dietz%usc-cse%USC-ECL%MINET-NAP-EM@sri-unix.UUCP (10/20/83)
REM is not correct when he says the microwave exposure in a town 10 miles from a rectenna will be high. The intensity decays *exponentially* with the square of the distance from the rectenna; at ten miles it should be very low. I just mentioned the figure at the edge of the rectenna (where the intensity is that outside a microwave oven) to give some numbers; of course no one will live there. Josh: Land use is a major reason for going to SPS (vs ground based solar). True, the energy density of the microwave beam is a fraction of sunlight, but: (1) we can convert that energy to electricity with 90-95% efficiency (compared to maybe 20%-25% with photovoltaics), (2) the power beam operates nearly 100% of the time and clouds don't affect it, so the total land area we need to cover is only 1/10 to 1/8 that of ground based solar schemes. Most importantly, (3) the rectenna is light weight and is made mostly of near transparent wire mesh, so crops can be grown under it. One can imagine a combination rectenna- greenhouse for growing fresh vegetables near large cities. Illuminating these green houses could be an excellent use of the energy the rectenna recieves during off peak hours (i.e., at night); also, properly designed greenhouses would be much less polluting than conventional agriculture (no fertilizer or pesticide runoff). Since the rectenna will reflect back to space or dissipate as heat all energy not converted to electricity you *could* live under it, if you wanted to. Probably you'd want to put your high energy industry under or near the rectenna and live elsewhere. If land becomes extremely valuable then rectennas can be floated at sea or (just conceivably) floated in the stratosphere on balloons (allowing much higher beam intensities and smaller rectennas because you don't have to worry about airplanes or birds). -- Paul Dietz