7.2. Space Solar Power System Concepts and Architectures The studies conducted by the DOE and NASA of space solar power in the 1970s validated that the concept of SSP was technically feasible. However, the extremely large initial costs associated with the 1979 SPS Reference Concept - more than $250 B to achieve the first commercially-delivered kilowatt- hour of power on the ground - unfortunately also demonstrated to many that the SSP concept was programmatically and economically unfeasible. The cost drivers inherent in the 1979 SPS Reference Concept were not associated with particular estimates of technology or performance (these in fact tended to be optimistic), but were instead inherent in the architecture and system concept itself In particular, the fact that the design required major in-space construction of discrete “piece parts” (albeit very large parts) and the concomitant massive in-space infrastructure required to conduct these construction and deployment operations drove the cost of placing the first operational SPS in space. The infrastructure associated with the Reference Concept involved several major elements: a very large, unique ETO transportation system, a major in-space construction base in LEO (housing perhaps as many as several hundreds of astronauts), a major in-space construction base in GEO (housing as many as scores of astronauts), and a very large, unique in-space transportation infrastructure derived from SPS system elements. All of these resuhs were dependent on the costs projected for ETO transportation. However, many of the estimates made in the 1970s were viewed by the “fresh look” study team as being quite optimistic. For example, the estimated cost of transportation to LEO used in the 1970s was only about $45 per payload-pound (in 1996 dollars): a value considered extremely low (and in fact, unrealistically low) in light of ETO vehicle conceptual designs available today. The greatest gains in driving down costs achieved by the “fresh look” study have come from moving toward modular,-self-deploying SPS system concepts. For example, in the SolarDisc concept, the phased array for RF beam generation is, although quite large, composed of many hundreds of individual modular units, each of which is in turn composed of many thousands of individual FET devices. In this case, assembly is accomplished by means of a small number of human-equivalent robotic systems that are resident on the SPS as it grows. There is no separate SPS construction facility in GEO. There are no hundreds of astronauts in LEO and GEO conducting construction operations. The same is true of both the SunTower concepts and the ReflectArray concepts in which a modular design approach, self assembly and/or simple robotic assembly, and simply deploying mechanical systems were employed throughout the designs. In addition, the modularization of SSP concepts enables the use of much smaller launch vehicles - launched more frequently and therefore at lower cost, even at the earliest stages of SSP evolution - than in the Reference SPS Concept. Real advantages can also be derived from SSP architectures that do not involve basing SPS in GEO. The range of potential system concepts and architectures for space-to-Earth power beaming spans the orbital region from LEO to GEO and encompasses a wide distribution of ground station locations. However, WPT from satellites not in GEO inherently involves a time-varying geometry of the space-to-ground and space-to-space (relay) links This will be a key determinant of system design requirements, power reception performance, and economic viability of different concepts. Three orbit types were considered in this study: a Low Earth Orbit (LEO), defined for this study’s purpose as an orbital altitude below about 3,000 km LEO sun-synchronous, circular orbits have a near-
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