3. 3. 3.2 Structural Member Evaluation Structural member analyses were carried out to establish a feasible structural arrangement and to calculate member sizes to arrive at the lowest weight compatible with the existing thermal environment. It should be noted that this study did not include overall structural geometry optimization and the general arrangement, Fig. 3.2-1 and 3.2-2 was used to determine member loads and sizes. The previously used applied loads based on gravity gradient induced torques, have been superseded by torques generated by slip ring/brush pressure and result in an average of 100 lb force compression loads in the upper and lower bending members. Our Task 1 sizing effort was based on aluminum tubular members to form the baseline triangular girder. The selection was based on the comparison of (1) a single circular tube 100 meters long and (2) a triangular girder with a tubular member at each apex with cross tubes and diagonal bracing. The later section was also assumed as an Euler column 100 meters long, since this member, while braced at 25 meter intervals by vertical members, can fail in the lateral column buckling mode. Figure 3. 3-33 and 3.3-34 show the wall thickness vs diameter at various compression loads for the Euler failure mode and were calculated for 5, 25 and 100 meter lengths. After the thermal profile was generated, it became evident that the tubular elements, particularly aluminum, could not be used. Considering that, plus the new loads, selection of a new shape and material was initiated, resulting in the "modified V" fabricated from graphite/epoxy or graphite/polyimide. Analysis of this section, Fig. 3.3-35 shows that it is capable of balancing a compressive load of 127 lb at 450°K. Local crippling does not appear to be critical. The current investigation did not include loads induced by preloads in cable cross bracing required to overcome cable slack or tension caused by thermal expansion. Further study is required for this investigation. 3.3.3.3 Structural Deflection The primary load which the antenna is subjected to is due to the torques generated by slip ring brush pressure. A bending moment curve Fig. 3. 3-36 was generated and resulting deflections calculated. As shown in Fig. 3.3-37 these deflections are within the allowable 1 arc-min. Initially a simplified thermal model was used to arrive at the deflections shown in Fig. 3. 3-37. With the selection of the 1 km diameter baseline, a more extensive thermal profile, Fig. 3.3-24, was generated and new deflections calculated. These calculations
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