A number of other potential energy system concept involving the use of space satellites have also been suggested: 1. Orbiting nuclear reactor power systems (in lieu of solar collector/ converters) with microwave transmission of power to earth. 2. The power relay satellite concept (Reference 12) in which power systems on the earth’s surface or in low orbit transmit power by microwave to geostationary satellites. These geosynchronous satellites then relay (reflect) the microwave energy to ground stations placed at desired locations on earth. 3. Solar reflecting satellites (mirrors) in earth orbit which reflect solar energy directly to earth to augment ground-based solar power plants, allowing night operation or increased output. 4. Laser power transmission (in lieu of microwave) from the satellite. The orbiting nuclear reactor concept has been evaluated to a limited extent. While it might offer the advantage of compactness relative to solar powered systems, its mass and complexity are significantly greater than solar powered systems. Significant safety and environmental questions remain to be addressed. The power relay satellite is a long distance power transmission concept rather than a primary electrical energy source; consequently, it is not viewed as a basic alternative to the SPS concept. The idea of placing large mirrors in earth orbit has been evaluated (Reference 14). Analysis indicates that with a mirror in geosynchronous orbit, the smallest illuminated "spot" on the earth would be about 330 km (205 miles) in diameter, governed by optical geometric considerations. If continuously illuminated at an average level of one sun, this large area would tend to rise in temperature to approximately 150°F, posing severe environmental problems. Placing large mirrors in lower altitude orbit reduces the size of the illuminated "spot." However, the mirrors would not be stationary with respect to a point on the earth. Thus, to achieve continuous illumination at a given location, numerous mirrors would have to be placed in low orbit. In addition, cloud cover and weather conditions would have an adverse effect on solar insolation precluding consideration
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