3.4 ASSEMBLY AND PACKAGING 3.4.1 Detail Parts A study of packaging structural members/elements was initiated to determine the optimum arrangement within Shuttle constraints, and to determine the sensitivity of various levels of ground prefabrication compared to corresponding levels of orbital assembly. The options selected for evaluation, shown in Fig. 3.4-1, span the potential split up of fabrication methods between ground based and space based operations. These cases are as follows: • Case I - Assemble collapsible beam members on earth which will provide the most efficient Shuttle packing density and deploy when in space • Case n - Prefabricate structural elements of tri-beams and manually assemble in space • Case III - Prefabricate flat stock on ground with required thermal coatings and auto assemble in space. Assembly of structural members on the ground requires that these members be stowed in a folded or compressed manner to achieve as high a density as possible. Efficient Shuttle utilization requires a cargo density of at least . A survey of existing stowable structural members (astromast, articulated lattice) suggest that an order of magnitude less is the best that can be achieved. Figure 3.4-2 was generated for typical articulated lattice girder members and, as can be seen, the densities are in the order of . This represents a Shuttle load factor of 1% and it is obvious that even with improved design techniques, the net gain would still fall far short of the desired goal. The attractive facet of this approach is that most of the subassembly work is done on the ground, not at the orbital site. If advanced launch systems were not as volume restricted as the Shuttle, this approach could become the preferred choice. Detail component fabrication on the ground and assembly at the orbital site offers opportunity for a much more efficient packaging density. The first step in this approach is to substitute very thin solid elements for the "Baseline" approach of thin walled tubes (Fig. 3.4-3). This immediately achieves a packaging density far in excess of the minimum 6 lb per cubic foot, but as the following example shows, also results in a weight increase. To balance a 100 lb load in a thin walled, 2. 5 in. diameter graphite/epoxy tube, supported at six meter intervals, the wall thickness would be 0. 0075 in. The resulting weight is 0. 039 Ib/ft. By
RkJQdWJsaXNoZXIy MTU5NjU0Mg==