Structure - Figure R-7 shows the configuration of the SPS point design solar array wing structure. The concept is a three-trough, two-tier system. The structure is made up of tri-beam girders whose longitudinal members and transverse struts are fabricated on orbit by a beam machine. Shear stabilization of the tri-beam girders and the wing itself is achieved by the use of X-tension cables. Current structure material is structural aluminum. Excessive stresses and/or deflections could drive the material selection to the regime of composites. The dimensions indicated have been verified to be adequate when the vehicle is subjected to operational forces and torques environment in geosynchronous orbit in that they result in an acceptable margin of safety for a basic material thickness of 0.254 mm (0.010 in.), which is considered minimum gauge. The girder is 50 m on a side, and each bay is 50 m in length, stabilized by X-tension ties. The three longitudinal elements and the transverse struts, are formed by basic beam elements fabricated on orbit by a beam machine. The basic beam element is 2 m on a side with transverse struts every 2 m and modified triangular cap sections at the vertices. The cap sections, transverse struts, and X-tension braces are made from three sheets of 0.254 mm (10 mil) 2000 series aluminum, with approximately 88 percent cutouts, which is roll-formed, flanged, and welded by the beam machine to form a basic beam element 2 m on a side. E. Power Collection and Distribution A flow diagram of the overall power distribution subsystem is presented in Figure R-8. Power obtained at the subarray is transferred to a summing bus through a switch gear (SG) and manually operated circuit-breaker. Power is then transferred from the nonrotating member to the rotating member of the rotary joint through slip rings and brushes. On the rotating member, power is conducted through switch gears to dc/dc converters which output the five primary voltages required by the klystrons. Each voltage is conducted to a summing bus through a switch gear. Subsequently, each voltage is conducted from the summing buses to the 135,864 klystrons. A more detailed schematic block diagram of the power distribution subsystem on the array or nonrotating portion of the satellite is presented in Figure R-9.
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