existing earthbound technology for power generation, while SPS depends on rather dramatic extensions of known technology. The power transmission and receiving portions of the system are similar, so the appropriate comparison is between space power satellites themselves and large hydroelectric facilities. STS Equipment in Space The major difference between STS and SPS is in the mirror structure that STS requires in geostationary orbit. This structure must be accurately oriented and very rigid to direct the beam from transmitter to receiver. It should be modular so it is readily transported and assembled, and so that the optimum reflector size can be chosen for each project without extensive development. Due to the lack of research on STS, a comparison of the mass of reflector required to the mass of an SPS is not possible. STS is likely to be orders of magnitude lighter due to its inherent simplicity. While an STS reflector and a photovoltaic SPS could both reasonably be assumed to be modular, it is difficult to see how the more appropriate thermodynamic power conversion technology could be modularized. These simple considerations make it clear that the space-based part of STS would be far simpler and lighter than those of SPS. In studying STS we should consider a variety of different designs, unlike the single basic design considered in most of the SPS literature. It would appear that an STS reflector need not be manned because: • Orientation control is the major task - and this is readily automated. • Very little on orbit maintenance would be required due to the passive nature of almost all of the reflector system. • Unforeseen events are extremely unlikely. The above factors suggest that an STS reflector will be available at all times without on-site personnel. Since there are not service shortfalls due to eclipses, STS availability should be greater than SPS availability. Projected availability problems with transmitting and receiving equipment affect SPS and STS equally since these parts of the system are very similar. Reasons to Study STS As stated in the NAS report [2], ‘Some types of SPS would be technically possible if costs were not a consideration, but the technical challenges are formidable on the basis of present scientific and engineering knowledge or its predictable extensions within the next decade', and ‘there are serious doubts that the technological requirements for several critical subsystems of the reference SPS can be met at acceptable costs through developments that can reasonably be foreseen.' They refer to, for example, low-cost launch, space-qualified solar cells, and automated construction in space. These and other authoritative statements make it clear that the major uncertainties in SPS stem from emplacing and operating a large part of the system in space. STS is not sensitive to most of these uncertainties. Traditionally the cost of photovoltaic power has been more than ten times that of hydroelectric power. Additionally, while the cost of transporting construction materials to remote sites on earth to exploit untapped hydroelectric resources may be substantial, it is bound to be far cheaper than the cost of transporting an SPS to its geostationary location. The Electric Power Research Institute [4] estimates that a baseline SPS
RkJQdWJsaXNoZXIy MTU5NjU0Mg==