nonconducting and conducting structures which carry the power to microwave generators for transmittal to the terrestrial rectenna. A reaction control system is required to keep the satellite in the appropriate orbit and to assure that the solar collector panels point towards the sun while the microwave antenna is directed towards the receiving antenna on earth. Rotary joints to permit rotation of the microwave transmitting antenna are the only continuously active components in an otherwise passive satellite. (2) The Solar Thermal Concept This concept uses huge concentrating mirrors to raise the temperature of a cavity absorber which in turn is used to drive an energy converter. There are generally four modules, each consisting of a hexagonal dish-like reflector (achieving concentration ratios up to 2000) and a cavity absorber. One module also carries the microwave generator and transmitter. The four modules are connected together in a row whose overall length is upwards of 10.5 miles (16.9 km) depending on conversion method. The module (and satellite) width is upwards of 2.4 miles (3.9 km). The heat is converted to electricity by one of three methods: (a) Thermionic Conversion In this scheme, thermionic diodes are mounted in the wall of the solar cavity absorber; the emitters are heated by the concentrated solar energy. By allowing the collectors to dissipate waste heat to space, the temperature differential required for operation is provided. Fins are added to the collectors to improve cooling. In one variation to this scheme, a liquid metal cooling loop is added to further lower collector temperatures and hence improve the conversion efficiency. Rotary convertors step-up the diode output voltage to achieve the level required by the microwave transmission. (b) Closed Brayton Cycle Conversion In this scheme, Brayton turbomachines are mounted on the outside wall of the solar cavity absorber. Thermal energy is added to the helium working fluid in heat exchanger tubing located within the
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