Figure 2.1-1. SPS Reference Configuration the microwave antenna is supported on a track-like ring, as indicated in the lower portion of the figure. The antenna is rotated about the large hexagonal structure which carries through the entire length of the satellite. Design concepts were generated for the antenna track ring and for power transfer across this rotary joint. However, a major disadvantage of the high-aspect- ratio concept was uncovered early in the study. Power distribution wiring weights were increased significantly over designs which have a more equal length-to-width ratio. Some configuration alternatives were briefly investigated based primarily on design variations for achieving higher concentration ratios and are shewn in Figure 2.1-2. A major concern with higher concentrations designs is in maintaining contour of the shaped reflectors. It was determined that to maintain a parabolic shape requires a more complex array structure with added rigidity. A contour may be formed by periodic attachments (a minimum of 5 points are required) of "tuning" wires, or similar devices, to the supporting substructure. In addition, the surface must be constantly supported in biaxial tension to assure shape retention. Other configuration alternatives are discussed in Section 2.4; however, for reasons stated above, the configuration of Figure 2.1-1 carried as the reference design. 2.1.2 Satellite Structure A library search of very lightweight structures was made to provide historical structural data from 1900 to 1976. Finite element theory using the NASTRAN computer program was used to analyze the steady-state thermal stresses
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