plant was estimated to cost between 2.5 and 5 billion dollars including machines and equipment. The estimated product cost of $40/m2 is about a factor of 250 below today's cost for space arrays. [1] Reduction in the number of Earth launches of rocket vehicles. Whereas there is great uncertainty in the environmental effects of launches, there are reasons for concern. [2] Minimizing of the packaging problems attendant to subjecting fragile components such as solar arrays to the launch environment. [3] Economic practicality of relatively thick glass encapsulation of solar arrays, probably eliminating the need for array annealing systems. The relatively high labor content (compared to space manufacturing estimates) of the reference scenario has been occasionally explained (by space manufacturing advocates) as the result of a “cottage industry” approach. The above array production scenario is hardly that. It does, however, incorporate a manufacturing process recognized as not suitable for space manufacturing (7). Processes that may be more suitable are not sufficiently well developed to support a credible labor estimate. Klystron production was assumed to be semiautomated. The estimated labor content of about two man-weeks per tube is consistent with automated production of all parts, but mostly manual final assembly, plus manual checkout test setup and tear-down with automated test operation. The cost reduction factors relative to today's tube cost is on the order of 20. An estimate of Klystron module assembly and checkout in space, for maintenance operations, estimated about 0.12 man-weeks per tube. The assembly work was partial in that undamaged parts of tubes would not be disassembled for maintenance. The workload per tube is estimated as about 1/5 that for new tube assembly from constituent parts. Extrapolated to new tube assembly, this estimate yields about 1500 people per SPS per year, about 1/3 the number shown in Table 5. The space-based repair operations are, of course, more automated than ground-based manufacture. Analyses of structure elements accorded nearly all cost to materials, i.e., graphite. Structure heads the list (Table 5) of space manufacturing candidates since it has relatively little labor content and since a low-cost material, aluminum, was substituted for the relatively high-cost graphite. Curiously, aluminum power conductors are far down the list. The results of this analysis are clearly highly sensitive to the unit pricing of SPS hardware. In certain instances, the unit pricing is suspect of being much too high. This is true in the example of power conductors. These were priced at about $35/kg. The power conductors are little more than sheet metal; a cost as low as $1-$2/kg might be realistic. Given the Earth-to-GEO cost of $60/kg and the fact that power conductors are a small part of SPS mass, there was little motivation in the systems studies to research this particular cost item carefully. From the standpoint of an infant lunar manufacturing industry, however, the sensitivities are far different. At $1-$2/kg, the lunar materials benefit is significant. So what may we conclude from all of this? First, that there is a large uncertainty in the actual cost of space manufacturing operations. The case in favor of space manufacturing has not been made, nor has the case against it. Second, there is a wide range of labor intensiveness in prospective products. Some are almost certain to benefit from space manufacturing. Others are as certain not to benefit. It is important to point out some relatively unquantified potential advantages for space manufacturing. Four examples:
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