(IAAM economic analysis of this case pushed the number of satellites to 72 to improve the return on investment). Reducing the angle to +/- 5 degrees, increases the required number of satellites to 126. Increasing the angle to +/- 45 degrees, reduces the required number of satellites to 10. 6.23. Power Conversion Efficiencies Tn the analysis of system sensitivity to power conversion efficiency, the effect of changes in the assumed values of power conversion efficiency was examined for both space segment mass and cost in the three Case Studies under exam. These analyses also covered the sensitivity to assumed levels of radiation- induced degradation of photovotaic efficiencies at their end-of-life (EOL). Results of the analyses are graphically presented in Figures 6-11, 6-12, and 6-13 for Case Studies 4,16 and 13 respectively. The conclusions to be drawn from the analyses are that: (1) small changes from the assumed nominal efficiency values, of either the FET devices or photovoltaics, do not result in significantly large percentage changes in flight segment mass or cost, 1 e., the nominal values are generally below the knee of the sensitivity curves; (2) large reductions in FET or PV efficiency can have a substantial impact on flight segment mass and cost - e.g., halving the FET device efficiency from 80% to 40% would, in the worst case, increase both the mass and recurring cost of a MEO SunTower by as much as 80 percent, and produce large increases (20 to 60 percent) in the mass and cost of the LEO SunTower and GEO SolarDisc concepts as well; (3) for all concepts, the mass sensitivity to reduced FET efficiency is fairly close to cost sensitivity on a percentage basis; (4) over the ranges of interest, the mass and cost sensitivity to variations in PV (concentrator augmented and thin film) efficiency is less than the sensitivity to changes in FET efficiency for all cases (5) SolarDisc is less sensitive to variations in efficiency than the Sun Tower concepts and; (6) over the indicated ranges of interest, the mass and cost sensitivity to the presumed PV efficiency losses at EOL is much less than the other sensitivities in this analysis; however it is clearly an important component of the system design as demonstrated by its significant impact on system sizing (mass and cost) for high levels of expected degradation. Perhaps the most meaningfill conclusion to be drawn from this analysis is the importance of the FET transmitter device efficiency. A reduction in the efficiency of this component has been shown to lead to mass and cost increases that can approach values of 1 to 2 percent for every 1 percent decrease in efficiency from the nominal Such degraded space segment performance can easily destroy the economic viability of the proposed concepts. Although PV efficiency has also been shown to be critical to space segment mass and cost, its impact is not quite as substantial
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