vironment and producing potentially serious effects on terrestrial communications. The Ar' deposited in lifting an SPS to geosynchronous earth orbit will have a greater total energy content than the ionosphere-plasmasphere system. However, if these SPS craft were to be built out of lunar materials as envisioned by some authors (26), the possible impacts discussed earlier could be largely avoided since the energy required to transport materials from the lunar surface to geosynchronous earth orbit is much less than hauling materials from low earth orbit to geosynchronous earth orbit. Thus, not only would less propellant be needed but it would be deposited much farther from regions where it may have a direct effect on human terrestrial activity. More specifically, given the large number of SPSs envisioned in order to significantly contribute to U.S. electrical power needs, the economic savings in transporting materials from the lunar surface to geosynchronous earth orbit compared to transport from the earth’s surface to geosynchronous earth orbit apparently more than offsets the probable capitalization cost of setting up lunar factories given current cost estimates (P. Glaser, verbal communication). We note that the terrestrial materials required to set up the lunar factories are small compared to an SPS mass in present studies (26). Since the environmental impacts discussed in our paper scale with the transported mass, the impacts of lunar factory construction on near earth space would be small compared to those due to the transport of one SPS. Lunar factory products could be lifted from the lunar surface to low lunar orbit via mass driver engines (26). From low lunar orbit partially assembled sections of an SPS could be lifted to geosynchronous earth orbit via ion propulsion. The energy expanded in low lunar orbit to geosynchronous earth orbit transport, E (LLO-^GEO) compared to the energy expended in low earth orbit to geosynchronous earth orbit, E (LEO—>GEO) is where Ve and V, are, respectively, the terrestrial and lunar escape velocities; re and r; are the planets’ radii; M,. and M,, the planets' masses; R is the earth-moon distance, and D is the distance from earth to geosynchronous earth orbit. Thus the energy expenditures are greatly reduced and for a given ion beam energy the total number of ions emitted would be reduced by a factor of —20. The greatly reduced amount of Ar required for each SPS placement (S105 kg) could be transported from earth with a small impact compared to earth based SPS transport which require —10* kg be transported per SPS. The number of Ar+ shed by the ion beam would be reduced by more than an order of magnitude. Not only would the number of Ar+ shed be sharply reduced, but the deposition would occur at L > 6.6 well beyond the plasmapause. The radiation belts would then be unaffected and potential low to mid-latitude communication disruptions avoided. Using a lunar based transport system, the reduced Ar+ ion deposition in the outer magnetosphere would only affect precipitation at high latitudes and would be less severe than that due to earth based transport because of the lower energy requirements for transportation. We conclude, on the basis of our preliminary study, that if a fleet of SPSs were to be fabricated, the use of lunar rather than terrestrial materials would appear to minimize the environmental impacts in addition to giving economic benefits derived from transportation cost reduction.
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