considerably less than unity (i.e., favorable, benefit > cost). The mass of the shield is considerable, on the order of 5 x 108 kg. If this mass were to be shipped from the Moon, a few tens of megawatts electric on the lunar surface would be needed — the power level required is similar for either a lunar oxygen plant (conventional propulsion) or a mass driver. Power might be provided by a solar array or by a small laser SPS at the LI liberation point. (Reference 10 provides a discussion of laser SPS.) Lunar Resources We come now to the main controversy. There is little doubt that raw materials can be freighted to geosynchronous orbit from the Moon at less cost than from the Earth. Whether this leads to less cost for completed products, however, is at issue. One can make strong qualitative arguments that it may not: • The total cost of any element of an SPS as installed in geosynchronous orbit is the sum of the cost of fabrication and the cost of transportation to the destination orbit. Fabrication includes raw materials cost and all value added during ground and space-based fabrication and assembly operations. (For SPS hardware, raw materials costs are in most cases a trivial fraction of the total.) • For typical SPS hardware costs as estimated by the DOE/NASA-sponsored SPS systems studies, the ground-based fabrication cost and the transportation cost are roughly equal. Thus, even if transportation cost can be reduced to zero, one cannot afford more than a doubling of the ground-based SPS hardware fabrication cost in a space-based fabrication scenario. • By any reasonable means of estimating, the cost of a man-year of labor in space will be on the order of 10 to 20 times that for a man-year on Earth. Estimating of capital facilities is more problematical but it is not irrational to believe a multiplier greater than two. Thus it is difficult to believe that transportation savings could offset the increased production cost associated with use of extraterrestrial raw materials, labor, and facilities, except in special cases of items exhibiting low manufacturing value-added costs, such as aluminum power conductors. On the other hand, a recent NASA-funded study (Contract NAS9-15560) has projected SPS hardware production costs in space to be much less (by a factor of about two) than the equivalent costs for Earth-based manufacture. Results of this study, which favored use of lunar resources, actually accorded as much savings to extraterrestrial hardware production as to transportation, for the lunar resources case. This was then “explained” by arguments involving labor unions, profit pyramiding, and use of industrial robots. These arguments are not an explanation in my view: • Are we to believe that space workers are immune to union organization? Organized or not, are we to believe that space workers will work for less salary than their Earth-based counterparts? (As discussed earlier in this paper, the cost of supporting a worker in space is expected to be on the order of $1 million per man-year; space worker salaries are not a primary economic factor. The basic issue is how many people are required.) • Profit margins in industry, unless an unregulated monopoly exists, generally run 10% to 15% per annum on invested capital. Since the capital investment in space manufacturing facilities will be greater than in comparable Earth-based facilities rather than less, one would expect aggregate profits for this case to be greater, not less. Even if one accepts the profit pyramiding argument at face value, it contributes little to explaining a factor of two.
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