The high voltage conversion is provided by 32 converters located near the antenna gimbal joints (16 at each gimbal). These converters are sized at 271 megawatts (6.73 kA). The secondary or low voltage converters are located adjacent to the various subsystem loads and are presently estimated to provide a maximum of 3.5 kW at each location. DC/RF Converters - The DC/RF conversion is performed by klystrons with an assumed efficiency of at least 85%. The klystron accepts the multiple level high voltage generated by the high voltage DC/DC converters and outputs a microwave segment at 2.45 GHz and at a nominal 50 kW level. The proposed operational klystron is a variation of a Varian VKS-7773 utilizing a depressed, multiple voltage collector fabricated of a refractory material such as pyrolytic graphite. Figure R-l6. Thermal control of the collector is by direct radiation to space. The baseline approach to cooling the klystron tube body is to utilize heat pipes with the radiating surfaces located on the front face of the resonant cavity radiator (RCR) associated with each klystron microwave generator. The baseline array specifies a makeup consisting of 135,864 klystron/RCR sets. With this number of converters, each unit will operate at a true value approaching 54.2 kW average. Mechanical Module, Subarray, and Power Module - The 50 kW klystrons, selected as power converters, are mounted in resonant cavity radiators (RCR) with their collectors protruding from the array base as shown in Figure R-l7. This assembly is a power module. Its area varies so as to set the radiated power densities required over the array surface. There are ten density steps and corresponding module designs. These modules are assembled to form ten subarray types. The SPS antenna is composed of subarrays. A subarray is defined as a portion of the total antenna array which has been phase shifted to point in the direction of the pilot beam. The center of the subarray has a phase, set by a single retroelectronics assembly. In addition, there is a phase variation across the array face used to steer the subarray antenna pattern.
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