3-8. Cryogenic Reactant Storage for Lunar Base Regenerative Fuel Cells LISA L. KOHOUT Summary There are major advantages to be gained by integrating a cryogenic reactant storage system with a hydrogen-oxygen regenerative fuel cell (RFC) to provide on-site electrical power during the lunar night. Although applicable to any power system using hydrogen-oxygen RFCs for energy storage, cryogenic reactant storage offers a significant benefit whenever the sun/shade cycle and energy storage period approach hundreds of hours. For solar power installations on the moon, cryogenic reactant storage reduces the overall specific mass and meteoroid vulnerability of the system. In addition, it offers synergistic benefits to on-site users, such as availability of primary fuel cell reactants for surface rover vehicles and cryogenic propellants for orbit transfer vehicles (OTVs). The integration involves processing and storing the RFC reactant streams as cryogenic liquids rather than pressurized gases, so that reactant containment (tankage per unit mass of reactants) can be greatly reduced. Hydrogen-oxygen alkaline RFCs, GaAs photovoltaic (PV) arrays and space cryogenic processing/refrigeration technologies are assumed to available for the conceptual system design. Advantages are demonstrated by comparing the characteristics of two power-system concepts: (1) a conventional lunar surface PV/RFC power system using pressurized gas storage in SOA filament wound pressure vessels, and (2) that same system with gas liquefaction and storage replacing the pressurized storage. Comparisons are made at 20 and 250 kWe. Although cryogenic storage adds a processing plant (drying and liquefaction) to the system plus 30% more solar array to provide processing power, the approximate order of magnitude reduction in tankage mass, confirmed by this analysis, results in a reduction in overall total system mass of approximately 50%. Introduction Solar photovoltaic power systems have provided reliable power for the majority of the United States space missions. At present, these systems have been confined to earth orbit domains. However, as the US space program moves into the 21st century, solar photovoltaic systems will also be applied to lunar surface missions. These systems will use a photovoltaic (PV) array to gather solar energy during the sunlit portion of the orbit and an energy storage subsystem to accumulate energy for release during solar eclipse. A primary candidate for the energy storage subsystem is the hydrogen-oxygen Lisa L. Kohout, National Aeronautics and Space Administration, Lewis Research Center, Cleveland, Ohio 44135, USA. Paper number IAF-ICOSP89-3-8. This paper is also available as NASA Technical Memorandum 101980.
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