dynamics requires new analytic tools for a problem of this magnitude (Ref. A4) . In terms of the general approach to the structure. Ref. A4 states that a "spider web" type structure is an attractive approach to meeting structural requirements. Ref. A14 discusses an approach that would allow the structure to operate at compressive stresses near the buckling point, and accept random unusual loads with a design that allowed the structure to return to operational shape when the short term, random disturbance is removed. With respect to the specific requirements/considerations, each of which is discussed below, various approaches and tradeoffs are possible. The two prime considerations are structural integrity and pointing accuracy (+1°, per Ref. A2) . There seems to be general agreement that these can be assured as development progresses. a. Material Technology Status Both metallic and composite structural materials have been investigated. Ref. A4 indicates that composite materials appear very promising in several respects, but that the infant state of their technology makes predicting difficult. Their long-term properties such as outgassing and strength maintenance need investigating. Ref. E4 considered aluminum, steel, titanium, berylium and graphite polyimide as candidate structural materials, and selected alloy steel as the most low-cost, practical material for the temperatures involved. The structural concepts advanced in Ref. All use metallic materials as a baseline, but composites are not ruled out as a more attractive alternative. For the solar-thermal approaches, Ref. A12 discusses the use of such materials as H-188 Cobalt Base Superalloy and B-66 Niobium for tubing in the cavity absorbers, manifolds, etc. To quote from this reference, "A trend of improvement of alloys for service above 1340°F (1000 K) is shown in the Figure.* Iron, cobalt, columbium and nickel base systems were compared. A number of alloys having good strength properties were not
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