4. GaAs cells are less sensitive to reduction in performance due to increased temperature (.45%/°C,Si and .25%/°C,GaAs), 5. The ultimate minimum cost for GaAs solar cells is significantly greater than that of silicon. 6. Some degree of spectral selectivity will be employed to minimize the steady state temperature of the solar blankets under all levels of concentration. 7. Blanket heat rejection will be performed passively. From the figures, one can readily see the benefits to be derived from a GaAs array as characterized herein. The reduced thermal sensitivity allows significant performance gains with higher concentration and reduced active solar cell blanket area. However, if solar array cost is to be a major drive (which it most probably will be ) it is readily seen in the cost curve that even under the most optimistic relative cost picture, a GaAs array must employ concentration ratios greater than 6X to effect the same array cost as a silicon array which has a 2X concentration ratio. Early in the activity it was decided that the desired system would minimize complexity. This then eliminates high concentration ratios on two counts: 1) The geometric arrangement necessary to achieve concentration ratios beyond 2X - 2.5X. For flat reflector, trough concentrators, concentration ratios higher than this range require more than a two sided concentrator or can lead to complex curved shapes. The more complex the concentrator geometry, the less forgiving it becomes to even minor misalignments of the whole array. It would also make more complex the highly automated system assembly process being envisioned for the SPS. 2) It is desirable to stay away from a system that requires any form of active cooling of the solar blanket. For an assembly of silicon cells, active cooling becomes a necessity in the region near 3X concentration; for GaAs this occurs near 10X concentration. Therefore, an array of silicon solar cells with a concentration of approximately 2X was chosen as the reference for this activity. Solar Array Blanket The basic solar array blankets used in the reference configuratio of the SPS are flexible substrate arrays typical of current advanced array hardware. Programs are currently generating a body of applicable data and experience are under contract both within NASA (Space Station and SEPS Solar Arrays) and the Air Force (FRUSA and Hardened FRUSA), The required volume of production and minimal production cost of an SPS array necessitates significantly different production techniques from even the most advanced production today. The whole process will be one
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