Broad Area Cooler Concepts for Cryogenic Propellant Tanks

ABSTRACT Numerous studies and ground tests have shown that broad area cooling (also known as distributed cooling) can reduce or eliminate cryogenic propellant boil-off and enable long duration storage in space. Various combinations of cryocoolers, circulators, heat exchangers and other hardware could be used to build the system. In this study, several configurations of broad area cooling systems were compared by weighing hardware combinations, input power requirements, component availability, and Technical Readiness Level (TRL). The preferred system has a high TRL and can be scaled up to provide cooling capacities on the order of 150W at 90K. INTRODUCTION Space missions to the Moon, near earth objects, and Mars will benefit from the reduction of cryogenic propellant boil-off because of the significant mass savings. NASA's Chief Technologist, Robert Braun, elaborates on this in the article “Investment in the Future: Overview of NASA’s Space Technology” [1]. Investing in technologies that yield improvements in cryogenic boil-off loss suggest a 40% mass savings is possible over a reference Mars mission as shown in Figure 1. Clearly, the boil-off can be reduced through passive techniques. Specifically, high efficiency multi-layer insulation (MLI) combined with low thermal conductivity support structures reduce heat loads by at least an order of magnitude. Zero-boil off, on the other hand, requires a combination of passive insulation and active refrigeration. Consequently, advanced passive insulation, when coupled to an active refrigeration system designed to reduce the heat leak, allows tank operation for long periods without venting. Using these techniques, zero boil-Off (ZBO) is attainable.