indigenous resources. The mass of base infrastructure, not counting radiation shielding, is on the order of 20 T per person (6 T for habitats and food growth modules alone). The infrastructure for an (admittedly large) base of 1000 people is 20000 T. At 17 T. per flight, estimated as a reasonable transportation delivery capability for base facilities. The flight rate for resupply and crew rotation logistics may be as few as 20 per year (Woodcock, 1986). If we double that rate to provide another 20 flights per year for facilities delivery, we project 60 years to deliver the base. Logistics support of a 1000-person base is actually credible; the problem is in delivering enough facilities in a reasonable period of time. This was the first surprise of this study: the great importance of construction materials for lunar base build-up. It seems to be tacitly assumed by many if not most analysts that production of lunar oxygen for propulsion use is much more important, and should occur much earlier, than production of construction materials. This may be true if the primary reason for a lunar base is production of oxygen for other space missions (case study 2, below). If buildup and expansion of a lunar base has high priority, however, construction materials are economically more important than oxygen. Studies of solar power satellites built from lunar materials, e.g. Kelso and colleagues (1985), have estimated lunar materials content as high as 98%. For a lunar base, a figure of 90% would relieve the build-up ‘choke point'; the number of delivery flights would be reduced from 1200 to 120. A brief review of the likely materials content of typical hardware indicates that 90% could be achieved with lunar manufacturing capability for such things as: • Structural pressure vessels—‘lunarcrete' or glass/glass composites could serve as could fabricated metal structures. • Structural framing and packaging—boxes, rack and shelf structures, walls, enclosures. These could be fabricated from sheet metal or glass/glass composites coated with a solar-fired glaze for smoothness and handling comfort. • Plumbing, ducting, and tubing. Smaller and high pressure sizes would have to be metallic. Larger, low pressure sizes such as for air ducting could be glass/glass or even cast basalt. • Insulated wiring and optical glass fibres—the former could be aluminum (I have not seen schemes for producing copper on the Moon) and the latter probably made from lunar glass. • Equipment housings could be of sintered ceramics or powder metallurgy, as could such things as pump or fan impellers. • Electric motors are mostly laminated iron. Aluminum windings could probably be used. • Common fasteners can be made on automated tools. • Powder metallurgy or metal/ceramics could probably be used for gears and other machine parts. Electronic components and things made from organic feedstocks would probably come from Earth. The plant and equipment needed to fabricate the kinds of items listed above would pay back their mass investment in a very short time. A possibly great amount of process research and development is needed before such production can be considered truly practical; a significant proportion of engineering work at the initial base should be so allocated because of the lead times involved. Producing most of the base facilities for accommodation of 1000 people, say in 20 years, requires a production rate of at least 1000 T/year if the mass efficiency of
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