This table shows that pure aluminum is the most weight-efficient material to use as a conductor to minimize resistive losses. A similar figure of merit combining density and thermal conductivity would show that aluminum is superior for passive radiative cooling. Based on the above, pure aluminum has been selected as the nominal conductor material with structural (6061) aluminum to be used if the electrical busses are integrated with a load-carrying structure. The desirability of integrating the distribution system with the structure or other subsystem components needs to be evaluated at the configuration synthesis level since it is not clear, at this point, that the advantages outweigh the problems associated with the integration. A key will be the weight savings which can be obtained by integration. If only a small percentage of the total configuration weight can be saved, it may be more appropriate to minimize the integration aspects until more of the total problem is understood. System Conductor Weight The technique used to establish the overall bus system weight was to find an "optimum" current density (amperage per cross-sectional area of conductor) which would minimize the bus weight relative to resistance (I2R) losses. That is, for a given current flow, the weight of conductor material (Wg) can be reduced by permitting larger current densities with at- tendent increases in temperature and I2R losses. Temperature considerations aside, a convenient method of rapidly arriving at an acceptable current density is to assume that the power losses will have to be made up by additional solar array area and that the area will weigh K gm/watt. The additional weight (W^) to compensate for the I2R losses will be:
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