Figure 2.2-17. Panel and Reflector Steady-State Temperatures 2.2.4 Slip Ring and Brush Assembly Slip rings are required for the SPS to transfer the generated power from the solar arrays to the microwave antenna which rotates once per day to track the rectenna on the ground. There are several devices that can transfer power across the rotating joint, but based on the design constraints of the SPS and the state of development of the rotating joint, a conservative approach was used in the design of the SPS. The SPS slip ring assembly consists of two sets of two rings. Each set has a positive and negative ring, and each ring of the set is 86 cm away from the other ring. Each set of rings is located 500 m on center. The brushes that ride on the rings support the microwave antenna structure by the trunnion structure, as shown in Figures 2.2-18 and 2.2-19. The slip rings and brushes operate at 20,622 vdc and each ring carries 196,308 amps. Power generated by the solar arrays is distributed down to the slip ring. The brushes ride on the slip ring track and serve as the rotating electrical joint, and also as the bearing for the trunnion. The slip ring is isolated and supported off the main SPS load-carrying, structure by insulated standoffs. A full 360° brush supporting assembly was employed for increased structural stiffness and for increased alignment and bearing considerations. The slip ring is 1.13 km in diameter and has a cross-sectional area of 41.3 cm^. The s]_;ip ring has an aluminum core with the contact surface clad with coin silver to increase conductivity and life. Each ring weighs 40,300 kg and the total weight for all four slip rings is 161,200 kg. Each slip ring
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