permissible exposure limit of 10 mW/cnf is adopted and if allowance for the maximum plausible accident is included, a protection radius of 300 to 800 m is appropriate. Note that because the propagation axis is not perpendicular to the earth's surface, an elongated “footprint” will be produced at the receptor site. This effect has been included in these results in addition to a safety margin of 2 to 6 times the maximum slew distance. The total land area required by the receptor site is estimated to be 0.3 to 2 km2. Security systems will be necessary at the receptor site to ensure public safety, although security problems will be more manageable due to the small land area involved. Note that if multiple receptor devices are located in close proximity at a common location, the required perimeter radius and land area will increase slowly with the number of devices and not in an additive fashion. Laser-SPS Mass Estimate Specific mass estimates for each subsystem are given in Ref. (51) along with the source of information. These data were used in conjunction with power distribution data to calculate the laser system masses and the mass per unit of radiated laser power. The estimated specific mass of the CO EDL power transmitter is 13.3 kg/kW. This value includes all associated subsystems but excludes the photoelectric collector array. For the 20 independent laser transmitters, the total mass is 29.22 x 10(i kg and the total power delivered to the utility interface under best-case conditions is 1.47 GW. For the Rockwell point design (4), the microwave antenna section specific and total masses are estimated to be 2.7 kg/kW and 18.17 x 106 kg, respectively, and the utility interface power is calculated to be 4.61 GW. Because of the high cost of transportation to GEO, the present CO EDL satellite power system concept is economically inferior to the microwave based concept. Monson (5) estimated that the total system specific mass is lowest for the CO EDL, followed in increasing magnitude by the CO2 EDL, a direct solar pumped laser (rp = 0.10), and finally by the CO2 GDL. Only a direct solar pumped laser having an overall efficiency rp a 0.20 is capable of bettering the system specific mass value estimated for the CO EDL. Clearly, the advent of an advanced laser concept will be necessary to overcome the limitations imposed by the large mass and low efficiency of molecular EDLs with recirculating gas flow. ENVIRONMENTAL IMPACT ASSESSMENT Heating of the Atmosphere Sources of Waste Heat. Waste thermal power from the laser-SPS will be available to the atmosphere as either sensible or latent heat. Sensible heating of the atmosphere will occur as the result of laser-beam propagation inefficiencies, i.e., aerosol and molecular absorption. As shown by the deposition profiles in Figures 10 and 11, most of the direct heating of the atmosphere occurs in close proximity to the receptor due to absorption processes in the lowest atmospheric layers. Mountaintop receptor operation largely mitigates any direct, sensible-heat input to the troposphere. Latent heating of the atmosphere, on the other hand, will occur as the result of waste heat generated by the receptor device and associated electrical power plant. The mag-
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