Mechanical coolers operating below 4.5 K for space application

This paper reports the 4 K- and 1 K-class mechanical coolers developed for space use. The 4 K-class cooler has been developed for Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), which is to be operated onboard the International Space Station (ISS). The cooling capacity is 20 mW at 4.5 K, with the total input power of approximately 120 W. The 1 K-class cooler has been developed for cooling far-infrared detectors to 1.7 K in the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The cooling capacity is 10 mW at 1.7 K and the total input power to the cooler is about 180 W. A future possible cryogen-free cooling system for temperature below 0.1 K is also presented, which uses these coolers as a pre-cooler.