tree, in which only the path leading to the reference design is illustrated. The new technologies which appear promising after this simple analysis can then be given more detailed study. This process may itself suggest new approaches, and it must in any case be updated as new technologies are proposed. 3) System Sensitivity Analysis. At the present stage of development of the SPS concept, the highest priority research areas are those where major improvements could be effected in the technical feasibility and/or cost of the system. An important output of the above system analysis is thus a classification of new technologies according to their potential impact on the performance of the system. 4) Technology Status and Risk Analysis. Some alternative technologies are clearly feasible and the costs and benefits which they imply can be estimated with confidence, but others must be regarded as quite speculative. A systematic technique is therefore needed to allow risk to be taken into account in decisions regarding research priorities. As an example, for each new SPS design which is proposed, a measure of the cost risk (e.g., the standard deviation of the cost probability distribution) can in principle be plotted against the nominal cost; in terms of cost, those designs which lie closest to the origin in such a plot are of highest interest. Difficulties may however arise because realistic estimates of cost and cost risk may be unobtainable without detailed analysis. 5) External Costs, Problem Areas and Criticisms of the SPS. Another important dimension in the assessment of new technologies is the effect which they may have in areas outside design engineering. For example, use of laser power transmission might change the military implications of the SPS, simplify or complicate integration with existing utility systems, and affect the societal acceptability of this form of electric power. One of the strengths of the SPS, as compared with other options for power generation, is the variety of technical alternatives which are available for virtually all the sub-systems and for providing support functions such as transportation. This characteristic increases confidence that the concept will prove feasible, but it greatly complicates the rational allocation of limited resources during the R&D phase. The methodology discussed here is a first step towards creation of a formal decision-analytic framework which can support design choices and program decisions as development proceeds. It provides a common basis for the assessment of alternative approaches which have been proposed or are evolving, it may facilitate innovation by identifying areas where new technologies can be of greatest benefit, and it should eventually allow creation of an extensive data base concerning design options which can be of value to the SPS design engineer as well as to management of the program.
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