6. ESTIMATED MASS STATEMENT FOR 5 GW SPS This section gives an estimate of the non-lunar mass required in an SPS. It includes estimates of the lunar fractions of all subsystems of the 5 GW silicon planar SPS described in reference 1, listed by Work Breakdown Structure (WBS) number. For each subsystem, the composition was estimated and lunar materials were substituted where possible. In many cases, subsystems have been re-designed for better utilization of lunar materials; these changes are described in section 6.2. Design alternatives are also described as appropriate. Many of the lunar substitutions required no design change. These substitutions were not made in the General Dynamics study because that study did not attempt substitutions in systems which comprised less than 1.22 of the SPS mass. Table 6-1 lists the estimated mass and lunar content of each subsystem studied. Some WBS numbers are not used in the silicon planar configuration. 6.1 GENERAL ASSUMPTIONS Most structural members are assumed to be made of aluminum alloy, with no non-lunar material. An exception is the microwave transmitter structure, which was assumed to be made of foamed glass because of the stringent flatness requirements and the demanding thermal environment of the transmitter. Any wires or cables which traverse distances of at least a meter are assumed to use aluminum conductor and some form of glass fabric insulation, so these cables require no non-lunar material. Radiators are assumed to be heat pipe radiators. The worst case encountered for these is 802 aluminum fins, 182 stainless steel heat pipes, and 22 working fluid. We estimate 982 lunar fraction for radiators in general; 99.62 lunar if water can be used as coolant and heat pipe fluid. 6.2 EXPLANATIONS OF SUBSYSTEM MASS STATEMENTS WBS 1.1.1.1: Primary Array Structure. The actual mass of the primary structure will vary greatly with the final design, but the aluminum composition is unlikely to change. If it does change, it will probably become titanium or a glass-aluminum composite, which should require no non-lunar material. WBS 1.1.1.3: Solar Array The silicon planar array described in section 2.1 is assumed. The only non- lunar material required in this design is less than one kilogram of dopant in the silicon cells. The most likely alternative to silicon planar is the GaAs concentrator system, which would require less than 100 tons of non-lunar material in the solar array. WBS 1.1.1.4: Power Distribution This WBS number does not include energy storage or the electrical slipjoint. Acquisition buses are assumed to be 1002 lunar aluminum, as are the main buses.
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