Flight Center and the Johnson Space Center have proposed alternate designs to the configuration proposed by A.D. Little, et al, for the photovoltaic system based primarily on structural considerations. Finally, Section 6 describes energy conversion from the standpoint of the technological developments needed if power conversion devices are to meet SPS requirements. Exhibit 16 is a highly abbreviated tabulation of the major parameters of a satellite solar power system (a photovoltaic approach is assumed), the NASA "baseline" assumption, and brief comments to indicate the magnitude of the achievement required. 1. Transportation System While the exact requirements of an SPS transportation system are dependent on the selected construction and configuration approaches, a number of reasonably specific requirements can be stated at this time. When these are compared to the capabilities of current transportation systems, the extent of required developments can be seen. In subsection a below, the capabilities of current systems, or currently emerging systems, are described. Subsection b then discusses the requirements for SPS transportation systems. a. Current Transportation Systems The launch vehicle with the greatest payload capability, is currently the Saturn V. Its payload is 120 tons (100,000 kg) and Ref. A9 indicates that it can transport 500 tons/year (450,000 kg/yr). It is an expendable vehicle, and its launch rate would be low. The Shuttle, which should become available in 1980, has a payload capacity to low earth orbit (LEO) of 30 tons (27,000 kg). It is partly reusable (the orbital propellant tasks are expendable), and with its capability for a moderate launch rate, can transport 1,200 to 2,000 tons per year (1 to 1.8 million kg/yr) to LEO (Ref. A9). The Shuttle payload bay is 60 feet (18 m) in length by 15 feet (4.6 m) in diameter, excluding payload structural attachment points. A pair of remote manipulator arms provides for payload deployment and retrieval, and a docking mechanism
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