Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Appendix K: Facility Reboost Studywhere L 1 is the new distance from the tether tip to the system’s center-of-rotation (=COM).Facility Orbit After Payload Toss:After tossing the payload, the new facility radius and velocity are:rfacility,2=r, 1( M + M + M )− r, 2MM + MCOM facility tether payload payload payloadfacilitytether(6)Vfacility,2( )−V, 1M + M + M V, 2M=M + MCOM facility tether payload payload payloadfacilitytether, (7)and we again use Eqns. (1) & (2) to calculate the new semimajor axis a 2 and eccentricity e 2 .In order for the tether boost facility to prepare itself to boost another payload, it must restore itsorbital parameters to the original values of a and e.Simulation MethodThe simulation was performed using the TetherSim numerical code. This run utilized the IGRFmagnetic field model and a heuristic plasma density model based upon IRI data for equatorial orbits.The model was run for 3 days of simulation time.System DesignThe Tether Boost Facility system design used in this simulation is detailed in Table 1. The orbitalparameters of this system were chosen to make the facility’s pre-catch orbit and the payload’s initial orbitresonant with a 36:17 ratio, so that they have a rendezvous opportunity approximately once every twodays. This choice of resonance enables the facility’s control station mass to be relatively small, just over 4times the payload mass, and the facility’s total mass is under 7 times the payload mass. Before payloadcatch, the facility is in a 385x8938 km elliptical orbit, and after payload toss it drops into a 370x5732 kmorbit. The geometry of the facility and payload GTO orbits immediately after payload toss, and thedesired final facility orbit and the payload GEO orbit are shown in Figure 1.Reboost Thrust OperationIn this simulation, the tether facility included an electrodynamic tether system in which a 500 kgaluminum conductor was included in 60 km of the tether length. The electrodynamic tether system hadFigure 1. LEFT: Orbital geometry of tether system immediately after payload toss. The inner yellowellipse is the facility’s post-toss orbit, and the outer ellipse is the payload’s geo-transfer orbit. The blueline is the vector to the sun, and the red line is the vector to the moon. RIGHT: Desired orbital geometry ofthe tether system at the end of reboost. The outer yellow circle is the payload’s geostationary orbit, andthe inner ellipse is the facility’s high-energy orbit.K-2