these costs should not he charged solely to SPS. With the possible exception of fusion, the up-front costs for SPS would be significantly higher than for competing baseload electrical-generating systems. Apportioning the various investment costs and management responsibilities between the public and private sectors, and among potential international participants, would he an essential part of SPS development. PUBLIC ISSUES Public opinion about SPS is currently not well formed. Discussion of SPS has been limited to a small number of public interest groups and professional societies. In general, those in favor of SPS also support a vigorous U.S. space program, whereas many of those who oppose SPS fear that it would drain resources from small-scale, terrestrial solar technologies. Assuming acceptance of a decision to deploy the SPS, public discussion is likely to be most intense at the siting stage of its development. Key issues which may enter into public thinking include environment and health risks, land-use, military implications, and costs. Centralization in the decisionmaking process and in the ownership and control of SPS may also be important. From the standpoint of public perceptions, the siting of land-based receivers could be an obstacle to the deployment of SPS unless [1] the public is actively involved in the siting process, [2] health and environment uncertainties are diminished, and [3] local residents are justly compensated for the use of their land. Offshore siting of receivers could minimize potential public resistance to SPS siting. ENVIRONMENT AND HEALTH Many of the environmental impacts associated with SPS are comparable in nature and magnitude to those resulting from other large scale terrestrial energy technologies. A possible exception is coal, particularly if CO2 concerns are proven justified. While these effects have not yet been quantified adequately, it is thought that conventional corrective measures could be prescribed to minimize their impacts. However, several health and environmental effects have also been identified which are unique to SPS and whose severity and likelihood are as yet highly uncertain. These include effects on the upper atmosphere from launch effluents and power transmission; health hazards associated with nonionizing radiation; electromagnetic interference with communications systems and astronomy; and radiation exposure for space workers. More research in these areas would be required before decisions about the deployment or development of SPS could be made. Little information is currently available on the environmental impacts of SPS designs other than the reference system. Clearly, environmental assessments of the alternative systems will be needed if choices are to be made between SPS designs. Too little is known about the biological effects of long-term exposure to low-level microwave radiation to assess the health risks associated with the SPS microwave systems. The information which is available is incomplete and not directly relevant to SPS. Further research is critically needed in order to set human health exposure limits. Currently, no microwave population exposure standard for the general population exists in the United States. The recommended limit for occupational exposure is set at 10 mW/cm2 in the U.S., one thousand times less stringent than the present U.S.S.R. occupational standard. Public exclusion boundaries around the reference
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