Tethers may be used to mediate Shuttle-to-space-station rendezvous. One part of the space station may be a transportation node, which serves as a service and propellant transfer area and as a momentum storage device. The Shuttle could be launched into a 73- by 400-kilometer direct-insertion trajectory and rendezvous with a 55-kilometer tether hanging down from the space station at Shuttle apogee. The tether would then be reeled in to recover the Shuttle. After the Shuttle completed its operations at the space station, it could be swung down and back at the end of the 55-kilometer tether.
Such tethered rendezvous between the Shuttle and the space station have a flexibility that contributes to both safety and reliability. The multistrand tether would have an orbital maneuvering vehicle at its tip; both would be deployed and checked before the Shuttle was launched. If the tether broke during the 6 hours between deployment and rendezvous, the OMV could take the Shuttle to the station. If both the tether and the OMV failed, the Shuttle could use its orbital maneuvering system (OMS) to climb to the space station's altitude, provided it carried enough OMS propellant. If it did not, then the Shuttle could abort to a lower orbit and await another OMV, if one was available. The probability that one strand of a tether would be cut by micrometeoroids during a 6-hour period is less than once in 1250 flights for a tether sized to take the required load. The probability that the OMV would fail during this time is also low.
The chances of successful rendezvous are also enhanced by the tether method. If the Shuttle failed to rendezvous with the tether tip, the OMV could be released to rendezvous with the co orbital Shuttle using freefall techniques. (in this case, it would be necessary to burn OMS fuel to raise the Shuttle's perigee to about 185 kilometers to prevent reentry.)
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