thermal energy of a maximum insolation orbit and to provide the required energy during the dark portion of a maximum eclipse orbit. The receiver cavity walls consist of rigid, high temperature, formed insulation which reflects as well as reradiates incident solar thermal energy to outer side of the canisters surrounding the tubes. Multifoil insulation is wrapped around the outside of the rigid insulation and the entire receiver is enclosed in an aluminum support structure. The inlet header and aperture frame are protected from incoming solar flux by a graphite shield. This shield is designed to withstand spillage of solar energy due to concentration accuracy limitations and during the times when the SD module is offpointed from the sun. Offpointing occurs during startup and shutdown operations and transiently during pointing control functioning after a disturbance. A more complete description of the receiver can be found in Ref. [2]. The receiver is expected to have a mass of about 1760 kg (3870 lb). Power Conversion Unit. The power conversion unit (PCU) is the heat-to-electric power conversion heart of the SD module. It contains the turbomachinery, alternator, combined recuperator/cycle gas cooler, ducting, and gas storage and management equipment. These components are shown in Fig. 10. The turbomachinery (turbine and compressor) and the alternator are on a common shaft forming a single rotating unit referred to as the Brayton Rotating Unit (BRU). Both the turbine and compressor are single stage radial machines and operate at a design speed of 32,000 rpm. The alternator is a solid rotor, modified Lundell type machine which converts shaft power to three phase ac electric power at 120 volts line-to-neutral with a nominal frequency
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