of the process is that it does not adapt to joining nonmetallic parts, which comprise the major portion of the SPS components. Electron beam welding is a process which produces heat with a concentrated beam of high velocity electrons impinging on the surfaces to be joined. The rate of energy input to the work piece being joined is generally expressed by the following relation (Ref. Welding Handbook): where: V = beam accelerating potential (volts) I = beam current (amperes) S = welding speed (cm/second) Typical power requirements for electron beam welding 0.127 cm. thick aluminum alloy are 27,000 volts, 21 milliamperes, 3 cm/second, resulting in a power requirement of 0.19 kilojoules per linear cm. of weld. Electron beam welding has been used for welding fairly thin aluminum foils (^0.02 mm.), but for all practicability considering the high volatilization of aluminum and precise electronic welding controls required, a lower limit of thickness for aluminum material is approximately 0.25 mm. Aluminum alloy thicker than 12.0 cm. has been successfully welded for terrestrial applications. One item requiring additional development before electron beam welding can be utilized for SPS construction is a flight type power supply for converting the available solar energy into high voltage welding energy for continuous operation and control of the space environment. In summary, electron beam welding does not appear to be a serious contender for SPS fabrication because of the limited amount of metallic materials requiring joint construction. Resistance welding is another candidate method for joining metallic materials on SPS. Like electron beam welding, resistance welding is not adaptable to joining of the nonmetallic materials which comprise the major portion of the SPS. Spot, roll-spot, seam, and projection welding are the group of specific processes which fall under the heading of resistance welding. Resistance welding is essentially a joining process where the required heat at the joint is generated by the resistance offered through the work parts to the relatively short-time flow of low-voltage, high-density electric current. Force is always applied before, during, and after current application to insure electrical continuity and to forge the heated parts together. For SPS application (aluminum waveguides), the seam weld process, where a continuous weld is made consisting of a single weld bead or a series of overlapping spot welds, would probably be used. Regarding energy requirements for resistance welding, the majority of terrestrial welding equipment uses alternating 60 Hz current, with a voltage between 1.0 to 25.0, and a current of 1000 to 100,000 amperes. The heat generated in the work being welded (and in the weld electrodes) is expressed by (Ref. Welding Handbook):
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