2. CONCEPT DEFINITION The study of SPS begins with a preliminary definition of the on-orbit satellite concept. This includes the overall configuration with its major structural systems and the power conversion, power distribution, power transmission, and attitude control/stationkeeping systems. The study of these systems and the evolution of design concepts was the objective of the concept definition task. Since orbital construction of the satellite will be required, the definition of equipment, facilities, crew sites, assembly schedules, and of the transportation systems required to support these operations must be considered in the design of a satellite concept. The iteration requirement between this and the other study tasks will become more apparent as each succeeding task is discussed. Finally, as the satellite configuration and its systems concepts progressed, an effort was made to reach realistic compromises between technology projections and costs. Wherever possible, the emphasis was on the conservative side. This approach is reflected in discussions of the satellite configuration, the major structural systems, and the wiring for power distribution. 2.1 SATELLITE CONFIGURATION The selection of a satellite configuration is tied inextricably to each of the satellite systems and to both assembly and operational processes. Alternatives to the reference concept selected for study were investigated. Although some configurations appeared promising for further study, it was determined that the reference concept should be analyzed—end-to-end—throughout the study. This decision was based on the rationale that the basic configuration can be analyzed for its apparent advantages yet it represented a more conservative design approach. The potential of other configurations is discussed in areas of the material to follow. 2.1.1 Configuration Concepts The reference concept for a 5-gigawatt satellite adopted for study is shown in Figure 2.1-1. This two-trough configuration was chosen for several potentially promising reasons. First-order analyses indicate that the long, deep structure reduces the energy required to control gravity gradient forces substantially over that of a wide, thin configuration. Due to its basic shape, even greater reductions may be achievable by redistributing some of the masses. At some point in the reduction - as yet undefined - the introduction of momentum-storage devices may eventually prove practical, thus alleviating the propellant resupply demands and significantly reducing the propulsion effluents emitted in the vicinity of reflectors, solar cells, high-voltage wiring, and amplitrons. Similarly, deep structures tend to achieve greater first-mode bending and torsional stiffness. Substantiating analyses of these potential advantages are discussed in Section 2.4. Also, to remove the problem of transmitting RF power through transparent structure, solar blankets, reflectors and their supporting structures are removed at the center of the satellite and
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