factor and to assume an inflation rate of 6 percent. At the same time, ECON's own cost estimates use a 7.5 percent discount factor and no general inflation assumption, although certain fuel cost escalation scenarios are presented. This divergence is recognized and comparable terrestrial unit costs recalculated using the same assumptions. In the estimates by JPL (Ref. A15) , the discount factor used is 10.5 percent and a 6 percent inflation factor is referenced with respect to terrestrial sources and, by implication, used in computing SSPS costs. Except for the above mentioned references, most of the literature either ignores or treats only very sketchily the specific factors used to derive unit costs. What data is provided on these assumptions does, however, clearly suggest some variation in discount rates although most explicit references are to 10 or 10.5 percent. Inflation assumptions vary over a wide range for terrestrial energy costs by type and by author, while SSPS costs are almost universally expressed in constant 1974 or 1975 dollars. ECON does, however, attempt to assure comparability by dealing explicitly with alternative estimates of the potential change in the "relative” cost of energy fuels. The recovery of DDT&E costs is treated explicitly in only one reference (All). In this report, ECON computes the number of 5-GW installations required to recover a total estimated DDT&E cost of $44 billion at various prices per kWh. Since the base cost, before any recovery of DDT&E, is approximately 27 mills/kWh, only at prices in excess of that is there any potential for DDT&E recovery. In this analysis, which uses a 7.5 percent discount rate and reduces all costs to single point present values, the DDT&E recovery function becomes asymptotic at about 31 mills. This suggests that only at terrestrial generation costs in excess of this rate could the proposed program pay for itself fully. They further estimate that at 35 mills/kWh, all costs could be recovered with a production run of 57 5-GW satellite systems, (285 GW total output) representing, in ECON's opinion, at least 10 percent of total national capacity at that time (2012). The recovery of DDT&E costs, therefore, depend on the extent to which the market will support energy costs which include an increment or surcharge of 10-20% over the "normal” charge that would
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