The microwave power transmitting antenna includes a power distribution system which transmits DC power from the slipring system to the DC-RF generators. Conductors from the slipring brushes are tied to DC/DC converters through switchgear tc allow isolation when performing maintenance. Conductors are then tied between voltage summing buses through other switchgear for transmitting the required power to the klystrons. An electrical energy storage power system is located on the antenna structure with a bus routed along the regular network for operation during powered-down periods such as may occur during solar eclipse periods. A battery energy storage system would be utilized for storage of about 12 MW- hours of electrical energy. F. Rotary Joint Power transfer from the solar array section to the microwave antenna is accomplished via a rotary joint (figure 12) using a siipring/brush assembly. Mechanical rotation and drive is provided by a mechnical turntable 350m in diameter. The antenna is suspended in the yoke by a compliant mechanical joint to isolate the antenna from turntable vibrations. The antenna is mechanically aimed by control moment gyroscopes (CMG’s) installed on its structure. A positive feedback with a low frequency band-pass allows the mechanical turntable to drive the yoke to follow the antenna and also provide sufficient torque through the joint to keep the CMG's desaturated. G. Attitude Control System (ACS) The attitude control system for the reference 5 GW system is described for a CR2 GaAlAs option. The ACS for the CR1 Si option will be similar, although the number of thrusters and propellant requirements will differ. Preliminary Baseline ACS Description - GaAlAs-CR2 - The baseline ACS features an argon ion bombartment thruster reaction control system (RCS) whose characteristics are given in figure 13. A total of 64 thrusters is included in the system to provide the required redundancy assuming: an annual maintenance interval, 5000 hour thruster grid lifetime and a 5-year thruster MTBF. Approxi-
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