On the basis of this qualitative assessment public health effects appear unlikely; however, there is some small risk concerning human reproductive processes and an uncertainty about behavioral effects. Risks for persons in poor health, receiving medications, or under stress may be somewhat higher than for other members of the public, but this likelihood cannot be assessed with confidence at this time. Workers at SPS rectenna sites would be exposed to higher levels of microwave energy than the public, with a proportionately higher risk of health effects. If health effects were to occur, they probably would affect the body's immune and blood systems, reproduction, general physiology, or behavior. The effects on spaceworkers of an accidental exposure to the relatively strong microwave energy in space are practically unknown, as there is almost no experience to which the SPS situation can be related. Undesirable effects might be possible. Microwave energy beams in the lower atmosphere and at rectenna sites have the potential to affect airborne and terrestrial animals that reside at or pass through rectenna sites. The greatest potential effects would be expected on immune or blood systems, reproduction processes, physiology, and behavior. In the current assessment of SPS almost all of the microwave exposure effects are ascribed to the biological effects of the heating produced by microwave energy. It is conceivable that levels of microwave energy too low to increase body temperatures measurably may nevertheless cause subtle, possibly important, changes in biological processes. The open question of nonheating effects thus increases the uncertainties in this assessment. Because of the lack of data on microwave biological effects, research is being started on airborne biota and immunology and hematology, teratology, and behavioral effects in animals. Airborne species are of high priority since some can be expected to inhabit or pass through typical rectenna sites. Extensive research is required to support a quantitative assessment of microwave effects on human health and the ecosystem. The assessment is needed to estimate the impacts of the SPS system, guide the design of an SPS microwave transmission system, and provide a base for international standards of microwave exposure. NONMICROWAVE HEALTH AND ECOLOGICAL EFFECTS Development of the satellite power system would require extracting certain natural resources, shipping those resources to factories for processing and manufacturing, transporting finished products to a launch site, and launching the products (and construction workers) into space for orbital assembly of the satellites. Relatively large areas of land
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