launched within the launch window ( ~ 15 minutes). Based on current launch operating techniques this seems to be an unacceptable traffic rate. It is interesting to note that if an assembly altitude of 255 n mi were chosen, proper phasing with the assembly point would exist on a daily basis and the launch overflow from one day to the next would be avoided. 3.5.2.4 Fleet Size/Traffic Recommendations Figure 3.5-9 presents a summary of the fleet size/traffic requirements of the three flight plans. Based on strictly fleet size consideration a two year assembly at LEO is recommended. From a launch opportunity point of view, a 255 n mi assembly altitude is recommended. This altitude also offers orbit decay advantages. 3.5.2.4.1 Concept Cost Comparison - Cost compilations were prepared for the following three cases: • Flight Plan 1 - Low altitude assembly, one year assembly period (Fig. 3.5-10) • Flight Plan 2 - High altitude assembly, one year assembly period (Fig. 3.5-11) • Flight Plan 3 - Low altitude assembly, two year assembly period (Fig. 3.5-12). The recurring and nonrecurring cost estimates for support equipments assumed in this concept comparison are outlined in Fig. 3.5-13. Previous cost data on Space Station (NAS 9-9953) were updated to 1974 dollars and applied as a unit cost factor ($/Kg) to space station, Shuttle Support modules, remote manipulators and auto manufacturing modules. Weight estimates were taken from Ref. 25 and 26 for the Modular Space Station and Shuttle Support Modules, respectively. Cost estimates for Shuttle were taken from Grumman Phase A study results while Tug estimates were based on recent Tug System Studies. The cost of SEPS and the control modules were assumed at $1M/Ib of thrust, Ref. 29. All equipments used in the cost comparison were amortized over the assembly of five SSPS. Figure 3.5-10 through 3. 5-12 summarize the transportation and assembly costs for the three flight plans cited above. An assembly cost of 1323/kw (5 GW system) can be achieved at a low altitude site with a one year assembly time (Flight Plan 1, Fig. 3.5-10). These costs can be reduced slightly, $1302/kw, if the assembly time is increased to two years. (Flight Plan 3, Fig. 3.5-12). Assembly at high altitude would cost 350/kw (Flight Plan 2, Fig. 3.5-11), an unacceptable cost level, if space based power generation is to be competitive with ground generated power.
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