Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Tether RendezvousDelayed CatchIn real-world missions, the payload and tether will likely have positional and/or velocity errors at thetime of rendezvous. The system can utilize the tether deployment method described above to extend therendezvous window for a number of seconds to allow time for the payload and PCV to maneuver toachieve a secure docking. When the PCV pays out tether to extend the rendezvous window, however,the centrifugal acceleration of the PCV relative to the tetherÕs center of mass causes it to build up avelocity along the direction of the tether. In the 1 km/s, 100 km long tether system studied here, the tipaccelerationlevel is approximately 1 gee. Thus, after a 5-second deployment maneuver, the PCV will bedeploying tether at a rate of almost 50 m/s. When the PCV captures the payload, it must stop the tetherdeployment. This will cause an additional tension spike on the tether.Figure 10 shows plots of the load level of the tether tip in simulations where the deployment isbrought to a halt in varying lengths of time, from an immediate halt (0.1 s braking) to a gradual braking1Load Level0.80.60.40.1 s braking5 s braking10 s braking20 s braking30 s braking0.200 10 20Time (s)30 40 50Figure 10. Load level on the segment of tether nearest the payload after a payload capture. In thesesimulations, the PCV pays out tether for 5 seconds to facilitate rendezvous, and then slows the tetherdeployment using braking.Length Deployed (m)1000009980099600994009920030 s braking20 s braking10 s braking5 s braking0.1 s braking99000010 20 30 40 50Time (s)Figure 11. Total length of tether deployed during a payload capture maneuver. In these simulations, thePCV pays out tether for 5 seconds to facilitate rendezvous, and then slows the tether deployment usingbraking.8