i e l d differences (measured minus computed) versus a l t i t u d e f o r an area near C a l i f o r n i a i s given i n Figure 8. The i n i t i a l value of such a presentation was to point out data that were d i s s i m i l a r from others i n the v i c i n i t y . I t was f i r s t thought that these p l o t s would be an ai d to determining erroneous values and to point out those f i e l d values that showed time f l u c t u a t i o n s . S u r p r i s i n g l y , the sharp breaks noted i n such curves were found to be due to d i s c o n t i n u i t i e s i n the o r b i t a l arcs used to compute s a t e l l i t e p o s i t i o n . The apparent f i e l d d ifferences due to errors i n the computed p o s i t i o n were commonly 50 gammas f o r data points taken near the time of d i s c o n t m u t i e s i n the o r b i t arc computations. The f i n d i n g of large e f f e c t s caused by the techniques of o r b i t reduction led to new procedures i n o r b i t reduction. Eventually through use of both radio and p o t i c a l tracking data and new procedures the l o c a t i o n accuracy was improved to the extent that estimates based on cross-comparisons gave rms errors of 9 gammas f o r the equivalent f i e l d e r r o r caused by l o c a t i o n e r r o r s . b. Computations of reference f i e l d s from spherical harmonics Computations from such curves as Figure 8 show that i n the areas covered by the s a t e l l i t e the computed values of t o t a l f i e l d agree w i t h those measured to w i t h i n 2%. Based on the probable accuracy of the data from which both the Finch and Leaton and the Jensen and Whitaker c o e f f i c i e n t s were derived, the agreement i s quite p l a u s i b l e . Looking over many curves s i m i l a r to Figure 8, i t i s apparent that the reference f i e l d could be appreciably improved over the areas inves t i g a t e d . At f i r s t i t was thought that i t would be necessary to use sets of spherical harmonics using about a hundred c o e f f i c i e n t s to f i t the data. However, l a t e r analysis has shown that these data, l i m i t e d i n area to only 3% of the earth's surface, are adequately f i t by a set using only 63 c o e f f i c i e n t s . These f i t s were made without regard to possible temporal v a r i a t i o n s and using pre- l i m i n a r y o r b i t s from the Smithsonian Astrophysical Observatory w i t h a quoted standard d e v i a t i o n of from 1 to 4 minutes of arc. The standard d e v i a t i o n of 23 gammas between 612

EARTH SATELLITE 4 0 0 0 3 5 0 0 3 0 0 0 £ 2 5 0 0 o> 'Si E o X 2 0 0 0 I 5 0 0 I 0 0 0 500 1 1 1 1 1 JENSEN FINCH a LEATON a WHITAKER ~ COEFFICIENTS • 'COEFFICIENTS Ftom U S IM H 0 .Qharts •• •* — V •• • • • « — > • • • • • • • *• v.- • : • • • I - • • • • • • • • » • * ••. * . • • • • • ; • . <̂ l 2 5 0 K m — •• • . • • •*• • • ••• _ . •••• • • '& . . . . • 1 1 1 1 1 - 4 0 0 - 3 0 0 - 2 0 0 -100 0 +100 +200 Measured Field minus Computed Fie lds (Gammas) Figure 8. Differences Between Measured F i e l d and Computed Reference Field s as Function of A l t i t u d e a t Latitudes 32° to 33.5°N, Longitudes 111° to 121°W, O r b i t Computation a t Ona-Week I n t e r v a l s . 613

EARTH SATELLITE the data and t h i s new c o e f f i c i e n t set could not be appreciably improved w i t h higher harmonics. I n the set of 2872 data p o i n t s , i n c l u d i n g points taken during magnetic storms, only 7 give a d e v i a t i o n over 100 gamma from the computed values and 2 of these are from the South A f r i c a n area where the f i t i s poor owing to sparse data. The considerable improvement of f i t to the data w i t h so few c o e f f i c i e n t s implies that I t should likewise be possible to improve the e x i s t i n g magnetic f i e l d charts by s i m i l a r f a c t o r s . The standard d e v i a t i o n of Vanguard data from the Finch & Leaton c o e f f i c i e n t s i s 110 gamma, a fa c t o r of about f i v e greater than that obtained from the new c o e f f i c i e n t s . c. Magnetic Storms During the s a t e l l i t e ' s operating l i f e , surface observatories showed s i x periods of magnetic disturbance. Three of the disturbed periods s t a r t e d w i t h w e l l defined sudden commencements. From preliminary analysis of measurements taken during the s i x periods (see reference i n bibliography f o r more d e t a i l ) the fo l l o w i n g features were evident. During the mam phase of magnetic storms, the maj o r i t y of measurements d i d not reveal disturbances of the main f i e l d greater than the data scatter r e s u l t i n g from u n c e r t a i n t i e s m s a t e l l i t e l o c a t i o n . Of the measure- ments which d e f i n i t e l y showed disturbances, the sign of the disturbance was more o f t e n negative than p o s i t i v e when the sign was negative on the earth's surface but d e t a i l e d c o r r e l a t i o n s w i t h surface magnitudes were poor. Measurements taken near the northern and southern l i m i t s of the inner Van A l l e n r a d i a t i o n b e l t (magnetic l a t i t u d e 40°) showed considerably more disturbance than those taken w i t h i n the inner b e l t a t magnetic l a t i t u d e s greater than 25 degrees. 6. Bibliography. J. P. Heppner, J. D. S t o l a r i k , I . R. Shapiro, and J. C. Cain " P r o j e c t Vanguard Magnetic F i e l d Instrumentation and Measurements." Proceedings of the 1st I n t e r n a t i o n a l Space Science Symposium COSPAR, Nice, Jan. 1960, Pub. i n Space Research, ed. by H. Kallmann-Bijl, North-Holland Pub. Co., 1960, pp. 982-999, NASA Tech.Note D-486. J. P. Heppner, J. C. Cain, I . R. Shapiro, J. D. S t o l a r i k . " S a t e l l i t e Magnetic F i e l d Mapping," X I I Gen. Ass. lUGG, H e l s i n k i , August 1960, NASA Tech. Note D-696. I . R. Shapiro, J. D. S t o l a r i k , and J. P. Heppner- "The Vector F i e l d Proton Magnetometer f o r IGY S a t e l l i t e Ground Stations," J. Geophys. Res., 65, pp. 913-120, March 1960, NASA Tech. Note D-358. J. C. Cain, I R. Shapiro, J. D. S t o l a r i k , and J. P. Heppner. "Note on Whistlers Observed Above the Ionosphere," J. Geophys. Res., 66, pp. 2677-2680, Sept. 1961 J. C. Cam, I . R. Shapiro, J. D. S t o l a r i k , and J. P. Heppner. "Whistler Signals Observed w i t h the Vanguard I I I S a t e l l i t e , Proceedings of the I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm, Kyoto, Japan, Sept. 4-15, 1961 (to be published) D. L. Mansir "Magnetometer at Work i n Outer Space," Radio E l e c t r o n i c s , pp. 38-41, A p r i l 1960. J. C. Cam, I . R. Shapiro, J. D. S t o l a r i k , and J. P. Heppner: "Vanguard-3 Magnetic F i e l d Observations," JGR, v o l . 67, p. 5055-5069, Dec. 1962. I . R. Shapiro, J. D. S t o l a r i k , and J. P. Heppner "Data Report on Whistlers observed by Vanguard-3," NASA Tech. Note D-2313, July 1964. 614

EARTH SATELLITE Project 32.10 - Measurement of Cosmic L i g h t and Radiation from a S a t e l l i t e 1. Ob.iectives. This p r o j e c t a t the Jet Propulsion Laboratory, C a l i f o r n i a I n s t i t u t e of Technology provided f o r development of instrumentation to measure the integrated l i g h t from various parts of the c e l e s t i a l sphere, using a set of color f i l t e r s and a p h o t o - m u l t i p l i e r detector. I n a d d i t i o n , i t was planned to measure the cosmic-ray f l u x w i t h an automatic i o n i z a t i o n chamber of a type used previously i n balloon surveys of the cosmic-ray i n t e n s i t y . 2. Operations. The detector and associated c i r c u i t r y were developed at JPL along w i t h the development of su i t a b l e telemetry c i r c u i t s f o r the Microlock r e c e i v i n g s t a t i o n s . 3. Personnel. This work was under the d i r e c t i o n of W. H. Pickering, other senior s c i e n t i s t s associated w i t h Dr. Pickering i n t h i s p r o j e c t were E. Rechtin, H. L. Richter, and W. A, Baum. 4. Results. The instrumentation developed under t h i s p r o j e c t was intended as backup i n the event t h a t i t proved possible to f l y more experiments than a n t i c i p a t e d . This p o s s i b i l i t y d i d not m a t e r i a l i z e and t h i s instrumentation was not flown as an IGY experiment. The work d i d prove u s e f u l , however, i n preparation f o r other post- IGY experiments p a r t i c i p a t e d i n by JPL. 615

EARTH SATELLITE Project 32.11 S a t e l l i t e Measurement of the Earth's Radiation Balance 1. Objectives. This p r o j e c t at the Department of Meteorology, U n i v e r s i t y of Wisconsin, provided f o r development of instrumentation to measure the d i r e c t solar r a d i a t i o n , the r a d i a t i o n r e f l e c t e d by the e a r t h , and the long wave r a d i a t i o n emitted by the e a r t h , i n order to determine the complete r a d i a t i o n balance. This information i s of p a r t i c u l a r importance to studies of the general atmospheric c i r c u l a t i o n . 2. Operations. The experiment was f i r s t planned f o r i n s t a l l a t i o n i n a Vanguard s a t e l l i t e , w i t h a tape recorder to store i n f o r m a t i o n and play back upon ground command. As the Vanguard program encountered delays, however, t h i s experiment was redesigned as p a r t of a complex instrument package f o r launching m the Explorer series. Four hemispherical s i l v e r bolometers were mounted i n the e q u a t o r i a l plane of the s a t e l l i t e , each hemisphere was mounted close to but thermally i n s u l a t e d from a m i r r o r e s p e c i a l l y coated to have high reflectance i n the u l t r a v i o l e t , and large enough so that the hemisphere d i d not "see" the s a t e l l i t e i t s e l f . I t was shown t h e o r e t i c a l l y that such mirror-backed hemispheres, spinning i n space as the s a t e l l i t e r o t a t e d , act as though they were i s o l a t e d spheres i n space. One hemisphere, coated white, was more se n s i t i v e to t e r r e s t r i a l (long wave) than solar r a d i a t i o n , two black-coated hemispheres responded about equally to solar and t e r r e s t r i a l r a d i a t i o n , the f o u r t h hemisphere, coated w i t h gold, was more s e n s i t i v e to solar than to t e r r e s t r i a l r a d i a t i o n . A black-coated sphere was mounted on the spin axis of the s a t e l l i t e to serve as a reference to determine any d e t e r i o r a t i o n of the m i r r o r surface. A sphere f i t t e d w i t h a shade to protect i t from d i r e c t s u n l i g h t was used to measure s u n l i g h t r e f l e c t e d from the earth when the spin axis of the s a t e l l i t e points to the earth's surface. Sensor temperatures were measured by glass-coated bead thermistors mounted to make good contact w i t h the sensors. The sensor thermistors were connected i n t u r n through a mechanical programming device to a blocking o s c i l l a t o r , so that sensor temperatures c o n t r o l l e d the frequency of the o s c i l l a t o r . A sealed mechanical p r e c i s i o n tuning f o r k was used t o generate a 512 cycle reference waveform, s u i t a b l y shaped and scaled down to two cycles per second. These pulses operated a stepping switch t h a t actuated the mechanical programmer. Programmed temperature observations were telemetered to ground s t a t i o n s v i a the 19.995 Mc t r a n s m i t t e r . The e n t i r e system was designed to have low power drai n by u t i l i z i n g t r a n s i s t o r c i r c u i t r y and arranging a low duty cycle f o r the el e - ments r e q u i r i n g high power, p a r t i c u l a r l y Che programmer. Transistors and components were chosen to minimize temperature s e n s i t i v i t y throughout the system. Along w i t h the on-board instrumentation, many t h e o r e t i c a l studies were undertaken i n preparation f o r analysis of the data, p a r t i c u l a r l y w i t h regard to the r e s o l u t i o n t h a t might be expected versus the averaging e f f e c t s of the large s o l i d angle viewed by the s a t e l l i t e . A tape read-out system was designed and constructed to permit reading out of the data a t 512 times the r a t e of t a k i n g the data. Computer programs were developed to convert the temperature measurements i n t o r a d i a t i o n fluxes using heat balance equations. 3. Personnel. V. E. Suomi was p r o j e c t d i r e c t o r f o r t h i s work, another senior s c i e n t i s t , associated w i t h Dr. Suomi, was Professor R. I . Parent of the E l e c t r i c a l Engineering Department, U n i v e r s i t y of Wisconsin. 4. Data. The reports c i t e d under Bibliography below contain reduced data. 5. Results. The heat balance experiment was included m Explorer V I I (1959 I o t a ) , launched October 13, 1959. I t a t t a i n e d an o r b i t of 50.3° i n c l i n a t i o n , apogee of approximately 1100 km, perigee of 560 km. A huge amount of data accumulated from t h i s experiment, f o r example, i n one month, 432,000 separate measurements were made. 616

EARTH SATELLITE The perigee a l t i t u d e of 560 km means that the experiment was above the F2 layer during the day and above the F layer a t n i g h t . The low frequency of telemetry accounted f o r considerable ionospheric e f f e c t i n reception of the s i g n a l . At n i g h t , u s e f u l signals were received f o r up to 15 or 20 minutes, during the day, however, when the ionosphere i s less transparent, signals were received f o r a much shorter time. At n i g h t , coverage a t each s t a t i o n was up to one f i f t h of the distance around the earth and g l o b a l coverage of the telemetered information was much higher than during daytime hours. However, since telemeter r e c e i v i n g s t a t i o n s were not uniformly d i s t r i b u t e d , true g l o b a l coverage was not a t t a i n e d i n the l a t i t u d e b e l t swept out by the s a t e l l i t e . I n a d d i t i o n , since each o r b i t a l pass was about 110 minutes l a t e r than the preceding one, and swept out only a l i m i t e d b e l t along the o r b i t , observations put together f o r a large area were not t r u l y synoptic, as are surface and upper a i r maps. This introduced a complication i n t o comparison of the maps of the r a d i a t i o n f i e l d against conventional meteorological maps. Preliminary computations have been made of nighttime data, chosen because of b e t t e r coverage and because only longwave r a d i a t i o n i s considered, making the com- putations simpler. The longwave r a d i a t i o n measured a t n i g h t i s shown m Figures 9 and 10, each dot on the map i s one observation. Shown also are 500 mb maps and a surface map, a l l chosen to have the best time c o r r e l a t i o n w i t h the r a d i a t i o n map. The f r o n t a l p o s i t i o n s shown on the surface map were obtained from several surface maps and are synoptic w i t h s a t e l l i t e passage m the respective areas. Some remarks should be made about the r a d i a t i o n p a t t e r n analysis. I n middle l a t i t u d e s where the telemetry contact i s most r e l i a b l e the analysis w i l l be more or less consistent from analyst to analyst. On the other hand, m the t r o p i c a l P a c i f i c where the telemetry coverage i s not as good and the distance between o r b i t s i s great, the analysis i s subject to a considerable amount of i n t e r p r e t a t i o n . The map of December 2 i s a case i n p o i n t . The o r b i t path SE along the Gulf of C a l i f o r n i a very d e f i n i t e l y establishes a low m outgoing r a d i a t i o n as l a t i t u d e 20°N. S i m i l a r l y the o r b i t path j u s t to the west of Hawaii d e f i n i t e l y establishes another low a t about 10°N. However, on the o r b i t between these two the data are not as complete and while I t shows a trend toward a low value, one cannot be sure, as the map i n d i c a t e s , that t h i s I S i n f a c t the same large scale low r a d i a t i o n area. There i s a general east- ward movement to the c e l l from map to map i n agreement w i t h the wind d i r e c t i o n a t high levels during t h i s season. Despite the necessary shortcomings i n the analysis there does seem to be a clear i n d i c a t i o n that large scale outward r a d i a t i o n f l u x patterns e x i s t and that these patterns are r e l a t e d to the large scale features of the weather. Meteorologists expected a v a r i a t i o n of outgoing r a d i a t i o n w i t h l a t i t u d e but the preliminary r e s u l t s show v a r i a t i o n of the outgoing longwave r a d i a t i o n w i t h longitude as w e l l . Rossby's statement that the r a d i a t i o n loss i s c o n t r o l l e d by the c i r c u l a t i o n patterns i s cer- t a i n l y v e r i f i e d . I t i s also apparent t h a t these r e s u l t s re-emphasize the important r o l e that clouds play i n c o n t r o l l i n g the outgoing r a d i a t i o n . The accuracy of previous estimates of outgoing r a d i a t i o n w i l l be governed to a large extent by the accuracy of the estimate of cloud cover. I t I S of some i n t e r e s t to note t h a t the r a d i a t i o n gradient w i t h l a t i t u d e f o r the A p r i l map i s somewhat steeper than the l a t i t u d i n a l gradient f o r the December maps. Also the heat loss from the northern p o r t i o n of the o r b i t b e l t i s less i n A p r i l than i n December. The A p r i l r a d i a t i o n p a t t e r n looks more l i k e a winter s i t u a t i o n than the December map. An inspection of the 500-mb charts shows th a t t h i s i s as i t should be. The north-south temperature gradient i s t i g h t e r i n the A p r i l case and the temperature at the northern border i s s i g n i f i c a n t l y colder as w e l l . 617

EARTH SATELLITE Figure 9a. Long Wave Radiation Loss in Cal/cm^in, December 2, 1959 Figure 9b. Height of 500-mb surface at 0000 UT, December 2, 1959 618

EARTH SATELLITE 0 Figure 10a. Long Wave Radiation Loss in Cal/cm^ min, A p r i l 4, 1959. 7 n Figure 10b. Height of 500-mb surface at 0000 UT, Ap r i l 4, 1959. Figure 10c. Analysis of Surface at 1200 UT, Ap r i l 4, 1959. 619

EARTH SATELLITE Of f a r greater importance to meteorology than the loss of r a d i a t i o n from the top of the atmosphere i s the v e r t i c a l divergence of net longwave r a d i a t i o n w i t h i n the atmosphere. The magnitude of t h i s term determines whether or not the atmosphere i s heating or cooling. Studies combining r a d i a t i o n measurements made w i t h Explorer V I I and balloon-borne radiometer sondes which measure the divergence j u s t mentioned show that I t I S possible to get good estimates of the heating and cooling of the atmosphere from s a t e l l i t e measurements alone. This i s h i g h l y u s e f u l since differences i n rates of cooling of the atmosphere can generate a v a i l a b l e p o t e n t i a l energy which drives the atmosphere. While t h i s part of the study i s m i t s e a r l y stages, enough has been learned to in d i c a t e that t h i s d i f f e r e n t i a l cooling i s an important part of the atmospheric energy supply. I t should be emphasized that these charts represent only the beginning of an enormous amount of data, and also that here only one h a l f of the problem, namely the r a d i a t i o n losses, has been tre a t e d . Equally important to the understanding of the earth's heat budget are the gains from the sun. These w i l l be treated i n f u t u r e publications stemming from these observations. I t appears t h a t very u s e f u l r a d i a t i o n data can be co l l e c t e d from a modestly instrumented earth s a t e l l i t e . Had Explorer V I I c a r r i e d a data storage u n i t so that the measurements f o r a complete o r b i t could be obtained by i n t e r r o g a t i o n from a ground s t a t i o n , i t would have been possible to have maps, such as herein described, f o r the whole earth. The problem of analysis would not have been more d i f f i c u l t because of the added data, i t would have been simpler. This i s because most of the work was involved w i t h f i t t i n g many pieces of data i n t o a comprehensive p i c t u r e . The experience gained from t h i s experiment was an important f a c t o r i n designing, fu t u r e meteorological s a t e l l i t e experiments TIROS I I I c a r r i e d a s i m i l a r experiment. 6. Bibliography. a. Papers presented at Meetings V. E. Suomi "Radiation Measurements from an Earth S a t e l l i t e , " Explorer V I I , X l l t h General Assembly lUGG, H e l s i n k i , August 1960. V. E. Suomi " V a r i a b i l i t y of Solar Constant from Explorer V I I . " New York Academy of Sciences, January 1961. V. E. Suomi- "Some Meteorological Data Obtained from Explorer V I I . " American Meteorological Society meeting at Washington, A p r i l 29, 1960. V. E. Suomi and R. J. Parent "A Simple High Capacity D i g i t a l Output Storage System for Space Experiments." Symposium on Electronics and Telemetry, Sec. IV-V, published i n IRE Transactions of 1960. R. J. Parent, H. H. M i l l e r , V. E. Suomi and W. B. S w i f t , "Instrumentation for a Thermal Radiation Budget S a t e l l i t e . " Proceedings of the National Electronics Conference. Vol. 15, 1959. V. E. Suomi and R. J. Parent, " S a t e l l i t e Instrumentation f o r Measurement of Thermal Radiation Budget of the Earth." National Telemetering Conference. Sponsored by AIEE, ISA, American Rocket Society, I n s t i t u t e of Aeronautical Science, June 1958. Baltimore paper published i n Proceedings, pp. 186-190. b. Published Papers V. E. Suomi "The Thermal Radiation Balance Experiment on Board Explorer V I I , " Technical Note D-608, June I I Summary Project Report, pp. 273-305, Marshall Space F l i g h t Center, NASA, H u n t s v i l l e , Alabama, July 1, 1961. Melvin Wemstem and V. E. Suomi. "Analysis of S a t e l l i t e I n f r a r e d Radiation Measurements on a Synoptic Scale." Monthly Weather Review, October 1961. 620

EARTH SATELLITE Project 32.12 Determination of Flux of Heavy Primary Cosmic-Ray Nuclei 1. Objectives. This p r o j e c t , c a r r i e d out cooperatively at the B a r t o l Research Foundation, F r a n k l i n I n s t i t u t e , and the Research I n s t i t u t e of Advanced Studies (RIAS), the Martin Co., was undertaken to i n v e s t i g a t e the f l u x of heavy primary cosmic-ray n u c l e i . While most of the primary f l u x consists of hydrogen and helium n u c l e i , there I S important need to know the composition of the heavy primaries, which comprise about 17o of the t o t a l f l u x , to study modulation e f f e c t s stemming from solar d i s t u r b - ances, and to determine whether there might be any periodic v a r i a t i o n . The abundance of elements m the universe i s estimated from astronomical observations, cosmic-ray observations i n d i c a t e a number of d i s p a r t i e s i n the abundances, the explanation of which undoubtedly bears on cosmological questions such as the o r i g i n and development of stars and the o r i g i n and a c c e l e r a t i o n of cosmic rays. 2. Operations. Following e a r l i e r balloon-borne experiments by s c i e n t i s t s a t B a r t o l Research Foundation, instrumentation was developed to detect the number of heavy primaries t r a v e r s i n g an ion chamber. I t i s known th a t the i o n i z a t i o n of a r e l a t i v i s t i c p a r t i c l e i s energy-independent and depends on the square of the atomic number of the energetic p a r t i c l e . Thus, the number of electrons created along the path length i s also p r o p o r t i o n a l to the square of the atomic number and gives a pulse i n the c o l l e c t o r c i r c u i t , the amplitude of which i s a measure of the mass of p a r t i c l e detected. The c i r c u i t was arranged w i t h a very short gating time so that p o s i t i v e ions would not be c o l l e c t e d , and three pulse-height d i s c r i m i n a t o r channels were provided f o r detection of pulses corresponding to atomic masses equal to or greater than 6, 9, and 16. Previously measured heavy primary fluxes from balloon and rocket experiments were used to set the sca l i n g and storage c i r c u i t s so as to provide a range of operation judged w i t h i n the capacity of the storage and telemetry c i r c u i t s , i n t h i s way possible ambiguity was avoided. Instrumentation was prepared f o r i n s t a l l a t i o n m the Explorer series and was designed as part of a complex instrument package containing several experiment's of other groups. The i o n i z a t i o n chamber was constructed of a low Z m a t e r i a l , Dow metal, i n order to reduce the p o s s i b i l i t y of star formation would produce fragments of heavy i o n i z i n g power th a t would lead to spurious counts as they would be i n d i s t i n g u i s h a b l e from the heavy primaries. 3. Personnel. M a r t i n A. Pomerantz, B a r t o l Research Foundation, and Gerhard Groet- zinger of RIAS were the i n i t i a l p r o j e c t d i r e c t o r s . Dr. P h i l i p Schwed of RIAS assumed r e s p o n s i b i l i t y f o r the RIAS p o r t i o n of the work f o l l o w i n g Dr. Groetzinger's death. Dr. Louis Witten succeeded Dr. Schwed i n February 1961. Other s c i e n t i s t s associated w i t h t h i s work were S. P. Agarwal, B a r t o l , H. Hansen and H. Benjamin, RIAS. 4. Data. The reports c i t e d below under Bibliography include some of the reduced data. 5. Results. The experiment was flown on Explorer V I I (1959 I o t a ) launched October 13, 1959, w i t h an o r b i t of 50.3° i n c l i n a t i o n , 1100 km apogee and 560 km perigee, thus taking the vehicle through portions of the Van A l l e n Radiation B e l t s . D i f f i c u l t y was encountered w i t h interference from the NRL Solar r a d i a t i o n experiment, and the c i r c u i t r y associated w i t h one channel of the experiment underwent a change m mode of operation twelve days a f t e r launch. These problems introduced increased d i f f i c u l t i e s i n t o the reduction and analysis of r e s u l t s , but d i d not prove insurmountable. To i n v e s t i g a t e whether s i g n i f i c a n t time v a r i a t i o n s i n the energy spectrum occurred during the period October 1959-May 1960, the data were divided i n t o roughly equal ( 2 weeks) i n t e r v a l s f o r each of which the i n t e g r a l energy spectrum was determined. For the present purposes, the data recorded around the world i n the Northern Hemisphere were sorted i n t o 1° i n t e r v a l s of geomagnetic l a t i t u d e , and the 621

EARTH SATELLITE 3000 2000 3 O 1000 - \ H 3 o o UJ 500 A 300 200 100 1 1 1 1 1—I I I Explorer VII Heavy Primary Cosmic R a y s , Z > 6 Feb 1-14, I 9 6 0 N(>E) = k E " ' ' • - 10 Average i J I l _ l I I—L I 2 3 4 5 10 E - T o t a l E n e r g y - G e v / n u c l e o n Figure 11. I n t e g r a l Energy Spectrum 1 1 1 r Eip lorer VII H«ovy Primary Coimie R o y t , Z k 6 i \ i \ ' j N ( > E ) . l i E Octobir Na*in»«r Oietnbir Jdauoif FiBm I 9 S 9 Aerii usr Figure 12. Values of k and gamma. 622

EARTH SATELLITE corresponding geomagnetic c u t o f f energies were computed on the basis of the con- ven t i o n a l centered dipole approximation. Figure 11 shows a t y p i c a l p l o t of the re- s u l t i n g i n t e g r a l energy spectrum expressed i n the form N ( >E) KE'' where N i s the number of counts per hour, and E i s the t o t a l energy i n Gev/nucleon. For each of 13 periods, a s t r a i g h t l i n e was f i t t e d by the method of least squares to a l l the experi- mental points f o r whifh E_> 3 Gev/nucleon, The values of 7 and k determined i n t h i s manner are p l o t t e d i n Figure 12. S i g n i f i c a n t changes i n the spectrum of heavy n u c l e i curing the indicated period are revealed by t h i s analysis of the Explorer V I I observations. Changes i n the shape of the spectrum are also evident i n the range of E >3 Gev/nucleon. A d e t a i l e d study of the nature of the time v a r i a t i o n s detected i n the Explorer V I I heavy nucleus experiment i s continuing. There i s some i n d i c a t i o n of c o r r e l a t i o n s between the i n t e n s i t y of heavy n u c l e i and the primary proton f l u x as represented by ground neutron monitors. Other topics under i n v e s t i g a t i o n include work on approximations which represent the e f f e c t of the geomagnetic f i e l d upon cosmic-ray c u t o f f r i g i d i t i e s and the observation of heavy n u c l e i from the sun. 6. Bibliography. a. Papers Presented at Meetings M. A. Pomerantz, L. Witten " S a t e l l i t e I n v e s t i g a t i o n of Time V a r i a t i o n of Heavy Nuclei i n the Primary Radiation," V l l t h I n t e r n a t i o n a l Conference on Cosmic Rays, lUPAP, Kyoto, Japan, Sept. 1961 M. A. Pomerantz, S. P. Agarwal, P. Schwed and H. Hanson "A S a t e l l i t e I n v e s t i g a t i o n of Heavy Primary Cosmic Rays," X I I General Assembly lUGG Symposium on Geophysical Aspects of Cosmic Rays, H e l s i n k i , Finland, 28 July 1960 S. P. Duggal and M. A. Pomerantz. "Long Term V a r i a t i o n of Primary Cosmic Rays w i t h Z > 6." Washington Meeting of the American Physical Society, A p r i l 27-30, 1964. b. Published Papers. P. Schwed, M. A. Pomerantz, H. Hanson, H. Benjamin "Satellite-Borne Instrumentation f o r Observing Flux of Heavy Primary Cosmic Radiation," J. F r a n k l i n I n s t i t u t e , Vol. 271, p. 275, 1961 M. A. Pomerantz, S. P. Agarwal, P. Schwed, H. Hanson " S a t e l l i t e Deter- mination of Heavy Primary Cosmic-Ray Spectrum," Phys. Rev. L e t t e r s , Vol. 6, p. 352, 1961 P. Schwed, H. Hanson, H. Benjamin, M. A. Pomerantz "The Heavy Primary Cosmic Ray Experiment," Ch. 8 of Technical Note D-608, June summary project r e p o r t , Vol I , Explorer V I I S a t e l l i t e , G. C. Marshall Space F l i g h t Center, NASA, H u n t s v i l l e . Ala , July 1961 M. A. Pomerantz, S. P. Agarwal, P. Schwed and H. Hanson "A S a t e l l i t e I n v e s t i g a t i o n of Heavy Primary Cosmic Rays," Proceedings of X I I General Assembly of lUGG Symposium on Geophysical Aspects of Cosmic Rays, H e l s i n k i , Finland, 28 July 1960. Martin A. Pomerantz, and Louis Witten, " S a t e l l i t e I n v e s t i g a t i o n of Time Variations of Heavy Nuclei i n the Primary Cosmic Radiation." Journal of the Physical Society of Japan, Vol. 17, Supplement A - I I I , 1962, Part I I I , pp. 40 - 43 (1962), I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm. 623

EARTH SATELLITE Martin A. Pomerantz and Louis Witten. "Solar-Produced Heavy Nuclei During November, 1960." Space Research I I I , p. 692-699 (1962), Proceedings of the Third I n t e r n a t i o n a l Space Science Symposium, Washington, 1962. M. A. Pomerantz and S. P. Duggal. "Spectrum of Heavy Nuclei i n the Primary Cosmic Radiation." Space Research IV, pp. 972 - 988 (1963), Proceedings of the Fourth I n t e r n a t i o n a l Space Science Symposium, Warsaw, 1963. 624

EARTH SATELLITE Project 32.30 Special Equipment and Engineering Services f o r S c i e n t i f i c Experiments 1 Obiectives. This p r o j e c t at the Naval Research Laboratory provided f o r design and construction of s a t e l l i t e s h e l l s and i n t e r n a l framework, design and c o n s t r u c t i o n , as w e l l as t e s t i n g and modifying, of i n t e r n a l instrument packages and Mmitrack telemeter t r a n s m i t t e r s and command receivers, s o l u t i o n of temperature c o n t r o l problems of each s a t e l l i t e system, v i b r a t i o n t e s t i n g and c o n t r o l , dynamic balancing of the s a t e l l i t e s , p r o v i s i o n f o r c o n t r o l of s a t e l l i t e spin, s a t e l l i t e separation, pr o v i s i o n of telemeter records during s a t e l l i t e preparation and f l i g h t , and other special services at ground s t a t i o n s during s a t e l l i t e f l i g h t s . 2. Operations. A u n i t was organized at NRL ( l a t e r t r a n s f e r r e d to NASA) to undertake the design, f a b r i c a t i o n and t e s t i n g of s a t e l l i t e assemblies. The s h e l l s were designed to be l i g h t w e i g h t commensurate w i t h necessary strength, and were to be coated w i t h a succession of materials to e f f e c t temperature c o n t r o l through c o n t r o l of the r a d i a t i o n c h a r a c t e r i s t i c s of the surface. Test equipment was constructed and assembled i n t o a complete t e s t u n i t f o r the e l e c t r i c a l , thermal, and mechanical t e s t - ing of the systems. The t r a n s m i t t e r and receiver c i r c u i t r y was developed and con- structed f o r the various f l i g h t u n i t s . Telemetry operations were coordinated w i t h the Mmitrack program. See p r o j e c t 33.1 f o r d e t a i l s . a. S a t e l l i t e Payloads. During the course of the s a t e l l i t e program, many changes were made i n payloads as a r e s u l t of changes i n rocket vehicles. However, the pro- cedures adopted f o r the Vanguard payloads i l l u s t r a t e the general nature of the problems and means adopted f o r achieving the desired performance c h a r a c t e r i s t i c s . Vanguard payloads were b a s i c a l l y a 20-inch hollow sphere w i t h an i n t e r n a l spider framework supporting a c y l i n d r i c a l instrument assembly. Two hemispheres f o r the s h e l l were drawn while heated to 650"? from 0.091-inch sheet stock, spun at a temper- ature of 600°F on a p r e c i s i o n mandrel to inside dimension, trimmed and then machined to give a skin thickness of .026-in. except at the base section where a thinkness of .050-in. was maintained. Before the f i n a l machining and d r i l l i n g and tapping of holes f o r i n t e r n a l and e x t e r n a l connections, the u n i t s were s t r e s s - r e l i e v e d and f o r those s h e l l s intended f o r a micrometeorite penetration experiment, two pressure bands were formed by welding zonal segments inside the hemisphere, these pressure zones were f i t t e d w i t h pressure connection f i t t i n g s and h y d r o s t a t i c a l l y pressure tested f o r leaks. The inner support spider was constructed of tubular elements bent and welded using p r e c i s i o n j i g s , the ends of the supports were machined to a spherical surface to match the inner dimension of the s h e l l . For a magnetometer experiment, the design was q u i t e d i f f e r e n t , i n the o r i g i n a l design, the sensor was supported away from a 13-inch sphere on a stem, the s h e l l and stem being constructed of a f i b e r g l a s s - r e s i n m a t e r i a l . The inner equipment container was metal and a l l metal elements were of non-magnetic m a t e r i a l . This payload f a i l e d to o r b i t and was redesigned to incorporate an X-ray experiment and micrometeorite detectors. The l a t e r Vanguard vehicle was of improved performance p e r m i t t i n g a s u b s t a n t i a l increase m size and weight of the payload. Vanguard I I I consisted of a 20-inch sphere w i t h a 26-inch tube constructed of f i b e r g l a s s supporting the magneto- meter. The upper 90° sector of the sphere, facing the magnetometer, i s of f i b e r g l a s s , the remainder of the sphere i s polished aluminum. At one point i n the Vanguard program, i t was decided to include t e s t spheres i n the t e s t Vanguard vehicles. The t e s t spheres were designed to be minimum payloads, consisting of aluminum spheres approximately 6.5 inches i n diameter, weighing approximately 3.25 pounds. Mercury c e l l s were used to power one t r a n s m i t t e r , d r i v i n g four equally spaced antennas on the sphere's equator. Six solar c e l l s were mounted on the sphere to power a second t r a n s m i t t e r , d r i v i n g two antennas at the poles of the sphere. 625

EARTH SATELLITE b. S a t e l l i t e Testing. Various components were tested before assembly i n t o the system. The antennas were i n d i v i d u a l l y load-tested to insure proper heat treatment and the pressurized inner instrument container, pressure set valves, pressure zones, and pressure r e l i e f valves were leak-tested and then temperature cycled to insure maintenance of the seal over the required temperature and pressure range. Assemblies were given design acceptance tes t s i n c l u d i n g random v i b r a t i o n up to 26 g p a r a l l e l to t h r u s t and up to 20 g transverse to t h r u s t , and s i n u s o i d a l v i b r a t i o n s transverse to t h r u s t up to 35 g, steady state a c c e l e r a t i o n up to 75 g p a r a l l e l to t h r u s t , and extensive thermal-vacuum l i f e t e s t s between 0°C and 60°C. F i n a l acceptance t e s t s included random v i b r a t i o n to 10 g, s i n u s o i d a l v i b r a t i o n at 20 g, steady state a c c e l e r a t i o n to 35 g, simulation of i n i t i a l heating of s h e l l to 300° F, temperature c y c l i n g s i m i l a r to design acceptance t e s t s , and l i f e t e s t s under vacuum and thermal conditions. The thermal t e s t program could l a s t as long as three weeks i f no f a i l u r e s occurred, f o r t h i s f i n a l t e s t the s a t e l l i t e assembly was placed i n a vacuum chamber, i t s e l f housed i n a high a l t i t u d e chamber, the environment of which could be c o n t r o l l e d . Temperature was cycled to approximate expected o r b i t a l conditions and the pressure was reduced to 0.1 mm Hg. The temperature of s h e l l , inner package, and e l e c t r o n i c assemblies was monitored and equipment operated as i t would be m o r b i t , w i t h continuous monitoring. c. Separation Mechanisms. Several d i f f e r e n t kinds of separation mechanisms were designed f o r the various configurations of s a t e l l i t e payloads, i n c l u d i n g the 6-inch minimal t e s t sphere, which became Vanguard I . This system required a d i f f e r e n t design because the payload was much smaller and l i g h t e r than the 20-inch spheres, and i t had to be mounted i n an e x i s t i n g t e s t v e h i c l e . A system was employed wherein a strap held the 6-inch Vanguard I sphere to a c y l i n d e r containing the separation springs and a timing motor. The strap was held to the c y l i n d e r by another s t r a p , which was separated from the c y l i n d e r by explosive motors, thus releasing the strap holding the s a t e l l i t e . A g-weight held the timing motor m the o f f p o s i t i o n u n t i l t h i r d stage burnout reduced a c c e l e r a t i o n below a predetermined value. A time delay was then a c t i v a t e d as a precaution against a t r a n s i e n t f l u c t u a t i o n i n a c c e l e r a t i o n before burnout. When the safety time delay was exceeded the timing motor continued I t s cycle, a c t i v a t i n g the explosive motors, by the a c t i o n of l e a f springs, the freed s a t e l l i t e was given a d i f f e r e n t i a l v e l o c i t y of about one foot per second away from the t h i r d stage. This mechanism apparently functioned p e r f e c t l y f o r Vanguard I . The separation mechanism f o r the 20-inch spheres used a r e t a i n i n g strap anchored w i t h explosive b o l t s and a s i m i l a r g-weight timing motor. Separation was accomplished w i t h a h e l i c a l spring. 3. Personnel. This work was under the supervision of H. E. Newell, and c a r r i e d out under the tech n i c a l supervision of R.C. Baumann, F. T. M a r t i n , J. T. Shea, and A. Simkovich were also associated w i t h t h i s p r o j e c t . 4. Results. This work made possible the successful operation of the IGY Vanguard s a t e l l i t e instrument packages, aside from other d i f f i c u l t i e s not under c o n t r o l , such as interference from the Van A l l e n Radiation Belts or launching d i f f i c u l t i e s . 5. Bibliography. a. Papers presented at Meetings R. C. Baumann "Design, F a b r i c a t i o n and Testing of the F i r s t Man-made S a t e l l i t e , " Spring Meeting, Am. Rocket Soc, A p r i l 1957, Washington D. C. 626

EARTH SATELLITE b. Published Papers R. C. Baumann "Design, F a b r i c a t i o n , and Testing of the Vanguard S a t e l l i t e , " Jet Prop., Vol. 28, No. 4, pp. 244-48, A p r i l 1958 R. C. Baumann "Post F l i g h t Summary Report, Test Vehicle Series," Project Vanguard, NRL, 24 June 1958 R. C. Baumann "Spin Retarding Mechanism SLV-3 F l i g h t Evaluation," Project Vanguard, NRL, 5 November 1958 R. C. Baumann " S a t e l l i t e Structures and Engineering Testing," NRL Report 5165, January 1959 R. C. Baumann "Vanguard S a t e l l i t e Spin-Retarding Mechanism," Project Vanguard, NRL, March 1959 J. T. Shea, R. C. Baumann "Vanguard I S a t e l l i t e Structure and Separation Mechanism," NASA Technical Note D-495, March 1961, Washington D. C. R. C. Baumann- "Vanguard S a t e l l i t e Spin-Reduction Mechanism," NASA Technical Note D-496, A p r i l 1961, Washington, D. C. R. C. Baumann "Vanguard S a t e l l i t e Separation Mechanisms," NASA Technical Note D-497, A p r i l 1961, Washington, D. C. A. Simkovitch, R. C. Baumann "Balancing Vanguard S a t e l l i t e s , " NASA Technical Note D-498, A p r i l 1961, Washington, D. C. F. T. Martin " S t r u c t u r a l Aspects of the Magne-Ray Experiment," NASA Technical Note ( I n preparation). 627

EARTH SATELLITE Project 32.31 S a t e l l i t e Equipment and Engineering Services 1. Objectives. This p r o j e c t at the Jet Propulsion Laboratory, C a l i f o r n i a I n s t i t u t e of Technology, provided f o r the m o d i f i c a t i o n of the State U n i v e r s i t y of Iowa r a d i a t i o n experiment and the Geophysics Research Directorate micrometeorite experiments, o r i g i n a l l y designed f o r Vanguard s a t e l l i t e v e h i c l e s , f o r launching by the Army Jupi t e r rocket. 2. Operations. Personnel from JPL and from the Army B a l l i s t i c M i s s i l e Agency, H u n t s v i l l e , Alabama, cooperated w i t h SUI and GRD s c i e n t i s t s m preparing instrument packages f o r the Explorer I and I I I s a t e l l i t e s , which were to be launched by the Jupi t e r rocket system. The instrumented s a t e l l i t e s were constructed and f i t t e d w i t h the i n t e r n a l instrumentation, telemetry provisions were made, temperature c o n t r o l was studied and means provided f o r maintaining the i n t e r n a l temperature w i t h i n design l e v e l s , p r e f l i g h t t e s t and c a l i b r a t i o n services were performed, and m - f l i g h t telemetry and other services made av a i l a b l e to the experimenters. 3. Personnel. This work was under the d i r e c t i o n of W. H. Pickering, other senior s c i e n t i s t s associated w i t h the p r o j e c t were W. K. V i c t o r and A. R. Hibbs. 4. Results. The p r o j e c t made possible the successful launching and f u n c t i o n i n g of the Explorer I and I I I s a t e l l i t e s . For d e t a i l s of the s c i e n t i f i c experiments, see Projects 32.1 and 32.4. 628

EARTH SATELLITE Project 32.32 Micrometeor Detection 1. Objectives. This p r o j e c t at the Army B a l l i s t i c M i s s i l e Agency, H u n t s v i l l e , Ala., provided f o r the i n c o r p o r a t i o n i n t o the Explorer V I I instrument package of an experiment of the Naval Research Laboratory to determine the erosion and penetration e f f e c t s of micrometeorites and molecular s p u t t e r i n g of surfaces. 2. Operations. The experiment as designed at NRL consists of three Cds photo- s e n s i t i v e c e l l s mounted on a magnesium plate i n the e q u a t o r i a l plane of the s a t e l l i t e . The c e l l s were i d e n t i c a l but had d i f f e r e n t coverings, c e l l number 1 was coated w i t h 1/4 m i l mylar f i l m , coated w i t h a 1000 A layer of aluminum on the f r o n t side, to detect s p u t t e r i n g and penetration, c e l l number 2 was coated w i t h a s i m i l a r f i l m but w i t h the aluminum layer on both sides of the mylar to detect penetration only, c e l l number 3 had a 1 m i l aluminum cap w i t h a hole 0.0075 mm̂ i n area f o r c a l i b r a t i o n purposes. The c e l l s were c a l i b r a t e d i n the laboratory f o r response to a Xenon arc and s u n l i g h t f o r various amounts of l i g h t input as regulated by appropriate pinholes i n opaque covers. 3. Personnel. The work of designing the equipment f o r i n c o r p o r a t i o n i n t o a complex instrument package was di r e c t e d by L. Secretan, and the i n t e g r a t i o n of the package was under the d i r e c t i o n of J. Boehm, the s c i e n t i f i c experiment was under the d i r e c t i o n of H. E. LaGow. 4. Data. The r e s u l t s of the f i r s t period of operation are s t i l l under study. Since the data i s more or less d i s c r e t e , corresponding to i n d i v i d u a l events, there i s no body of reduced data. 5. Results. Explorer V I I (1959 I o t a ) was launched on October 13, 1959, w i t h an o r b i t of 50.3° i n c l i n a t i o n , 1100 km apogee, 560 km perigee. The 1959 I o t a experiment exposed the three CdS c e l l s to the space environment of micrometeorites, trapped r a d i a t i o n , and s p u t t e r i n g f o r 38 days of ac t i v e l i f e . C e l l No. 1 was damaged and desensitized during launch and C e l l No. 3 was r e l a t i v e l y i n s e n s i t i v e because i t s primary f u n c t i o n was c a l i b r a t i o n . The telemetry signals from C e l l No. 2 show.(a) f o r the f i r s t 13 days, neither s u n l i g h t nor energetic p a r t i c l e s caused a readable r e - sponse, (b) on the 16th day, s u n l i g h t was entering the c e l l , causing a response that corresponded t o a hole 1 x 10'^ mm i n s i z e , that i s , 10-15 microns i n diameter, (c) a f t e r the 16th day, the recordings made when the s a t e l l i t e was i n darkness showed normal dark response, and (d) hole size d i d not change from 16th to 38th day by a readable amount. I t i s concluded t h a t the response on C e l l No. 2 a f t e r the 16th day was due to a micrometeorite penetrating the 1/4 m i l mylar and the opaque aluminum coatings on each face. I t should be noted that there i s a f i n i t e p o s s i b i l i t y t h a t the hole was produced by molecular s p u t t e r i n g , t h i s , however, seems improbable becuase i t would have required a l a t e n t pinhole m the inner coating. 6. Bibliography. H. LaGow, L. Secretan "The Micrometeorite Penetration Experiment," Chap. 10 in Technical Note D-608, Juno I I Summary Project Report, Vol. I , Explorer V I I Earth S a t e l l i t e , G. C. Marshall Space F l i g h t Center, NASA, H u n t s v i l l e , Ala., July 1961. 629

EARTH SATELLITE Project 32.40 Radio Interferometry and Data Analysis 1. Objectives. This p r o j e c t a t the E l e c t r i c a l Engineering Research Laboratory, U n i v e r s i t y of I l l i n o i s , was i n i t i a t e d to reduce and analyze radio data taken from the f i r s t e a r t h s a t e l l i t e . Sputnik I (1957 Alpha), and to provide f o r a continuing program of radio observation and data reduction f o r USSR and US s a t e l l i t e s . Since the s a t e l l i t e , t r a n s m i t t i n g at frequencies where ionospheric e f f e c t s are large (a t least f o r the USSR transmissions a t 20 and 40 Mc), emitted a coherent s i g n a l of d e f i n i t e p o l a r i z a t i o n , swept across the sky i n a short time, and was sometimes above ionospheric regions of i n t e r e s t , i t was a n t i c i p a t e d that information could be obtained on e l e c t r o n density between the maxima of the various " l a y e r s " along w i t h regular or anomalous v a r i a t i o n of the layers. 2. Operations. When Sputnik I was launched on October 4, 1957, many la b o r a t o r i e s had equipment of some kind already a v a i l a b l e and m a short time were able to com- plete observational set-ups to record the s a t e l l i t e transmissions during l o c a l passes. In November 1957 at a conference a t CRPL, Boulder, records from Stanford, Boulder, and Urbana were compared. Enough s i g n i f i c a n t s i m i l a r i t i e s and differences were found to stimulate inception of a program of coordinated recording, so that information on the state of the ionosphere could perhaps be obtained across the United States. Stable communication receivers were combined wi^h low-noise p r e a m p l i f i e r s and c r y s t a l - c o n t r o l l e d converters to give o v e r - a l l noise f i g u r e s of between 4.5 and 5 db. The automatic gain c o n t r o l c i r c u i t s of the receivers were modified to give approxi- mately logarithmic response, the a.g.c. voltages were recorded as a measure of the input s i g n a l I n i t i a l l y , three antennas were provided f o r simultaneous operation, ( i ) a h o r i z o n t a l l y - p o l a r i z e d , t o t a l power interferometer, c o n s i s t i n g of four s i x - element Yagis on an east-west baseline p o i n t i n g south at 45° e l e v a t i o n , ( i i ) a s i x - element v e r t i c a l l y - p o l a r i z e d Yagi located at the center of the interferometer p o i n t i n g south a t an e l e v a t i o n of 20°. The outputs of the three antennas were passed through the receivers and recorded on a multi-channel Sanborn recorder, on loan from Project Vanguard, running at 5 mm per second chart speed during each discernable s a t e l l i t e passage. An Esterline-Angus recorder was run at three inches per hour on one channel as a monitor. For p a r t i c u l a r l y close passages, telemetering modulation was recorded on tape. Duplicate equipment, app r o p r i a t e l y scaled, was used f o r 20 and 40 mc transmissions. I n order to obtain more precise information on the s a t e l l i t e s t r a n s m i t t i n g at 108 mc, a phase-switching interferometer was also con- structed. As the pro j e c t progressed, new antenna f i e l d s were designed and constructed. Interferometers f o r 20, 40 and 108 mc were b u i l t on both north-south and east-west baselines w i t h e f f e c t i v e lengths of 4, 8, and 21 wavelengths, the antennas were of the four-element, ambiguity-resolving v a r i e t y . Late i n 1958, a low-power lonosonde was provided by CRPL f o r ionospheric observations i n conjunction w i t h the radio observations. 3. Data. The o r i g i n a l charts and tapes are retained at the U n i v e r s i t y f o r d e t a i l e d study and analysis. Papers published on the r e s u l t s of such analysis contain some of the reduced data. 4. Personnel The pr o j e c t d i r e c t o r f o r t h i s work was G. W. Swenson, J r . , other senior s c i e n t i s t s associated w i t h Dr. Swenson were E. C. Hayden, G. C. M c V i t t i e , K, C. Yeh, I . R, King, and S. P. Wyatt, J r . 630

EARTH SATELLITE 5. Results. During the f i r s t months of observations, a great many recordings were made of the USSR s a t e l l i t e s on 20 and 40 mc, from the 40 mc signals of the southbound crossings i t was possible to deduce the period of r e v o l u t i o n of the s a t e l l i t e and the times of longitude crossings. US s a t e l l i t e s , t r a n s m i t t i n g a t 108 mc, showed marked fading, w i t h periods being constant f o r each s a t e l l i t e , but d i f f e r i n g con- siderably from one s a t e l l i t e to another. One of the important f a c t o r s c o n t r i b u t i n g to the fading was the tumbling and spinning motion of the s a t e l l i t e s , obscuring any fading that might have been due to ionospheric e f f e c t s and making d i f f i c u l t the i d e n t i f i c a t i o n of interferometer n u l l s . A method was developed f o r determining o r b i t a l elements from observations made w i t h two crossed interferometers and programmed f o r the University's e l e c t r o n i c computer. Such computations, combined w i t h some o p t i c a l observations of c e r t a i n passes, were used i n a program of o r b i t a nalysis. Extended observations of 1958 Beta (Vanguard I ) disclosed accelerations r e l a t e d to solar e f f e c t s i n the atmosphere, as discovered by Jacchia (see Project 30.10). I n a d d i t i o n to the d i u r n a l exosphere expansion postulated by Jacchia to account f o r the motion of Vanguard I , seasonal and l a t i t u d e e f f e c t s were deduced from the data. While i t had been found by Jacchia that the d i u r n a l e f f e c t lagged the sun by one to two hours, the seasonal lag of the exo- sphere was not determinable from the I l l i n o i s observations. During low passes of 1957 Alpha, there were c h a r a c t e r i s t i c sudden changes i n signal strength. During s a t e l l i t e approach the s i g n a l would t y p i c a l l y b u i l d up to a peak value and then suddenly decrease to i n a u d i b i l i t y i n less than a second, when the s a t e l l i t e receded, the s i g n a l strength would increase from noise levels to f u l l strength i n less than a second. Occasionally, two such sudden decreases were observed i n a four-minute i n t e r v a l during approach and two sudden increases observed m a si m i l a r time i n t e r v a l during recession. Computations of skip distances were made based on NBS data, and agreed w e l l w i t h the distances deduced from the observations of time of sudden change i n the s i g n a l . For high passes of 1957 Alpha, the s i g n a l was characterized by f a s t fading, "hash," as the s i g n a l came m when the s a t e l l i t e approached from the n o r t h . Since the s a t e l l i t e was above the F-layer maximum ion density and such hashy signals were received even when the s a t e l l i t e was nearly over- head. I t I S believed that t h i s behavior cannot be explained w i t h m u l t i p a t h phenomena. The evidence suggests that an inhomogeneous medium intervened between the s a t e l l i t e and the receiving s t a t i o n and that f u r t h e r d e t a i l s would have to await a spaced- receiver experiment. I t i s thought probable that the f a s t fading may be due to the same mechanism responsible f o r radio star s c i n t i l l a t i o n , i . e . , the movement across the ground s t a t i o n of a d i f f r a c t i o n p a t t e r n . I n the case of radio star s c i n t i l l a t i o n , however, i t i s the h o r i z o n t a l movement of the ionospheric i r r e g u l a r i t i e s that causes the f a s t fading w h i l e , f o r the s a t e l l i t e , i t r e s u l t s from the motion of the s a t e l l i t e t r a n s m i t t e r above the i r r e g u l a r i t i e s , since the d r i f t v e l o c i t y of i r r e g u l a r i t i e s must be n e g l i g i b l e against the s a t e l l i t e v e l o c i t y . From data taken by ionospheric sounder s t a t i o n s i n the v i c i n i t y , a c o r r e l a t i o n was found between s a t e l l i t e n i g h t - time s c i n t i l l a t i o n occurrence and spread-F, as i s the case f o r radio star s c i n t i l - l a t i o n . From the i n i t i a l observations, i t was concluded by the i n v e s t i g a t o r s t h a t n i g h t - time s c i n t i l l a t i o n o r i g i n a t e s m a region near 300 km a l t i t u d e and i n most cases north of about 40° no r t h l a t i t u d e at the longitude of the U n i v e r s i t y of I l l i n o i s and that daytime s c i n t i l l a t i o n o r i g i n a t e s i n smaller, inhomogeneous patches d i s t r i b u t e d over wide ranges of l a t i t u d e . This p r o j e c t has been continued i n operation past the IGY period through support from the National Aeronautics and Space Adm i n i s t r a t i o n and considerable c l a r i f i c a t i o n has been obtained of the ionospheric phenomena under i n v e s t i g a t i o n . Through t h i s means, for example, observations were made of the 20 Mc frequency emission of Explorer V I I , the l a s t s a t e l l i t e i n the IGY program, the 1960 papers l i s t e d below resulted from t h i s continued work under NASA sponsorship, but may also be considered as r e s u l t s of the IGY program. 631

EARTH SATELLITE 6. Bibliography. C. D. Hendricks, J r . , G. W. Swenson, J r . , R. S. Schorn. "Radio Reflections from Satellite-Produced Ion Columns," Proc. IRE, Vol. 45, p. 1763, 1958 K. C. Yeh, G. W. Swenson, J r . . "The S c i n t i l l a t i o n of Radio Signals from S a t e l l i t e s , J. Geophys. Res., Vol. 64, No. 12, p. 2281, 1959, IGY S a t e l l i t e Report No. 12, p. 73, December 1960, National Academy of Sciences, Washighton, D. C. K. C. Yeh "Second-Order Faraday Rotation Formulas," J. Geophys. Res., Vol. 65 No. 8, August 1960, pp. 2548-50 K. C. Yeh, V. H. Gonzalez- "Note of the Geometry of the Earth's Magnetic F i e l d Useful to Faraday E f f e c t Experiments," J. Geophys. Res., Vol. 65, No. 10, October 1960, pp. 3209-14 K. C. Yeh, G. W. Swenson, J r . . "Observed F i e l d Strength i n the Neighborhood of the Skip Distance." J. Geophys. Res., Vol. 66, No. 2, February 1961, pp. 654-56 K. C. Yeh, "Ionospheric Electron Content and I t s Variations Deduced from S a t e l l i t e Observations," J. Geophys. Res., Vol. 66, No, 4, A p r i l 1961, pp. 1061-67 G. W. Swenson, J r . , K. C. Yeh "Summary of S a t e l l i t e Observations a t the Univ e r s i t y of I l l i n o i s , " August 4, 1961, NASA Grant NsG 24-59, Aug. 4, 1961, Elec. Eng. Res. Lab., Un i v e r s i t y of I l l i n o i s 632

EARTH SATELLITE Project 32.41 - Interferometer and Doppler Measurements of S a t e l l i t e Radio Transmissions 1. Objectives. This p r o j e c t at the Central Radio Propagation Laboratory, Boulder Laboratories, National Bureau of Standards, provided f o r recording s a t e l l i t e radio transmissions as a means of studying the large and small scale s t r u c t u r e of the ionosphere and to determine the accuracy w i t h which radio d i r e c t i o n - f i n d i n g measure- ments might be made on radio sources w i t h i n or beyond the ionosphere. 2. Operations. Within 12 hours of r e c e i v i n g the announcement on 4 October 1957 concerning the launching of Sputnik I , two groups at CRPL had modified c e r t a i n e x i s t - ing pieces of equipment to receive the 20- and 40-Mc signals from the f i r s t a r t i f i c a l e a r th s a t e l l i t e . Soon t h e r e a f t e r , a t h i r d group made measurements using a continuous phase-difference measuring technique developed e a r l i e r f o r studying atmospheric turbulence i n the troposphere. The instrumentation consisted of two s i m i l a r Hamerlund SP-600 receivers operating on 20 (or 40) Mc. Continuously recording meters were used which compared the audiofrequency tones from the two receivers. At f i r s t , half-wave dipoles were used, but l a t e r c i r c u l a r l y polarized antennas were employed. Two e f f e c t s were contained i n the records, regular geometrical changes such as those r e l a t e d to the o r b i t and i r r e g u l a r changes presumahly r e l a t e d to ionospheric t u r b u l - ence and r e f r a c t i o n . The receivers m two 12-meter dishes used f o r the radio star s c i n t i l l a t i o n measurements were modified i n order to receive the 40 Mc s a t e l l i t e s i g n a l , the two dishes were separated by a spacing of 450 meters. Wi t h i n a few hours, dipole antennas were set up a t twice the spacing of the dishes i n order to receive the 20-Mc s i g n a l on an e l e c t r i c a l l y equivalent baseline. The phase-switching and detect- ing equipment, that had previously been used f o r the Jup i t e r p r o j e c t , was put i n operation here. Measurements were made of the d i r e c t i o n of a r r i v a l of the 20- and 40 Mc signals. Simple ionospheric theory suggests that simultaneous measurements of r e f r e a c t i o n , at 20 and 40 Mc, should be i n the r a t i o of 4 to 1. I f t h i s were c o r r e c t , simultaneous measurements on the two frequencies could be used to deduce the true s a t e l l i t e d i r e c t i o n . Observations have shown, th a t i n f a c t the i r r e g u l a r s t r u c t u r e of the ionosphere i n v a l i d a t e s t h i s procedure. Following the i n i t i a l program, more permanent interferometer arrangements were made at Table Mesa near Boulder. Pairs of half-wave d i p o l e s , w i t h h o r i z o n t a l east- west p o l a r i z a t i o n and mounted one t h i r d wavelength above the ground, were set up at the corners of e q u i l a t e r a l t r i a n g l e s of 900 meters and 45 meters. Observations were made a t both 20- and 40 Mc. I n a d d i t i o n , c i r c u l a r l y polarized antennas were i n s t a l l e d . The output could be recorded on magnetic tape or on two 6-channel Sandborn recorders. The equipment was f u l l y automatic and could be set to come on automatically during the passage of a s a t e l l i t e beacon t r a n s m i t t e r at these frequencies. Two Yagi antennas on a frequency of 108 Mc were also i n s t a l l e d as w e l l as a v e r t i c a l l y - p o l a r i z e d antenna f o r 20 Mc. With t h i s arrangement of antennas, measurements of angle of a r r i v a l . Faraday r o t a t i o n , p o l a r i z a t i o n , s c i n t i l l a t i o n , d i v e r s i t y e f f e c t s , and Doppler frequency changes have been made. 3. Data. Records and tapes are retained at CRPL f o r analysis and study. 4. Personnel. This p r o j e c t was i n i t i a l l y under the d i r e c t i o n of R. J. Slutz, and then under C. G. L i t t l e , other senior s c i e n t i s i s associated w i t h t h i s work were R. S. Lawrence, E. R. Gehiffinacher, and during the ea r l y observations of Sputnik I , R. S. Kirby and J, M. Watts. 633

EARTH SATELLITE 5. Results. Inspection of the Faraday fading records of the 20 Mc signals made during the f i r s t 4 months of s a t e l l i t e 1958 Delta show the f o l l o w i n g systematic varations i n the fading r a t e . (a) The fading rate i s slowest when the s a t e l l i t e i s i n the north and greatest when i t i s i n the south, (b) the greater height of the s a t e l l i t e during the north-to-south passes, and hence the longer ionospheric paths of the radio s i g n a l s , accounts f o r the greater fading rates during these passes than during the south-to-north passes, (c) nighttime passes are characterized by a fading ra t e t h a t i s much slower than f o r d a y l i g h t passes a t the same height. When the fad- ing rate was compared w i t h the square of the F-layer c r i t i c a l frequency, taken from the Boulder lonograms, i t shows that the d a i l y v a r i a t i o n s i n fading rate are l a r g e l y due to the d a i l y v a r i a t i o n s i n the i o n i z a t i o n content of the ionosphere. Many of the Faraday-rotation r a t e s , rather than varying smoothly throughout a single passage of the s a t e l l i t e , vary i r r e g u l a r l y and i n d i c a t e the existence of ionospheric i r r e g u l a r - i t i e s . I n some instances these i r r e g u l a r i t i e s are of the order of 100 km m l a t e r a l extent. Calculations using the 20 Mc s i g n a l from 1958 Delta I I show t h a t the observed i r r e g u l a r i t i e s i n the Faraday r o t a t i o n r a t e can be accounted f o r i f the i n t e g r a t e d e l e c t r o n content, along the l i n e of s i g h t per square centimeter column, varies i r r e g u l a r l y w i t h v a r i a t i o n s of the order of 10^ during a 1-km change ( h o r i z o n t a l ) i n s a t e l l i t e p o s i t i o n . From a determination of the number of complete r o t a t i o n s of the plane of p o l a r i z a t i o n of the radio s i g n a l s , the t o t a l e l e c t r o n content, up to the height of the s a t e l l i t e , can be calculated. For a pass of s a t e l l i t e 1958 Delta I I , a t a height of about 232 km, low i n the F-region, the integrated e l e c t r o n content i n a v e r t i c a l column was estimated as 3.1 x lO-*-̂ electrons/cm^ column. In conjunction w i t h the s a t e l l i t e observations, a computer program was set up fo r t r a c i n g the paths of the rays between the s a t e l l i t e and the receiver. The ordinary and extraordinary rays were traced separately through the ionosphere and the d i f f e r e n c e i n t h e i r phase paths gives the instantaneous r o t a t i o n of the p o l a r i z a t i o n vector. Actual ionospheric p r o f i l e s from lonograms were used up to the F-region peak, but various assumed p r o f i l e s were t r i e d f o r the upper ionosphere. The ray- t r a c i n g program was coupled to a computing program to give successive p o s i t i o n s of the s a t e l l i t e along an e l l i p t i c a l o r b i t . The combination of these two programs gives a complete p i c t u r e of the Doppler frequency, the Faraday r o t a t i o n , and the angle of a r r i v a l of the s a t e l l i t e s i g n a l . A comparison between the d i r e c t i o n of a r r i v a l and l i n e of sight to the s a t e l l i t e gave a measure of the angular e r r o r s introduced by the ionosphere. This work was continued under support from NASA. 6. Bibliography. a. Papers presented a t Meetings R. S. Lawrence, C. G. L i t t l e : "On the Analysis of P o l a r i z a t i o n Rotation Recordings," URSI-AGI meeting, Brussels, 1959 C. G. L i t t l e , R. S. Lawrence: "The Use of P o l a r i z a t i o n Fading of S a t e l l i t e Signals to Study the Electron Content and I r r e g u l a r i t i e s i n the Ionosphere," COSPAR F i r s t I n t e r n a t i o n a l Space Science Symposium, Nice, France, January 1960 (Pub. i n Space Research, H. K. B i j l , ed., pp. 340-365, North-Holland Pub. Co., Amsterdam, 1960) R. S. Lawrence, C. G. L i t t l e : "On the Analysis of P o l a r i z a t i o n Rotation Recordings of S a t e l l i t e Radio Signals," URSI, Commission 3, October, 1959, San Diego, C a l i f o r n i a . 634

EARTH SATELLITE b. Published Papers R. S. Lawrence, C. G. L i t t l e "On the Analysis of P o l a r i z a t i o n Rotation Recordings of S a t e l l i t e Radio Signals," pp. 391-399, Some Ionospheric Results Obtained During the I n t e r n a t i o n a l Geophysical Year, Proceedings of a Symposium organized by the URSI/AGI Committee a t Brussels, Belgium, September, 1959, edited by W. J. G. Beynon, publ. by Elsevier Publishing Co., 1960 C. G. L i t t l e , R. S. Lawrence- "The Use of P o l a r i z a t i o n Fading of S a t e l l i t e Signals to Study the Electron Content and I r r e g u l a r i t i e s i n the Ionosphere, 1, 2, NBS Journal of Research, Vol. 64D, No. 4, pp. 335-346, July-August 1960 R. S. Lawrence and J. W. Warwick- "The Use of Interferometer Observations of S a t e l l i t e s f o r Measurement of I r r e g u l a r Ionospheric Refraction," Annals of the IGY. Vol. X I I , Part 2 (1961) R. S. Lawrence, D. Jane Posakony. "A D i g i t a l Ray-tracing Program f o r Ionospheric Research," COSPAR Second I n t e r n a t i o n a l Space Science Symposium, Florence, I t a l y , A p r i l 1961 (Pub. i n Space Research I I , H. C. Van de Hulst, C. de Jager, A. F. Moore, ed., pp. 258-276, North-Holland Pub. Co., Amsterdam, 1961) R. S. Lawrence, D. Jane Posakony, 0, K. G a r r i o t t , S. C. H a l l : "The T o t a l Electron Content of the Ionosphere at Middle,Latitudes near the Peak of the Solar Cycle," JGR 68. 7 pp. 1889-1898 (1963) R. G. M e r r i l l , R. S. Lawrence, N. J. Roper: "Synoptic V a r i a t i o n s and V e r t i c a l P r o f i l e s of Large-Scale Ionospheric I r r e g u l a r i t i e s , " JGR 68, 19 pp. 5453-5459, (1963). 635

EARTH SATELLITE Project 32.42 Auroral Ionosphere Studies In v o l v i n g S a t e l l i t e Radio Transmission 1. Objectives. This p r o j e c t a t the Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska, was organized to provide f o r i n t e r f e r o m e t r i c and Doppler radio observations of s a t e l l i t e transmissions a t 20, 40, and 108 Mc. This would provide the opportunity to derive information on ionospheric i r r e g u l a r i t i e s and e l e c t r o n d e n s i t i e s , w i t h the important p o s s i b i l i t y of obtaining information above the levels probed by conventional lonosonde techniques. I n a d d i t i o n , information might be obtained on the behavior of the ionosphere during polar blackouts, when ground signals cannot penetrate the dense absorbing layer formed beneath the E layer. 2. Operations. A t r i - p a r t i t e Doppler network was constructed f o r both 20 and 40 Mc. The s t a t i o n at College went i n t o operation i n A p r i l 1958. The second s t a t i o n , at Anchorage, some 420 km southwest, went i n t o operation i n May. A t h i r d s t a t i o n was established at Northway, some 360 km southeast of College, and began operation l a t e i n 1958. A l l three receivers use t u r n s t i l e antennas at a frequency of 20.005 Mc, signals from the o u t l y i n g s t a t i o n s were relayed to College by means of a d i r e c t telephone l i n e connection and recorded there simultaneously w i t h the College s i g n a l on magnetic tape. FM-type d i s c r i m i n a t o r c i r c u i t s were devised to convert the Doppler signals to a DC voltage approximately l i n e a r l y p r o p o r t i o n a l to the Doppler d e v i a t i o n . The recorded signals were analyzed by such di s c r i m i n a t o r s and displayed on a frequency-time p l o t using Sanborn recorders. Interferometers were planned, and the plans modified i n expectation of having a Mini t r a c k s t a t i o n i n s t a l l e d a t College by the Naval Research Laboratory. This d i d not m a t e r i a l i z e , however, and the proposed arrays of interferometers were not b u i l t . R efraction studies were c a r r i e d out, though, w i t h spaced receivers. A series of other antennas was i n s t a l l e d a t College, i n c l u d i n g dipoles and c i r c u l a r l y polarized antennas, f o r study of si g n a l s t r e n g t h , fading Faraday r o t a t i o n . 3. Personnel. This p r o j e c t was under the d i r e c t i o n of C. T. Elvey, C. G. L i t t l e was p r o j e c t supervisor of t h i s work u n t i l June 30, 1958 when he joined the Boulder Laboratories of the National Bureau of Standards. G. C. Reid then assumed respons- i b i l i t y , other senior personnel associated w i t h the work were R. Parthasarathy, R. P. M e r r i t t , W. Murcray, G. C. Rumi, and J. C. Cain. 4. Data. Records are retained at College f o r d e t a i l e d a n a l y s i s . Copies of magnetic tapes of USSR s a t e l l i t e Sputnik I I I were provided through the USNC to USSR s c i e n t i s t s a t t h e i r request. 5. Results. a. Early P o l a r i z a t i o n , S c i n t i l l a t i o n and S a t e l l i t e Rotation Studies. Routine recordings of the 20 Mc s i g n a l strength from 1958 Delta I I as received on a h o r i z o n t a l north-south d i p o l e were c a r r i e d out. Several of these records show very clean traces w i t h c l e a r l y v i s i b l e Faraday r o t a t i o n , whereas others are characterized by intense amplitude s c i n t i l l a t i o n which o f t e n completely obscures the Faraday e f f e c t . The onset of t h i s s c i n t i l l a t i o n on any p a r t i c u l a r record may be very sudden, as may I t s disappearance, sometimes i t i s present throughout the s a t e l l i t e pass, and some- times I t occurs only during a short section of the recording. A few sample records showing f a i r l y sudden onsets or disappearances of s c i n t i l l a t i o n have been examined w i t h a view to f i n d i n g any possible r e l a t i o n s h i p m the geographical p o s i t i o n s of the s a t e l l i t e a t these times. No such r e l a t i o n s h i p was found. The du r a t i o n of i n d i v i d u a l s c i n t i l l a t i o n s appears t o be consistent w i t h the existence of ionospheric i r r e g u l a r i t i e s having h o r i z o n t a l dimensions of the order of a few km., i f the v e l o c i t y of the i r r e g u l a r i t i e s i s assumed to be much less than that of the s a t e l l i t e . 636

EARTH SATELLITE At the l a t i t u d e of College, s a t e l l i t e 1958 Delta I I t r a v e l l e d approximately i n a west-east d i r e c t i o n during passes which were close to overhead. Under these co n d i t i o n s , i t could be shown th a t the time i n t e r v a l between successive zeros on a record showing Faraday r o t a t i o n becomes constant, and i s simply r e l a t e d to the s a t e l l i t e height and v e l o c i t y , and to the integrated e l e c t r o n density along the l i n e of s i g h t . Several records were selected which showed t h i s constancy of period near the time of closest approach, and estimates of the integrated e l e c t r o n density were obtamedt b. Ionospheric Absorption and S c i n t i l l a t i o n Studies. An i n v e s t i g a t i o n was ca r r i e d out of ionospheric absorption of the 20.005 Mc s i g n a l from 1958 Delta I I during periods of a u r o r a l a c t i v i t y . C. G. L i t t l e , now at the National Bureau of Standards, suggested that the ionospheric absorption could be obtained f r e e from contamination by other e f f e c t s by measuring the d i f f e r e n t i a l absorption between the two magneto-ionic components of the s i g n a l . The method of measurement involves switching a t an audio frequency between two c i r c u l a r l y polarized antennas, one of which accepts the ordinary and one the extraordinary wave. I f ionospheric absorption I S present, the two waves would s u f f e r d i f f e r e n t amounts of absorption, and the receiver output would contain an audio component a t the switching frequency whose amplitude and phase could be measured, and which would i n theory provide an estimate of the t o t a l absorption. Equipment of t h i s type was assembled and several record- ings were obtained, some during periods of au r o r a l a c t i v i t y . However, the records contained several unexpected features (such as the instances where an extraordinary (-) wave was stronger than the ordinary (+) wave) whose cause has not yet been f u l l y ascertained and which e f f e c t i v e l y prevented the measurement of d i f f e r e n t i a l absorption (presumably, they could be due to d i f f e r e n t i a l r e f r a c t i o n and/or r e f l e c t i o n ) . During the course of these attempts, several recordings of t o t a l s i g n a l strength were made on Esterline-Angus charts operating at a chart speed of 12 inches per hour. During normal conditions the s i g n a l from the s a t e l l i t e traced out a cross-section of the antenna pattern on these c h a r t s , w i t h a superimposed high-frequency component due to ionospheric s c i n t i l l a t i o n and w i t h a small Faraday fading component a t e i t h e r end due to the departure of the t u r n s t i l e antenna from the c i r c u l a r l y p olarized c o n d i t i o n . During passages covering periods of a c t i v e aurora, however, two d i s t i n c t absorption e f f e c t s were noticed. One was a general decrease i n s i g n a l throughout the pass, as would be expected from a widespread d i s - t r i b u t i o n of the absorbing region, while the other consisted of one or more deep fades i n the s i g n a l suggesting the existence of strong l o c a l i z e d regions of absorption. A deep fade of t h i s time was o f t e n very p e r s i s t e n t , l a s t i n g f o r two or three passes of the s a t e l l i t e m roughly the same p o s i t i o n of the sky. The discovery of t h i s second type of absorption event immediately suggested that the region of the ionosphere responsible could possibly be i d e n t i f i e d both m extent and height by simultaneous recording at two st a t i o n s l y i n g along the track of the s a t e l l i t e . Accordingly a second s t a t i o n was established at a l o c a t i o n approximately 19 km east of the mam s t a t i o n a t College. I t i s f e l t t h a t the d i s - covery of these e f f e c t s points up the usefulness of making low speed chart record- ings of s a t e l l i t e s i g n a l strength which can show large-scale e f f e c t s that may be l o s t i n the wealth of d e t a i l and q u a n t i t y of chart paper produced by the usual high-speed recording technique. c. A u r o r a l l y associated absorption. The s a t e l l i t e pass on June 5, 1959 coincided w i t h the appearance of absorption of the 27.6 Mc cosmic noise s i g n a l as recorded at College, t h i s absorption was of the type which i s usually associated w i t h the occurrence of v i s i b l e aurora i n the ze n i t h . The corresponding onsets of the absorption of the s a t e l l i t e s i g n a l at the two rec e i v i n g s i t e s were displaced m time by about 33 seconds, the absorption appearing f i r s t at the eastern s i t e , as would be expected f o r a l o c a l i z e d absorbing cloud seen by a s a t e l l i t e t r a v e l l i n g 637

EARTH SATELLITE from West to east. From simple geometry i t can be shown th a t i f F i s the height of the s a t e l l i t e , h the height of the absorbing cloud, L the separation between the s t a t i o n s , and V the v e l o c i t y of the s a t e l l i t e , then the time separation T m the appearance of the absorption i s given by H - h = VT h L At t h i s time the s a t e l l i t e was close to apogee (about 1250 km), and the v a r i a t i o n i n height during the pass was n e g l i g i b l e . The height deduced f o r the absorbing cloud was m the neighborhood of 104 km. No other d e f i n i t e instances of t h i s phenomenon have been observed to date. d. Height of the i r r e g u l a r i t i e s causing " s c i n t i l l a t i o n " of the s a t e l l i t e s i g n a l . I t had been concluded e a r l i e r t h a t the v i o l e n t f l u c t u a t i o n s sometimes observed i n the s a t e l l i t e s i g n a l were probably due to the same ionospheric i r r e g u l a r - i t i e s that give r i s e to radio s t a r s c i n t i l l a t i o n . These f l u c t u a t i o n s show very abrupt onsets on many occasions, i n d i c a t i n g t h a t the i r r e g u l a r i t i e s are o f t e n confined i n sharply bounded zones. The two spaced s t a t i o n s have also been used to measure the height of the region responsible f o r the s i g n a l - s t r e n g t h s c i n t i l l a t i o n s . I n many cases, the onset of s c i n t i l l a t i o n m a previously q u i e t record was very sudden, and could be determined to an accuracy of a f r a c t i o n of a second i n time. The d i f f e r e n c e m time between sudden onsets observed a t the two s t a t i o n s spaced along the s u b s a t e l l i t e t r a c k could then be used to give a measure of the height of the region containing the ionospheric i r r e g u l a r i t i e s which were presumably responsible f o r the s c i n t i l l a t i o n . This method I S based on the assumption t h a t the s a t e l l i t e suddenly encountered a f i x e d region of disturbance i n the course of i t s o r b i t , rather than t h a t disturbed conditions were suddenly imposed on a q u i e t ionosphere. This p h y s i c a l l y plausible assumption seemed to be borne out by the existence of a measurable time d i f f e r e n c e between sudden on- sets at the two receivers. I t was also assumed that the region responsible f o r the s c i n t i l l a t i o n was w e l l defined i n height. I f , as seems more l i k e l y , t h i s region extended over a f i n i t e range i n height, i t would be impossible to determine whether the measured height r e f e r s to the top or the bottom or to some intermediate p o i n t i n the layer. This would be determined s o l e l y by the geometry of the face of the region of which we have no knowledge. The time separations which have been measured i n t h i s way have a l l been of the order of a second or two f o r a s t a t i o n spacing of about 19 km, g i v i n g heights which have ranged from about 400 km up to 1000 km or more. These great heights were sur- p r i s i n g at f i r s t s i g h t , i n view of the current estimates of the l o c a t i o n of the region responsible f o r the s c i n t i l l a t i o n of radio stars as being lower than, or close t o , the maximum of the F2 region. An important point to consider here, however, I S t h a t these measurements r e f e r to the a u r o r a l zone, where i t might be expected that disturbances would be much more intense, and may extend to much greater heights than at middle l a t i t u d e s . Measurements of radio s t a r s c i n t i l l a t i o n s c a r r i e d out over a number of years a t College have indeed shown that the amplitude of s c i n t i l l a t i o n I S a t least an order of magnitude greater than that observed w e l l to the south of the a u r o r a l zone. A s t a t i s t i c a l analysis of the amount of s c i n t i l l a t i o n as deter- mined by the height of the s a t e l l i t e suggested t h a t i r r e g u l a r i t i e s occur mostly below 650 km and t h a t occurrence a t greater heights i s less frequent. A paper discussing the heights of i r r e g u l a r i t i e s has been prepared f o r p u b l i c a t i o n . 638

EARTH SATELLITE e. Spurious absorption of the s i g n a l - Instances have occurred of sudden, b r i e f loss of s i g n a l strength. The time d i f f e r e n c e s i n the occurrences of these fades at the two s t a t i o n s i n d i c a t e that the region responsible must l i e i n the neighbor- hood of 250 to 350 km. At these heights the occurrence of non-deviative absorption i s r u l ed out, and the most pl a u s i b l e explanation i s that there must be a cloud of high e l e c t r o n density capable of r e f l e c t i n g the s i g n a l . However, the corresponding C3 ionospheric sounder recordings do not show any sporadic echoes at these heights extending to frequencies greater than 3 or 5 Mc, and i n some cases there i s no evidence of any echoes from these regions whatsoever. I t i s suggested t h a t the explanation i s t h a t these clouds are l y i n g along the magnetic l i n e s of force. Since the l o c a l magnetic dip angle a t College i s 77°, when the s a t e l l i t e i s nearly overhead the angle of incidence of the s i g n a l on the i o n i z a t i o n cloud w i l l be about 77°, and a cloud having a " c r i t i c a l frequency" of 4.5 Mc w i l l be s u f f i c i e n t to cause t o t a l r e f l e c t i o n of the s a t e l l i t e s i g n a l . For a s i m i l a r reason, the v e r t i c a l lonosonde might not record an echo. f . Decay of the s a t e l l i t e spin- I t was observed t h a t f o l l o w i n g October 27, 1958, the s a t e l l i t e 1958 Delta I I showed evidence of spinning. The period of spin was about 25 seconds during e a r l y November, and the angular v e l o c i t y decreased dur- ing the month at an average ra t e of 6.5 x 10" radians per second per day, though there were considerable f l u c t u a t i o n s m t h i s r a t e from day to day. A comparison w i t h the solar noise data i n the centimeter wavelengths indicated that the f l u c t u - ations were not s o l a r - c o n t r o l l e d i n any d i r e c t manner, as has been observed f o r the f l u c t u a t i o n s i n the r a t e of change of o r b i t a l period. This would i n d i c a t e t h a t the spin decay i s not predominantly c o n t r o l l e d by e i t h e r charge drag or gas drag. As has been pointed out by Harvard College Observatory workers, t h i s suggests that at least f o r 1958 Delta I I , magnetic drag predominates i n the spin decay. g. Reception of antipodal signals: On four occasions during March and A p r i l 1959 signals were received when the s a t e l l i t e was approximately a t the antipodal po i n t . The corresponding s a t e l l i t e heights were between 240 and 340 km. A l l of these signals occurred only i n recordings made using a t u r n s t i l e antenna phased to receive the ordinary wave, and simultaneous recordings made at the second s i t e using extraordinary wave reception showed no trace of the s i g n a l . Since the t u r n s t i l e antennas are t r u l y c i r c u l a r l y polarized only i n a narrow cone around the z e n i t h , t h i s implies t h a t the wave must have a r r i v e d from close to the z e n i t h a l d i r e c t i o n , and I t would appear th a t a mode of propagation i s involved which favors the ordinary mode. I f i t I S assumed that the propagation i s due to some kind of trapping between two layers, then whenever a f i e l d - a l i g n e d i r r e g u l a r i t y intervenes i n t h i s t r a p , the wave might be d i v e r t e d along t h i s i r r e g u l a r i t y , the l o c a l dip angle of 77° could therefore r e s u l t i n a high angle of reception. The strength of the antipodal s i g n a l amounted to about 0.3 microvolts a t the receiver input. h. Radiation measurements The telemetered r a d i a t i o n data from 1958 Delta has been analyzed using the USSR telemetry codes f o r 62 separate passes, from May 18, 1958 through June 17, 1958. The s u b s a t e l l i t e tracks and a l t i t u d e s f o r each of these passes were determined from Space Track B u l l e t i n s . The values f o r r a d i a t i o n i n t e n s i t y incident on the detector range from 0.7 to 2.8 BEV/Sec and the a l t i t u d e s from 238 to 530 km. A graph of r a d i a t i o n i n t e n s i t y as a f u n c t i o n of a l t i t u d e presents a f a i r l y w e l l-defined curve f o r lower a l t i t u d e s , but there i s a large scatter of points fo r height above 360 Km. This s c a t t e r was studied i n r e l a t i o n to ionospheric d i s - turbances and magnetic a c t i v i t y . The p o r t i o n of the incident r a d i a t i o n m the form of high energy pulses (greater than 1 or 2 Mev) has been determined, the values ranging from .11 to .68 BEV/Sec, the most common value being .22 BEV/Sec. A graph of r a d i a t i o n i n t e n s i t y i n c i d e n t on the detector versus height shows an approximately l i n e a r increase i n the range from 258 to 530 km, though w i t h a con- siderable amount of s c a t t e r i n the upper region. Attempts to c o r r e l a t e t h i s s c a t t e r w i t h ionospheric disturbances have so f a r been unsuccessful. 639

EARTH SATELLITE 1 . Observations of Explorer V I I . Some usable recordings have been made of the si g n a l s t r e n g t h of s a t e l l i t e 1959 I o t a (Explorer V I I ) on i t s t r a n s m i t t i n g frequency of approximately 20 Mc. This s a t e l l i t e had an o r b i t a l i n c l i n a t i o n of about 51°, and reached a maximum e l e v a t i o n above the southern horizon at College ( l a t i t u d e 65°N) of about 20° when apogee coincided w i t h the most n o r t h e r l y point of the o r b i t . At t h i s time, however, i t s distance from the College receivers was about 2000 km, so tha t the s i g n a l was rather weak. Because of the o b l i q u i t y of incidence of the r a d i a t i o n on the ionosphere, the 20 Mc s i g n a l would not have been received even under the most favorable conditions i f the College v e r t i c a l incidence c r i t i c a l frequency was greater than about 11 Mc. The records which have been obtained show a large degree of fading, together w i t h v a r i a t i o n s of longer period due to Faraday r o t a t i o n and tumbling of the s a t e l - l i t e . At I t s low angles of e l e v a t i o n above the southern horizon, the d i r e c t i o n of propagation of the s a t e l l i t e s i g n a l makes a large angle w i t h the d i r e c t i o n of the geomagnetic f i e l d i n the ionosphere. This raises the p o s s i b i l i t y of measuring the elongation along the f i e l d d i r e c t i o n of the i r r e g u l a r i t i e s responsible f o r the fad- ing. Radio star s c i n t i l l a t i o n measurements made a t College suggest that elongations of the order of 10-1 can be expected. Some preliminary i n v e s t i g a t i o n of t h i s p o s s i b i l i t y was c a r r i e d out by using spaced receivers to measure the c o r r e l a t i o n distance of the ground d i f f r a c t i o n p a t t e r n . J. Continuation of t h i s program: The two s t a t i o n study of s a t e l l i t e radio s i g n a l s trength s c i n t i l l a t i o n i s being continued w i t h NASA support under the d i r e c t - ion of Dr. L e i f Owren. 6. Bibliography. R. Parthasarathy, R. P. Easier, R. N. DeWitt. "A New Method f o r Studying the Auroral Ionosphere using Earth S a t e l l i t e , " Proc. IRE, Vol. 47, No. 9, p. 1660, 1959. R. Parthasarathy, G. C. Reid- "Signal Strength Recordings of the S a t e l l i t e 1958 Delta I I (Sputnik I I I ) at College, Alaska," Proc. IRE, Vol. 47, No. 1, January 1959. R. P. Easier, R. N. DeWitt, G. C. Reid "Radiation Information from 1958 Delta 2," J. Geo. Res. Vol. 65, No. 4, A p r i l 1960, p. 1135, IGY S a t e l l i t e Report No. 6, p. 83, June 1960, National Academy of Sciences, Washington, D.C. 640

EARTH SATELLITE Project 32.43 Electron Density and Radio Propagation Studies U t i l i z i n g S a t e l l i t e Transmissions 1. Objectives. This p r o j e c t at the Radio Propagation Laboratory (now the Radio- Science Laboratory) of Stanford U n i v e r s i t y , provided f o r Doppler, interferometer and p o l a r i z a t i o n r o t a t i o n measurements f o r the purpose of determining in t e g r a t e d e l e c t r o n d e n s i t i e s along the propagation path and also estimates of the e l e c t r o n density p r o f i l e above the height of maximum density. Observations were also to be made of long-distance propagation e f f e c t s -- multiple-hop propagation, t i l t e d layer modes or focusing, -- i n conjunction w i t h other radio studies i n progress a t Stanford. 2. Operations. Equipment was set up m the v i c i n i t y of Stanford m a mobile van, and consisted i n i t i a l l y of a dual frequency (20 and 40 Mc) interf e r o m e t e r , two- frequency p r e c i s i o n Doppler measuring equipment, and s i g n a l - s t r e n g t h recording equipment f o r s o l a r i z a t i o n r o t a t i o n studies. Two harmonically-related frequencies provided a convenient way to study the Doppler " e r r o r " imposed on a s a t e l l i t e s i g n a l when the transmission path included the ionosphere. The 20-Mc signals from Sputnik I I I and t h e i r second harmonic a t 40 Mc were s a t i s f a c t o r y f o r t h i s purpose. A c r y s t a l o s c i l l a t o r w i t h frequency near that of the s a t e l l i t e o s c i l l a t o r was mixed w i t h the incoming 20 Mc s i g n a l and the r e s u l t a n t audio tone was recorded on magnetic tape. The second harmonic of the c r y s t a l o s c i l l a t o r was mixed w i t h the second harmonic of the s a t e l l i t e s i g n a l and t h i s tone recorded simultaneously. I n the absence of an ionosphere these two audio tones would be exact harmonics, by noting t h e i r departure from t h i s r e l a t i o n the Doppler " e r r o r " due to the ionosphere could be determined. I t should be noted t h a t s a t e l l i t e o s c i l l a t o r d r i f t does not a f f e c t the accuracy of t h i s measurement. The frequency of the c r y s t a l o s c i l l a t o r was measured throughout the run by comparison w i t h a secondary standard. From t h i s measurement the absolute frequency could be determined. A t h i r d adjacent track on the magnetic tape was used to record WWV. From recordings obtained m October, 1957, of the signals from Sputnik I , i t was clear t h a t the Faraday e f f e c t could be confused by the free body motion of the s a t e l l i t e i t s e l f . I n order to a s s i s t i n the separation of these e f f e c t s , means were provided to determine the complete p o l a r i z a t i o n of the downcommg s i g n a l . This required three independent measurements, the r e l a t i v e s i g n a l strength on E-W, N-S dipoles and a " t u r n s t i l e " antenna were chosen. I n the case of Sputnik I I I these precautions were found to be unnecessary since very l i t t l e body motion was e x h i b i t e d . Each of the three 20-Mc antennas and a 40-Mc dipole were connected to a separate communications receiver and t h e i r diode outputs recorded on a multi-channel Sanborn recorder. This chart also provided a record o£ any si g n a l f l u t t e r . At a time midway between two d i r e c t passages near Stanford, the s a t e l l i t e passed i n the v i c i n i t y of the antipodes. For several minutes on e i t h e r side of t h i s time a close watch was maintained f o r s a t e l l i t e s i g n a l s . A three-element h o r i z o n t a l Yagi antenna which could be rot a t e d was employed to estimate the d i r e c t i o n of a r r i v a l of the s i g n a l s , and the absolute frequency was determined m the same manner as f o r a d i r e c t passage. An a d d i t i o n a l f i e l d s t a t i o n was established at the Uni v e r s i t y of Puerto Rico under the supervision of Professor B. DueTio. The f a c i l i t y included a dual channel magnetic tape recorder f o r the purpose of recording 20 Mc Doppler and WWV simultaneously. Signal strength v a r i a t i o n s observed w i t h a receiver fed by a dipole antenna were recorded on paper tape. 641

EARTH SATELLITE 3. Personnel. 0. G. V i l l a r d was pr o j e c t d i r e c t o r f o r t h i s work, other senior personnel associated w i t h Dr. V i l l a r d were R. N. Eracewell, A. M. Peterson, and 0. K. G a r r i o t t . 4. Data O r i g i n a l records are retained at Stanford f o r f u r t h e r d e t a i l e d analysis. 5. Results. The pulsed nature of the signals from Sputnik I I I , i n a d d i t i o n to an inadequate signal-to-noise r a d i o , d i d not permit a d i r e c t count to be made of the Doppler frequency. Rough curves were obtained by f o l l o w i n g the audio beat frequency w i t h an audio o s c i l l a t o r , but these were not of the desired accuracy. Another system f o r obtaining Doppler curves was therefore constructed. a. F l u t t e r Observation. Signal f l u t t e r as demonstrated by rapid v a r i a t i o n s m si g n a l strength has been observed on numerous passages. The most frequent cause on low passages appears to have been interference between components a r r i v i n g from several d i r e c t i o n s . Many times there were a t least three possible ray paths which could be formed between the receiver and the s a t e l l i t e the upper and lower rays vi a normal ionospheric r e f l e c t i o n and a " d i r e c t " ray possible because of the elevated p o s i t i o n of the s a t e l l i t e . The Doppler s h i f t imparted t o the signals radiated i n each d i r e c t i o n was, i n general, d i f f e r e n t , r e s u l t i n g i n r a p i d f l u t t e r a t the receiver. The f l u t t e r observed on signals o r i g i n a t i n g w e l l above the F2 layer maximum was presumably associated w i t h ionospheric i r r e g u l a r i t i e s . b. Antipodal Signals. Antipodal signals at 20 Mc have been observed a t le a s t twenty times when Sputnik I I I was i n the v i c i n i t y of the antipodes. On a l l but two occasions the signals were observed m the afternoon or evening at a time midway between two high passages near Stanford. Perhaps the most important s i g n a l char- a c t e r i s t i c was a nearly constant frequency throughout each antipodal passage. This implies a f i x e d d i r e c t i o n of a r r i v a l , f o r i f t h i s d i r e c t i o n had changed appreciably a corresponding change i n Doppler frequency would have been observed. The d i r e c t i o n s of a r r i v a l were estimated to be between south and southeast on a l l afternoon or evening antipodal observations. The absolute frequencies of the signals indicated Doppler s h i f t s consistent w i t h these d i r e c t i o n s . The ionospheric t i l t to the south- east of the r e c i e v i n g l o c a t i o n which i s associated w i t h sunset conditions i s believed to be important i n providing a propagation path and f o r s e l e c t i n g a narrow azimuth of a r r i v a l This work continued a f t e r the IGY under support from NASA. 6. Bibliography. R N. Eracewell, 0. K. G a r r i o t t "Rotation of A r t i f i c i a l Earth S a t e l l i t e s , " Nature, 182, 760-762, Sept. 20, 1958 0. K. G a r r i o t t and 0. G. V i l l a r d , Jr. "Antipodal Reception of Sputnik I I I , " Proc. IRE, Vol 46, No. 12, 1958 0. K. G a r r i o t t "The Determination of Ionospheric Electron Content and D i s t r i b u t i o n from S a t e l l i t e Observations," IGY S a t e l l i t e Report No. 10, Jan. 1960, National Acad. Sciences, Washington, D. C, Space Research, H. Kallmann-Eijl, Ed., North-Holland Pub. Co , 1960, JGR, Vol. 65, No. 4, A p r i l 1960, pp. 1139-1157. 642

EARTH SATELLITE Project 32.44 S a t e l l i t e Doppler Measurements from Spaced Locations 1. Objectives. This p r o j e c t a t the Ionosphere Research Laboratory, Pennsylvania State U n i v e r s i t y , was organized t o obtain simultaneous recordings of the frequency of s a t e l l i t e transmissions a t three locations separated by approximately 400 km, i n order to provide Doppler data over a long segment of the s a t e l l i t e path. This was to make possible pseudo-coherent analysis methods w i t h non-coherent frequency pairs as were a v a i l a b l e i n the e a r l i e r s a t e l l i t e s , and to enable studies to be made of large scale ionospheric i r r e g u l a r i t i e s . As i n the other s i m i l a r p r o j e c t s i n t h i s s e c t i o n , these data, along w i t h o r b i t a l i n formation and l o c a l ionospheric soundings, permit, under favorable c o n d i t i o n s , the deduction of int e g r a t e d e l e c t r o n density, and possibly other information on the ionosphere as w e l l . 2. Operations. I n a d d i t i o n to the main r e c e i v i n g s t a t i o n a t U n i v e r s i t y Park, Penna, arrangements were made w i t h the Department of Physics, U n i v e r s i t y of V i r g i n i a and the Ohio State Research Foundation, Ohio State U n i v e r s i t y , f o r i n s t a l l a t i o n and operation of receivers at C h a r l o t t e s v i l l e , V i r g i n i a and Columbus, Ohio. Telephone l i n e s provided the means of d i r e c t r e l a y of the am p l i f i e d signals to U n i v e r s i t y Park. The V i r g i n i a s t a t i o n was placed i n t o operation on May 19, the s t a t i o n a t Univ e r s i t y Park on May 21, and the Columbus s t a t i o n on June 2, 1958, using the 20 Mc and 40 Mc transmissions from s a t e l l i t e 1958 Delta 2. Special equipment was designed and constructed a t the Ionosphere Research Laboratory t o be used i n conjunction w i t h standard communications receivers and tape recorders. Preamplifiers f o r the 20 Mc receivers were found necessary to improve receivers noise f i g u r e and reduce image response; the u n i t s also included a mixing c i r c u i t f o r i n j e c t i o n of the reference frequency. A frequency comparison u n i t was constructed f o r use i n keeping a 1 Mc standard o s c i l l a t o r a t each of the s t a t i o n s c a l i b r a t e d and aligned. A 108 Mc receiver w i t h an antenna f o r p o l a r i z a t i o n sutdies was constructed f o r use w i t h the l a t e r U. S. s a t e l l i t e s , and several improvements were made m the s t a b i l i t y of the reference o s c i l l a t o r s and input a m p l i f i e r s . I n a d d i t i o n , stepped, ganged, audio-frequency f i l t e r s were introduced to improve the s i g n a l to noise r a t i o of the Doppler signals recorded on magnetic tape. Several methods of analysis of the ionospheric Doppler e r r o r were devised and tested. A f t e r a period of checking and m o d i f i c a t i o n , and the a r r i v a l of a high speed recorder, w i t h response f l a t t o about 100 cps, the analysis program was i n i t i a t e d . 3. Personnel. A. H. Waynick was the p r o j e c t d i r e c t o r , w i t h W. J. Ross the p r i n c i p a l i n v e s t i g a t o r . 4. Data. O r i g i n a l tape records are retai n e d a t the Ionosphere Research Laboratory f o r continued reduction and anal y s i s . The determination of the e l e c t r o n content of the ionosphere f o r a l l s u f f i c i e n t l y good records of 1958 Delta 2 has been completed and the f i n a l data published m tabular form i n ICY S a t e l l i t e Report Series No. 12 (See B i b l i o g r a p h y ) . 5. Results. E s s e n t i a l l y continuous recordings of the 20 Mc and 40 Mc transmissions of s a t e l l i t e 1958 Delta 2 were made a t State College from June 1958 to June 30, 1959 and beyond. I n t h i s time the o r b i t plane processed approximately four r e v o l u t i o n s i n solar time while the perigee processed about one h a l f r e v o l u t i o n . Approximately seven months' records were also taken i n t h i s period on the t h r e e - s t a t i o n network, from June through September 1958, and from January through March 1959, w i t h usually 643

EARTH SATELLITE between two and four passes recorded each day, of average du r a t i o n about 10 minutes, g i v i n g about 120 hours pass time on tape, and some 700-800 pass records. Analysis procedures were established experimentally e a r l y i n 1959 and were i n r e l i a b l e operation by about A p r i l 1959. Further studies u t i l i z i n g these data appear m the papers and reports included m the bibliography. The f o l l o w i n g general features of the r e s u l t s have been observed (a) during d a y l i g h t hours the expected dispersive Doppler frequency p a t t e r n follows the pre- d i c t e d course of a scaled down Doppler p a t t e r n w i t h only r e l a t i v e l y small s c a t t e r i n the readings, but t h i s behovior breaks down at large z e n i t h angles, as would be expected from theory. The integrated e l e c t r o n column has values of t y p i c a l l y about 0.8 - 1.0 x 10^^/m^ near noon i n w i n t e r . (b) Away from noontime conditions, increasing s c a t t e r i s seen, at n i g h t , when the e l e c t r o n content drops to about 0.1 - 0.2 x 10 °/m , sc a t t e r becomes so great that a well-defined dispersive Doppler p a t t e r n i s not seen, but merely a trend i n the expected d i r e c t i o n . The analysis methods then do not apply. The played-back Doppler signals were f i l t e r e d i n a manually-tracked heterodyne f i l t e r having bandwidths of 100 cps at the output frequencies of 2500 cps and 5000 cps which contain r e s p e c t i v e l y the 20 Mc and 40 Mc channel information. The 20 Mc channel s i g n a l i s frequency doubled and i t s phase compared w i t h the 40 Mc channel s i g n a l i n two phase detectors. The quadrature r e l a t i o n s h i p between the inputs permits d i s c r i m i n a t i o n of p o s i t i v e and negative dispersive Doppler frequencies and f a c i l i t a t e s the analysis generally. The normal Doppler p a t t e r n i s displayed as the beat frequency between the s a t e l l i t e s i g n a l and a sequence of l i n e frequencies spaced 120 cps apart, A t y p i c a l section of recorder chart i s shown m Figure 13. The i n f o r m a t i o n i s displayed as f o l l o w s . Channel 1 - Doppler frequency c a l i b r a t i o n Channel 2 - 20 Mc s i g n a l amplitude Channel 3 - 40 Mc s i g n a l amplitude Channel 4 - Dispersive Doppler p a t t e r n Channel 5 - quadrature dispersive Doppler p a t t e r n Channel 6 - 20 Mc Doppler p a t t e r n The keyed nature of the t r a n s m i t t e r i s evident from channels 2 and 3, and the Faraday r o t a t i o n fading can be c l e a r l y seen on these channels also. During the "on" periods of the t r a n s m i t t e r the dispersive Doppler information can be seen on channels 4 and 5, and the normal Doppler information on Channel 6. The dispersive Doppler frequency on channels 4 and 5 can be i n t e r p o l a t e d through- out the " o f f " periods since i t i s e s s e n t i a l l y a measure of changing d i f f e r e n t i a l phase path length between 20 Mc and 40 Mc, and i s therefore a continuous f u n c t i o n even i f the s a t e l l i t e o s c i l l a t o r i s discontinuous i n frequency. However, the Doppler dis p l a y on channel 6 cannot be i n t e r p o l a t e d and must be read w i t h i n a s i n g l e pulse. The " p u l l i n g " of the s a t e l l i t e t r a n s m i t t e r during each "on" pulse can be seen i n t h i s channel. When the Doppler and the dispersive Doppler patterns are p l o t t e d against time they give r i s e to a r e l a t i o n such as shown i n Figure 14. I n t h i s f i g u r e the a r b i t r a r y zero of the Doppler frequency has been chosen to make the curves l i e close together, so t h a t the s i m i l a r i t y of the two curves, apart from a scale f a c t o r , i s r e a d i l y seen. 644

EARTH SATELLITE -TIME I SECOND CHANNELS CHANNEL 5 CHANNEL 4 CHANNEL 2 CHANNEL I m '7/ fc-y*<wy NMMNvS SAMPLE ANAUrSS RECORD Figure 13. Typical Section Recorder Chart S a t e l l i t e Signals 645

EARTH SATELLITE e DISPERSIVE DOPPLER FREOUENCY (C/S) 4 < * • 4 * -ao o 970 020 OTO 20 MC/S DOPPLER FREOUENCY (C/S) 1020 loro IISO irro 1220 0 -55 as SB n BB IBJ rtB m As Ao TIIK(SeOONOS) Figure 14. Relation of Doppler and Dispersive Doppler Patterns 646

EARTH SATELLITE 8 0 0 7 0 0 6 0 0 500 4 0 0 HEIGHT Km 3 0 0 2 0 0 100 r DISPf DOPF POIN :R:IV£ ̂ 'LEW / ' 1 / ') / / • / / y A / < o o > 2 / 2 6 / 5 9 1320 EST o o o o o o o o o c\ o o REDUCED e lONOGRAM Q 9 i REDUCED ^ ̂ Ndh PUOT 0.2 0.4 0.6 ELECTRON INTEGRAL (Xio"'^ m"^) 0.8 Figure 15. Plot of Electron Integral as Function of Height Derived from S a t e l l i t e Signals. 647

EARTH SATELLITE Using the scale f a c t o r , and applying ionospheric theory, i t was calculated t h a t the average e l e c t r o n density up to the height of the s a t e l l i t e (790 km) was 1.1.10l2/ni-^ and the columnar density to t h i s height These f i g u r e s are estimated to be accurate probably to about 10%. These data are p l o t t e d i n Figure 15, together w i t h reduced sounding data from Washington, D.C., taken e s s e n t i a l l y simultaneously. The curve shows e l e c t r o n i n t e g r a l as a f u n c t i o n of height. Note th a t the dispersive Doppler f i g u r e i s consistent w i t h the sounding data, since continuation of the layer a t i t s maximum density value (curve A) accumulates the required columnar density at a lower height than the s a t e l l i t e . The best polynomial f i t to these data, i . e . matching slopes a t layer maximum and passing through the s a t e l l i t e - d e r i v e d p o i n t , i s shown (curve B). The in v e s t - i g a t o r s point out, however, t h a t t h i s curve should not be taken as cor r e c t since c e r t a i n l y higher order curves are necessary to describe the a c t u a l d i s t r i b u t i o n , and on physical grounds an exponential curve would be pre f e r r e d . The ambient e l e c t r o n density which curve B shows at 790 km i s approximately 10 m corresponding to a c r i t i c a l frequency of about 9 Mc which, the i n v e s t i g a t o r s f e e l , I S almost c e r t a i n l y high. The true d i s t r i b u t i o n curve, they suggest, probably l i e s between curves A and B although from t h i s data no f u r t h e r deductions on i t s shape can be drawn. This work was continued under NASA support. 6. Bibliography. a. Papers Presented a t Meetings W. J. Ross: "Ionospheric Measurements Using Spaced-Receiver Doppler Observations of Earth S a t e l l i t e Radio Transmissions," URSI-IRE Spring Meeting, A p r i l 1958. W. J. Ross: "Integrated Electron Densities from S a t e l l i t e Radio Doppler Frequency Observations," URSI-IRE F a l l Meeting, October 21, 1959, San Diego, C a l i f . W. J. Ross. "Diurnal and Seasonal Va r i a t i o n s m Ionospheric Electron Content from S a t e l l i t e Doppler Studies," URSI-IRE Spring Meeting, May 1960. W. J. Ross, " S a t e l l i t e Studies of the Ionosphere," Annual Meeting of the Central Pennsylvania, Emporium, and Williamsport Sections of IRE, May 1960. D. S. Anderson and W. J. Ross "Some Properties of the T o t a l Ionosphere," URSI-IRE F a l l Meeting, December 13, 1960. W. J. Ross and D. S. Anderson, "The V a r i a t i o n of Ionospheric P r o f i l e w i t h Season and Solar Cycle," NATO Advanced Study I n s t i t u t e , Oslo, Norway, A p r i l 1961 (Presented by S. A. B o w h i l l ) . b. Published Papers W. J. Ross, "Ionospheric I n v e s t i g a t i o n from S a t e l l i t e Radio Observations. 1. Doppler E f f e c t Recording Instrumentation," Sci. Rep. No. 120, July 15, 1959. D. S. Anderson, "Ionospheric Studies from an Analysis of S a t e l l i t e Radio Signals w i t h an Automatic Tracking F i l t e r , " Sci. Rep. No. 138, Sept. 1960. 648

EARTH SATELLITE W. J, Ross, "Ionospheric I n v e s t i g a t i o n s Using S a t e l l i t e Radio Observations. 2. Doppler E f f e c t Analysis Methods and Preliminary Data," Sci. Rep. No. 143, Ion, Res. Lab., Penn. State Univ,, December 15, 1960 ICY S a t e l l i t e Report No. 12, p, 1, December 1960, National Academy of Sciences, Washington, D. C. W, J, Ross, "The Determination of Ionospheric Electron Content from S a t e l l i t e Doppler Measurements," Journal of Geoph, Res, Vol. 65, No. 9, pp. 2601-2615, September, 1960. L, J, Blumle* "Studies of the E q u a t o r i a l Ionosphere using the Faraday e f f e c t on S a t e l l i t e Radio Transmissions," Sci. Rep. No, 156, March 1962. H. W, Butler- "An I n v e s t i g a t i o n of H o r i z o n t a l Gradients i n the Electron Content of the Ionosphere," Sci. Rep. No. 165, July 1962. G. E. Chisholm "Observations of large scale ionospheric i r r e g u l a r i t i e s as deduced from s a t e l l i t e i n formation," Sci. Rep. No. 166, August 1962. J. P. de Barber "The d i f f r a c t i o n of High Frequency Radio Waves by I r r e g u l a r - i t i e s i n the Ionosphere w i t h Emphasis on waves emanating from a r t i f i c i a l e a r t h s a t e l l i t e s , " Sci. Rep. No. 169, Sept. 1962. 649

EARTH SATELLITE Project 32.46 Absolute Signal Strength and Frequency Measurements 1. Objectives. This p r o j e c t a t the L i n f i e l d Research I n s t i t u t e , L m f i e l d College, McMinnville, Oregon, was organized to record s a t e l l i t e radio transmissions, and from analysis of the absolute s i g n a l strength and frequency deduce (a) the t o t a l i o n i z a t i o n along the propagation path (by observations of p o l a r i z a t i o n fading on 20 and 40 Mc), (b) the i o n i z a t i o n density a t the F2 maximum (by comparison of simultaneous 20 and 40 Mc s i g n a l strengths a t oblique incidence, and (c) char- a c t e r i s t i c s of the a u r o r a l region other than as covered above (by observing s a t e l l i t e signals r e f l e c t e d from a u r o r a l s t r u c t u r e s , i n a d d i t i o n , i t was planned t o undertake s t a t i s t i c a l studies of propagation conditions during the incidence of meteor showers. 2. Operations. Yagi and t u r n s t i l e antennas were provided f o r 20 and 40 Mc, along w i t h stable receivers, a 1 Mc frequency standard, a WWV stable r e c e i v e r , and the necessary a u x i l i a r y mixer and switching c i r c u i t s . The receiver outputs and r e f e r - ence standards were recorded on both twin-channel tape and chart recorders. A f i e l d s t a t i o n was established several miles from the c i t y i n a t r a i l e r van, w i t h t e s t and re p a i r f a c i l i t i e s . I n order to increase range and improve the beam p a t t e r n f o r 20 Mc reception, a six-element Yagi was constructed t h a t could be c o n t r o l l e d i n azimuth and e l e v a t i o n , but i t s c o n s t r u c t i o n was not completed u n t i l almost the end of the p r o j e c t , and so few data from t h i s source were analyzed. 3. Personnel. W. P. Dyke was the p r o j e c t d i r e c t o r and p r i n c i p a l i n v e s t i g a t o r , w i t h R. E. Jones the senior p h y s i c i s t associated w i t h Dr. Dyke. 4. Data. O r i g i n a l tapes and records are r e t a i n e d a t L i n f i e l d f o r continuing analysis by the i n v e s t i g a t o r s and students at the College. 5. Results. As soon as monitoring was begun i n October 1958, reception of trans- mitted signals was achieved over s u b s t a n t i a l l y long i n t e r v a l s of time and at times when the s a t e l l i t e must have been a great distance away. This i s i n accord w i t h the experience of other experimenters on a l l three Sputniks, some of whom have reported, s p e c i f i c a l l y , reception when the v e h i c l e was at the antipodal p o i n t . I n order t o ob t a i n a clearer o v e r - a l l p i c t u r e of the s i t u a t i o n , the locus of the sub- s a t e l l i t e p o s i t i o n when the s i g n a l was received a t t h i s s t a t i o n was p l o t t e d on a world map. On a Mercator p r o j e c t i o n these l o c i are segments of approximate sinusoids and t h e i r density d i s t r i b u t i o n over a period of one or more days gives a q u a l i t a t i v e estimate of propagation conditions at a glance. The l o c i of s u b s a t e l l i t e points f o r a two-or three-day run i n February and March, 1959 are i n Figures 16 and 17. The receiver and i t s antipodal point are indi c a t e d by R and A, r e s p e c t i v e l y . The mean l a t i t u d e s of the s a t e l l i t e ' s apogee and perigee during the period are shoim by dashed l i n e s and the d i r e c t i o n of the s u b s a t e l l i t e motion at apogee and perigee are indic a t e d by arrows. The dashed curves around the receiver are contours of great c i r c l e ranges of 1600, 3200, and 3900 km. The l a s t i s approximately the maximum great c i r c l e distance to the s u l j s a t e l l i t e p o i n t a t apogee. I t i s evident t h a t l i n e - o f - s i g h t transmission was of t e n exceeded and also t h a t d i s t i n c t patterns of reception of the d i s t a n t transmissions occur but vary from month to month. While the antipodal s i g n a l was present a few times, i t was cer- t a i n l y not so prevalent as those long distance transmissions from other regions, such as the e q u a t o r i a l and South P a c i f i c Ocean. The l a t t e r passes were almost always northgoing and usually not f a r from perigee. A check on f i v e of these passes on November 8 and 9 showed them a l l t o occur a t times between 1400 and 1600, l o c a l mean solar time. At these times F-layer conditions were such t h a t the s a t e l l i t e was w e l l below the F-2 maximum and the 4200 km MUF was w e l l above 20 Mc, a c t u a l l y above 30 Mc. Skip propagation was therefore e n t i r e l y possible as the mechanism. 650

EARTH SATELLITE _60_ \ AlfOGEE PERIG Figure 16. Geographical distribution of subsatellite position when signal received February 13-15, 1959, UT Figure 17. Geographical distribution of subsatellite position when signal received. March 17-19, 1959, UT (Regular World Days.) 651

EARTH SATELLITE The frequency reduction of the received 20 Mc data showed s i g n i f i c a n t i r r e g u l a r , but o f t e n smooth, deviations from the predicted Doppler curves based on the known o r b i t a l geometry and free-space l i n e - o f - s i g h t propagation. These deviations were too large i n magnitude and too i r r e g u l a r i n nature to be counted f o r by changes m propagation conditions, e i t h e r a t the s a t e l l i t e p o s i t i o n or along a l i n e - o f - s i g h t path, caused by a r e g u l a r l y s t r a t i f i e d ionosphere. I t i s suspected that these frequency anomalies were caused by i r r e g u l a r i t i e s i n the ionosphere e l e c t r o n density d i s t r i b u t i o n and t h a t parameters of the i r r e g u l a r i t i e s may be obtained by analysis of the data, probably w i t h the a i d of other i n f o r m a t i o n from other sources, such as simultaneous sweep-frequency soundings. While an extremely s i m p l i f i e d model, used to compute the phase changes and hence frequency s h i f t s due to the passage of the transmitted s i g n a l through a region of varying e l e c t r o n density, does not e x h i b i t large enough phase-change r a t e s , the extension to more complicated model, i n c l u d i n g s p e c i f i c a l l y those allowing an appreciable change i n d i r e c t i o n of propagation and the consequent i n t r o d u c t i o n of a d d i t i o n a l Doppler components, would y i e l d frequency s h i f t s of the order of magnitude observed. Although the simple model proves inadequate i n i t s assumption of small path d e v i a t i o n , the time and d i r e c t i o n computations based on i t may s t i l l give an i n d i c a t i o n of the rough dimensions and heights of the i r r e g u l a r i t i e s detected. These computed values are not inconsistent w i t h the observations of others using d i f f e r e n t methods. A d d i t i o n a l reduction and analysis of the considerable amount of data, m p a r t i c u l a r m c o r r e l a t i o n of the simultaneous frequency and s i g n a l amplitude records, should y i e l d more information. The nature of the frequency f l u c t u a t i o n s and of the phenomena causing them seems to be subject to a d d i t i o n a l probing from the data already a v a i l a b l e . 6. Bibliography. a. Papers Presented at Meetings R. E. Jones "Low Frequency S a t e l l i t e Radio Propagation Studies of the Upper Atmosphere," P a c i f i c Northwest Reg. AGU Meeting, C o r v a l l i s , Oregon, Nov. 1959. b. Published Papers R. E. Jones- "Absolute Signal Strength and Frequency Measurements, F i n a l Report," 28 February 1961, L i n f i e l d Res. I n s t . S. M. Spray "Analysis of Frequency Variations Observed i n Signals Received from A r t i f i c i a l S a t e l l i t e Sputnik I I I (1958 Delta-2)" Physics Department, L i n f i e l d College, August 1963. 652

EARTH SATELLITE Project 32.47 - Electron Density P r o f i l e s From lonograms 1. Obiectives. This p r o j e c t at the Central Radio Propagation Laboratory, Boulder Laboratories of the National Bureau of Standards, provided f o r the c a l c u l a t i o n of el e c t r o n density p r o f i l e s from the " v i r t u a l " height information of lonograms obtained by v e r t i c a l incidence radio soundings of the ionosphere. The p a r t i c u l a r o b j e c t i v e of t h i s p r o j e c t was to provide the information necessary to determine properties of the radio transmission path between s a t e l l i t e s and ground t r a c k i n g s t a t i o n s . P r o f i l e s were desired f o r locations near s a t e l l i t e t r a c k i n g s t a t i o n s or s a t e l l i t e radio observing s t a t i o n s , and f o r times when s a t e l l i t e s passed near such l o c a t i o n s . 2. Operations. Although a great deal of information concerning the e l e c t r o n d i s - t r i b u t i o n of the upper atmosphere i s contained m the sweep-frequency radio sound- ings of the ionosphere obtained from the large network of observing s t a t i o n s , extensive computations are necessary to obtain t h i s information. The computing methods used by the National Bureau of Standards were i n i t i a l l y s i m i l a r to those discussed under Project 6.9 i n Chapter V - IONOSPHERE, although a number of r e f i n e - ments were soon added. I n p a r a l l e l w i t h the development of a c a p a b i l i t y to provide experimenters w i t h e l e c t r o n density p r o f i l e c a l c u l a t i o n s f o r special occasions, l o c a t i o n s , and a p p l i c a t i o n s , the p r o j e c t proceeded also to make use of the close association between CRPL and the US network of v e r t i c a l sounding s t a t i o n s . This led to the i n c l u s i o n of e l e c t r o n density p r o f i l e analyses on a synoptic basis as part of the regular data reduction program f o r the U. S. network. 3. Personnel. This p r o j e c t was under the d i r e c t i o n of J. W. Wright, Other senior personnel c o n t r i b u t i n g h e a v i l y to the development of the program were G. H. Stonehocker, T. E. VanZandt, and H. H. Howe. 4. Data. Special p r o f i l e analyses were provided g r a t i s to workers i n s a t e l l i t e - associated ionosphere studies, vehicle t r a c k i n g , and s a t e l l i t e o r b i t a l determinations. With the development of improved methods f o r handling large volumes of e l e c t r o n density p r o f i l e data, a series of pu b l i c a t i o n s (designated NBS Technical Notes 40-1 ... 13) were puljlished to represent the m i d - l a t i t u d e q u i e t ionosphere over a one year period. The remainder of the i n d i v i d u a l p r o f i l e c a l c u l a t i o n s are a v a i l - able through the IGY World Data Center A - Ionosphere and Airglow, a t CRPL. 5. Results. A major r e s u l t of t h i s work was the i n i t i a t i o n of a program from which a synoptic climatology of the ionosphere a t a s i g n i f i c a n t number of widely spaced l o c a t i o n s , could be derived f o r the solar maximum period. These r e s u l t s were s i g n i f i c a n t i n revealing several properties about the d i u r n a l and seasonal anomalies of the ionosphere, and m suggesting some of the possible physical processes involved. These r e s u l t s have been used at CRPL and elsewhere i n a v a r i e t y of studies i n ionospheric physics. An e a r l y r e s u l t was the development of a model to describe the e l e c t r o n d i s t r i b u t i o n above the F2 layer maximum, a region not other- wise observable by the ground based sounding technique. 6. Bibliography. a. Papers Presented a t Meetings T. E. VanZandt: "Accuracy of True Height Ca l c u l a t i o n s " , S a t e l l i t e - Ionosphere Conference, Boulder, Sept. 1958. J. W. Wright: "Instantaneous Ionosphere P r o f i l e s and Their Relationship to Radio Tracking", Conference on Or b i t and Space Tr a j e c t o r y Determinations, NASA, Washington, D. C, March 1959. 653

EARTH SATELLITE J . W. Wright- "A Model of the F Region Above hmax F2/' AGARD Conference, P a n s , 1959. b. Published Papers J . W. Wright, "A T e s t of a Procedure for Easy E s t i m a t i o n of Representative Monthly E l e c t r o n Density P r o f i l e s f o r the Ionosphere," JGR, Vol. 65, No. 10, October 1960. J . W. Wright, "Comment on Models of the Ionosphere above \[ax^^^>" JGR, Vol. 65, No. 9, September 1960. J . W. Wright, "A Model of the F Region Above \^x^2," JGR, Vol. 65, No. 1, January 1960. J . W. Wright, "Note on Quiet-Day V e r t i c a l Cross S e c t i o n s of the Ionosphere along 75° W Geographic Meridian," JGR, Vol. 64, No. 10, October 1959. J . W. Wright, "The F-Region Seasonal Anomaly," JGR, Vol. 68, No. 14, J u l y 1963. J . W. Wright, "Mean E l e c t r o n Density V a r i a t i o n s of the Quiet Ionosphere," NBS T e c h n i c a l Notes 40-1 ... 13, March 1959 - February 1960. J . W. Wright, " D i u r n a l and Seasonal Changes i n S t r u c t u r e of the Mid- L a t i t u d e Quiet Ionosphere," NBS J . Res. Pt. D, Vol. 66D, No. 3, May-June 1962. J . W. Wright, "The CRPL E l e c t r o n Density P r o f i l e Program Some Feat u r e s and E a r l y R e s u l t s " , Some Ionospheric R e s u l t s Obtained during the IGY (W. J . G. Beynon, ed.) E l e s e v i e r , 1960. T. Shimazaki, Nighttime V a r i a t i o n s of F-Region E l e c t r o n Density P r o f i l e s a t Puerto Ric o , " JGR, Vol. 69, No. 13, J u l y 1964. 654

EARTH SATELLITE P r o j e c t 32.48 - Po l a r S a t e l l i t e Propagation Measurements 1. O b j e c t i v e s . T h i s p r o j e c t a t the Geophysics Research D i r e c t o r a t e , A i r Force Cambridge Research L a b o r a t o r i e s , provided for simple r e c e i v i n g systems on 20 and 40 Mc i n the A r c t i c , m order to provide monitoring of the unusual continuous propagation c o n d i t i o n s i n the polar regions reported for s a t e l l i t e s 1957 Alpha and Beta. I t was o r i g i n a l l y contemplated t h a t the equipment would be i n s t a l l e d on IGY D r i f t i n g S t a t i o n B ( F l e t c h e r ' s I c e I s l a n d ) i n the A r c t i c B a s i n , but i n view of the f a c t that t h i s s t a t i o n had d r i f t e d to where i t was p r e d i c t e d i t would remain a t a l a t i t u d e s u b s t a n t i a l l y equal to Thule, the experiment was i n s t a l l e d a t the s t a t IGY r e s e a r c h s t a t i o n on the Thule s i t e . 2. Operations. The rigorous winter c o n d i t i o n s d i c t a t e d the use of a r e l a t i v e l y simple antenna system and precluded the use of externally-mounted e l e c t r o n i c s ; simple antennas, w i t h adequate replacements, were provided a t the laboratory s i t e a t North Mountain, s e v e r a l m i l e s away from the a i r b a s e proper. Standard communica- t i o n r e c e i v e r s were employed preceded by c o n v e r t e r s . At f i r s t , the r e l a t i v e s i g n a l s t r e n g t h was monitored by recording the diode load voltage of the r e c e i v e r , the s a t e l l i t e Doppler d e v i a t i o n being produced w i t h the a i d of the r e c e i v e r beat- frequency o s c i l l a t o r . L a t e r , a more ela b o r a t e arrangement was provided. The r e c e i v e r s were modified to provide two s e n s i t i v i t i e s , one from 0-0.1 m i c r o v o l t , the second from 0-1.0 m i c r o v o l t , both of which produced a diode load voltage ranging from 0 - -3 v o l t s , the I F outputs of the r e c e i v e r s were beat w i t h a s t a b l e c r y s t a l - c o n t r o l l e d o s c i l l a t o r d i f f e r i n g from the I F i n frequency by one k i l o c y c l e . Thus the modulation of the r e s u l t i n g one kc beat note gave the Doppler d e v i a t i o n , which was detected by a s p e c i a l c o n v e r t e r . Timing s i g n a l s were provided through the use of a s t a b l e WWV r e c e i v e r . A Norrmann timer provided timing marks for the tape r e c o r d e r . 3. Personnel. Wolfgang P f i s t e r was p r o j e c t d i r e c t o r for t h i s work; personnel from Lowel l T e c h n o l o g i c a l Research I n s t i t u t e a s s i s t e d i n the p r o j e c t through a c o n t r a c t w i t h GRD. \ 4. Data. Magnetic tapes and c h a r t records are r e t a i n e d a t GRD and L o w e l l for a n a l y s i s . S u b s t a n t i a l l y complete recordings were made of the r a d i o t r a n s m i s s i o n s from 1958 D e l t a (Sputnik I I I ) . 5. R e s u l t s . As a means of cataloguing the data, record c h a r t s were inspected and the good passes mounted on c a r d s , each pass was i d e n t i f i e d by date, o r b i t r e v o l u t i o n number, time of maximum s i g n a l s t r e n g t h , time s i g n a l appeared, s i g n a l d u r a t i o n , s i g n a l s t r e n g t h , f l u c t u a t i o n , period, and c l a s s i f i c a t i o n of pass. I t was commonly found that the s i g n a l o s c i l l a t e d w i t h a period of between s i x and f i f t y seconds, and there was a great tendency for the shape of the s i g n a l s t r e n g t h p l o t to f a l l w i t h i n one of s i x p a t t e r n s , symmetrical and r i g h t - o r left-handed unsymmatrical, both mono-and b i - n o d a l . a. Ghost s i g n a l s . On e leven o c c a s i o n s , a l l between March 8 and 13, 1960, s i g n a l s were r e c e i v e d when the s a t e l l i t e t r a n s m i s s i o n s would not be expected from l o n e - o f - s i g h t c o n s i d e r a t i o n s . For nine of these occasions the s a t e l l i t e was over the A t l a n t i c Ocean a r e a , the two other cases occurred when the s a t e l l i t e was a t con- s i d e r a b l y higher a l t i t u d e and much f u r t h e r south. Because of the high l a t i t u d e of Thule, i t was not p o s s i b l e to corroborate the a n t i p o d a l e f f e c t s reported by other observers a t lower l a t i t u d e s , f o r the s a t e l l i t e o r b i t never passed Thule's antipodes. On the b a s i s of these o b s e r v a t i o n s , and the ionospheric c o n d i t i o n s noted during the r e c e p t i o n of ghost s i g n a l s , the i n v e s t i g a t o r s concluded that the e f f e c t arose from ducting m the F - l a y e r and occurred when the s a t e l l i t e t r ansmissions o r i g i n a t e d w i t h i n the F l a y e r under s u i t a b l e c o n d i t i o n s . 655

EARTH SATELLITE b. S i g n a l Duration. A study was made of the a c t u a l d u r a t i o n of the s a t e l l i t e s i g n a l a g a i n s t the expected duration as computed from r i s e and s e t time. I t was found that for f i f t y - s e v e n percent of the passes, the observed d u r a t i o n was s i g n i f i c a n t l y s h o r t e r than the p r e d i c t e d duration, and the average observed time was about two-thirds of the p r e d i c t e d time. A hypothesis i s advanced by the i n v e s t - i g a t o r s to the e f f e c t that for the s a t e l l i t e l o c a t i o n (approximately 300 km) above the F l a y e r , the 20 Mc s i g n a l i s r e f l e c t e d by the F l a y e r u n t i l the angle of i n c i d - ence i s reduced to a c e r t a i n c r i t i c a l v a l u e , which depends on the e l e c t r o n d e n s i t y . I t I S considered t h a t t h i s e f f e c t a f f o r d s a means of e s t i m a t i n g the e l e c t r o n d e n s i t y a t the point where the ray path e n t e r s the ionosphere. c. S c i n t i l l a t i o n . S i g n a l s t r e n g t h records for 1958 D e l t a showed random s h o r t - period f l u c t u a t i o n s a t approximately 10 c y c l e s per second. Study of the s c i n t i l - l a t i o n s , caused by s m a l l - s c a l e ionospheric i r r e g u l a r i t i e s m c o n j u n c t i o n w i t h a u r o r a l and magnetic a c t i v i t y , a f f o r d s the opportunity to o b t a i n information on these i r r e g u l a r i t i e s and t h e i r r e l a t i o n s h i p s to other phenomena. d. Faraday Fading. Owing to the geomagnetic f i e l d , the ionosphere e x h i b i t s the phenomenon of double r e f r a c t i o n w i t h two c h a r a c t e r i s t i c modes of propagation, the ordinary and e x t r a - o r d i n a r y . Consequently a l i n e a r l y p o l a r i z e d wave i n c i d e n t on the ionosphere t r a v e l s through the i o n i z e d medium and emerges w i t h i t s plane of p o l a r - i z a t i o n r o t a t e d because of the d i f f e r e n c e i n phase v e l o c i t y of the two modes. The s i g n a l r e c e i v e d a t a l i n e a r l y p o l a r i z e d antenna, t h e r e f o r e , shows amplitude fading w i t h c h a r a c t e r i s t i c n u l l s as the s a t e l l i t e moves through the ionosphere. From s i m p l i f i e d t h e o r e t i c a l c o n s i d e r a t i o n s , i t i s p o s s i b l e to deduce some of the pro- p e r t i e s of the i o n i z e d medium from the observations of fading. However, observations of 1958 D e l t a showed l i t t l e Faraday r o t a t i o n observed a t Thule, I t i s thought t h a t owing to the long oblique ray path, one of the modes, most l i k e l y the e x t r a - o r d i n a r y mode, may be h i g h l y absorbed and thereby reduce the depth of fading. Or, the high s c i n t i l l a t i o n r a t e observed a t Thule may mask the fading. Or, f i n a l l y , the t h e o r e t - i c a l c o n s i d e r a t i o n s on which were based the c a l c u l a t i o n s of the expected magnitude of the e f f e c t might have to be r e v i s e d i n c o n s i d e r a t i o n of the extremely oblique path through the ionosphere. e. O r b i t C a l c u l a t i o n s . I n order to complete the c o r o l l a r y information necessary to the a n a l y s i s of the recorded data, o r b i t c a l c u l a t i o n s were made, based on a v a i l a b l e information from t r a c k i n g networks. 6. Bibliography. C. D i e t e r , K. Kinnard, W. P f i s t e r , G. S a l e s , J . Waararaaa: " P o l a r S a t e l l i t e Propagation Measurements," S c i e n t i f i c Report No. 1, IGY P r o j e c t 32.48, L o w e l l T e c h n o l o g i c a l I n s t i t u t e Research Foundation, May 1960, (AFCLR-TN-60-647). 656

EARTH SATELLITE P r o j e c t 33.1 Radio T r a c k i n g Equipment and Operations 1. O b j e c t i v e s . T h i s p r o j e c t a t the Naval Research Laboratory provided f or the development of a r a d i o t r a c k i n g system - M i n i t r a c k , the c o n s t r u c t i o n of equipment for e l e v e n t r a c k i n g s t a t i o n s ; the establishment of these s t a t i o n s , and the s t a f f i n g r e q u i r e d f or t h e i r operation. The r a d i o t r a c k i n g network was located so as to pro- vide downrange information j u s t a f t e r launching of the v e h i c l e s , information on whether or not the s a t e l l i t e s had achieved one o r b i t a l c i r c u i t , and a " p i c k e t fence" along the 70-80 West Meridian so as to provide a t l e a s t one obs e r v a t i o n f o r each o r b i t a l c i r c u i t . 2. Operations. a. R e c e i v i n g system U. S. s a t e l l i t e s were equipped w i t h an unmodulated t r a n s m i t t e r operating a t 108.00 Mc, which was designed to be s t a b l e , w i t h the exception that the s a t e l l i t e i n t e r n a l temperature c o n t r o l l e d a s m a l l frequency d e v i a t i o n so that environmental temperatures could be obtained. S a t e l l i t e s i g n a l s were r e c e i v e d a t the ground by an a r r a y of f i v e antenna p a i r s , on east-west and north-south b a s e l i n e s . Comparison of the phase of the s i g n a l a t each of a given p a i r of antennas allowed the determination of the angular displacement of the s a t e l - l i t e from the perpendicular b i s e c t o r plane of that given antenna p a i r . A s i m i l a r angular measurement from the antenna p a i r s i t u a t e d perpendicular to the given p a i r permitted complete determination of the d i r e c t i o n of the s a t e l l i t e . The b a s e l i n e s were chosen to give acceptable r e s o l u t i o n commensurate w i t h unambiguous phase i n - formation. S e v e r a l such d i r e c t i o n measurements during one s a t e l l i t e pass were s u f f i c i e n t to determine the s a t e l l i t e ' s o r b i t w i t h r e s p e c t to the c e n t e r of the e a r t h . An NRL-developed r e c e i v i n g system using h i g h l y s t a b l e l o c a l l y - g e n e r a t e d r e f e r - ence sources completed the ground i n s t a l l a t i o n . S a t e l l i t e s u s u a l l y c a r r i e d a second t r a n s m i t t e r operating j u s t o f f of 108.00 Mc to provide telemetry of on-board instrumentation. These s i g n a l s were a l s o r ecord- ed by the r e c e i v i n g system and provided to the experimenters f o r i n t e r p r e t a t i o n . b. M i n i t r a c k S t a t i o n s - Coolidge F i e l d , Antigua I s l a n d , provided down-range information j u s t a f t e r launch, the " p i c k e t fence" network c o n s i s t e d of Blossom Po i n t , Maryland; Savannah, Georgia, Havana, Cuba, Mt. Cotopaxi, near Quito, Ecuador, Lima, Peru; Antofagasta, C h i l e ; and Santiago, C h i l e . S t a t i o n s a t Bloemfontein. Union of South A f r i c a and San Diego, C a l i f o r n i a , provided information of the f i r s t o r b i t , and a s t a t i o n a t Woomera, A u s t r a l i a , was e s t a b l i s h e d to give e x t r a l o n g i t u d i n a l coverage. The antenna p a t t e r n was designed to be 100° wide m the north-south d i r e c t i o n and 10° wide east-west. T h i s c o n f i g u r a t i o n provided about a 95/!, prob- a b i l i t y that the p i c k e t fence would be i n t e r c e p t e d on each c i r c u i t . The ICY Committees of the v a r i o u s c o u n t r i e s cooperated i n e s t a b l i s h i n g and maintaining the s t a t i o n s ; p a r t i c i p a t i o n by the U. S. Army and A i r Force , the Naval E l e c t r o n i c s Laboratory, and the Inter-American Geodetic Survey a l s o was instrumental i n the s u c c e s s f u l operation of the M i n i t r a c k network. 3. Personnel. J . T. Mengel was the p r o j e c t d i r e c t o r f o r t h i s work, other s e n i o r s c i e n t i s t s a s s o c i a t e d w i t h t h i s work were Roger L. Easton, Clarence A. Schroeder, Dr. Joseph W. S i r y ( o r b i t a l c a l c u l a t i o n s ) , Edmund J . Habib, Chesley H. Looney, and Dr. Paul Heyet ( o r b i t a l c a l c u l a t i o n , Univ. of C i n c i n n a t t i ) . 4. R e s u l t s . The M i n i s t r a c k network was s u c c e s s f u l i n a l l r e s p e c t s m i t s operation, permitting r a p i d o r b i t information i n the e a r l y phases a f t e r launch, and providing a high e f f i c i e n c y i n coverage during s a t e l l i t e l i f e t i m e s . I t a l s o proved p o s s i b l e to modify the M i n i t r a c k system to permit t r a c k i n g of the USSR s a t e l l i t e s , which r a d i a t e d a t frequencies of 20 and 40 Mc. 657

EARTH SATELLITE 5. Bibliography. a. Papers Presented a t Meetings "The M i n i t r a c k System," Symposium on the I n t e r n a t i o n a l Geophysical Year & the E a r t h S a t e l l i t e Program, Instrument S o c i e t y of America, American Rocket S o c i e t y , and U. S. Committee for IGY, September 17, 1956. "Transmission of Data by Radio from U. S. S a t e l l i t e s , " 1st Conference on advanced A e r o n a u t i c a l S c i e n c e s , Vol. 2, pp. 1026-1032, 1958. " E l e c t r o n i c s i n the E a r t h S a t e l l i t e Program", Ta l k to the Westchester S e c t i o n , IRE on 16 A p r i l 1958. "An A n a l y s i s of T e c h n i c a l C o n s i d e r a t i o n Leading to the Choices of Space Frequencies," M i s s i l e & A s t r o n a u t i c s D i v i s i o n of the American Ordnance A s s o c i a t i o n , J a c k s o n v i l l e , F l a . , May, 1959. b. Published Papers "Minitrack System T r a i n i n g Manual", NRL, Undated, Document #199762 "Tracking the E a r t h S a t e l l i t e , and Data Transmission, by Radio," Proc. IRE, pp. 755-760, June, 1956, "Minitrack D e t a i l s S a t e l l i t e T racking Based on Phase Comparison," A v i a t i o n Age, Vol. 27, pp. 98-105, March, 1957. "Radio System W i l l T r a c k E a r t h S a t e l l i t e , " Soc. Automotive Eng., V o l . 65, pp. 30-33, A p r i l , 1957. "Minitrack System Design C r i t e r i a , " E l e c t r i c a l Engineering, Vol. 76, No. 8, pp. 666-672, August, 1957. "Tracking S a t e l l i t e s by Radio," S c i e n t i f i c American, Vol. 198, No. 1, pp. 23-29, January, 1958. "Minitrack System Design C r i t e r i a , " J o u r n a l UIT. Telecommunication J o u r n a l , Vol. 25, pp. 68f-73£, 64e-74e, and 63s-73s, A p r i l , 1958. "Transmission of Data by Radio from U. S. S a t e l l i t e s , " Ad. of A e r o n a u t i c a l S c i . , Vol. 2, pp. 1026-1032, 1958. 658

EARTH SATELLITE P r o j e c t 33.2 Radio T r a c k i n g - O r b i t Computations and Data A n a l y s i s 1 O b j e c t i v e s . T h i s p r o j e c t a t the Naval Research Laboratory ( l a t e r t r a n s f e r r e d to NASA) provided for an a n a l y s i s center to handle M i n i t r a c k data and to perform c e r t a i n c a l c u l a t i o n s i n connection w i t h planning launchings. 2. Operations. I n order to undertake the t a s k of p r e d i c t i n g o r b i t s for t r a c k i n g s t a t i o n s and developing the p r e c i s i o n o r b i t using the accumulated t r a c k i n g i n - formation, many t h e o r e t i c a l s t u d i e s were undertaken, i n c l u d i n g , t h e o r e t i c a l a n a l y s e s of launching v e h i c l e systems and t r a c k i n g systems, t h e o r e t i c a l i n v e s t i g a t i o n s of radio wave propagation and atmospheric turbulence m the ionosphere, t h e o r e t i c a l s t u d i e s of gas dynamics and aerodynamics of s a t e l l i t e and launching v e h i c l e p a r t i c u l a r l y under c o n d i t i o n s a s s o c i a t e d w i t h i o n i z e d gases and very high v e h i c l e speeds, mathematical a n a l y s e s of p h y s i c a l and engineering systems used for launching and t r a c k i n g the s a t e l l i t e , o v e r - a l l v e h i c l e f l i g h t requirements, v e h i c l e perform- ance and accuracy requirements for t r a j e c t o r y data and data a n a l y s i s . Data from the r a d i o t r a c k i n g s t a t i o n s for o r b i t computations were transmitted to a c e n t r a l computing f a c i l i t y f or computation of the ephemerides. The ephemerides were then transmitted not only to permit a c q u i s i t i o n of the s a t e l l i t e by o p t i c a l t r a c k i n g s t a t i o n s but f o r g e n e r a l i n t e r e s t as w e l l . Data gathered over the l i f e span of t r a c k i n g emissions from the v a r i o u s s a t e l l i t e s were used to compute the best probable o r b i t s . 3. Personnel. J . W. S i r y , NRL was p r o j e c t d i r e c t o r for t h i s work. 4. R e s u l t s . The M i n i t r a c k observations made p o s s i b l e the development of p r e d i c t i o n ephemerides u s e f u l to the t r a c k i n g s t a t i o n s and other t r a c k i n g groups. F i n a l o r b i t s were determined and published. I t has r e c e n t l y been determined by a s p e c i a l study group of the Academy's Space Science Board that w h i l e the p r e c i s i o n of the M i n i t r a c k observations was one- f o r t i e t h that of the Baker-Nunn cameras, the p r e c i s i o n of the o r b i t s obtained from Mi n i t r a c k observations was one-tenth that of those obtained from the Baker-Nunn measurements, t h i s may p o s s i b l y be a t t r i b u t e d to the d i f f e r e n t geographical d i s - t r i b u t i o n of the two networks and the f a c t that o p t i c a l data depended on weather conditions and therefore was not always obtained for a given pass. F i n a l l y , the d i s p a r i t i e s between the M i n i t r a c k and Baker-Nunn o r b i t s were l e s s , according to date a v a i l a b l e i n l a t e 1960, than the unpredictable o r b i t a l d e v i a t i o n s a r i s i n g from f l u c t u a t i o n s i n upper-air d e n s i t y . M i n i t r a c k observations of Vanguard I provided the b a s i s f o r s e v e r a l important d i s c o v e r i e s concerning upper-air d e n s i t y f l u c t u a t i o n s and provided unique information fo r the a n a l y s i s of the e a r t h ' s g r a v i t a t i o n a l f i e l d . S c i e n t i s t s from the Army Map S e r v i c e , and l a t e r NASA, were able to compute the second and t h i r d order c o e f f i c i e n t s of the g r a v i t a t i o n a l p o t e n t i a l f u n c t i o n , the second order c o e f f i c i e n t gave a r e f i n e d value for the polar f l a t t e n i n g , and the t h i r d order c o e f f i c i e n t was derived for the f i r s t time, making p o s s i b l e an e s t i m a t i o n of the three-node lumpmess of the geoidal s u r f a c e . T h i s kind of a n a l y s i s was a l s o done abroad by King-Hele and Buchar, who came to the same c o n c l u s i o n regarding second-order c o e f f i c i e n t ; K a z ai a t the Smithsonian A s t r o p h y s i c a l Observatory confirmed the computation of the t h i r d - o r d e r c o e f f i c i e n t . The term "pear-shaped e a r t h " has been used popularly to d e s c r i b e the "new shape of the e a r t h , " but i t must be remembered that the two-node d e v i a t i o n (polar f l a t t e n i n g ) i s some 27 m i l e s m 4000 while the "pear-shape" d e v i a t i o n i s of the order of s e v e r a l tens of f e e t . 5. Bibliography. J . A. O'Keefe, A. E c k e l s , R. K. S q u i r e s . "The G r a v i t a t i o n a l F i e l d of the E a r t h , " Astron. J . . Vol. 64, p. 245, Sept. 1959. 659

EARTH SATELLITE P r o j e c t 34.1 - S c i e n t i f i c Telemetering and S a t e l l i t e Instrumentation 1. O b j e c t i v e s . T h i s p r o j e c t a t the U. S. Naval Research Laboratory ( l a t e r t r a n s - f e r r e d to NASA) was organized to develop a f l i g h t telemetry system f o r c o l l e c t i o n of s c i e n t i f i c data from U. S. s a t e l l i t e s . F l i g h t equipment was to be of high r e l i - a b i l i t y while meeting very s t r i n g e n t l i m i t a t i o n s m weight, space and power consumption. Ground r e c e i v i n g equipment was part of p r o j e c t 33.1. 2. Operations. A b a s i c a l l y new s o l i d s t a t e f l i g h t telemetry encoder was developed to meet the above needs. Switching t r a n s i s t o r s were used i n conj u n c t i o n w i t h square h y s t e r e s i s loop t o r o i d a l magnetic cores to generate a time s e q u e n t i a l pulsed frequency modulated s i g n a l . The b a s i c encoder i s capable of accepting inputs i n the form of varying v o l t a g e s , c u r r e n t s and/or r e s i s t a n c e s . As flown m Vanguard I I I s a t e l l i t e , a b a s i c 48 channel encoder used super-commutation to provide 17 channels of s c i e n t i f i c and "housekeeping" information. The encoder occupied a space of l e s s than 18 cubic inches and weighed l e s s than seven ounces complete w i t h mercury b a t t e r i e s f o r four weeks continuous operation. Encoder power consumption was l e s s than 11 m i l l i w a t t s . Two a d d i t i o n a l d e v i c e s a l s o using magnetic s o l i d s t a t e techniques were developed for i n - f l i g h t data p r o c e s s i n g . Both used new p r i n c i p l e s i n v o l v i n g storage of i n - formation i n the form of f l u x l e v e l s m multi-a p e r a t u r e magnetic cores w i t h a u x i l i a r y c i r c u i t r y f o r non-destructive readout of stored data. One such device was a counter used to s t o r e and continuously transmit three decimal d i g i t s of cumulative counts of impacts between the s a t e l l i t e and micrometeorites. A second device c o n s i s t e d of a peak memory u n i t w i t h o r b i t a l maximum va l u e s of s o l a r X r a y s f or c o r r e l a t i o n w i t h otherwise observed s o l a r d i s t u r b a n c e s . A l l m - f l i g h t functions were s e l f contained to e l i m i n a t e power r e q u i r e d to operate command r e c e i v e r s . S a t e l l i t e s i g n a l s were r e c e i v e d a t the M i n i t r a c k t r a c k i n g s i t e s where magnetic tape recordings were prepared and mailed back f or e x t r a c t i o n of the s c i e n t i f i c data. 3. Personnel. Whitney Matthews was p r o j e c t d i r e c t o r for t h i s work, other s e n i o r s c i e n t i s t s a s s o c i a t e d w i t h him were. R. W. R o c h e l l e , N. J . Peake, R. L. Van A l l e n , C. B. House, D. H. Schaefer, and J . C. S c h a f f e r t . 4. R e s u l t s . The f u l l telemetry system was f l o m i n the Vanguard I I I s a t e l l i t e and functioned properly u n t i l exhaustion of the chemical b a t t e r i e s a f t e r 85 days of continuous operation. T h i s IGY development has provided the b a s i s f o r telemetry systems f o r subsequent s p a c e c r a f t . 660

EARTH SATELLITE P r o j e c t 34.2 Telemetry Recording and T e c h n i c a l A s s i s t a n c e 1. O b j e c t i v e s . T h i s p r o j e c t a t the J e t Propulsion Laboratory, C a l i f o r n i a I n s t i t u t e of Technology, provided for a s s i s t a n c e m the form of equipment m o d i f i c a t i o n , tech- n i c a l cooperation, and s u p p l i e s for telemetry s t a t i o n s i n Singapore and Ibadan. 2. Operations. The U. K. IGY Committee o f f e r e d to operate two Microlock s t a t i o n s (see P r o j e c t 30.21) a t the l o c a t i o n s mentioned above. These l o c a t i o n s , s i t u a t e d near the geomagnetic equator, were s t r a t e g i c a l l y located for recording information from cosmic ray experiments. The s t a t i o n s played an important r o l e i n s e c u r i n g information from the e a r l y E x p l o r e r s a t e l l i t e s , which c a r r i e d State U n i v e r s i t y of Iowa r a d i a t i o n d e t e c t o r s , observations from these s a t e l l i t e s led to the d i s c o v e r y and d e l i n e a t i o n of the zones of magnetically-trapped r a d i a t i o n - the Van A l l e n R a d i a t i o n Zones. For d i s c u s s i o n of these observations see p r o j e c t 32.1. 3. Personnel. T h i s p r o j e c t was under the s u p e r v i s i o n of W. H. P i c k e r i n g , JPL. 661

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