The basic design decisions made are summarized in Table I and typical applications are illustrated in Fig. 2. For the structure, we selected a flat-fold packaging rather than the drum-type ‘window shade' approach which several investigators had developed in smaller sizes. Analyses showed that in these large sizes, with these orbital loads, the tubular-type deployment booms were completely inadequate, and we therefore selected a truss-type boom. The Astromast was selected from among the truss booms studied because it was completely retractable and capable of sustaining load while partially deployed—a feature which many of the candidates did not have. The selection of this particular combination of packaging and deployment rather than the ‘drum' type allowed us to decouple the mechanics of the packaging and deployment hardware, resulting in a much less complex system. The selection of solar module design approach represented an even more radical departure from conventional designs in that it depended on a wraparound solar cell. Although a few were made under this initial contract, none had yet been developed with acceptable performance, nor had the associated welding processes required to perform automated panel assembly been developed or demonstrated. Some work had been done on copper printed circuit substrates, but this had not been applied to welded solar array assemblies. Most important, the ability of the proposed assembly techniques to stand up to the packaged launch environment and the tens of thousands of thermal cycles experienced in low earth orbit had not been demonstrated. Nonetheless, the concept had promise and, more important, the commitment of the associated NASA and contractor organizations to follow through on development and demonstration of the key technologies.
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