Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Tether RendezvousUsing Deployment At Controlled Tension To Dampen Reflected Tension WaveAlthough at first consideration it might seem preferable to deploy all of the stored tether during theinitial braking, inspection of Figure 10 and Figure 11 reveals that there is little difference in the maximumtension if the tether deployment is braked over 5 seconds (using 150 m of tether) or if the tetherdeployment is braked over 30 seconds (using 850 m of tether). It may, therefore, be most advantageous tobrake the initial tether deployment relatively quickly, and then use the tether remaining on the deployerto reduce the tension excursion experienced when the reflected tension wave returns to the tether tip.The idea here is to allow the tether to deploy under lower tension when the reflected wave reaches thetether tip. Figure 14 shows the total length of tether deployed for such a maneuver. From T=0 to T=5, thetether is deployed at minimum tension to extend the rendezvous window. The deployment is thenbrought to a halt in 10 seconds. Ten seconds later, when the first tension wave returns tot he tether tip,the PCV again pays out tether, this time at a controlled tension. Figure 15 shows the tip load level forsimulations with and without this additional deployment maneuver. Comparison of the traces indicatesthat the additional deployment succeeds in reducing the peak tension from 0.6 of the tetherÕs capacity tojust over 0.5 of capacity; if the PCV had more tether on the spool, it could reduce the maximum tensioneven further. Note also that this additional deployment actually prevents the tether from going slack atT=60. Figure 16 shows the tether load level at the tip, middle, and facility end of the tether during thisrendezvous maneuver.100000Deployed Length (m)99800996009940099200990000Capture after 5 sec.Deployment Braked over 10 sec.Additional Deployment atcontrolled tension from 25s-35s20 40 60 80 100Time (s)Figure 14. Total length of tether deployed during rendezvous maneuver in which the PCV deploys thetether for 5 seconds to facilitate rendezvous, then captures the payload and slows the deployment over aperiod of 10 seconds, and then later allows the tether to deploy under controlled tension to dampen thetether tension wave.10