For purpose of selecting candidate materials for the support structure, the maximum expected temperature must be determined. Should the support structure be used as an electrical distribution system from the solar arrays to the microwave converters, temperature level will also be required to establish the electrical resistance of the conductors. Reference 11 states that the antenna power transmission distribution will be Gaussian in cross-section. With the present method of rejecting heat from the microwave converters, the radiant heat flux to the antenna support structure will also have a Gaussian distribution. Figure 3. 3-9 gives such a distribution for a 1 km diameter antenna transmitting 10 GW with a microwave converter efficiency of 90%. The maximum structural temperature will occur in the member that is closest to the center of the antenna where the radiant flux is maximum. Temperature magnitude will depend on the ratio of the element, the geometric shape of the element, to a minor extent the distance of the element from the antenna surface (for distances up to 50 meters the variation is less than 5°K) and, to a major extent, the magnitude of the radiant flux at the center of the antenna. This last factor depends on microwave converter efficiency, spacing and power transmitted. Figure 3.3-10 shows maximum structural temperatures as a function of transmitted power for three antenna diameters and two microwave converter efficiencies. The three basic trends are: (1) increasing the transmitted power increases the maximum structural temperature, (2) increasing the efficiency of the microwave power converter decreases the maximum structural temperature, and (3) increasing the diameter of the antenna decreases the maximum structural temperature. After completion of Task 1, Raytheon selected the following values for the antenna parameters (Ref 13):
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