b. Physical Configuration The system is generally composed of power generating modules consisting of solar concentrators and cavity absorbers, and the transmitter antenna as shown in Exhibit 9. These modules are individually assembled in low orbit and self-powered to high orbit; one module carries the antenna. The long (roll) axis panels are mounted on two cavity absorber support arms so as to move edge-on to the predominant meteoroid flux. The panels are inclined 11.8 degrees relative to the perpendicular to the concentrator to reduce solar absorption and shadowing of the concentrator. The solar concentrators each consist of a framework supporting 10,000 individual reflector facets. The cavity absorbers each mount 12 closed Brayton cycle turbomachine sets although there is some indication that only 4 sets of higher capacity would be used. In thermionic configurations, the diode panels are mounted directly on the cavity as shown in Exhibit 10. A five GW ground output version of this system would employ only two concentrator modules. Each of the 10,000 individual reflector facets incorporates active mirror control to maintain focusing in spite of disturbing forces due to thermal and gravity loads, aging and assembling inaccuracies. Each facet is made of metallized plastic film (aluminized Kapton) and is tensioned to form a plane surface. The cavity absorber receives the solar energy flux which for the most part is absorbed into the cavity walls. This is because multiple reflections must in general take place before the reflection back out the aperture can occur. Once absorbed, the energy is available for removal by the energy converter (Brayton cycle or thermionic devices). c. Efficiency The Brayton cycle efficiency is currently on the order of 45 percent although efficiencies up to 66 percent are projected for the 1990 time frame, although Reference A4 indicates optimum in-space efficiencies less than 40 percent. Thermionic converters are less efficient with current technology providing only about ten to fifteen percent, a figure that is projected to rise to as much as 36 percent by 1995.
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