Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Rapid Interplanetary Tether Transport SystemsIAF-99-A.5.10experiences apsidal precession, the angle λ willhave the proper value only periodically.Consequently, in our designs we will seek tochoose the orbital parameters such that theapsidal precession of the orbit will have aconvenient resonance with the Moon's orbit.Elliptical-Orbit Tether Boost FacilityIn the Cislunar Tether Transport System, thetransfer of payloads between a low-LEO andlunar transfer orbits is performed by a singlerotating tether facility. This facility performs acatch and release maneuver to provide thepayload with two boosts of approximately1.5Êkm/s each. To enable the tether to performtwo ÒseparateÓ ∆V operations on the payload,the facility is placed into a highly ellipticalorbit with its perigee in LEO. First, the tetherrotation is arranged such that when the facilityis at perigee, the tether is swinging verticallybelow the facility so that it can catch a payloadmoving more slowly than the facility. After i tcatches the payload, it waits for one orbit andadjusts its rotation slightly (by reeling the tetherin or out) so that when it returns to perigee, thetether is swinging above the facility and it canrelease the payload into a trajectory movingfaster than the facility.HEFT Tether Boost FacilityIn order to enable the Earth-orbit tetherfacility to boost materials to the Moon before alunar base has been established and beginssending return payloads back to LEO, we proposeto combine the principle of rotating momentumexchangetethers with the techniques ofOrbitalVelocityThrustTorqueEarth's MagneticFieldGrapple VehicleJxB ForcePlasma ContactorCenter of MassCurrentFacilityHigh StrengthConducting TetherPlasma ContactorPayloadFigure 4. Schematic of the HEFT Facility design.electrodynamictether propulsion tocreate a facility capable of reboostingits orbit after each payload transfer withoutrequiring return traffic or propellant expenditure.This concept, the ÒHigh-strength ElectrodynamicForce TetherÓ (HEFT) Facility, 10 is illustrated inFigure 4. The HEFT Facility would include acentral facility housing a power supply, ballastmass, plasma contactor, and tether deployer,which would extend a long, tapered, highstrengthtether. A small grapple vehicle wouldreside at the tip of the tether to facilitaterendezvous and capture of the payloads. Thetether would include a conducting core, and asecond plasma contactor would be placed near thetether tip. By using the power supply to drivecurrent along the tether, the HEFT Facility couldgenerate electrodynamic forces on the tether. Byproperly varying the direction of the current asthe tether rotates and orbits the Earth, thefacility can use these electrodynamic forces togenerate either a net torque on the system toincrease its rotation rate, or a net thrust on thesystem to boost its orbit. The HEFT Facility thuscould repeatedly boost payloads from LEO to theMoon, using propellantless electrodynamic propulsionto restore its orbit in between eachpayload boost operation.Tether DesignIn order to design the tether boost facility, wemust determine the tether length, rotation rate,and orbit characteristics that will permit thetether to rendezvous with the payload and throwit into the desired lunar transfer trajectory.In the baseline design, the payload begins ina circular Initial Payload Orbit (IPO) with avelocity ofV = µep,0 . (6)rThe facility is placed into an elliptical orbitwith a perigee above the payloadÕs orbit, withthe difference between the facilityÕs initialperigee and the payload orbital radius equal tothe distance from the tether tip to the center ofmass of the facility and tether:r = r + ( L− l ), (7)IPOp, 0 IP0cm,unloadedwhere l cm,unloaded is the distance from the facility tothe center of mass of the system before the5