Table 2.4-2 was developed using the mass statement of the NASA report (1) as the primary reference. That report presented a solar Brayton cycle with 17 GW of output power to two transmitters. The efficiency of this cycle is 43.9Z. Figure 2.4-2 shows the overall configuration of this SPS. The masses of the components of the NASA paper were corrected for material substitutions, design changes, and temperature ranges considered in this study. These adjustments were done with conservative assumptions. More accurate estimates of the masses of these components should be made if the Brayton cycle is considered further as an option for the SPS energy conversion system. As shown in Table 2.4-2, the lower temperature cycle gives the lower specific non-lunar mass. However, the decrease in non-lunar mass is offset by a forty times greater increase in total mass. Since the cost ratio of non-lunar to lunar materials is estimated to be no better than fifty, there are no grounds for preferring one temperature cycle over another. FIGURE 2.4-2, BRATTON SPS CONFIGURATION
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