with spur geax* drive, but a linear induction drive may prove superior for longer life. Sizing requirements exhibit high torques but surprisingly low power demands: The overall structural concept for the transmitting antenna is shown in Figure 28. Nominal design is 40 meters deep and, depending upon system considerations to be covered later, is about 1 km in diameter. It is assembled in two rectangular grid structural layers. The rectangular grid was found to be less massive than a competing radial spoke design. Primary structure is built up in 108 x 108 x 35 meter bays using triangular grid compression members 18 meters long and 3 meters deep, The secondary structure is used as support points for the waveguide subarrays and is built up as 18 x 18 x 5 meter bays. The structure to waveguide^ interface shown in Figure 29 uses three gimballed screwjack assemblies to correct up to a 4 arc min subarray misalignment and a 40.5 cm linear displacement. Temperature considerations resulted in a choice of a triangular hat construction technique as noted in Figure 30, and a simple locking mechanism to expedite assembly of structural joints is suggested as shown in Figure 31. Thermal analysis of the overall structure was a key aspect of the study since distortion and bending impact the error budget for beam phase control. Figures 32 and 33 show the displacements and slopes over the antenna for a full range of sun angle conditions and for aluminum and composite materials. The adaptive phase front control will compensate for the deflection effects, and the screwjacks previously noted can be set to compensate for the average slope error; however, the subarray size must be sufficiently small to keep efficiency (gain) loss tolerable for the deviations about the mean slope that will occur on a daily basis. A further result of the thermal analysis was a determination of maximum heat flux density that could be tolerated at the center of the antenna to stay within structural material temperature limits. It was found that microwave converters could be fully packed with their individual radiators touching for any of the materials investigated, with graphite polyimide showing the greatest temperature margin.
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