TABLE 2 5-GW SPS SUBSYSTEM MASS COMPARISON FOR Si AND G(Ai SOLAR ARRAYS MASS-106 kg 30-year exposure period. Because of the lesser probability of impact, larger meteoroids are less likely to affect the solar cell array. Several photovoltaic energy conversion configurations applicable to the SPS concept are being considered. For purposes of comparison and assessment an SPS reference system design has been adopted by NASA. (Figs, la and b). For these configurations, silicon, and gallium arsenide solar cells with and without concentrators could be used. For use in the SPS the solar cells will have to be highly efficient, of low mass per unit area, and radiation-resistant during transit to and in operation in GEO. They will have to be producible at rates and in volumes consistent with an SPS deployment schedule. To extend the lifetime of the solar cells, annealing methods could be utilized to eliminate or reduce the degrading effects of accumulated radiation exposure. Of interest for the SPS is the use of gallium arsenide for solar cells because at elevated temperatures their efficiency does not degrade as fast as that of the lower-
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