IRAS Explanatory Supplement
II. Satellite Description
C. Telescope System Overview
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Figure II.C.1 Telescope system configuration. larger largest |
The IRAS telescope system configuration is shown in Fig. II.C.1. The telescope system comprised the upper part of the satellite and was composed of a two mirror, Ritchey-Chretien telescope mounted within a toroidal superfluid helium tank, which in turn was mounted within the evacuated main shell. The optical system was protected from contamimation before launch and during the first week of the mission by an aperture cover cooled with supercritical helium. After the cover was ejected, the sunshade limited heat flow to the aperture by blocking direct solar radiation and reflecting away terrestrial infrared radiation. The telescope orientation was constrained to prevent sunlight from striking the inner surface of the sunshade and radiation from the Earth from illuminating the radiators around the telescope aperture. The telescope was cooled by contact with the superfluid helium tank to temperatures ranging from 2 to 5K. The surfaces of the sunshade which could be viewed by the telescope aperture were cooled by a three-stage radiator to about 95K.
The telescope system consisted of the cryogenics (Section II.C.1), the thermal control system (Section II.C.2), the optics (Section II.C.3), the focal plane assembly (Section II.C.4) and the electronics (Section II.C.5). The telescope system also provided interfaces at and behind the image plane for the low resolution spectrometer (Chapter IX) and the chopped photometric channel; the latter was not used for the survey. Key physical characteristics of the telescope system are listed in Table II.C.1.
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