[4] There are instances, e.g., transmitter subarray final assembly, where space manufacturing could relieve payload bay dimension requirements on launch vehicles. This advantage does not require use of extraterrestrial resources. So what to do? I believe a change in our approach to space manufacturing is needed. Evolutionary Paths The most important objection to the contemporary space settlement scenario has been the perception that the whole ball of wax must be adopted from the outset. If any element fails to work, the entire program is perceived as a loss. In this paper, I have suggested that a habitat suitable for extended crew stays in space may be beneficial on its own merits if certain issues can be resolved. Construction of such a habitat, in turn, may benefit from a relatively unsophisticated use of lunar materials, e.g., for shielding. Evolutionary steps in the use of lunar materials, i.e., for steelplate and oxygen, were also identified; these materials may require only relatively simple processing and manufacturing technology. One may gain useful insight from the analogy of space communications. Early communications satellites were simple reflectors or transponders requiring large, sophisticated ground stations. Since the beginning, the trend has been to more sophistication in space and more services with less sophistication on the ground. ATS-6 provided TV broadcast to village receivers in India. Platform-type satellites presently under study could provide various services to households and individual users. Similarly, we may expect an evolutionary trend of more labor activities in space to support space industrialization as experience is accumulated and costs come down. Already, the SPS studies are examining the potential benefits of using a smaller heavy-lift launch vehicle (HLLV); the present reference vehicle has a 400-ton HLLV, 17 x 23 m payload capability. A smaller vehicle of, say, 120-ton capability will necessitate a somewhat greater degree of final assembly work in space. An unpublished design study by Dan Gregory of Boeing examined the use of electromagnetic accelerators for Earth launch; vertical launch of 1-ton pay loads from Earth's surface to geosynchronous orbit was indicated to be feasible. Transportation costs were roughly estimated to be in the $5/kg to $10/kg range. If such a scheme were eventually adopted, SPSs would be transported as components rather than as subassemblies, resulting in a substantial increase in space-based assembly work. Extraterrestrial materials would, of course, lead to a still further increase. Space manufacturing of aluminum structure and power conductors from extraterrestrial resources is quite plausible. Space assembly of subarrays and possibly of Klystrons offers conceivable advantages. Space manufacturing of solar arrays from lunar resources would be an important breakthrough, if a suitable set of processes could be developed. RESEARCH RECOMMENDATIONS [Ij The construction of large habitats will require two techniques, adoption of which will be very traumatic to the conventional space systems engineer: (a) Welding of a pressure vessel, the integrity of which all life within obviously depends, in space; (b) Installation, integration, and checkout of the subsystems (upon which life also depends) in space. Development and adoption of these techniques could have early payoff: the freeing of space station habitats from the 4.4-m diameter
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