RADIATIVE AND HYBRID COOLING OF INFRARED SPACE TELESCOPES

The designs of cold space telescopes, cryogenic and radiatively cooled , are similar in most elements and both benefit from orbits distant fr om the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling rad iators for the individual radiation shields. Designs incorporating the se features have predicted T-tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE) . Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to pr ovide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telesco pe option under study for Edison, which should offer T-tel less than o r equal to 5 K for a little extra mechanical cooling capacity.