Figure 6. Configuration Options Eight different satellite configuration options (Figure 6) were studied to obtain a better understanding of the impact of solar cell selection (GaAs versus Si), antenna mounting location (end versus center), number of troughs (range 3 to 10), concentration ratio (CR=2 versus nonconcentrated), and radiation degradation assumption (annealable versus non-annealable). For these studies, solar cell and power distribution efficiencies were held constant, as was antenna mass. The data are summarized in Table 2. Very little SPS mass difference was calculated between configurations with different numbers of troughs; however, construction considerations strongly favor a narrow configuration. A relatively small mass savings is indicated for a center-mounted antenna (0.4 kg/kWut); similarly, a relatively small difference in mass was shown between GaAs annealable and non-annealable CR=1 configurations (0.36 kg/kWut) and between GaAs CR=1 and CR=2 (0.89 kg/kWut). Figure 7 shows a plot of SPS mass estimates made over the last few years. A mass curve was prepared which normalized to an early estimate made by Dr. Peter Glaser in 1974 (~2.3 kg/kW utility power). As shown, SPS mass estimates have grown by a factor of approximately 2.3 for GaAs configurations and 3.5 for Si configurations (NASA reference concepts). The GaAs concept falls near the nominal range of uncertainty established initially by NASA/JSC in-house studies conducted in 1975. Various alternative concepts are compared, including solid-state (SS) configurations which replace klystrons with solid-state power amplifiers for the de to RF microwave system and multi-bandgap (MBG) solar cells replacing the reference GaAs single function cells. The impact felt by cell efficiency improvements is demonstrated by the MBG concepts, which use a 30% nominal cell efficiency.
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