inflatable bag to provide the interior of the tank. This uses the tank primarily for micrometeorite protection and insulation. Setup is quick, clean, and very simple. Additional partitions can be inflated, erected, or unfolded in the tank to fit the needs and requirements inside. As an aside, inflatables also have a long successful history in the American space program. These inflatables were the Echo I and II reflective communications satellites flown in the early 1960s. The hydrogen tank will provide a huge space - over 53,500 cubic feet - which is five to ten times larger than any proposed space station module that is known of at this writing (25). Once again, the advantage to the use of the ET is large size and availability for use after a single launch. The program savings here are mainly in launch and orbital construction costs. In addition to the Hydrogen tank, the liquid oxygen tank is also available for use as a habitat. The early studies on External Tank applications by Marshall Space Flight Center proposed the adaptation of the oxygen tank to a manned mission as a first step (12). There are a few disadvantages to its use which are useful to mention. These include a slightly more difficult access problem due to the location of the manholes and intertank section, more internal hardware to consider due to the slosh baffles, and a shape that is less than optimum for the use of the entire tank for habitation. These disadvantages make the early use of the oxygen tank less attractive than the hydrogen tank and the ET/ACC combination. However, it may serve very nicely as water storage facility, a lifeboat, a passive life support habitat, a cryogenics storage facility, a biological experimentation station, or a farm in conjunction with an ET/ACC based space station (25,56, 95). It also has a very large volume - comparable with Skylab (70) - which will be useful in future applications in orbit. B. Hangar or servicing platform in the Hydrogen Tank The Hydrogen tank can also be turned into a hangar for satellite and vehicle servicing and repair. The top dome of the tank can be removed completely, swung aside, or removed and converted into a hangar door. The tank can also be left open as an unpressurized servicing facility. The Space Operations Center (SOC) studies of the late 1970s suggested a hangar and/or berthing facility be developed for this purpose. As a hangar, the ET can serve this purpose quite nicely with a minimum of modifications. If a
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