Handling of the large, flimsy solar cell blanket and concentrator films is a problem that will require further study. These handling techniques are probably impractical under the Earth's gravity; therefore, they may require development and verification in Earth orbit. 7.1.2.3 KEY ISSUES The particular photovoltaic system selected impacts the amount of solar concentration, the planform area, the structural design, the thermal design, and the manufacture and application of the solar array. Final selection of an SPS photovoltaic system will be dependent upon the results of research and development of the competing alternate photovoltaic systems and systems studies of the integration of these technologies into the SPS project. Table 7-3 summarizes some of the key issues in the selection and conceptual design of an SPS photovoltaic system. SPS power distribution is a critical performance area. The power lost in transmission from photovoltaic device to the microwave conversion system is a substantial fraction of the total generated power, resulting in undesired and costly oversizing of the solar array. Transmission losses may be minimized by using high voltage transmission, but this poses inherent technology hurdles in handling and controlling the high voltage. Other key issues, which need further study, relate to the power needed to support the upkeep and maintenance of the SPS; the power supply during eclipse of the SPS (not necessarily to maintain power transmission but to support station activity); and the power needed to maintain SPS attitude control, communication, and control within the SPS. 7.1. 3 SOLAR ARRAY STRUCTURE SUBSYSTEM 7.1. 3.1 PRIMARY STRUCTURE The primary solar array structure consists of current carrying structure, non-current carrying structure, and dielectric structure. The current carrying structure utilizes the lateral beam trusses by proper beam element sizing and by electrically isolating the conducting lateral beams from the nonconducting longitudinal beams. Approximately 45 percent of the lateral beams must be increased in cross sectional area above that required for structural purposes to meet the current carrying requirements. This is accomplished by increasing the material thickness of the basic structural elements. The non-current carrying structure consists of longitudinal beam truss members and tensioning wires. The support structure between the arrays is referred to as the dielectric structure and is assumed to be fabricated from a fiberglass type material, such as an S-glass/epoxy composite, so that it is transparent to the microwave beam from the transmitting antenna.
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