Development of an efficient 4 K space JT cryocooler precooling with Stirling and pulse tube coolers

Helium Joule-Thomson (JT) refrigeration technology has established itself as the primary cooling scheme for space liquid helium temperature applications owing to its low vibration, high efficiency and high reliability. With the continuous advancement of space science payloads, the cooling capacity requirement in the liquid helium temperature region has escalated from tens of milliwatts in early missions to the hundred-milliwatt level. To satisfy future space requirements for high-efficiency cooling in the hundred-milliwatt regime, this paper presents the experimental performance testing and operating condition tuning of a compact STC/SPTC/JT hybrid cryocooler prototype, targeting 110 mW@4.2 K. During performance testing, the effects of initial charge pressure and second-stage pre-cooling temperature on the overall system efficiency were systematically investigated. Experimental results show that under matched operating conditions of a charge pressure of 1.02 MPa, a second-stage pre-cooling temperature of 18 K, and a compressor pressure ratio of 13.56, the hybrid system achieves the performance milestone of 110 mW@4.2 K with a total input electric power of only 506 W, yielding a relative coefficient of performance (rCOP) of 1.53%. Furthermore, extended performance testing under a 200 mW load demonstrates 4.25 K cooling with an input power of 836 W, corresponding to an rCOP of 1.66%. These findings offer valuable design and operational insights for the high-efficiency application of helium JT cryocoolers in space applications.