The "column-cable" concept (figure A-26) emphasized a very efficient use of compression and tension members to minimize structural weight. In the "column-cable configuration", orthogonal central columns were stabilized by cables with the solar cell blankets stretched on the cables also. Construction facilities necessarily were dispersed because the configuration had to grow symmetrically to be structurally stable. Equipment to install solar cell blankets and power distribution had to be supported on the satellite structure and cables. In order to provide a continuous automatic assembly process, a long narrow geometry was conceived called the "truss configuration" (figure A-27). Structural efficiency was sacrificed to improve construction. Structure was automatically fabricated and the concentrator membranes, solar cell blankets and power distribution were installed from a facility which was the full width of the SPS. In later designs, this approach is exemplified by the Rockwell International extrusion concept (figure A-28). This concept results in a facility with a size and shape similar to the cross section of the SPS. The "extrusion" concept features uniform generation of longitudinal structure with solar cell blankets and power distribution (figure A-29) added as the structure leaves the facility. An alternative concept is the Boeing configuration (figure A-30) which builds a structural bay then steps one bay to build the next bay while solar cell blankets and power distribution are installed in the just completed bay. Thermal engine satellite configurations are relatively more difficult to construct than photovoltaic system because the geometry is irregular and they require large active systems with fluids systems associated with the heat absorber cavity and thermal radiators (figures A-31 and A-32). The concentrating reflectors must approximate a parabolic segment. Building the concentrator support in a cylindrical shape (figure A-33) was an improvement, but constructability has remained one of several disadvantages of the thermal conversion approach relative to photovoltaic configurations. Launch Vehicle Packing Density - The capability to handle the construction logistic requirements in a manner that minimizes the impact on the HLLV is an important economic factor. The HLLV payload volume for efficient
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