The ET can also be used as a part of any space station. It can be partially disassembled to make a hangar or easily turned into a space station habitation module of a far larger volume than any past, present, or future space station module. The oxygen tank can be turned into a liquid or gas storage reservoir. The cost savings by ET utilization in these operations are unspecified at this time. However, any specially designed space station module which will fill the needs addressed above must be compared against the ET in two ways. The first comparison is launch cost. With the ET, you get a large rigid body already in orbit. You must lift anything else at $2000 per pound. The second comparison concerns possible future expansion of the structure. If a future expansion is being planned, then the costs of R&D and on-orbit construction from the STS pay load bay during an EVA must be compared to the cost of on-orbit modification of a body that is already in space. This analysis should show in most cases, that the adaptation of an orbiting ET will provide enormous cost savings to the program. In addition, the use of the ET as part of a manned space effort will give the program a new perspective. As soon as the ET is inserted into orbit, the program has made large, massive, structurally strong bodies available to prospective users at a very low cost. The volume restrictions for manned habitations are removed. The storage limitations for liquids and gases are removed. This means that a specially designed structure does not need to be planned, sold to uninterested congressmen, launched, and constructed over a period of several flights. The planning turns to an emphasis on the adaptation of structures already in orbit. This adaptation will take a bit more EVA time, (at over $40,000 per hour), but the savings in launch cost alone will more than cover the difference. III. ET as a Propellent Resource Analysis of future requirements for space based operations show the largest mass requirement is for fuels. These include OTV operations, satellite launch and recovery, and space station orbital maintenance. NASA has a requirement for 2.5 million pounds of propellents over the next ten years. Analysis based on this requirement show the scavenging of residual cryogenics from the ET can fill up to 92X of the requirement at a total cost
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