Abstract
I a cooled high-sensitivity infrared telescope is to be used in manned space flight, the undesirable effects of contamination on such an instrument must be understood. First, absorption and scattering can be caused by deposition of condensible gas molecules on cooled surfaces; second, radiation emission and absorption can come from solid particles and molecules surrounding the satellite. This paper is concerned with the former effect on a large infrared (IR) telescope (about 1 m in diameter) cooled to about 20 K. The primary purpose of this investigation is to estimate the effectiveness of the purge gas method of contamination control. This method attempts to drive condensible molecules from the telescope tube by venting coolant gas (helium) out the telescope tube. Numerical results are presented for the Shuttle Infrared Telescope Facility (SIRTF) orbiting at an altitude of 350-400 km for 7-28 days, which offers sensitivities over the IjLtm to 1mm spectrum at least 1000 times greater than can be achieved from the ground.
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