Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Appendix K: Facility Reboost Studyreboost.Thrust Efficiency:The thrust efficiency is shown in the bottom graph of Figure 2. The graph shows that the thrust efficiencyvaries cyclically during each day; this variation is due to the fact that the Earth, and its magnetic field,are rotating inside the facility’s orbit, and thus the angle between the geomagnetic field’s axis and theorbit plane varies once per day. In addition, not apparent on this timescale, the thrust efficiency varieswith altitude and with the angle of the tether relative to local vertical. Over this three day period, theaverage thrust efficiency is 33.5 µN/W (thrust efficiency calculated using the power input to the electrodynamictether).Reboost Time: Since the rate of semimajor axis increase varies during the reboost operation, the best wayto estimate the time needed to reboost the orbit is to assume that the rate at which the orbital energy ofthe system is increased is relatively constant during the reboost period. To reboost the orbit from370x5732 km to 385x8938 km, the electrodynamic system must restore 100 GJ of energy to the tetherfacility’s orbit. In the 3-day simulation, the electrodynamic thrusting restored the facility’s orbital energyPerigee Altitude (km)Apogee Altitude (km)Perigee Velocity (m/s)3903853803753700 0.5 1 1.5 2 2.5 3Time (days)60506000595059005850580057500 0.5 1 1.5 2 2.5 3Time (days)873087258720871587100 0.5 1 1.5 2 2.5 3Time (days)Figure 3. Perigee and apogee altitude, and perigee velocity during the first three days ofthe reboost operation.K-5