Space cryogenics is described from its creation to the current state while touching on the physical principle of each technological application. The reason why cryogenically cooled astrophysical observation missions from space are required is explained. In infrared observations, it is necessary to avoid the atmospheric absorption of feeble infrared signal and to minimize the infrared background noise from the warm telescope itself. In X-ray observation, X-ray detection devices require cryogenic cooling down to approximately 50 mK for an extremely high sensitivity micro calorimeter. Some technologies and the design concept that are the key factors for reliable long-life cryogenically cooled space astrophysical missions are introduced. The genealogy of the cryogenically cooled space infrared observation missions is traced to understand the actual aspects and the future plans.

The “Shikisai” Global Change Observation Mission – Climate (GCOM-C), the second satellite of the GCOM program, was successfully launched on December 23, 2017 via a H-IIA rocket. The mission of the satellite is monitoring global climate change by observing the surface and atmosphere of the Earth over the course of five years. Following an in-orbit checkout onboard systems, JAXA is carrying out initial calibration activities. A single-stage Stirling cooler for space use is installed in the satellite for cooling the thermal infrared detector, and it has been working properly in orbit. This paper provides an overview of the GCOMC mission, especially the cryogenic technics applied to the satellite and shows, for the first time, some typical Earth observation images obtainable owing to those technics.

The space cryogenics cooling system for the X-ray spectrometer installed on the ASTRO-H is introduced in this report. ASTRO-H is an X-ray astronomy satellite that the Japan Aerospace Exploration Agency (JAXA) developed to support studying the evolution of the universe and other physical phenomena yet to be discovered. The primary scientific instrument installed on the ASTRO-H is a soft X-ray spectrometer (SXS). Its detectors are cooled to 50 mK using a complex cryogenic system with a multistage adiabatic demagnetization refrigerator (ADR) developed by the National Aeronautics and Space Administration (NASA), and a cryogenics system developed by Sumitomo Heavy Industries, Ltd. (SHI). SHI’s cryogenics system is needed to cool the heatsink of the ADR to 1.3 K or less while in orbit, and is capable of doing so for three years or longer. To meet these requirements, SHI developed a hybrid cryogenics system consisting of a liquid helium tank, a 4 K cooler, and two two-stage Stirling coolers. ASTROH was launched from Tanegashima Space Center on February 17, 2016. Initial operation of the SXS cryogenics system in orbit has been completed successfully. The cooling performance was as expected and may exceed the lifetime requirement of three years.

This report describes a summary of the heritage regarding on-orbit Japanese mechanical coolers and their development history and status, as well as the achievements of on-orbit SHI coolers for space use. These coolers have produced useful results for future on-orbit projects. By investigating results related to cooling performance degradation, we have learned that the contamination caused by filling gases, especially by CO₂ and H₂O, is crucially important. Advanced models of a two-stage Stirling cooler and JT cooler have been improved in terms of abrasion, and further development and investigations continue to decrease the contamination in the coolers. In closing three items to be developed for next-generation coolers are suggested.