these developments will probably occur with or without SPS, and should not be viewed as research and development chargeable to SPS. They were merely included in the reference program to acknowledge that they were necessary ingredients. (c) Total reliance on government funding. The reference program did not actually discuss sources of funding, but its description could cause one to infer that all funds, including capital investment in production assets, were to come from the public sector. The total nonrecurring cost approached 120 billion dollars. No other high- technology energy concept has ever created such a scenario. None, for example, have estimated the cost of production capacity. If one creates an SPS R&D scenario similar to other energy technologies, with (i) generic research and development not charged to the program, and (ii) investment in production capacity not charged, then the cost of SPS R&D is in the vicinity of twenty billion, not markedly different than similar estimates for thermonuclear fusion. The reference SPS program appeared to make the government responsible for supplying energy to the U.S. economy, a role historically played mainly by the private sector. It implied that SPS development would be another major draw on an already overstressed federal budget. The research recommendations of SPS advocates, proposed at only tens of millions per year, were seen as the “camel's nose under the tent.” The reference program, more than any other single factor, doomed further SPS research to political rejection. COST ISSUES The reference SPSs represented relatively expensive energy systems, estimated at roughly $3000/kW installed capacity in 1980 dollars. However, with little operations and maintenance and no fuel cost, they were predicted to be roughly competitive with alternative forms of new energy construction in their early years of operation, and very advantageous in later years, as their capital investment was amortized (13). In some respects, the reference system estimates were conservative, as they included allowances for uncertainties in system mass and cost. In some respects, they were speculative, as they relied, in instances such as solar array manufacture, on undeveloped processes. The National Academy of Sciences review of SPS cost estimates was highly critical, especially of estimates of solar array and space transportation costs. With regard to solar arrays, the NAS report said, in effect, that since no process is now known for attaining the projected SPS array costs, none can be invented. For space transportation, the review committee was simply unable to accept the idea that transportation costs exhibited by the space shuttle could, in the future, be reduced by a factor of thirty to fifty. The NAS review was a narrow review of only the reference system, its costs, and its faults. Alternatives were not considered. No notice was given to the conclusion of the SPS studies that thermal cycle SPSs offered a hedge against the possibility that solar array costs might not come down. The potentials of automated production and the historical effects of production rates received little consideration. A recent JPL study has estimated that current space array costs of $800 per watt could be reduced to roughly $25 per watt if the present demand were increased from 50 kW per year to 50 MW per year (14). The cost-rate slope of 70% is the same as estimated by the SPS studies. This JPL study considered production rate effects only, “without any major changes in the materials or processes currently em-
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