A Scientific Assessment of a New Technology Orbital Telescope (1995) / Chapter Skim
Currently Skimming:
3 SCIENTIFIC AND OPERATIONAL NICHES
3 SCIENTIFIC AND OPERATIONAL NICHES
Pages 30-39
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 30... ...
NEAR-INFRARED AND OPTICAL PERFORMANCE Earth's atmosphere hampers infrared observations from terrestrial observatories in several ways: · Broad regions of the spectrum are blocked by strong absorption from H2O in the atmosphere; · These absorption bands emit thermal radiation characterized by the mean temperature of the troposphere; · Strong emission by OH makes the sky very bright at wavelengths from about 0.7 to 2 microns; and · Turbulence, primarily in the tropopause, degrades a telescope's theoretical spatial resolution by introducing rapidly varying phase errors on scales smaller than the size of the aperture of the telescope. Moreover, a telescope's own support structure and mirrors, which ideally are in thermal equilibrium with their surroundings, emit thermal radiation characterized by the emissivity of the mirrors and the ambient temperature (~280 K)
|
From page 31... ...
Infrared observations from space are limited only by a telescope's collecting area, thermal emission, and the natural background set by zodiacal dust. Figure 3.2 shows the zodiacal background at an ecliptic latitude of 45 degrees, calculated using a standard set of assumptions.)
|
From page 32... ...
Thermal em~ssion from the Hubble Space Telescope and the ground-based, 8-meter, infrared-optimized Gemini telescope is included for comparison. has sufficiently low dark current and read noise.
|
From page 33... ...
The biggest advantage of the 4-meter telescope is its deep limiting magnitude at all wavelengths between 2 and 3 microns, where the Gemini telescope is severely limited by the strong telluric absorption centered at 2.7 microns. Because the 5- to 8-micron interval is strongly blocked from the ground, exploiting the ATD/NTOT's performance in this region would be especially valuable, provided a suitable infrared detector was added to its instrument suite.
|
From page 34... ...
Table 3.1 compares the limiting magnitude attainable by the ATD/NTOT equipped with an enhanced primary mirror and an optical framing camera, and by the Hubble Space Telescope equipped with either the existing second-generation Wide Field/Planetary Camera-2 (WFPC2) or the proposed Advanced Camera (AC)
|
From page 35... ...
The initial team would start the science projects, including overseeing the sequencing of the observations and the verification of science quality. If the demonstrations of the astronomical technology are successful and if the ATD/NTOT survives beyond its 1-year design lifetime, as is expected, the task group recommends that NASA select additional members of the science team at approximately yearly intervals to ensure that the mission is always pursuing current, important astronomical questions.
|
From page 36... ...
There is a huge difference in the cost to support a guest observer program versus one with a few knowledgeable co-investigators. A large number of guest observers increases initial costs and greatly increases recurring costs.
|
From page 37... ...
Selecting guide stars is generally automated, and so it drives the initial costs of the ground system but is a minor driver of recurring costs. Although the task group thinks that many of the cost drivers such as observing targets of opportunity and observing moving targets are scientifically desirable, it makes the following assumptions in order to estimate a lower limit to the cost of science operations: The telescope will be in a 12-hour Molniya orbit; The telescope will acquire guide stars autonomously; Sun, Earth, and Moon constraints will be comparable to those of the HST; · There will be minimal support for time-critical observations, observing targets of opportunity, or observing moving targets; · The telescope will have sufficient on-board memory to store the data from two orbits; and · There will not be a guest observer community.
|
From page 38... ...
Approximately two people for each of the two instruments (infrared and optical) would be needed at the STScI to monitor science data quality, plan calibration observations, reduce the calibration observations, produce the calibration files, and deliver the reduced data to the science teams.
|
From page 39... ...
REFERENCES 1. Thompson, R.I., "NICMOS: A Second Generation Infrared Instrument for the Hubble Space Telescope'" Advances in Space Research 13(12)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.