advantage of the abundant material and energy resources within the solar system and, in the distant future, even within the Galaxy. Economic Feasibility The economic justification for proceeding with an SPS development program is based on a classical risk/decision analysis which acknowledges that it is not possible to know the cost of a technology which will not be fully developed for at least ten years and commercialized (i.e., produced, operated, and maintained) in not less than 20 years. Justification, of course, is equally difficult to provide for other advanced energy technology projects. This justification, therefore, requires an appreciation of the competitive cost of alternative energy sources for the generation of electrical power which would be available in the same period. Any SPS development program should be timed-phased so that the “economic” purpose of each program segment will be to obtain information that will permit the decision makers to make a deliberate decision to continue the program or to terminate it and thereby to control the overall risk. Cost-effectiveness analyses alone would be inappropriate as they would require postulating scenarios of the future which could be extremely difficult, if not impossible. The near-term decisions regarding the SPS program should be based on resources allocated to the SPS research tasks and their priorities rather than the projected economics of the SPS in the 21st Century. To date, studies have shown no likely “show stoppers” which would justify abandoning the pursuit of the SPS program, but have indicated technical, economic, environmental, and societal issues which require more detailed definition. For the SPS reference system which utilizes demonstratable technology, cost estimates, rough as they are and subjected to criticism as they may be, fall within a potentially interesting range — clearly sufficient to justify not a major commitment to development and deployment of the SPS, but a continued research and technology verification program. (Advanced technology could lead to the development of an even more competitive SPS system.) The magnitude of this R&D program has been projected at $25-$50 million per year during the next five years. Projections of SPS construction and operational costs between the years 2000 and 2030 are speculative, as forecasts of future costs of a scenario, e.g., for constructing an SPS system consisting of 60 satellites and generating 300 GW, presume a knowledge of future technology which when contrasted with the revolutionary advances of technology during the past few decades make such projections of doubtful validity. Cost projections, falling in a range of $1500 to $4000 per kW, which imply a trillion-dollar capital investment over a 30-year time period for this scenario, underline the magnitude of the investments for an SPS system. However, introduction of any alternative advanced energy technology on a global scale would also require an unprecedented and similar level of investment over the extended time period required to make the transition from nonrenewable to renewable energy resources. For example, the capital investment in terrestrial solar conversion technologies to produce heat and generate electricity to meet 20% of U.S. energy requirements is projected to reach one-trillion dollars by the year 2000. Cost projections do not provide meaningful estimates of potential market penetration of the SPS, because uncertainties in forecasting prices are much larger than the cost differentials on which the cost comparisons among competing technologies will eventually be based. However, such cost studies provide estimates of upper bounds
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