Note that this parameter is independent of the configuration geometry. For pure aluminum at 100°F, and */ith a solar array weight-to-power ratio of 2.13 gm/watt, the resulting current density is 558 amp/cm2. This value was used to design the bus structure, and for a given bus configuration and geometry, a quick check of the cooling was made to insure that the system would run at, or below, the design temperature. Conductor Bus Design Concepts The preceding section developed the distribution bus system based on the assumption of constant current density which specifies the amount of material required for the conduction of electricity. The geometrical shape of the conductor is largely a thermal problem. The ideal geometry is a thin flat sheet since it maximizes the radiative surface area to cross-section area. Alternately, large diameter thin-walled tubes are attractive if the bus is to become a structural member. The thin flat sheet geometry leads to the consideration of using the aluminum solar array concentrators as conductors. A one-half mil thickness will provide sufficient cross-section to maintain the current density at the specified level for the configurations analyzed and are ideally oriented for passive cooling. While this concept offers a significant weight savings, several problems require additional research. For example, it may be difficult to maintain uniform current distribution and uniform resistivity throughout the conductor. Nonuniform effects could cause localized heating and adverse distortion of the reflective surface. A design compromise may be possible which would increase the thickness beyond that required for a concentrator in order to provide better electrical, thermal, and mechanical properties. If the "conductive foil" concept proves valid, the flat sheet geometry can be extended to the main bus system carrying power to the transmitting antenna. If the load-carrying structural truss cross-section is square or rectangular, the flat sheet conductors would be attached to the sides of the load-carrying structural truss. The juncture between the concentrator and the main bus is a curved sheet extension of the reflector surface transitioning smoothly to the main bus for electrical continuity
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