F. Construction 1. Satellite Construction The early SPS configuration studies indicated that construction in space was desirable because fabrication of a large area of lightweight structure in orbit takes advantage of the absence of severe loading conditions. Favorable packaging density requirements for heavy lift launch vehicles can be accomplished with space fabrication. This allows a reduction in the number of flights and greater load capability of satellite components when the components are most efficiently packaged. As concepts for construction have been developed, the concepts have been reflected in various satellite configurations and constructability of a configuration is a major parameter in selecting a design configuration. The difficulty of constructing a configuration is generally related to the concentration ratio, where concentration ratios greater than two begin to become more difficult to construct. With regard to construction location in GEO or LEO, the transportation and operation requirements are the principal drivers in the selection. A variety of construction and support equipment will be necessary to complete a satellite. Because of the very large scale of the operation, a high degree of automation will be employed to keep the number of personnel to a reasonable level and the total construction time to a minimum. These personnel will principally perform monitoring and repair functions. As SPS systems have been defined, the need for a maintenance capability has become an important operational consideration. Construction Location - Low Earth Orbit (LEO) vs. Geosynchronous Earth Orbit (GEO) - The issue of where to construct the SPS received considerable study effort. Conclusions varied due to the sensitivity to assumptions and performance parameters. Construction of the satellite in GEO offers many desirable features. Gravity gradient loads are two orders of magnitude lower than in LEO, aerodynamic drag loads are not significant, thermal effects from passing through the earth's
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