Cooling Systems for Far-Infrared Telescopes and Instruments

NASA will need technology to cool detector systems to sub Kelvin temperatures for its future science program which includes missions such as the BLISS on SPICA, IXO, CMB-Pol, SPIRIT and SAFIR. Building on missions such as Spitzer, Planck, and ASTRO-E and the James Webb Space Telescope (JWST), new cooling technologies offer major advantages including long lifetimes, lower mass, and new capabilities such as cooling a large telescope to 4 K. Instruments on the ground or balloons are valuable, but technical approaches for space are really unique. For example passive cooling to < 50K is only possible in space. Also, flight-like cryocoolers and optimized thermal support structures are too expensive for ground or balloon based programs since both must be made highly efficient due to strict power limitations on board spacecraft. Furthermore, interactions between passive radiators, multiple active cooling stages, and detectors, as on Planck or JWST, are system specific, which makes ground testing of space instruments technically challenging. Thus, cryogenic mission costs are driven by cryogenic technology readiness. So, it is in the best interest of NASA to support development of space worthy cryogenic technology now to save money later. We outline several key investments in cryogenic technology, including support of a strong US role in the Japanese space mission SPICA, that will enable NASA to achieve future science goals.