• Electrical charging of spacecraft will occur at geosynchronous orbit when sun is active (typically ^3 percent of the time. • This phenomenon will not be a problem if all surfaces have resistivities <10^0 ohm-cm (avoid Teflon and Kapton on outer surfaces; aluminum, steel, and graphite composites are recommended). • Even if electrical discharges occur, no problems are expected (may cause noise on RF data channels, but energies are too small to affect power generation transmission). 6.3 SPS MICROWAVE RADIATIONS The SPS is a large-sized satellite in geosynchronous orbit which generates electricity via solar cells and beams energy to the surface of the earth in the form of microwaves. By having the satellite in a high-altitude orbit, it not only is almost perpetually exposed to full sunlight (which a ground-based array of solar cells would not) but also the energy produced can be transmitted through the earth's atmosphere with almost no attenuation due to dust, rain, etc. (which would attenuate sunlight). A geosynchronous orbit permits the satellite to be continuously beaming its microwave energy to a single ground station, avoiding the problems associated with multiple ground stations. The parameters for a SPS design are given in Table 6.3-1. The ground station consists of an array of rectifying antennas (rectennas) covering a 6 km x 10 km eclipse. If the power density has Gaussian distributions in both Table 6.3-1* SPS Microwave Radiations
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