Two Stage Hybrid Cryocooler Development

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Two Stage Hybrid Cryocooler Development

Price, K.D. / Kirkconnell, C.S.

Abstract Raytheon has demonstrated a two-stage hybrid Stirling/pulse tube cryocooler for long life space infrared (IR) sensor applications. The first expander stage is a conventional Oxford-class Stirling expander. The second expander stage is a U-turn pulse tube mechanically and thermodynamically extended from the first stage Stirling cold end. The combination Stirling and pulse tube expander has higher efficiency, lower weight and size, and lower production costs relative to the current state-of-the-art approaches. The first hybrid experimental unit has now been built and tested. The engineering model delivers 0.5W at 35K plus 2.2W at 80K. Data obtained from these tests have identified a set of cold head modifications that will increase performance up to 1W at 35K plus 7W at 100K for a drive motor input power of less than 170W. One of the motivations behind this development is the versatility of the hybrid technology. In addition to supporting heat loads at two different temperatures, the hybrid has the unique ability to allocate refrigerating power between stages on command by changing the Stirling expander piston phase and/or amplitude. This capability broadens cooler utility in two ways. One, a single cryocooler design can be tuned to perform optimally over an unprecedented broad range of temperature and heat load combinations. This reduces or eliminates development cost for many applications. Two, expander heat lift distribution can be adjusted in real time to optimize performance if heat loads change on orbit or if actual loads are different from predicted. This reduces performance risk on sensors in development where predicted loads may change significantly during design. The cooler has separate compressor and expander modules,weighs less than 7Kg and will be powered and controlled by radiation hard Command and Control Electronics now entering production.