ET Project - Structures This section will discuss the structural advantages in an ET based operation. The tank can be partially to completely disassembled in orbit without excessive difficulty. The SOFI can be stripped and discarded or used for other needs. The tank can be cut into pieces and those pieces either used for construction or melted or powdered for other needs. In addition to applications mentioned in other sections, the ET itself can be used as a structural member, workbench, or platform for the construction or deploment of large structures. It also can be used to conduct experiments on large structures as a testbed. The advantage of the strongback/testbed concept is that the ET is fully suited for future growth and expansion with the addition of more ETs, ET/ACC combinations, ACCs, or other modules. I. Disassembly of the ET in orbit A. SOFI Any operation which proposes the structural use of the ET needs to remove the SOFI from the ET exterior. The SOFI is sprayed on the ET over an adhesive base. The adhesive is extremely effective, so much so that the removal of the SOFI from the tank sections on the ground is done with fiberglass scrapers in a very dirty, labor intensive job (48). This type operation will be unacceptable in flight. Work on the subject by the California Space Institute has proposed several methods which should work well in orbit (15, 56, 95). The best choice for removal appears to be the space equivalent of a hot wire 'cheese slicer*. Tests indicate cutting rates better than 33 feet per hour (15, 56). The problem with this technique is that there remains a thin layer of SOFI after the operation. The tradeoff here is how much contamination can the cutting, melting, or construction operation tolerate (92)? If the layer needs to be removed there are several removal methods. It can be stripped over the space of a month or two by molecular oxygen impact (14). It can be removed by a ’Weed Eater' type rotary device or wire brush. This operation would tend to dirty up the vicinity of the station quickly with small bits of debris. It can also be removed thermally by use of a solar fumance or an electron beam gun (56).
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