teristics of the Van Allen radiation belt, which may affect satellite communications. They could slightly decrease the concentration of ozone in the ozone layer in a locally limited area, but the launch could be controlled to minize such effects by reducing the rocket power during transit through the layer. They could locally change the properties of the ionosphere, resulting in interference with the telecommunication systems using the ionosphere’s signal-reflecting properties. However, such rocket exhaust effluent interactions with the upper atmosphere could be effectively eliminated by using extraterrestrial materials for the construction of a global SPS system. Electromagnetic Interference. The microwave transmission from the SPS is a potential source of electromagnetic interference. There are indications that the interference could be avoided by designing the microwave transmission system to stringent specifications. Furthermore, terrestrial electronic systems could be designed with filters to minimize interference effects. However, radio and optical astronomy observations could be significantly inhibited by microwave transmission and by light reflected from the surfaces of the large number of SPS’s in a global system. One approach would be to construct radio telescopes on the back side of the Moon where they would be shielded from all forms of terrestrially produced electromagnetic interference. Space telescopes could be built in orbiting astronomical observatories, where the conditions for observations would be ideal compared to those at even the best locations on Earth. Comparative Effects. Any environmental effects induced by the SPS have to be compared with the environmental effects of alternative power-generation methods. For example, the following comparisons indicate that the SPS has the potential to be environmentally benign, even if introduced on a global scale: benign, even if introduced on a global scale: • Generation of power with fifty 5-GW SPS’s over a 10-year period will eliminate 20-30 billion tons of CO2 that would be emitted from coal-fired, steam-power plants to provide an equivalent power output, thus reducing the possible “greenhouse effect.’’ • Solid wastes produced during the manufacture and construction of the SPS, the receiving antenna, launch sites and the space transportation system are projected to be approximately 0.1 mt/MW-yr, primarily attributable to aluminum, steel, and silicon production, compared to the 900 to 2100 mt/MW-yr from a coal-fired, steam-power plant. • The air releases of the pollutants produced in the mining, processing, fabrication, and assembly of the SPS, the receiving antennas, the space transportation system, and the launch-site complexes are projected to be 0.4 mt/MW-yr compared to the 10 to 100 mt/MW-yr of pollutants from a coal-fired steam plant. • The heat release at the receiving antenna site will be about 7.5 W/m2, about twice that from a typical suburban community. No climatic changes will be induced, and no cooling water will be required, as is the case with power-generation cycles based on thermodynamic energy conversion. • Land use requirements are significantly smaller compared to coal power plants (including strip mining) and terrestrial solar systems. • Energy required for construction of the terrestrial and space portion of the SPS and for the propellants for launch to GEO will be regenerated during less than one year of SPS operation.
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