in space. The transportation problem has two distinct parts. The first is lifting the required payload to low earth orbit. This will require a new, very large launch vehicle. The second part of the problem is transportation from LEO to geosynchronous orbit. This will also require a completely new space vehicle. Because of the magnitude of the SPS program, considering both the size of each satellite as well as the number of satellites required, the transportation problem cannot be avoided by weight reduction programs or breakthroughs even though these are also required for economic viability. The solar array problem is to achieve large reductions in cost and weight while improving array performance and lifetime. Unless this problem is solved, the satellite power station concept based on photovoltaic conversion cannot become economically viable. Finally, since any of the SPS concepts require satellites with several square miles of area and since virtually no space construction esqje- rience has been accumulated to date, the large construction in space required by the SPS is a problem area of the first magnitude. These problem areas are dealt with in the next four subsections followed by a treatment of the SPS economic issues (Section VIII.2) and its environmental effects (Section VIII.3). a. New Large Launch Vehicle There is a strong relationship between the three topics in this subsection (i.e., large launch vehicle, new transfer stage, and large construction in space). For instance, the payload weight and volume capabilities of the launch vehicle strongly influence the construction approach of the satellite, as do the capabilities of the transfer stage vehicle. Many of the studies examined during this effort have, to varying extents, considered trade-offs between these three areas. With respect to the topic under consideration, there is, however, fairly general agreement that a launch vehicle with a payload weight capacity on the order of a half-million pounds (200,000 kilograms) will be needed. This is about an order of magnitude greater than the payload capacity of 30 tons (27,000 kilograms) for the Space Shuttle now being developed. In
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