Innovative Stirling-Cycle Cryocooler for Long Term In-Space Storage of Cryogenic Liquid Propellants

Numerous studies have concluded that increasing effectiveness of long-term storage of cryogenic liquid propellants, primarily LO2 and LH2, offers the largest single opportunity for reducing the mass and cost of associated space missions. The goal of this Phase I SBIR project is to evaluate and complete the preliminary design of an innovative integrated Stirling-cycle-based cryogenic refrigeration and coolant circulating subsystem for use with broad area cooling systems to deliver reduced or zero boil-off propellant storage. The Stirling cryocooler offers higher cooling efficiency than conventional reverse turbo-Brayton cooling approaches. Furthermore, the close integration of our unique open-bore cryocooler and coolant circulator reduces connecting duct length, mass and associated pumping and thermal losses and can also eliminate the need for separate coolant recuperator heat exchangers used by other cryocooler-circulator combinations. Finally, the modularity of our unique cryocooler and circulator components enables the system designer to build inherent redundancy into the system to boost propellant storage robustness over long missions. Phase I will result in a report detailing the most appropriate cryocooler, gas circulator, and integrated system configuration. The report will include projected performance characteristics for the integrated system and overall physical characteristics based on a concept layout drawing.

Space-based Cryocooling - The cryocooler can be used to produce cooling in the temperature range of 50 - 100 K. Lower operating temperatures are possible via staging. Potential applications include direct cooling of space sensors, vapor re-liquefaction for zero boil-off fluid storage or cooling superconducting magnetic bearings in support of flywheel energy storage systems. Space-based Refrigeration and Compression - The core cryocooler and linear motor technology could be applied to build higher-temperature Stirling coolers for in-space scientific experimentation or biological material preservation. The same enabling technology could be used to build linear compressors for refrigerant-based cooling or other working gas compression or fluid pumping. Space Power Generation - The proposed innovation has the potential to support space power generation applications in the 75-500 W electrical power range using thermal input from one or more radioisotope heat sources, with waste heat radiated to space.

Cryocooling - The cryocooler could be used to cool high-temperature superconducting magnetic bearings in industrial spindles and motors. The ability to cool a central load and reject heat at the periphery is ideal for zero boil-off re-condensation of liquid nitrogen, volatile fuels and other substances. Refrigeration and Gas Compression - The core hydrodynamic bearing technology could be applied to linear free-piston compressors for domestic refrigeration. The Department of Energy Office recently issued a new report which prioritized accelerating the commercialization of high-efficiency appliance technologies. This Roadmap ranked the development of advanced compressor technologies for refrigerators and freezers as having the highest overall importance and potential impact.

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