ET Project - Executive Summary This report will review possible applications of the External Tank (ET) of the Space Transportation System (STS) in orbit. Enhancements of the space program through ET utilization in orbit will be covered in depth. Problems will be reviewed. Recommendations will be made. This report is intended to make a coherent case for the use of the External Tank in the American space program. I. Tank Introduction The ET is carried almost to orbit with the orbiter and jettisoned with approximately 98% of the energy necessary to insert it in orbit. When jettisoned, each ET carries internally an average of 15,000 pounds of residual cryogenic fuels. These residuals are available for scavenging from the tank in a variety of scenarios. The availability of cryogenics already in orbit can potentially fuel planned OTV operations at a cost far lower than if the cryogenics are carried aloft in a tanker version of the orbiter. The ET mass is over 69,000 pounds. Of this mass, there are approximately 53,000 pounds of aerospace grade aluminium. This aluminium can be cut, melted, powdered, welded, and manipulated to suit any number of present and future structural needs. If the tanks are partially disassembled in orbit, the pieces can also be reassembled in the construction of large structures. The oxygen and hydrogen tanks making up the ET provide two factory tested pressure vessels that are two to five times larger in volume than any space station yet flown or planned for the future. These large volumes are clean and able to be entered through inspection manholes in the respective tank domes. The on-orbit adaptation of the respective tank interiors for habitation, storage, or maintenence facilities will require minimal time and effort. There are two major problems with the use of the ET in orbit. The first and most critical is orbital maintenance. This is a result of the desire not to randomly drop large bodies on the surface of the earth from space. At typical STS orbits (160 - 220 nautical miles), the orbital lifetime of a tank inserted into a parking orbit can be measured in days to months. A plan
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