Abstract
Mechanical cryocooler for space application is efficient way to cool down the optical detector, telescope and thermal shields to cryogenic temperature below about 100 K in the aspect of mass and size. The 20 K-class double-stage Stirling cycle cryocooler with cooling power of 200 mW at 20 K and lifetime of 1.5 years was originally developed for a cooling component of the Japanese IR telescope satellite AKARI launched in 2006. Based on this AKARI cryocooler, improvements with higher cooling performance and reliability with 1) the optimized 8-mm diameter displacer at second stage, 2) the flexure bearings for displacer supporting and 3) selection of low-outgassing materials and optimal baking process were investigated to develop the second-generation double-stage Stirling cryocooler for application to the next innovative astronomy mission such as ASTRO-H/SXS (2015) and SPICA (2022). The verification tests by using the EM (Engineering Model) were performed and maximum cooling power of 17.6 K with 200 mW at the 2nd cold stage and 96.1 K with 1000 mW at the 1st cold stage was obtained with margin. Mechanical performance test was also carried out and proved tolerability for mechanical environment of qualification level of ASTRO-H⁄SXS. Continuous running to verify specified lifetime of over 3 years is still under testing and 13545 hours (~ 560 days) in total has just achieved as of August 2012.
