percent and a throughput of up to a million tons per year - ample capacity for the initial colony and space power station; additional devices could be added as needed. No such devices currently exist but the theory is apparently all worked out. Implementation of a system of this size containing the requisite accuracies may well present some engineering problems but none are foreseen which are insurmountable. MSFC, in their assessment, sees the primary problem at the termination end of this transportation system rather than at the launching end, however. They state (Ref. A20, p. 53), "The single most challenging technical problem, with no practical solution to date, is collection of the material transported to the libration point from the moon by the transport linear accelerator. Failure to solve this problem could void the entire concept." 3. Space Manufacturing and Assembly The basic scheme for deriving the necessary construction materials is to extract lunar surface material, transport it to L5, refine it, and from the refined material fabricate the elements of the space colony or power station. Sufficient material for the first colony - 500,000 tons g (450 x 10 kg) - would leave a hole on the surface of the moon about 16 feet deep and 650 feet square (5 m x 200 m x 200 m). The initial space manufacturing facility (SMF) requires about 3000 g to 1000 tons (2.7 - 9.1 x 10 kg) of earth-fabricated materials at the g lunar surface and about 10,000 to 40,000 tons (9.1 - 36 x 10 kg) of such materials at L5. The lunar soil, based on Apollo samples, contains about 40 percent oxygen, 19 percent silicon, 14 percent iron, 8 percent calcium, 6 percent titanium, a little over 5 percent aluminum, and a little less than 5 percent magnesium. All these materials are, of course, quite useful and, if these proportions hold generally, provide virtually all the metals and all the oxygen that will be needed. Note that the no less needed carbon,
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