V. Additional ET Enhancements There are several additional ET enhancements which have been proposed (25). These include a Forward Cargo Carrier (FCC), an exterior track system, an interior track array, and a variety of flanges for opening the end of the tank for orbital applications. With the exception of the FCC, all the enhancements are relatively inexpensive and easy to add to the tank. The FCC is the same size as the ACC and can carry a similar payload. It does not require the protective shroud that the ACC does. However, it poses a larger problem than the ACC because it will require additional mass and structure in the intertank and possibly the hydrogen tank to support the loads imposed by it on the tank. This makes the impact of the FCC greater on the STS program and thus increases the potential costs of the FCC. This cost increase due to program impact and increased tank costs may not be as attractive as the ACC. The next enhancements are the interior and exterior rails or tracks. These tracks allow things like mobile robots, mobile cranes, interior hangar operations, the attachment of station modules to the exterior of the tank, and the possible use of the tank itself as a linear accelerator. The track/rail enhancement will allow a variety of tank enhancements which utilize the structural strength and inertia of the tank (25). The last class of proposed enhancements are lumped together as things that will make the tanks easier to attach together end to end, easier to enter, and easier to attach external payloads for launch. These include flanges, attach hardware, large seals, hangar hinges, a variety of entry hatches, and additional hardware. These all are relatively simple enhancements that are inexpensive, lightweight, and easy to add to a tank (25).
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