power density level beneath which nonlinear interactions are not expected to occur. This level has been used in this and other studies as an upper limit with a resulting effect on the sizing of the microwave transmission system. Similarly, current U.S. standards have been taken into consideration in the conceptual design of the system such that power levels outside of the area of the rectenna are one-tenth or less of the existing U.S. standards. A substantial effort will be required to investigate the long- and short-term effects of low-level microwave radiation on humans, plants, and animals. Studies and tests will also be required to assess the effects of the radiation on radio astronomy, communications, and electronic equipment. Although environmental questions related to the Earth and its populations are of particular concern, questions related to operations in the space environment must also be considered. It has been estimated in earlier sections that hundreds to thousands of personnel will be required in space depending upon the scope of the commercial construction program. Many of these personnel may be required in geosynchronous orbit where the converging radiation environment is significantly different from that existing in low-Earth orbit. This subject is treated in some detail in Volume II. Consideration of this environment is reflected in conceptual construction concepts that emphasize automated techniques with most crew activity taking place in "protected" locations. C. Comparisons With Conventional Systems The introduction of satellite power systems will yield environmental benefits in the areas of air pollution caused by combustion of fossil fuels, cooling water requirements and associated thermal pollution, and nuclear waste disposal. Table VIII-1 presents the results of a preliminary analysis and comparison of a 10-GW SPS system with coal and nuclear powerplants of the same capacity. The data of table VIII-1 illustrate the relatively minor quantities of air pollutants (oxides of sulfur and nitrogen and particulates) resulting from launch vehicle engine exhaust in comparison to a coal-burning plant. The air pollutants from the vehicle launches required to implement an SPS are seen to be negligible compared to the pollutants from a coal-burning plant.
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