The recommended operating frequency of 2.45 GHz in the USA industrial band results in near optimum efficiency, avoids brownouts in rain and should have minimal problems in radio frequency interference and allocation. A recommended 5 GW ground power output level provides economy of scale while limiting the peak microwave power density in the center of the beam at earth to about 20 mW/ cm2. Microwave system transmission efficiency is about 60% and cost is about 500 $/kW including orbital assembly and transport of the transmitting antenna from the ground to geosynchronous orbit at 200 $/kg. The orbital transportation and assembly cost should not exceed about 200 $/kg if a satellite power system is to have energy costs comparable with projections for ground based nuclear plants. The recommended flight plan is transport to low earth orbit using a reusable heavy lift launch vehicle, assembly in low earth orbit and then transport to synchronous orbit using a solar electric propulsion stage. Emphasis should be placed on orbital manufacture and assembly to achieve favorable launch vehicle packaging densities. The critical technology items of the MPTS needing early development are the de to microwave converters, materials, electronic phase control subsystems, transmitting antenna waveguide including its interface with the microwave converters, and structures. A six-year, three-phase critical technology development and ground test program is recommended at a rough order of magnitude cost of $27M. The ground test involves transmitting and receiving antennas to obtain data on beam controllability and radio frequency interference, which will provide design confidence for orbital tests. The planned orbital test program implements defined objectives and relies on the Shuttle transportation system to develop and demonstrate orbital assembly techniques and to establish learning for cost and schedule projections. In order to accomplish all defined objectives it culminates in an orbital test facility which could be the nucleus for a pilot plant in geosynchronous orbit. The objectives and their implementation are subject to change and should be reassessed periodically as further in-depth studies are completed and technology developments are matured. The rough order of magnitude cost for the currently indicated flight test and associated technology development is $3500M.
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