microwave transmission. This list of major components reflects the ECON study and primarily relates to solar-photovoltaic systems. A slightly modified set of components are designated in Exhibit 28 which shows the cost of a 10-gigawatt satellite as estimated in several references. As can be seen from the list, not all sources categorize costs in the same way, and the more general term ''energy conversion systems” is used, sometimes including the satellite microwave transmission system. The component categories used in the table are intended only for gross illustrative comparisons since there may be substantial differences in what is included in each category, particularly with respect to "transportation," "assembly," and "other" which frequently overlap. In some instances, notably the Boeing estimates, costs were not grouped by the original authors into major categories but were collected for illustrative purposes by authors of this summary. The specific sources should be consulted if detailed definition or subcomponent estimates are needed. Notwithstanding differences in apparent definition, certain general comparisons can be made. The microwave transmission and receiving costs together comprise a relatively stable proportion of the total across all estimates, although the absolute dollar costs vary widely. The combined costs of microwave transmission and reception vary from 19 percent (JPL- photovoltaic) to 24 percent (ECON-photovoltaic). Similarly, assembly and fabrication costs are a consistently small proportion of the total ranging from 6-8 percent in all examples except Boeing, which did not separately break out assembly costs. For purposes of this table, the only costs that can be specifically associated with assembly were "LEO (and GEO) bases and Manipulators." Although the items included in "other" vary widely, the proportionate share is consistently low ranging from 1-3 percent. It is inevitable that estimates of such a preliminary nature would vary substantially. Certain differences in the absolute dollar estimates should probably be examined more closely, however, to be sure that some or all of the difference is not accounted for by some generic assumption; e.g., the rate of inflation. This applies specifically to the factor of four differences between the JPL and Boeing estimates for a solar-thermal
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