Required Capability: Assembly techniques and equipment must be developed and demonstrated in each of the specific areas listed in Table 5.3-1. These specific capabilities must be assembled into a fabrication/assembly system that can build a complete SPS, consisting of a large lightweight structure, attached lightweight blanket, and other required equipment in a few months at low cost with minimal in-orbit crew. It is also necessary that structures of the type that will ultimately be used for SPS be amendable to construction with the equipment developed. For example, equipment designed to construct a truss-type microwave antenna may not be able to construct a compression frame tension web-type antenna. Development Plan: The first step is to better define and detail the operations required during construction. Next preliminary techniques and equipment can be defined to perform these operations given the inherent limitations and advantages that space environment provides. These first two steps must be sufficiently general to cover all types of operations that may be encountered in the most viable SPS configurations. Next, the most promising techniques and equipment should be developed and tested on the ground to prove their validity. After Shuttle and Space Station become available, inflight experiments should verify the validity of the approach in a space environment. 5.3.2 Structures Technology Item — Structural Design Criteria Criticality — Critical to program success An important problem to be addressed in large space structures is that of size and thicknesses of the beams and the joints that make up the structure. The design and behavior of these elements have a significant effect on thermal distortions, structural alignment, initial imperfections, and on-orbit assembly. The demand for ultra-lightweight, yet dependable, structures demand member thickness beyond those currently used in aerospace technology. Lacking for this type of structure are local crippling stress evaluation design curves as a function of parameters, such as geometry, initial imperfections, material properties, and applied axial compression loads and temperature load time histories. Major and significant errors in predicting structural response under dynamic and thermal loading has been caused by unmodeled joint actions. Math modeling of the joints have not been sufficient for past analysis and should be more necessary for large systems made up of numerous joints. Present Capability: Some test data on local crippling stress evaluation has been generated in low thickness ranges and are summarized in the NASA Handbook of Structural Stability. However, the thickness does not extend in the ranges for those proposed or demanded by large lightweight space structures. Methods of testing joint action on earth are readily available. The method of testing under simulated space environment will require extension of present methods and development of new test methods.
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