The impact of the SPS microwave transmission on the environment, as well as impacts related to other elements of the total satellite power system, are being determined by several research efforts funded by the Department of Energy. ... Volume 2 provides a preliminary assessment of the impact of the SPS on the environment in a technically detailed format more suitable for peer review than the executive summary of Vol. 1. ... Although a sizeable effort has been expended on investigating the biological effects of microwave radiation, no firm conclusions can yet be drawn concerning the effects of exposure to relatively low levels. Results obtained so far are difficult to interpret in terms of hazards, and in many cases conflicting results have been obtained from similar experiments. ... The intent behind the retrospective studies is to determine the validity of reports that are germane to the SPS environmental assessment program.