Lifetime test of the 4K Joule-Thomson cryocooler

•The 4K Joule-Thomson cryocooler was tested to verify its lifetime.•Over three-year operation was successfully demonstrated.•Performance of the subcomponents was evaluated over the long term.•The cooling performance diagram with various drive conditions was obtained. The 4K Joule-Thomson (JT) cryocooler is a key cryogenic component for future astronomy missions such as ATHENA and LiteBIRD. It was originally developed for SMILES (2009) and upgraded for ASTRO-H/SXS (2016) and SPICA. The 20K two-stage Stirling cryocooler developed for AKARI (2006) was also upgraded and used as a precooler. The operational life is a critical factor in planning long-term missions. An engineering model of the 4K-JT cryocooler was built for continuous operation to verify its lifetime. Testing was done from 2010 to 2019 and successful three-year operation was demonstrated with an extended operation; this was beyond the design specification. This paper describes the overall history of the lifetime test of the 4K-JT cryocooler and an evaluation of the end-of-life cooling performance and performance changes during long-term operation.