Research on the effects of ionizing radiation in space is essential to the establishment of the requirements for developing space construction and operational missions for a variety of projects in GEO. This research will provide generic information and will strongly influence specific SPS construction and maintenance scenarios. It is likely that most SPS construction activities will take place in LEO where radiation is less severe and more predictable. Assembly in GEO could be performed by automated equipment and controlled from an LEO space station or terrestrial location. EFFECTS ON ATMOSPHERE The Earth's atmosphere from the ground to GEO would be affected by the construction launches and operation of the SPS. Climatic effects caused by waste heat released at the receiving antenna’site would be small and comparable to the heat release in suburban areas. The absorption of microwave in the troposphere will increase during heavy rain storms, but would have only a marginal effect on local conditions. The most important SPS-related effects on the atmosphere are associated with inadvertent weather modifications and air-quality degradation by launch vehicles, e.g., frequent launches of space shuttles and heavy lift launch vehicles (HLLV). Ground clouds could be formed as a result of the large thermal energy injected into the atmosphere during a launch. Weather modifications will depend strongly on meteorological conditions, the type of launch vehicle, and the launch location. HLLV launches could affect convection patterns, alter cloud populations, and induce precipitation. Air-quality impacts of HLLV launches are predicted to be small, and the increase in the acidity from combustion product would not be great enough to cause environmental effects. The induced changes in the globally averaged ozone layer and the effects of nitrogen oxide releases are expected to be minimal. The ratified nature of the upper atmosphere makes it susceptible to disturbances by external sources of mass and energy that may be deposited during SPS-related launches, depending on the launch frequency. Significant growth of the space industrial infrastructure related to other space missions will provide the information that would be essential to define mitigating measures and select alternative systems for use in SPS construction and operation. The projected atmospheric effects include: o Atmospheric modifications caused by launch vehicle exhaust effluents and reentry products; o Ionospheric heating produced by microwave power transmission; o Increase of water content and alteration of the natural hydrogen cycle above 80-km altitude; o Formation of clouds at mid-latitudes near 85 km altitude; and o Effects on the magnetosphere caused by space vehicle exhaust effluents discharged when traversing from LEO to GEO. Except for microwave heating of the ionosphere, similar effects will be associated with space systems supporting a variety of projected space missions. Possible mitigating strategies for preventing atmospheric effects of transportation to LEO include the selection of the most appropriate orbit insertion technique and fuels that are least likely to interact with atmospheric constituents and exhibit long-term residence. Potential alternatives to chemical propulsion for expendable launch vehicles include laser propulsion and electromagnetic launchers, especially for commodity materials that would constitute a major portion of SPS payloads. Another strategy is to select vehicle trajectories that minimize possible effects in critical atmospheric regions. Ion thrusters will most likely be utilized for electrical propulsion to transport payloads from LEO to GEO and to control the position of the SPS, its solar array, and microwave transmitting antenna. Ion thrusters will inject ions into the plasmasphere and magnetosphere. The ion density there is very low, and the motion of ions is dominated by the Earth's magnetic field. The composition and dynamics of the magnetosphere are complex and not completely understood. SPS-related launch and orbital transfer vehicles and attitude and position control systems may induce effects that include: o Van Allen belt radiation enhancement; o Generation of electric currents in the ionosphere; o Modified auroral response to solar activity; o Satellite communication interference; o Enhanced air glow that may interfere with remote sensing systems on GEO satel1ites; and o Potential changes in weather and climates. As information on exhaust effluent effects on the magnetosphere from other space missions becomes available, alternative space transportation strategies could be selected and ameliorative measures developed to resolve uncertainties surrounding atmospheric effects of the SPS. Microwave heating of the ionosphere as a result of beam transmission could increase ambient energy levels and temperatures of the electrons comprising the D and E regions. Heating of regions of the ionosphere could lead to interference with telecommunication systems. Experiments on the effects of microwave beam heating of the ionosphere have indicated that at a peak level of 23 mW/cm , the
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