IV. History Interest in the spent stages of launch vehicles has been a part of the American manned space program since the days of Gemini. The USAF proposed the Manned Orbiting Lab (MOL) program in the early 1960s as a DOD space station. This utilized the upper stage of a Titan booster and a modified Gemini capsule as the space platform. This program had crews selected before it was cancelled. The Skylab program following Apollo utilized the Saturn V third stage as the heart of a space station. The program used Apollo hardware intended for lunar flight as a space platform. In the planning stage, there was serious consideration given to actual on orbit construction of the Skylab. This did not happen because a Saturn V booster came available to launch a ground constructed platform and because there was concern that Hydrogen leaking out of the spend third stage insulation (inside the tank - not outside, like the ET) would pose a fire hazard. The American space program is historically very good at adapting hardware from the intended to a new use. On orbit use of the ET is nothing new from this perspective. V. Costs and ramifications of ET applications As mentioned previously, the ET is attractive primarily due to launch costs and capabilities that do not exist in other launch systems. For example, the scavenging of residual cryogenics from the ET alone can give a program savings of $3.5 billion when compared to the cost of launching the same cryogenics in the payload bay to support an Orbital Transfer Vehicle (OTV) operation (29, 32, 69). A partial disassembly of the ET on-orbit and construction of a hangar out of the hydrogen tank will eliminate the need to design and launch a maintenance structure in the orbiter. The savings here is the difference between on-orbit construction using the ET and the design, launching, and on-orbit construction of a specialized structure. The capabilities that do not exist with current or planned operations that the ET can provide are limited only by the imagination. These have been broken down into the following areas: 1. External Tank Description - What properties of the ET can we take advantage of? How is it put together?
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