p. Progressive technology risk assessments and rankings must be established as the technology developments mature and the system concept is established. This will play an important part in technology development, ground test and flight test program definition and re-definition as well as in the details of the overall concept. 1.2.3 SYSTEM ANALYSIS AND EVALUATION The system analysis and evaluation section incorporates and reflects the subsystem and technology study results in arriving at the following: a. Capital specific cost decreases as ground power output increases. b. At higher power levels, cost is lowest near 2 GHz. c. Frequency of 2.45 GHz in the industrial band is the recommended choice. d. System configurations having ground bus power levels above 5 GW 2 exceed 20 mW/cm peak ground power density which is beginning to affect the ionosphere and so 5 GW is currently recommended as the maximum for planning purposes. Further in-depth analysis and testing is required to understand these effects more thoroughly and perhaps relax the constraint. e. Overall MPTS efficiency is expected to be about 54%-56% initially with improvement potential to about 63%-67% for amplitron configurations; klystron configurations would be 49%-52% to 56%-59%. f . Amplitrons result in lower cost systems than do klystrons. g. Aluminum results in potentially lower cost but more complex systems than do graphite composites. h. Dominant cost factors for SPS are the power source and transportation. i. As a guide, the power source parameters should not exceed the combination of 350 $/kW with 1. 0 kg/kW or possibly 250 $/kW with 1. 5 kg/kW where the power is as delivered to the transmitting antenna. j . As a guide, transportation and orbital assembly should not exceed 200 $/kg.
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