mounts. The overall thermal efficiency of the absorber is estimated by Boeing to be 87%. In addition to reflector (facet) efficiency and absorber efficiency, a concentration penalty is involved due to the fact that the facets are flat and the surface is not a perfect mirror (the reflected energy is somewhat diffuse). Thus a "concentration efficiency" of 0.69 is used in reflector-absorber system calculations. 2.813 Thermal Engine/Generator/Radiator The turbine, compressor and generator are mounted on a common shaft supported by gas bearings. Each turboset generates 300 Mwe. The recuperator and heat rejection heat exchanger are mounted together on the engine pallet in the latest conceptual design, which uses a liquid metal radiator fluid loop with conventional fluid pumps (liquid metals are acceptable at the low-temperature side of the cycle). 2.82 Design Characteristics A summary of the design characteristics of the system is presented in Table IV-B-l-c-1. Figure IV-B-l-c-15 summarizes the efficiency chain for the system, indicating an overall system efficiency from solar input to generator output of 18.3% based on 1984 technology. Using this efficiency chain, an overall energy balance for the system is shown in Figure IV-B-l-c-16. This system is designed to beam microwave energy to earth through a 1000-meter diameter transmitting antenna, where the microwave energy is then reconverted to a net usable 10 GWe which is fed into the terrestrial grid. 2.83 Transport and Assembly Considerations The subject of transport systems is dealt with in much detail in other sections of this report, but this section deals onlv with the concents of transport and assembly as applied to the Brayton cycle conversion system. Several concepts are currently under study for transportation and orbital assembly of the thermal engine system. One concept consists of the use of a heavy lift launch vehicle (HLLV) to get the system into low earth orbit (LEO), where it is partially assembled to provide some fraction of its total rated output to power a system of electric thrusters. Other concepts involve the use of hybrid chemical-electrical propulsion systems from LEO to GEO. But regardless, all concepts use the HLLV, a high-launch- rate/low-cost vehicle with a payload capability of between 500,000 and 1,000,000 lbs. One 300 MW turbo-compressor-alternator package would weigh close to 1,000,000 lbs implying 48 launches into LEO for the turbo units. It would then take about twice as many launches as this to get the rest of the system into LEO (heat exchangers, absorber, reflectors, auxiliaries).
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