d. Subarrays consist of slotted waveguide radiators providing a high overall beam formation and interception efficiency of at least 95 percent for a contiguous rectenna within the main lobe. e. Waveguide wall thickness nominally is 0. 5 mm, but additional investigation may show this can be reduced; width is 12 cm and depth is 6 cm. Cross sections other than rectangular should be included in future detailed investigations. f. Aluminum, graphite epoxy, and graphite polyimide are candidate materials for the slotted array waveguides. g. Aluminum configurations require structural segmenting of the subarrays and variation of operating frequency to compensate for longitudinal thermal distortions. h. Graphite polyimide configurations offer the highest temperature margin with minimal distortion, but all composites must be evaluated for stability and outgassing properties. i. Waveguide manufacture and subarray assembly on orbit is recommended to achieve favorable launch vehicle packaging density. j . Microwave interferometers are recommended for MPTS and SPS attitude control, and for initial and periodic alignment of subarrays using screwjack actuators on each subarray. 1.2.2. 5 Phase Front Control a. Adaptive (retrodirective) approach needed for maximum efficiency. b. Command approach needed for safety and back-up. c. Calibrated transmission line and/or subarray-to-subarray transfer of reference phase data for adaptive phase control mechanization. d. Phase estimation for command mechanization. e. Investigate bit wiggle technique as diagnostic tool. f. Detailed investigations should be conducted to minimize phase control electronics costs, weight, and blockage for each subarray.
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