(2) Assembly of components delivered to synchronous orbit by an assembly crew operating from a space station support base as part of extravehicular activities. Assembly by tele-operators can be expected to be less costly than assembly by work crews based in synchronous orbit, which would require a space station for support of their operations. The choice between manned or tele-operator assembly will depend on the cost effectiveness of either approach. Tele-operators using remote assembly techniques should achieve assembly rates in excess of about 10 lb an hour, and would appear to be more effective than manned assembly, which would have to achieve rates of about 20 lb an hour to justify the cost of space stations and recycling of crews. It is highly likely that a combination of both manned operations and tele-operators will evolve, where man's most important function will be to exercise control over the assembly process. Maintenance With any major system such as the SSPS, the design criteria, materials choices, and data on component life and the expected operating conditions will determine reliability. Redundancy of components through the use of large numbers of identical components, for example, solar cells, will tend to reduce maintenance requirements. The cost of performing repairs has to be evaluated and compared with the option of delaying repairs and accepting the potential loss of revenue while achieving operational lifetimes consistent with cost analyses of the SSPS operation. The goal will be to evolve maintenance-free designs, particularly for the solar cell blankets and the microwave generator subsystems. SPACE-BASED MANUFACTURE The SSPS provides a unique opportunity to evolve manufacturing methods which are particularly suited for operations in space. The space transportation system, which will evolve to transport payloads from Earth to synchronous orbit, will have a substantially greater lift capability than even a space shuttle. However, this lift capability can be utilized appropriately only when the payload is designed to be weight limited rather than volume limited. Prefabricated beams (required, for example, for the microwave transmitting antenna structure) transported to orbit for subsequent deployment may be less desirable because packaging densities of about 5 Ib/cubic foot are typical for folded and compressed designs for deployable structures. Thus available volume probably will be the limiting factor rather than lifting capacity if components are prefabricated on Earth. The required high load factor could be achieved if fabrication and assembly were performed in orbit from appropriately prepared flat-rolled stock from which girders and other mechanical components could be produced by automated
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