Major system considerations are the cost, mass, and efficiency of the solar cell blanket. Methods to achieve the goals needed for a cost- effective SSPS are summarized as follows: (a) Near-term systems studies • Selection of concentration ratio Introduce active or semi-active cooling Introduce alternate photovoltaic devices • Concepts for annealing solar cell Optical and/or chemical • Investigation of Ga As and other cell materials (b) Technology developments • Improve efficiency of silicon cell to 18-20 percent (air mass zero; concentration ratio of one) 2 • Reduce blanket specific mass to 0.0576 Ib/ft (0.282 kg/m2) 2 • Reduce cost to $5 per square foot ($54/m ) 3 to 5 reduction in cost for bringing raw materials to semi-conductor grade silicon 10 to 100 reduction in crystal growth costs Automated blanket fabrication processes Improved packaging to achieve 30-year life The above plan should utilize to the greatest possible extent the large efforts going into development of photovoltaic cells for terrestrial application. d. Large Construction in Space All SPS concepts under consideration, i.e., the solar photovoltaic, solar-thermal, nuclear, and power relay satellite, would involve large construction in space. Three basic trade-offs are common to these concepts, namely: • The extent of construction and assembly to be performed in LEO, an intermediate orbit, or GEO • The fabrication approach, i.e., space construction from basic materials and stock or from modules preformed on the ground • Packing density in the launch vehicles.
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