option would be to fund a dedicated SPS effort at $5-$10 million, to gather the minimum necessary information, or to fund a program at $20-$30 million to gain the maximum information at the earliest possible time. SPS research in the United States was effectively brought to a halt by the publication in 1981 of a study carried out at a cost of $500,000 by the National Research Council, acting for the National Academy of Sciences. That study focused on the NASA SPS Reference Design, and concluded that the SPS concept was economically impractical because of: 1) Costs of lifting components from the Earth. 2) Costs of fabricating single-crystalline silicon solar cells for the SPS reference system. However, the NAS report stated, "there is a possibility that some future combination of high demand and constrained supply would make a more advanced SPS an important option in the more distant future." A brief remark was made in the NRC Study Report to the effect that the NRC conclusions would not be altered by the substitution of lunar- derived materials for Earth-derived materials. In a subsequent exchange of letters between Dr. Frank Press, President of the NAS, and Dr. Gerard O'Neill, President of Space Studies Institute, the Academy acknowledged that its study had not, in fact, addressed the potential cost savings associated with removing SPS mass constraints and using primarily lunar materials. The studies of 1968-1982 recognized that development of a commercially attractive SPS might require advances in materials and generic space technologies, but not discoveries of new science. Developmental advances of that kind are taking place, for example in amorphous thin film solar cells, materials processing in space, improved magnetrons, waveguide lasers, and automated assembly methods.
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