Subscripts and Superscripts a accumulation d dissipated 1 load min minimum orb orbit ref reference s net solar to receiver 1 first segment in worst case scenario 2 second segment in worst case scenario 3 third segment in worst case scenario * melting point Introduction Solar dynamic (SD) power systems are an attractive option for future space exploration and utilization. These systems offer higher efficiency, lower launch mass, and significant life cycle cost savings, compared to current photovoltaic power systems [1]. Consequently, SD power systems in the 100 kW range have been considered for the Space Station Freedom’s (SSF) growth configuration. Multiple SD power modules would be used to achieve this power level. The SD system proposed for SSF would use the latent heat of fusion from a phase change material (PCM), stored during the sunlit portion of an orbit, for use during the eclipse periods [2]- This paper presents an energy balance analysis technique for a solar dynamic power system that will determine the stored energy in the PCM as a function of time. The approach models the receiver as a single node, and it is assumed that the receiver phase change material remains at a constant temperature. The modeled solar dynamic system in low earth orbit was subjected to realistic loads and the analysis uses a combined overall thermal efficiency for the receiver, heat engine and power distribution system. It assumes that the engine power varies to account for coarse load changes and that the unused power due to instantaneous load changes is dissipated through a parasitic load resistor. A block diagram of the SD power system is shown in Figure 1 (P. 204). This paper will discuss the analytical model used in the program, and the methods by which the mass of the phase change material, and the minimum required liquid fraction (reserve capacity) of the PCM are computed. Results comparing the state of the PCM for the Brayton and the Organic Rankine power systems, subjected to an average load demand of 75 kWe, will be made. Analytical Model The governing equation for a single node receiver storage system takes into account (1) the solar power to the receiver from the concentrator, 0 s, (2) the loads
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