V. SPS CONSTRUCTION AND MAINTENANCE SYSTEM A. System Requirements and Analysis The large size and low density of an SPS and the advantages of not designing for launch loads dictate an orbital fabrication and assembly approach to construction of the SPS. The complex elements or components such as antenna rotary joints and control system modules can be manufactured on the ground for assembly into the overall system. Other components such as the microwave generators, solar cell blankets, concentrator sheets, and power distribution harnesses are amenable to dense packaging for launch and deployment in orbit. SPS structure is low density in its final configuration when designed for orbital loading conditions. The packing density of fold-deploy systems is much too low for efficient operation of the transportation system. In addition, structural joint design and launch loading conditions have an adverse effect on structural weight. An alternative is to manufacture the structure in orbit. Concepts under current consideration include the use of automatic machines that generate structural elements from preprocessed stock as illustrated in figure V-l. Combinations of the machines are utilized to build trusses for the primary structure. Another candidate for orbital manufacture is the antenna subarray. The waveguides of the phased array must be built to very precise geometry, yet the finished product has very low density. By fabricating the subarrays on orbit, problems with launch loading and low density packaging can be avoided. Figure V-l.- Beam builder machine concept.
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