shadow are negligible, collision hazard from other satellites is low, and the construction sequence is simpler. Personnel logistics requirements, on the other hand, are greater than in LEO, but the percentage cost impact of personnel is not significant. The most effective mode of construction in LEO is to build the satellite in modules sized to be compatible with the thruster requirements for the control of the SPS in GEO operation. The modules are berthed together in GEO. Building the satellite as a complete unit in LEO for transport to GEO is not practical because of control requirements and loads to the structure due to gravity gradients. LEO construction offers a potential cost saving by using a self-powered mode where the output from the partially deployed SPS solar cells is used to power a LEO-to-GEO propulsion system. The degree of degradation of the deployed solar cells by Van Allen belt radiation is an important parameter in the LEO-GEO trade. For self-powered transfer, the satellite solar array must be oversized to maintain the specified output or the cells subjected to an annealing process to restore efficiency. The use of an electric OTV concept for GEO construction may reduce the cost differential between LEO and GEO sites; however, radiation effects also affect the efficiency of the electric OTV. Studies to date have indicated that either LEO or GEO construction appears feasible. The GEO construction location is used as the reference. Configuration Constructability - In the initial phases of the SPS studies, the satellite configurations were generated and then methods were devised to construct the configuration. Relative ease of construction was sometimes used as a parameter in comparison of various power systems. As the understanding of space construction improved and the percentage of satellite weight required for structure was determined to be small, the configurations were modified or originated to improve the ability to rapidly and simply construct them. This may be illustrated by two early configurations, which are the "column-cable configuration" and the "truss configuration".
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