Should the Rockwell resonant cavity radiator (RCR) eventually prove successful, then by integrating amplitrons into the backside RCR panel for heat rejection, as much as 1.5 x 10$ kg additional weight savings may be effected. New concepts for attitude control and vehicle orientation were also introduced which hold promise for minimizing satellite weight. In summary, the reference configuration, systems, and satellite weight should represent realizable design goals. These results from the first task are not, however, without engineering challenges. The development of high-purity, very thin GaAlAs cells which can be produced as large blankets at low cost is a critical technology. Providing proof-of-concept for phase-control of the 1-km diameter microwave antenna is yet another and may represent the most difficult technological challenge to SPS feasibility. Assembly at geosynchronous oribt—the second major study task, Orbital Operations (Section 3)—poses no design or operational problems over LEO construction other than providing for increased radiation protection and minimizing extravehicular activities (refer also to Section 6.1). In the assembly concepts selected, it was assumed that EVA activities would be needed only for unforeseen failure modes which might require "hands-on" actions not designed into the equipment provided. The results from this study task show that the very large sizes and numbers of subsystem elements readily lend themselves to consideration of continuous-flow assembly processes. With these processes, relatively simple machinery operating continuously at appropriate periods and at very reduced rates (as compared to earth-based production rates) can result in greatly reduced assembly times and minimal crew size requirements. Concepts were developed and machine operating times were typically only 15 percent of the total assembly time requirements. Full 24-hour assembly operations were assumed and crew size estimates were made. Interestingly, major portions of the crew complements were devoted to performing on-orbit logistics functions, and it was determined that three construction bases were required for assembly of an SPS. Iteration of the logistics demands/ capabilities with construction processes showed that a staggered assembly schedule was needed wherein initiation of assembly of the satellite structure preceded solar blanket, reflector, and MW RF element installations by approximately a month. Figure 1.3-1 illustrates the resulting schedule. If the basic concepts and processes developed in this task are eventually proven by orbital tests, an assembly rate of four satellites per year—on a 90-day cycle—appears feasible. An earth launch vehicle (ELV) concept new to SPS studies was introduced in the third study task, Transportation (Section 4): a horizontal takeoff, single-stage-to-orbit (HTO-SSTO) vehicle using a combined airbreathing-rocket propulsion system. The ELV (Figure 1.3-2), is an uprated version of a design study initiated at Rockwell just prior to the decision that Space Shuttle studies would be limited to vertically launched concepts. Although insufficient hard data exist today as to its development feasibility (the earlier studies were dropped eight years ago), comparisons with other postulated vehicles indicate that this concept would be equally cost-effective for an SPS program.