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Chapter I INTRODUCTI ON In the Summer of l968 the Space Science Board convened a group to recommend a planetary exploration program for the years l968-l975. The emphasis of the study was on the earth's near neighbors â Venus, Mercury, and Mars. This emphasis resulted in part from technological considerations, since boosters were available in this time period that would permit substantial scientific exploration of the inner planets. In addition, the strong interest in possible life forms on Mars made the explo- ration of that planet a goal with high priority. The present report proposes a program for the exploration of the outer reaches of the solar system in the years 1974 to l980. The stress on the giant planets and their surroundings does not imply that we do not support a continuing program in the study of the smaller planets. We believe, however, that there are compelling reasons for directing attention to the outer solar system. First, existing knowledge suggests that j.n situ study of the solar system may provide answers to some of the great scientific problems of our day. Second, an unusual configuration of the great planets in the late 1970's makes possible missions in which several planets can be visited on a single operation -- the "grand tour" concept discussed in the l968 report. An equally favorable opportu- nity will not be available for l80 years, although subsidiary opportunities for multiple planet missions will recur in the period l989-l996. Third, rapid developments in chemical booster technology and in particular the Titan IIID-Centaur combination make it possible to place, in the vicinity of the giant planets, scientifically meaningful payloads. Finally, with the approaching end of the Apollo program it is essential that the scientific community examine opportunities for the advancement of science making use of the technology of space developed during the past ten years. In proposing a program for the exploration of the outer solar system we recognize that the technological requirements of the many-year missions and the vast distances represent new and difficult challenges in many technological areas such as communication, reliability, and miniaturization.
This report examines the nature of the program for the exploration of the outer parts of the solar system. We present a substantive account of the major scientific objec- tives of flight missions to the outer planets, and we discuss the technical requirements in typical missions. We note that for certain missions, in particular those probing the planetary atmospheres, engineering studies have not been completed; there- fore, final statements cannot be made at this time.
