including assembly tolerance and joint effects, can be used for comparison with and updating the model* The third step would develop the main structural system models, made up from substructural elements. The final step should be the demonstration of a space based experiment such as a pilot SPS. Item — Structural Material Development Criticality — Greatly enhance program probability Material selection for large space structures must be optimized in terms of specific strength and specific modulus, packaging density compatibility, resistance to environmental degradation (i.e., aging) and compatibility with anticipated on-orbit fabrication techniques. High specific strength and modulus are necessary for optimization of structure design and minimization of mass required in orbit. Packaging density considerations require that maximum material be transported in a given cargo volume. The structure must survive long duration (>30 years) mission without succumbing to environmental aging effects. Finally, the materials must lend themselves to rapid on-orbit fabrication. Present Capability; Metallics such as aluminum and steel are well characterized for all the above considerations. Composite materials (with thermosetting resin) are well characterized relating to physical properties and earth oriented fabrication techniques. Required Capabilities: Composite materials provide an attractive alternate to metallics for large space structures. However, thermoplastic resin systems must be evaluated from a standpoint of service temperature capability, chemical characteristics, fabrication (i.e., forming, welding, etc.) characteristics, and finally aging characteristics in a space environment. Development Plan: • Aging — 1. Accelerate space failure mechanisms on earth using controlled aging environments. 2. Compare material properties obtained from space-aged to ground-aged specimens. 3. Create software correlations. 4. Use software to predict performance. • Fabrication using thermoplastic composites — 1. Work with generic resin systems and develop physical and chemical characteristics.
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