k. Provide stock control and delivery of materials, subassemblies, and modules. 1. Attach and remove temporary supports or handling members. m. Checkout and troubleshoot active subsystems. n. Inspect completed operations. Each of these processes may be expanded into additional detail when subsystem configurations are firm and if a particular process is expected to be a driver in defining a construction approach. Appendix V-A-l describes some construction related contractor studies. Appendix V-A-2 discusses joining processes for SPS construction. 5. Construction Options a. Fabrication Locations - The principal option in construction location is between LEO (Low Earth Orbit) and GEO (Geosynchronous Earth Orbit) since the SPS is a little large for a single launch. Table V-A-5-1 summarizes the important parameters in the comparison and indicates the effect of each. One of the major considerations for LEO construction is the potential use of the solar array as a power source for a high ISp propulsion system. Significant problems with this approach may offset the energy efficiencies. The exposed solar cells will be degraded by radiation from the Van Allen Belts. Offsetting gravity gradient torques to maintain orientation toward the sun combined with thrust loads will affect the array structural design. Orientation to reduce drag will be an important consideration. The long transit time associated with low thrust levels results in an additional capital investment period for interest charges. On the other hand, logistics and support will be simpler and cheaper in LEO. Lead time for delivery of components is shorter than to GEO particularly if the OTV is ion propelled. The launch penalty to place construction equipment in orbit is much greater to GEO, but if a large number of stations are built, the impact is much smaller for each station. Another important difference in construction in LEO is the continual sunlight-darkness cycle. The construction facility will need the capability to store power and provide lighting to maintain continuous operations. Also, the changing thermal gradients may cause problems in aligning the station to required geometry during construction.
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