3. ORBITAL OPERATIONS A combination of interrelated design and analytical tasks were conducted to define operational processes and facility requirements. From concepts generated in the study, each major mass- and dimensionally-sensitive subsystem was analyzed to develop assembly processes. Depending on the subsystem configuration and materials, each process should reflect a near-optimum combination of man and machine which yields a realistic assembly schedule. These processes ranged from continuous-flow to discrete element assemblies, with the former typically preferred. As the system processes, crew requirements and support equipment were defined, they were combined and iterated to resolve schedule conflicts and to develop assembly sequences, overall crew sizes, and assembly timelines. 3.1 STRUCTURES FABRICATION The structure configuration described in Section 2.1 is built up from 2-meter triangular shaped beams. Each beam is roll-formed in space from pre-punched, thin gage aluminum sheets. Figure 3.1-1 shows the flat pattern and some of the hole flanging and roll form operations required to process the thin sheet-metal ribbon into a side sub-element of the equilateral triangular beam. Figure 3.1-2 is a cutaway view of the SPS structural element fabricator designed to provide an in-space, continuous fabricator of the triangular beam elements. Prepunched material transported in rolls to the structural fabrication facility (to be discussed) are loaded into cassettes. These(cassettes are then installed on the supply end of a beam machine. The material in each cassette is automatically threaded into and through the beam machine. Initially, the sheet material enters a shear station where the material rolls are longitudinally indexed. The material next passes into a hole-flanging and strutforming station. At entry to this station, rolls turn up a small 0.5-cm edge which, when passing through the beam fabricator, maintains a cross-load on the sheet when flanged and brake-formed to prevent loss of flat pattern width control. The material then progresses through longitudinal roll forms and is guided through the ribbon cross-over station into a roll seam welder used in a spaced spot-weld mode. The assembled sheet metal element next passes through the prestressing and alignment station where three sheet-metal shrinking-heads shorten and thicken the ribbon cross-braces. Tension-sensing elements control the operation on the basis of preload and alignment requirements fed into the machine from a central computer. The finished triangular shape exits the beam fabricator via a truss-rigging station. Here cable connections, quick-connects, and fittings are installed, when required, that permit the next higher level of assembly by automatic means. Six beam machines are required to produce one 50-meter triangular truss (Figure 3.1-3).
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