The principal mitigation strategy for preventing SPS interference by direct energy coupling to any class of equipment is a part of the engineering design of the solar power satellite and the rectenna. Interference can be minimized by designing the SPS microwave system to stringent specifications, thereby reducing undesirable emissions at frequencies other than its operating frequency and constraining the size and shape of the transmitted microwave beam. Judicious rectenna siting-- including rational tradeoffs between the desire to locate rectennas as near to energy load centers as practical and the need to avoid interference with the maximum number of other users of the radio spectrum--also is an important mitigation strategy. Military communications equipment is generally complex; uses especially low operating signal levels and therefore is particularly sensitive to electromagnetic interference. Possibilities for modifying the equipment to reduce interference are limited by the nature of its uses. A study has been completed that characterized the potential for SPS interference if a rectenna were located near a large military facility. The China Lake Naval Test Center and two Air Force bases in the Mojave Desert in Southern California were selected for the study. The site selected was especially useful because a wide range of civil telecommunications systems is located nearby and a major electric load center (Los Angeles) is some distance west of the Test Center. Thus the site may be regarded as potentially typical of an actual SPS rectenna site insofar as it conforms to several basic criteria (infrequent cloud cover, near a load center, low population density in the immediate vicinity, etc.). At least 813 government and 685 civil systems were on record as located in a 21,000 square-kilometer area surrounding the hypothetical rectenna and were analyzed. The study showed there would be a significant potential for the satellite power system to interfere with national defense requirements as represented by large military operational, test, and evaluation facilities. The performance of radar instruments used at airstrips and on test ranges to acquire and track targets might be degraded by 10 to 65 percent. The reception and reliability of command and control communications could be reduced to 5 to 30 percent, and tactical systems performance could be reduced greatly. Recognizing the constraints inherent in ameliorating interference involving military equipment, the sole mitigation strategy considered in the study was changing the location of the hypothetical SPS rectenna. A relatively minor change in location substantially reduced the impact on national defense facilities without increasing interference effects on civil systems. This scheme may be applicable in other places where large, essentially unoccupied land areas are potentially available as rectenna sites but may be of limited value because of nearby military and civil electromagnetic systems. Geosynchronous earth orbit (GEO) is currently occupied by a number of space satellites, and undoubtedly will be occupied by others in the
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