Figure 55 Suggested Nominal Values for SPS and MPTS compatible in the sense that they probably involve about equal risk for achievement in the required time frame. The set represents a 1500 $/kW SPS capital cost, of which 600 $/kW is attributed to MPTS, and results in 45 mills/kWhr for 80% load factor and 15% annual rate of return. 8. CRITICAL TECHNOLOGY An assessment of technology status and risk was made and a ranking was establ ished to help guide future development, of the MPTS concept. The approach used is described in Figure 56. The work breakdown structure (WBS) developed for the evaluation is shown in Figure 57 together with the appropriate numerical rankings in each block. For items outside the normal purview of MPTS the assessment was made primarily for the impact on the MPTS. The status and rankings should be re-assessed periodically as further in-depth studies are conducted and technology development pro- aresses. Description of all the SPS category 4 items involving relatively high risk is beyond the scope of this discussion, but a review of the hardware items to be given highest priority is in order. These are the dc-rf converters and filters, materials, phase control subsystems, waveguide and structure. The dc-rf converters contribute the most power losses in the MPTS; they must have excellent phase stability; and their noise output must be low. The amplitron offers the greater promise for long life, high efficiency, low cost and low weight at lower risk than the klystron. A similar CFA device, the magnetron, has demonstrated the appropriate unit cost in million quantities, and in particular cases has shown 90% efficiency; however it is most important that an amplitron design show at least 85% efficiency, good phase stability and acceptable noise level while operating under environmental conditions appropriate to MPTS. The role of non-metallic materials such as graphite composites for waveguide and structures depends upon their outgassing properties and long term stability in the space environment, and these aspects must be investigated. The outgassing can interfere with dc-rf converters operating open jacketed to save weight and reach long life. Graphite polyimide, for example, has great potential for reducing transmitting antenna weight, simplifying subarray design by providing great dimensional stability and providing a substantial high temperature safety factor at the center of the transmitting antenna.
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