existing studies. Even the ECON study deals with system costs exclusive of DDT&E, incorporating this cost element only in a final calculation of the number of satellites required to recover DDT&E costs at various projected terrestrial energy cost levels. The relationship of the remaining three cost components and their contribution to total per unit costs are summarized in Exhibit 54 for two of the more comprehensive references (All and A9). The recovery of capital costs is clearly the largest component, accounting for 56-68 percent of the total. Recurring maintenance costs are a generally minor consideration at 12-15 percent although little hard data exists to verify this estimate. Other recurring costs are generally estimated at 5 percent of the total capital costs (excluding DDT&E) with no attempt to further disaggregate or independently estimate the component costs. To this extent, other (non-maintenance) recurring costs, which account of 17-32 percent of total annual costs, are not independent, but essentially represent another aspect of capital costs. The critical issues related to economic viability would appear to be limited to: (1) The estimation of capital costs, including assembly and transportation (2) The methodology used to express these costs on a per unit basis (3) The recovery of DDT&E. One of the major problems of the existing literature is that except for the ECON study, the major and often exclusive emphasis is on the first issue of capital costs. b. The Major Components of Capital Cost Although there is some variation in definition, all references which deal with total capital costs essentially identify four major components : (1) The energy conversion system (photocell array or thermal converter) (2) Microwave transmission system
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