Fig. 21. Graphite/acrylic thermal gradient in LEO. 4. CONCLUSION The automatic fabrication of basic building block aluminum beams has been ground demonstrated with the aluminum beam builder now operating at NASA- MSFC. The automatic fabrication of basic building block composite beams still is to be demonstrated. Machine elements, composite beam cap forming and brace to cap fastening have been ground demonstrated. A composite beam builder still needs to be constructed. To date, composite efforts have demonstrated the need for real improvements in basic thermoplastic composite processing, in order to obtain better fiber wetting and continuous laminate strip stock. Short (1 to 3 m), press formed, strips have been used for process development and demonstration purposes, but the real need is for continuous strip up to 300 m long (the beam builder storage reel capacity). Material suppliers have been given this challenge. Further effort is required to improve the structural characteristics, ease of preprocessing and final forming of graphite reinforced thermoplastics. Other resin systems and graphite fiber orientations need to be examined. The performance of these materials in both vacuum and radiation environments also needs to be determined. Finally, once all ground feasibility tests have been completed and the choice has been made between aluminum and composite for the first space flight demonstration, a flight beam builder will be built and integrated aboard the Orbiter and a still to be determined mission flown (Figure 22).
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