A High Efficiency Cryocooler for In-Space Cryogenic Propellant Storage

NASA is considering multiple missions involving long-term cryogen storage in space. Liquid hydrogen and liquid oxygen are the typical cryogens as they provide the highest specific impulse of practical chemical propellants. These cryogens are stored at temperatures of nominally 20 K for hydrogen and 90 K for oxygen. Due to the large size of these tanks, refrigeration loads to maintain zero-boil-off are high, on the order of tens of watts at 20 K and hundreds of watts at 90 K. Space cryocoolers have been developed for cooling space sensors that have modest cooling loads and are not suitable for high capacity applications. On this program, we proposed to develop a high capacity turbo-Brayton cryocooler that provides 150 W of refrigeration at 90 K. On the Phase I project, we developed a preliminary design of the 90 K cryocooler, assessing its size, mass, performance, and maturity. The proposed cryocooler significantly exceeds the performance targets set forth in the solicitation -- the cryocooler specific power is only 8 W/W (solicitation goal of 15 W/W), and the specific mass is 0.4 kg/W (solicitation goal of 12 kg/W). On the Phase II project, we propose to develop and demonstrate the least mature components, the compressor and its inverter drive. On a future Phase III project, we plan to build and demonstrate an engineering model cryocooler. Successful completion of this project fills a clear void in space cryocooler technology.