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.