Passive Capillary Pumped Cryocooling System for Zero-Boil-Off Cryogen Storage Tanks

Significant cost and weight savings of a space mission can be achieved by improving the cryogenic storage technology. Added cryogen mass due to the cryogen boil-off, the oversized tanks and storage systems make the planetary missions prohibitive. The recently proposed Zero-Boil-Off (ZBO) strategy for cryogen tanks, which combines both thermal insulation and "cryocooling" technologies to manage the heat leaks. It is a straightforward concept that could lead to a significant weight/cost reduction for long-duration missions. However, several issues must be resolved before the ZBO benefits can be realized. One of which is the management of the through-the-tank-wall "heat leaks". Loop Heat Pipe (LHP) is a passive two-phase heat transport device that utilizes solely capillary action to circulate the working fluid in a closed loop to transfer heat from one location to another. LHPs do not contain mechanical moving parts and therefore are highly reliable and durable for space applications. A novel cryogenic LHP system is proposed for the ZBO cryocooling. It is capable of acquiring heat from a large area of the cryo-tank wall, transporting it to a cryocooler for heat rejection, and meeting other design requirements of cryogen storage systems for space missions.