The most dramatic difference between the LEO base and the GEO base may be the power system. Since the GEO base gets continuous sunlight with only brief Earth eclipsing (maximum 72 minutes of darkness daily) during the spring and fall months, it seems likely that solar arrays will be the preferred source. 2.4 Power Satellites The Reference Design system envisions large power satellites located in geosynchronous Earth orbit (GEO) at zero inclination with zero eccentricity. Two alternative versions of the power satellite are included in the Reference Design system. One of these is based on photovoltaic cells made of single crystal silicon (Si), while the other uses photovoltaic cells made of single crystal gallium aluminum aresnide (GaAlAs), with thin reflectors providing 2-to-l concentration of sunlight on the photovoltaic cells. Photovoltaic array (silicon option). Silicon solar cells 6.55 cm by 7.44 cm in size are assembled into panels with overall dimensions of 1.0687 m by 1.059 m, with the cells interconnected in a series/parallel manner, 16 cells in series, 14 cells in parallel across the entire panel. (Thin copper tabs 0.75 cm by 4 cm in size are soldered to the corners of the backs of four adjacent cells, providing both electrical and mechanical interconnection.) These panels of 224 cells are then assembled into blanket segments 15 m across by 656 m long by welding electrical interconnect tabs between ends of adjacent panels in series, and mechanically taping parallel strings together, with tape reinforcing the electrical interconnect tabs as well. A total of 44 blanket segments, side by side, then fill up a square bay (667.5 m on an edge) of the power satellite. The blanket segments are attached to catenary tension cables running across each end of the trusswork structure of the bay, holding the blanket segments taut. A power satellite designed to deliver 5 GW of busbar electrical power on the ground then requires 128 bays (8 by 16) , with a total active solar cell area of 50.9 , 2 km and a total photovoltaic blanket mass of 22,051 metric tons. Photovoltaic array (gallium option). The general scheme for assembly into panels, blankets, and bays is similar to the silicon option. The solar cells
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