(Brayton cycle) satellite. It may also apply to the difference of a factor of two between the JPL solar-photovoltaic ($9,300 million) and the MSFC solar-photovoltaic ($18,220 million). In both cases the use of some adjustment for inflation is alluded to but not made explicit in the estimation of satellite costs. Exhibit 28 also shows that the Boeing estimates are consistently much higher in absolute dollars for all systems shown and virtually all cost categories. Since there is very little overlap between the types of energy systems considered by Boeing and the types considered in other cost- comprehensive references, it is difficult to determine whether these differences reflect differences in analytic and estimating procedures or differences inherent in the concepts under study. 7. Energy Conversion System Costs The cost of the satellite-borne energy conversion system is consistently the first or second most important cost in percentage terms. In absolute dollar terms, its cost, for a 10 GW satellite excluding microwave transmission, ranges from a low of $3,800 million (JPL-thermal) to a high of $6,190 (MSFC-photovoltaic). Even within the class of photovoltaic satellites, total cost ranges from $3,596 to $6,190. As a proportion of total costs, the energy conversion system ranges from 24 to 53 percent. The key area of cost sensitivity or cost driver within this category is the unit cost of the solar collector which may be expressed in several ways. The most direct unit expression would obviously be $/kW delivered at the rectenna bus bar. This may not, however, be the most informative since there are substantial losses (about 40 percent) between the energy delivered from the solar cells and the energy output at the earth receiving antenna. Consequently, the more meaningful cost term may be the cost/kW at the solar cell. This is also the cost unit most frequently used in the 2 analysis. Another measure is the cost per square foot (or m ). These measures of cost and some tentative calculations of the sensitivity of overall cost and cost per kilowatt-hour are shown in Exhibit 29. The relatively modest sensitivity of overall costs to a 10 percent
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