ET Project - Tethers Tethers are essentially long flexible ’ropes' which connect two bodies. They have been suggested for a number of future space applications which are meaningful when discussing External Tank uses in space. The following section will detail possible tether enhancements of space shuttle, space station, and ET based missions. I. Introduction Tethers are important to future operations in space for several reasons. These include momentum transfer and storage, energy storage, stabilization and control enhancements, controllable microgravity environments, structural strength of a tether based rotating station, and electrical power generation and/or propulsion. Any operation that can take advantage of tethers for these applications will expand capabilities significantly. Enhancements of the energy and momentum storage, structural strength, and attitude control translate directly to increased capabilities without the increased launch costs (13, 56, 84). The basic tether makes use of the dynamics of long flexible bodies in orbit. Typically, two bodies are connected by a tether of some length (on the order of miles in some proposals) and either swung around one another or left to dangle in a gravity gradient stabilized mode. Tether based stabilization can be accomplished in a gravity gradient mode, a swinging or rotating (librating) mode, or in a drag stabilized mode. The more massive that the body is on either end of the tether, the more energy it takes to move it and disturb the structure. The ET is ideally suited for tethers due to its large inexpensive mass on-orbit. This allows it to be used as a counterweight or momentum storage device for either static or librating tethers. It also is suited to tethers because it is the strong structural member of the STS stack. In an ET based tether application, tethers can be attached to the SRB attach points and the Orbiter attach points and the ET can be spun up (50, 56). Tensile loads on the ET are far lower than those during launch. This allows a substantial safety margin without tank modifications.
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