Progress on low temperature, vibration-free cryocoolers for space instruments☆

Future astrophysics missions equipped with infrared detectors are likely to require mechanical cooling at temperatures as low as 4 K. Candidate mechanical coolers for these missions need to deliver nearly constant cooling at a high thermal efficiency without disrupting the detector through vibration emissions. Very few 4 K mechanical cryocoolers are available for spaceflight. Available coolers demonstrate low efficiency and often require additional vibration reduction systems. This paper describes progress on low temperature cooling technology for Reverse Brayton Cryocoolers and lower stage expanders. Recent advancements include the lowest known operation of a gas bearing turbomachine at 4.9  K. Additionally, a case study reviews the performance of two cryocooler designs including Reverse Brayton Cycle and a hybrid model that uses a Joule Thomson expander at the lower stage. Each cryocooler provides 3  W at 75  K, 1  W at 15  K, and 100 mW at 4.5  K. Both coolers are much more efficient than any available 4  K coolers, and the hybrid design has the additional advantage of extremely low vibration emission, near 0.01 mN–rms at the cold end of the cryocooler.