Fig. 1. Lunar-based solar power stations and Earth rectennas necessary for semi-continuous power transmission (not to scale). arrays and associated microwave antenna systems and three rectennas in order to be comparable with a single geosynchronous SPS satellite/rectenna system. The silicon solar cells on the moon are assumed to be constructed from lunar soil at one-third ('A) the cost per unit area for conventional SPS solar cells. However, the sunlight-to-DC power conversion efficiency for the lunar cells will be 5% as compared to the 15% efficiency for geosynchronous cells. Larger solar cell arrays are required to compensate for lunar orbital motions. As the sun follows a biweekly path from lunar horizon to horizon, solar array panels must either be steered or be constructed with structural redundancies in order to maintain a high incident solar radiation throughout the lunar day. One scenario has a system of triangular lunar dust mounds coated with photovoltaic material on both exposed surfaces (Fig. 2). This arrangement maintains a fairly steady solar flux over the two-week activity period, but also requires twice the photovoltaic surface area of a steered array. (In the figure side C, if steered, receives illumination equivalent to sides A and B together.) When this additional collection surface is included with the reduced photovoltaic efficiency and requirement for duplicate lunar stations, LPS solar collection area must be increased by a factor of 12 (2 for oblique solar incidence, 3 for efficiency reduction, 2 for light/darkness phases) to produce the equivalent energy of a geosynchronous SPS. It will also be assumed for the lunar power system that there are no transportation costs for the solar arrays, no costs assessed for a lunar manufacturing facility for these arrays, 'A per unit area costs for subarray materials, '/io per unit area antenna transportation costs, and 1 /10 per unit area construction costs for all lunar operations,
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