8. 43 While some success has been had in welding large surfaces of compound curvature, especially in the aerospace and shipbuilding industry (8.9), it has only been done in workshop type situations with the help of large, heavy hold down bars and sometimes the special tongue-and-groove milling of the edges to be welded. It is felt that the large scale welding is free space of large sections held in place only by a crane, or for that matter by any other device, is virtually impossible (8.12). Thus it was decided that threaded fasteners would be used to hold together section, bulkhead and major stiffener pieces. Fasteners have the advantages that the hole through both pieces being connected can be drilled at once assuring proper alignment at the time of assembly (as outlined in Section VIII.5.3.3). Further, as two pieces are assembled using fasteners, there is no force pushing the pieces apart or out of line. Instead, when one fastener is put in, it tends to pull the next hole into alignment. Fasteners were chosen instead of rivets because they tend to hold tighter over a long period of periodic loading. Of course, fasteners also have their disadvantages. The hole for each must be drilled and each fastener installed, but the estimates of time required are not prohibitive (Sections VIII.5.3.3 and VIII.7.3.2). The inspection of each hole for flaws must be done (as discussed in Section VIII.8.4) and the section and stiffener must be designed to transfer load through a row of fasteners (Section VII.5.3). The fastener design was chosen because it provides a simpler assembly operation and because it seems that all the problems discussed above can be overcome. VIII.7.3.2: Assembly Sequence: Now that the construction site, shacks, and fastener system have been presented, it is simple to describe the colony assembly sequence. The final fabrication shack produces a finished hull section or inter-hull bulkhead once every 17 hours (average). Recall that the fabrication shack is a depressurized area with one open (or openable) end. The hoist moves to a position alongside this shack and uses its manipulator arms to pull
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