Space Studies Institute Report on Space Shuttle External Tank Applications by J. Alex Gimarc 12-01-1985 copyright Space Studies Institute B. Shuttle to Station Advantages There are significant advantages in placing the tether in a space station and only launching the orbiter partway to the altitude of the station. This is refered to as Tether Mediated Rendezvous (16). The basic idea is to launch the STS to a highly elliptical orbit that intersects that of the end of a space station mounted tether 41 - 47 minutes after launch. The orbiter will rendezvous with the tip of the tether using the ET nose itself as a docking probe for the Orbiter/ET. After the docking is complete, the stack is winched the remaining 40 - 55 km up to the station. The advantages include the delivery of several tons of OMS fuel to the space station holding tanks for future use in OTV operations, the delivery of the ET and Orbiter to the station, the settling of the residual cryogenics and possible scavenging of them during the winching procedure into tether mounted holding tanks. All of these advantages translate directly into fuels delivered to the station. There is also an additional safety factor in the use of the ET as the docking probe. The ET nose will protect the nose and windows of the orbiter from possible impact with the tether tip by being 50 feet closer to the tip than the orbiter itself. This appears at first glance to be a procedure that requires precise timing. This is partially true in that it does inflict another constraint on the launch timing itself and continue to narrow the launch window. The arrival at the tether is timed based on midcourse corrections flown enroute and the venting of residuals as they slowly boil off for thrust through cold-gas engines. The orbiter arrives at the tip of the tether with sufficient OMS fuel to conduct several abort scenarios. The mission rules should always allow the orbiter to carry enough OMS fuel to complete the rendezvous in case the tether technique does not work for whatever reason. The strategy also allows the orbiter to ’brute force* the departure and reentry by the use of the OMS engines. It is important to point out that there are three levels of success in this plan. The most successful mission would be one that allows the orbiter to dock with the tether tip with a minimum of hovering, delay, or the requirement to ’wave off’ the docking for another orbit. This delivers the maximum OMS fuel to the station in the minimum time. An intermediate success would be an OMS bum for rendezvous with the station and a tethered release for departure. This allows the scavenging of the OMS fuel necessary for an unaided release for the station
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