the implementation of the cryogenic storage system is more than compensated by the decrease in hydrogen and oxygen reactant tank-mass alone. A secondary reason for the significant reduction in mass, as is shown in Table V, is a 7210 kg decrease in reactant mass, reflecting the reduction in hydrogen and oxygen residuals as compared to gaseous storage. It should be noted that the mass of the FC/EU plant (fuel cell and electrolyzer stacks and associated mechanical ancillaries and radiators) is the same for both the gaseous and cryogenic systems. This reflects the fact that only the subsystems within the established boundaries were changed during the course of the analysis (Figs 1 and 4). A detailed mass breakdown for the 20 kWe system is given in Table VI and depicted graphically in Fig. 10. Again, the total cryogenic system mass was found to be less than half of the mass of the gaseous system. A similar discussion holds for this system as was presented for the 250 kWe system. An artist's impression of a 50 kWe PV-RFC power system with cryogenic storage for a lunar observatory is shown in Fig. 11. In addition to providing reactants for the regenerative fuel cells, the cryogenic hydrogen and oxygen can also be used as reactants for primary fuel cells to power surface rovers or as propellants for cargo/ crew ascent vehicles, as depicted in the illustration. Thus, the system can provide synergistic benefits for on-site users as well as offer a significant reduction in total mass.
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