Degradat=on of passwe thermal control systems m space =s a matter of senous concern and has been observed =n many missions We report here the performance of the pass=ve thermal control systems of the Infrared Astronomical Satelhte (IRAS) over a period of three years An extenor temperature of 200 K and a sunshade temperature of approx=mately 100 K were mamta=ned over th~s period w=thout s=gmficant degradation The temperature of the telescope contained in the IRAS cryostat was also observed for two years after expend=ture of the hehum cryogen It remained at 100 K with no degradation
Keywords cryostats, hehum, space cryogemcs
Passive thermal control systems play an important part m the performance of space cryogenic systems Their possible degradation over time is a matter of considerable concern in the design of h~gh performance systems now under consideration, such as the NASA Space Infrared Telescope Facility, Large Deployable Reflector and the ESA Infrared Observatory This Paper reports the performance of the passive thermal control systems of the Infrared Astronomical Spacecraft (IRAS) in the three year period from midmission on 26 July 1983, through final tracking and data acquisition on 1 July 1986 The conclusion reached is that there was no measurable degradation of any of the thermal control systems over this period