9.5 In-Space Manufacturing As presented in section 9.3 above, the time constraints of the near-term design examples make it difficult to propose a viable role for in-space manufacturing within the scope of the space solar power program. However, a plan for developing these technologies is necessary so that we have the capability to realize the larger systems which may follow. The near-term goals of this in-space manufacturing should justified themselves separate from a solar power program. The same studies which conclude that large scale SPS's require non-terrestrial material imply that there must be a manufacturing element present to transform these raw feedstocks into useful parts. In considering where to focus our efforts for in-space manufacturing and construction, it is useful to consider what location makes the most sense for each operation. Realizing that lunar regolith must be chemically processed to provide the materials of interest to a Space Solar Power Program, it makes sense to consider doing chemical processing on the Moon, where gravity helps to hold material in place. Once the desired refined materials are in hand, the physical processing of these metals or other feedstocks might be best accomplished on orbit, where micro-gravity can aid in the production of large structures with unique properties. When the chemical processing is done on the Moon, the mass of the waste material which will be generated will not need to be lifted, thus saving a great deal of launch energy. We can launch refined ingots of Fe, Al, and Si to L2 or some other construction/assembly point very easily by using electromagnetic launchers. These metals will not need a "bucket" for launch and will not tend to disaggregate, simplifying both the launcher and catcher design. Physical processing of these metals at micro-gravity into foamed beams or thin films can utilize the properties of space to produce materials that could not be made on the Moon or would not survive launch. 9.5.1 Lunar Manufacturing The availability of nonterrestrial resources is the key both to greatly increased energy on Earth and to large scale human exploration and exploitation of space [Energy Enterprise Task Force, 1990], However, limitations in technology and the cost of sending and maintaining equipment and humans in space make manufacturing in space expensive. The cost of lifting one pound of material from the lunar surface into LEO is less than one-twentieth that of launching from Earth to LEO. Manufacturing materials on the Moon for use on the Moon is even more favorable. The use of the lunar regolith as a radiation shield for lunar outposts could be a first step in exploiting non-terrestrial resources for large scale projects in space. This could be followed by extraction of oxygen and metals for use as propellants and structural elements, production of cast basalt or glassy structural materials, fabrication of refractory materials, etc. Manufacture of composites in space, using glass fibers or metals produced on the Moon as both reinforcing material and matrix, could provide structural materials for future space structures [Goldsworthy, 1985]. We must ask if we can make all the necessary items for such a large project from the resources available on the Moon. The possible items required include solar cells, wires, microwave reflectors, and metal support structures. It has already been demonstrated in the laboratory that iron for structures and wires, fiberglass and iron for antennae and reflectors, and a variety of other individual products have been produced from simulated lunar materials. The vacuum and lower gravity present on the Moon or in space may actually make it easier to produce many of the articles we need(it should be noted that chemical processing may be difficult). It remains to be shown in a research and development program that large scale production of these materials and fabrication of such items can actually be carried out on the Moon, but a focused effort should be able to accomplish many, if not all, of these goals. The most "high tech" elements of such systems may still be imported from Earth, however. An interesting self replicating, expanding lunar factory design was proposed by Freitas and Zachary [Freitas and Zachary, 1981]. The idea was to let the system grow itself from a 100 ton "seed" into a much larger, more capable system. The latest developments in artificial intelligence and robotics may provide alternative solutions to the problems such a system would face. Whether the space solar power program considers the use of large satellites or the lunar surface as the platform for the collection and transmission of energy manufacturing capabilities at the lunar base would need to be developed. An evolutionary plan to provide a facility which can use metal stock to manufacture spare parts for the lunar base is one approach. At first, this metal stock (bar, plate, rod) would be provided from Earth and would use computer controlled tools to
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