public acceptance of SPS, RFI, and a number of other more remote technical problems like space collision on GEO orbit availability. Under the third level — undesirable but not potential show-stoppers, he lists safety and control of launch vehicles, orbital crew safety, terrestrial workers’ health and safety, chemical pollutants on land and land use near rectenna. Clearly, there is a heightened perception of hazard due to microwave exposure in Gutman's ranking. This heightened perception of microwave hazard is reflected in studies of attitude of the general public towards the SPS, summarized in Table 5 and taken from the 1980 DOE report (9). One can see that the majority of student and environmental groups surveyed responded negatively to SPS and always with prominent concern about the generalized microwave hazard. Only technically involved students (MIT) and the pro-space L-5 society were supportive. No doubt there is pervasive fear of “Microwaves” among the general public that underlies this lack of public acceptance. No doubt Gutman recognizes this public perception and therefore assigns a high — in fact, the highest — rank to the microwave exposure problem. Why is there a heightened perception — even fear — of microwave hazards among the general public? One should note that it is not only the SPS, but any source of “microwave” (RF) radiation that has been increasingly subject to fear and opposition; This includes things like relay towers, broadcast towers, radars, microwave ovens and even the video-display terminal (10). In fact, one can’t be sure whether public opposition to these things is truly based on fear of “microwaves” or whether this fear is feigned and the true reason for opposition is something else — e.g., the fear of loss of land value in the case of a proposed microwave relay tower. In the case of SPS, one can’t be sure if the true reason for opposition is anti-technology or a cited microwave hazard (e.g., in the case of the Sierra Club). It is the conviction of many, including the author, “that the microwave hazard problem is one of misperception.” The causes for and solutions to this misperception are beyond the scope of this paper but will be briefly reexamined at the end of this paper. In terms of rational scientific bases, there will be a quick resolution to the question of microwave hazard. Throughout the world scientific opinion supports the existence of thresholds for effects on humans from RF (microwave) radiation. Therefore, long-term exposure limits for true absolute safety are possible and are likely to be selected in the range of 0.1-1.0 mW/cm2, for the range of microwave frequency of interest to the SPS by international consensus. The resolution of the frequency allocation problem for SPS was dealt with in the 1979 World Administrative Radio Conference (12). The ISM band around 2.45 GHz was made world-wide and assigned for possible use in SPS work. Before 1979, the 2.45 GHz band was not reserved for ISM in Eastern Europe (which used 2.375 GHz instead). Now that it is a world-wide frequency, the international trade in microwave ovens is facilitated and a future SPS frequency allocation seems assured. A proposal by ISM interests (e.g., the International Microwave Power Institute) to make the principal harmonic frequencies (i.e., 4.9, 7.35, 9.8 GHz) ISM frequencies was rejected. New millimeter-wave band ISM frequencies were, however, made harmonics of 2.45 GHz (namely, 61.25, 122.5, and 245 GHz). The rejection of the harmonic ISM frequency proposal means that SPS will be faced with severe problems of harmonic suppression of at least 4.9, 7.35, 9.8 and 12.25 GHz — which are generally assigned to communications services or radioastronomy. Note that from the group of radio astronomers comes a potent fear (13) of "pollution” from ISM sources such as the microwave oven and the SPS.
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