SPS Feasability Study SD76SA0239-2

utilizes eight brush block assemblies, with the brushes made of 75 percent MoS2, 25% Mo + Ta. The brushes are spring-loaded in the brush block assemblies, as shown in Figure 2.2-20. Brush pressure is 0.705 kg/cm2 (10 lb/in2) and the contact surface area is sized for 7.75 amp/cm (100 amp/in2). Since each ring carries 196,308 amps, a total contact surface area of 12,903 cm2 (2,000 in2) is required for each brush assembly. The brush assembly is further divided in eight brush blocks, each having 1651 cm2 (256 in2) of contact surface area. A brush block is shown in Figure 2.2-21. The overall dimensions of the brush block are 17.78 cm x 12.7 xm x 6.1 m. Each block weighs 381 kg. A thermal analysis was performed on the brush block and the calculated operating temperature was approximately 90°C. It was assumed that of the total heat generated at the sliding surface, 50 percent went into the brush block and 50 percent into the track. A total of 32 brush blocks (eight per slip ring) are required, and the total weight is 12,192 kg. The total weight of the brushes and slip rings is 173,392 kg. A preliminary specification of the slip ring and brush assembly is presented in Table 2.2-6. 2.2.5 Power Distribution The power distribution network for the SPS delivers the generated power from the solar cells down the array, from the array to the slip rings, from the slip rings to the antenna, and then through the antenna to the RF devices. Aluminum conductors were used because of their high conductivity combined with Figure 2.2-20. Shoe and Slip Ring Drive Assembly