or thermoplastic resin matrices and adhesives. For higher temperature requirements, high temperature resistant resins (i.e., polyimide) will be required which could result in more complex, heavier, and higher temperature resistant fabrication and forming equipment. The joining of the nonstructural elements of the SPS comprise the majority of the fabrication requirements on the SPS. Attachment of the solar reflectors (aluminized polyester or polyimide films) to each other and to attachment structural interfaces presents some problems. Heat joining of polyimides films (Kapton) which do not exhibit melting or softening properties, require an intermediate film or coating such as FEP fluorocarbon (Teflon) which does "soften" sufficiently to facilitate bonding. The only significant metal joining requirement on the SPS is the antenna waveguides which are fabricated from aluminum alloy. The waveguides must be accurately fabricated into rectangular tubular sections, requiring full length continuous seam joints in each element. Welding these joints using resistance or ultrasonic welding techniques are two potential fabrication methods for accomplishing this task. In reviewing joining processes for use in the space environment, past studies have been concentrated on metals joining. In 1966, Hughes Aircraft conducted a study on "Space Environment Fabrication and Repair Technique" (Contract NAS 9-4546), and Hamilton Standard developed a "Hand-held Electron Beam Welding Gun" (Contract NAS 9-4501) under contract to NASA-JSC. In 1968, Westinghouse produced a battery powered electron beam welder under contract to NASA-MSFC which was subsequently evaluated and tested in orbit during a Skylab mission. In 1969, Battelle conducted a study on "Feasibility of Resistance Welding in Hard Vacuum" (Contract NAS 8-21196) with NASA-MSFC. The results of these studies concluded that resistance welding and electron beam welding were both viable candidates for the joining of a variety of metals in the space environment. In contrast, there has been very little work done in developing joining techniques for non-metal materials for in-space fabrication until recently. Recent advancements in composites for structural use for aerospace/aircraft programs reveal that the high strength, low density, composites definitely promise advantages for in-space structures that metals cannot meet. "Tailoring" of graphite composites to produce "almost" zero coefficient of thermal expansion, for example, is one prime requirement which is desirable if large continuous space structures are to endure the thermal cyclic extremes experienced in space. In summary, methods for joining metals in the environment of space are well advanced when compared to non-metals. However, the apparent advantages of non-metals such as graphite composites, require that suitable joining techniques be developed to allow the efficient fabrication of non-metals for space structures.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==