A BSTRACT An advanced two-stage Stirling (2ST) cryocooler has been developed for the cryogenic systems of future astronomical and Earth-observation missions in JAXA. The key near-term focus, SPICA, is a Japanese infrared space telescope with a primary mirror of 3.5 m diameter and an optical bench to be maintained at 4.5 ¶K for over 5 years via radiant and mechanical cooling. The temperature of 4.5 ¶K is achieved using a Joule-Thomson (JT) circuit combined with the 2ST cryocooler for precooling

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... o 15-20 ¶K; this precooling contributes strongly to the JT-circuit cooling performance. Therefore, the cooling performance and reliability of the 2ST cryocooler is key to the success of the SPICA mission. Reduction of vibration induced by the 2ST cryocoolers is another important technical issue to avoid deterioration of spatial resolution and pointing stability of optical devices. This paper describes the development status of the advanced 2ST cryocooler and discusses several technical approaches for achieving higher cooling performance, better reliability, and less vibration for upcoming space missions.