VIII. ENVIRONMENTAL CONSIDERATIONS A. Methodology An evaluation of the space solar power concept must involve an assessment of the potential impact on the environment and the people living within that environment. This impact can be either positive or negative in an absolute sense or in relation to other potential sources of energy. The present study has identified those environmental topics that must be addressed in the solar power concept assessment and has presented estimates of relative environmental impact in selected areas for the solar power concept and other sources. B. Environmental Questions Solar energy is considered a "clean" form of energy; however, the collection, conversion, and transmission of this energy introduce environmental questions. These questions or topics may be grouped into four categories. Vehicle Emissions/Operations Microwave Beam Space Operational Environment Earth Activities A detailed listing of topics related to each of these categories is presented later in the report (fig. X-2, D.l through D.4) in the context of areas needing analysis and testing to provide definitive answers to environmental questions. Considerable experience has been developed in the course of analyzing emissions from the Shuttle propulsion systems and this potential impact on the environment. Reflecting Shuttle experience, SPS studies have emphasized consideration of fuels that are projected to be compatible with the natural environment. For example, launch vehicles have previously considered the use of hydrocarbon, hydrogen and oxygen propellants, whereas orbital transfer vehicle studies have considered argon in preference to mercury. SPS environmental studies must emphasize the size and quantity of vehicles and launches involved as well as the particular emissions from a given vehicle in view of the large numbers involved in a significant size commercial program. Specific topics to be considered include noise, gas cloud formation, and thermal effects in the launch area; emission effects on the stratosphere; and noise and N0x production during reentry. Transmission of large amounts of power by microwave radiation from the SPS to Earth introduces questions related to its effects. Preliminary analyses of the beam-ionosphere interaction have indicated a
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