corner installation is illustrated in figure B-10. The ACS consists of thruster, power processor, structure, propellant feed, control systems, and instrumentation. The thrusters include the primary electric thruster and auxiliary chemical thrusters required for establishment of attitude control when electric power is not generated by the SPS. The electric thrusters are 100 cm diameter ion engines using argon as primary propellant. Thruster Isp is 20,000 sec. Each panel contains 25 thrusters. The net thrust per panel is 150 newtons. The operating life of the system is 2 years with a 50% duty cycle and 80 amp beam current. The chemical thrusters use LO^/LH^ as propellants and are used for control during equinoctal occultations. The engine Isp is 400 sec. H. Microwave Power Transmission System General - The microwave transmission system includes the entire spaceborne array power transmitter which includes the de distribution system from the rotary joint to the rf transmitters, the rf transmitters themselves (klystrons), their de and rf control and monitor circuitry, and the rf antenna elements composed of slotted waveguides, support structure, rf feed circuits, mechanical pointing control, all the components required for distribution and control of the phase of the retrodirective antenna subarrays, and the ground receiving stations (rectenna). Figure B-ll shows sketches of the major components of the transmitter system. The design utilizes a retrodirective phased array powered by dc-rf klystron converters. DC power from the rotary joint is 2 distributed in a manner to minimize I R losses to the klystrons, utilizing 85% unprocessed power with a maximum voltage of 42 kv. The klystrons are combined to provide a tapered (10 db quantized Gaussian) illumination of the array resulting in low sidelobe levels and high antenna efficiency (over 95%). The 2 thermal loading in the center of the array (22 kw/m rf) permits a design for a 1 km diameter array which provides roughly 5 GW of de power on the ground per antenna. The phased distribution system is designed to minimize line lengths and cumulative phase errors in the distributing transmission lines by using a 3-node reference distribution system with line length compensation. The pilot
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