The Materials Transportation costs are evaluated for a low altitude assembly site only. The high altitude option was deopped because of the non-competitive costs (see Subsection 3.5.2). The cost of transporting assembly crews and in-flight processing modules are not included under this cost element. Assembly costs for the structural materials (i. e., aluminum and graphite composites) options considered were assumed the same. The results of the assembly cost comparison (Subsection 3.5.2) were used to establish a proportionate cost for support equipments, SEP transportation cost, etc. based on antenna weight relative to the entire SSPS. The assembly cost of structure varies with the number of joints or pieces of material that must be assembled and is independent of the properties or weight of the material. 3.5.3.1 Materials and Manufacturing Costs The microwave power transmission section of the orbiting solar energy collector can be designed from advanced composite material or aluminum to meet three criteria. These are (a) 30-year life, (b) low or zero thermal expansion and (c) operating temperature range between 450°K and 480°K. This structure can be designed as thin-wall tubes, 3-6 inches in diameter, 18m (60 ft) or less in length, or as thin (0. 010) slats which roll up to a helix 4. 6m (15 ft) in diameter. A summary of material and processing costs are given in Fig. 3. 5-17 for several candidates. Thermal control coating costs are included. Material costs were obtained during the week of August 19, 1974 from Grumman purchasing agents, who are in direct contact with vendors and who used most recent purchase orders and quotes as their basis. These costs are listed in Fig. 3.5-17 as "present material cost", and would be the price paid today for a large quantity order. The only exception is 2-mil-thick graphite/epoxy 3-inch-wide tape whose price would drop from 726 $/Kg ($330 per lb) (which is the small batch cost) to less than 210 $/Kg ($100 per lb) for large volume orders; a firm price could not be obtained from the vendors. Minimum prices shown in Fig. 3.5-17 are generally the same as present prices or are based on recent prices (e.g. 236 $/Kg ($107/lb) for boron/epoxy in January 1974), projected near term lower costs (e.g. 44 $/Kg ($20/lb) for graphite/epoxy) or different forms of the material (e.g., Kevlar prices, aluminum alloy types).
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