considerations for the smaller triangular beams range from 0.7 m to more than 1 m. Height considerations for the large truss girders range from 5 to 20 m. Nominal sizing of all members will require further iteration and refinement. Beam side loads imposed by the tensioning requirements of the reflectors and solar cell blankets must be addressed. Effects of thermal distortion and manufacturing anomalies must also be considered. Final beam truss sizing will depend on these additional considerations, plus any changes in orbit transfer thrust loads. Beam truss girder height requirements can be reduced considerably by reducing the beam length. In high bending stress areas, additional intermediate lateral members could be installed to decrease the effective length of the longitudinal beam truss girders. This would not require a change in the overall bay size nor would it affect the reflector panels and blankets. 7.1. 4 POWER DISTRIBUTION AND CONTROL SUBSYSTEM A simplified diagram of the selected power distribution system is shown in Figure 7-15. The solar array is divided into 792 modules producing 22 MW each. The solar array modules develop 20 kV which permits connection directly to the amplitrons without complex power conditioning equipment. Circuit protection and voltage regulation are provided at each module. The very large conductors required to transfer power to the amplitrons are the most significant consideration to the power distribution system. Methods were developed to minimize the mass required for power conductors, and criteria were established for combining the functions of power conductors with structural support. 7.1. 4.1 POWER CONDUCTORS The selected voltage of 20 kV is relatively low when compared to terrestrial transmission lines operating at 382 kV ac and 750 Vdc. The low voltage was selected to reduce power conditioning requirements, but it created the necessity to transmit a large current. The task for the SPS was to transmit 10G A over a distance of 20 mi. This obviously required large conductors (or structures). Compared to terrestrial transmission lines, the SPS task was easier because of the freedom from corona effects but more difficult from the standpoint of heat dissipation.
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