simultaneously be of very high efficiency of operation, low specific mass (for example kW/kg), adaptable to launch from Earth onboard a rocket, able to be packaged, unpacked, and assembled and so on, can be relaxed or circumvented by space manufacturing. The weightlessness and vacuum of space permit considerable simplifications in the design, embodiment and operation of systems for the high volume fabrication than can be conducted on Earth. We note that Woodcock is already assuming the use of lunar derived oxygen for use as propellant. The rate of mass processing and the type required is not appreciably different from that associated with construction of SPS's from NTM's. Large space structures considered to date (including SPS) are extremely redundant in both basic units of construction and in assembly operations. It seems very likely that manufacturing systems with a high degree of redundancy or parallelism can be used. The first complete production units may be rather small, perhaps compatible with deployment in a few shuttle missions. If significant fractions of the manufacturing systems can be produced from lunar materials then growth may be decoupled from labor, production, and investment considerations on Earth. The MIT study supports the possibilities of parallelism and considerable flexibility of output products of initial small space manufacturing facilities (SMF). There are terrestrial analogues to the high levels of automation production assumed in the LRU and MIT studies. Current automated production facilities can be used to assess whether the LRU study estimate for space workers is reasonable. The Nissan (Datsun) Assembly Plant at Zama, Japan, is 97% automated. It produces automobiles, which are more complicated than SPS components, at a rate of 8.2 metric tons/day-worker. To build one 10 GW SPS per year requires manufacturing of 374 tons/day of components, based on LRU study assumptions of 112,200 ton SPS mass and 300 working days per year. This requires 46 workers each producing 8.2 tons/day. Obviously additional in-space personnel will be required for such functions as materials processing, stock production, detail parts manufacturing, facility maintenance, and service. Except for maintenance and services, these can and should also be highly automated. The LRU study estimated 1400 SMF personnel. It is estimated that 540 workers were required for SPS final assembly based on Boeing's estimate. The LRU study used Boeing's estimate for final assembly personnel and facilities weight and cost. Thus 860 inspace personnel remain for manufacturing SPS components and subassemblies. This is a factor of 18 more than the 46 required for existing highly automated, complicated production processes and seems to be a very conservative estimate. The Woodcock model that requires the transport into space of more than 82,000 personnel and the need for construction of very large initial habitats does not appear to be justified. As previously noted, Woodcock contends that habitat construction paces the economic development of SPS construction using NTM's because of the large number of workers (more than 82,000). He then proposes an evolutionary development of habitats which eventually leads to large constructs made in part from NTM's. We note that this scenario is not intrinsically different from that explored in Ref. 1 except that in the production of one 10 GW SPS each year the SMF could be constructed of assemblies of modified shuttle propellant tanks which are encased in several meters of lunar soil for radiation protection of the crews. There is not a requirement for the immediate production of large monolithic habitats are argued by Woodcock. However, this early SMF or others like it could be adapted to manufacture such habitats. It seems clear at this time that major investments (tens of billions of dollars) will be required to bring economically beneficial space industries into existence. One of
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