Present Capability: Gallium is produced as a biproduct of aluminum refining. About 20 percent of the available gallium in aluminum ore is recovered for a total production of less than 100 metric tons per year at a cost of $500/kg. The Reynolds Aluminum Company claims to have a proprietary process for recovering 80 percent of the available gallium if there existed a market. Significant quantities of gallium also exist in coal which may be recoverable as a biproduct of desulfurization. Required Capability: Construction of four SPS's per year will require gallium production at a rate in excess of 10,000 metric tons per year. Processes that improve the yield and decrease the cost are required to meet production rates and cost goals of SPS. New sources, such as coal, may need to be developed to provide sufficient production rates. Development Plan: The first step is to develop and demonstrate processes that improve the yield and reduce the cost of gallium recovered from aluminum. Next, processes that recover gallium as a goal by-product need to be developed and demonstrated. The goals of this should be to be to improve production rate capability while reducing costs. 5.3.4 Microwave Transmission Technology Item — Microwave Transmission Criticality — Critical to program success Energy is transmitted from the satellite to the ground over the microwave link. Good efficiency and control is required to minimize radio interference, safety hazards, and energy loss. Present Capability: A large number of microwave transmission systems are in use today in such applications as radar, communications, and ovens. However, none of these systems have requirements close to SPS requirements for number of tubes, phase control, operational environment, and total power. In limited laboratory tests, several tubes have been simultaneously controlled to remain phase and frequency locked. However, no test has approached SPS in complexity in terms of physical size, number of tubes, or power level. Existing high- power tubes are of heavy construction with good thermal and power supply control. They also operate at efficiencies on the order of 60 percent. Required Capability: The phase and frequency control system must be able to tightly control as many as 1.6 x 10$ tubes to within 10° phase error. Each tube must be of lightweight and high-efficiency while exposed to the space environment of GEO. Each of the specific items of Table 5.3-1 must exhibit satisfactory performance. Development Plans: The first step is to develop and demonstrate methods of controlling the phase of a large number of dc-RF tubes. After good control is assured, each of the remaining specific areas of Table 5.3-1 must be developed and demonstrated. In-orbit tests of a subscale system will demonstrate the overall feasibility of microwave power transmission.
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