Figure 5. Hexagon Frame Mass Versus Surface Deviation (cm) Figure 6. Minimum Modal Frequency Implications The present 1980 view pertaining to the major issues delineated are shown in Table 2. At present the use of graphite composites is favored in view of the superiority of operational performance and minimal construction built-in loads in indeterminate structures. Hopefully, the material suitability issue will be resolved in the next five years. This is not to say aluminum cannot satisfy all the requirements; with design ingenuity, the significant disadvantages may be eliminated. It should be noted that no structures problem capable of placing significant limitations on the SPS is visible now. The near-term efforts required to strengthen structures technology sufficient to support SPS program definition include: (1) composite material 30-year suitability, (2) system implications of determinate structures, (3) studies to identify structural requirements, (4) parametric studies to identify most promising constructions, (5) machine made composite beam element development, (6) beam to-beam joint development and inspection requirements, (7) reflector surface/ cable attachment development, (8) qualification issues, and (9) engineering to support design of proof-of-concept demonstration article. Of primary concern is the development/ space suitability verification of composite materials. Also, the activities listed should be pursued to the level of depth necessary to permit start of engineering for a proof-of-concept demonstration article within this decade. Table 2. 1980 Status of Issues Most cost-effective construction Choice of construction material Definition of structural requirements Knowledge of as-built structure Predictability of structural behavior MPTS passive figure control feasibility Structure stiffness compatible with pointing Passive control through damping Feasibility of space fabrication of ultra-large reflectors and blankets Qualification, model verification, inspection
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