the receiver. Pump motors for the heat rejection assembly and their drive electronics are also in the EEA. Finally the EEA includes the frequency changer which converts the nominal 1067 Hz, 3-phase power from the alternator to 20 kHz single phase power for primary distribution. The mass of the EEA is expected to be about 260 kg (570 lb). Beta Gimbal. The beta gimbal is a single degree-of-freedom gimbal, which together with the alpha gimbal, provides the coarse pointing of the SD power module. Although it only rotates through an angle of + and — 52 degrees during normal operation, it can rotate a full 360 degrees to allow full detracking of the SD module from the sunline for assembly, maintenance, and emergency operations. It includes both electric power and data coupling between the assemblies of the SD power module and the truss. The mass of the complete beta gimbal is expected to be about 280 kg (610 lb). Interface Structure. All the functional SD assemblies described above are mounted on the interface assembly as shown in Fig. 4. It is oriented in inertial space by the alpha and beta gimbals, and is the base from which the fine pointing of the concentrator operates. The interface structure mass is expected to be about 375 kg (825 lb). Technology Base The Solar Dynamic power module is based on a solid technological heritage at both the system and component levels. For the Closed Brayton Cycle (CBC) Power Conversion Unit (PCU), the technology to build this engine exists. A 10.5 kW Brayton power conversion system was developed by AirResearch under the management of NASA- Lewis Research Center in the 1960s and 1970s. Several sets of hardware were produced and tested [3]. These included BRUs, heat exchangers, controls, accumulators, etc. These BRUs have a physical size, turbine inlet temperature (1600°F) and shaft speed (36,000 RPM) roughly comparable to the current design of the CBC Solar Dynamic power module for Space Station Freedom. The same type of working fluid, a mixture of He and Xe gases, was also used. Two of the BRUs were successfully operated for 41,000 and 11,000 hours each with no failures or physical degradation. In fact, 13,600 hours of continuous operation were achieved on one of the units without any failures, maintenance or signs of wear or excessive creep. On a component basis, the Freedom PCU uses turbine, compressor and alternator design concepts the same as those developed previously. Aircraft Auxiliary Power Units (APUs) have endured over 200 million unit-hours with over 200 million start/stop cycles with turbine and compressor designs that are similar. Gas foil bearings in the Freedom CBC rotating machinery design are of the same design and size as those used in the DC-10 environmental control cooling turbines (over 100 million unit-hours of operation and 71,000 start-stop cycles before replacement). Because of the experience in Brayton development, extensive government and industry experience in related aircraft components, and conservative design, extreme confidence exists in the capability of producing a space qualified PCU. The radiator is another major assembly for which the technology base exists for the SD power module. Single phase, pumped liquid radiators have been previously flown aboard Apollo and Skylab and are now in use on the Shuttle [4]. The SD radiator, which uses adhesively bonded honeycomb construction techniques, takes advantage of the current state-of-the-art fabrication methods which are demonstrated by the Space Shuttle Orbiter's large single phase pumped loop radiators mounted on the cargo bay doors. In addition, the SD radiator uses an integrated automatic deployment mech-
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