Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.Future astronomical observatories and surveillance satellites utilizing infrared, far infrared, and submillimeter detectors will require long-life mechanical cryocoolers that provide cooling at temperatures down to 4 K. These missions share a common set of core requirements. The thermal efficiency of current space cryocoolers for 4 K operation is inadequate, and laboratory cryocoolers that provide cooling at 4 K are inefficient and lack a clear development path towards flight. This paper describes a hybrid cryocooler that is lightweight, compact, reliable, efficient and suitable for space missions. The cryocooler consists of centrifugal compressors at the warm end that provide continuous flow to a reverse-Brayton upper temperature stage and a Joule-Thomson (J-T) lower temperature stage. The Brayton stage is expected to operate at nominally 15 K, and the J-T stage is expected to operate at 3-5 K. The Brayton and J-T cycles are both continuous flow cycles, allowing significant separation distances between the warm and cold components. The cryocooler produces negligible vibration and can uniformly cool remote and distributed loads with extremely small temperature differences and performance penalties. In addition, the components utilized in the cryocooler are relatively mature with a high Technology Readiness Level (TRL)
