Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Rapid Interplanetary Tether Transport SystemsIAF-99-A.5.10remove launch errors before the arrival of theEarthWhip tether.In the example scenario, the payload, in itssuborbital trajectory, is picked up by theEarthWhip tether and tossed from Earth toMars. At Mars it is caught by the MarsWhiptether without the use of aerobraking, and putinto a trajectory that enters the Martianatmosphere at low velocity. Since this scenariodoes not use aerobraking, the return scenario is justthe reverse of the outgoing scenario.Payload MassWe have chosen a canonical mass for thepayload of 1000 kg. If a larger payload mass isdesired, the masses of the tethers scaleproportionately. The scenario assumes that thepayload is passive during the catch and throwoperations. In practice, it might make sense forthe payload to have some divert rocketpropulsion capability to assist the grapple duringthe catch operations. In any case, the payloadwill need some divert rocket propulsioncapability to be used at the midpoint of thetransfer trajectory to correct for injection errors.Tether MassBoth the EarthWhip and MarsWhip tetherswere assumed to consist of a robotic centralstation, two similar tethers, two grapples at theends of the two tethers, and, to make theanalysis simpler, one grapple would be holding adummy payload so that when the active payloadis caught, the tether would be symmetricallybalanced.The tether central station would consist of asolar electric power supply, tether winches, andcommand and control electronics. There may be noneed to use center of mass rocket propulsion forordinary tether operations. Both tethers can beadequately controlled in both their rotationalparameters and center-of-mass orbitalparameters by "gravity-gradient" propulsionforces and torques generated by changing thetether length at appropriate times in the tetherorbit. 11,13,The EarthWhip tether would also have asmall conductive portion of the tether that woulduse electrodynamic tether propulsion, 18 whereelectrical current pumped through the tetherpushes against the magnetic field of the Earth toadd or subtract both energy and angularmomentum from the EarthWhip orbitaldynamics, thus ultimately maintaining the totalenergy and angular momentum of the entireMERITT system against losses without the use ofpropellant.The grapple mechanisms are assumed in thisscenario to mass 20% of the mass of the payload,or 200 kg for a 1000 kg payload. It is expected,however, that the grapple mass will not growproportionately as the payload mass increases tothe many tens of tons needed for crewed Marsmissions.In the scenario presented here, it is assumedthat the grapples remain at the ends of thetethers during the rendezvous procedure. Inpractice, the grapples will contain their owntether winches powered by storage batteries, plussome form of propulsion.As the time for capture approaches, thegrapple, under centrifugal repulsion from therotation of the tether, will release its tetherwinches, activate its propulsion system, and flyahead to the rendezvous point. It will then reelin tether as needed to counteract planetarygravity forces in order to "hover" along therendezvous trajectory, while the divert thrustersmatch velocities with the approaching payload.In this manner, the rendezvous interval can bestretched to many tens of seconds.If needed, the rendezvous interval can beextended past the time when the tip of the tetherpasses through the rendezvous point by havingthe grapple let out tether again, while using t h edivert thrusters to complete the payload capture.The grapple batteries can be recharged betweenmissions by the grapple winch motor/dynamos,by allowing the grapple winches to reel outwhile the central winches are being reeled inusing the central station power supply. Thegrapple rocket propellant will have to beresupplied either by bringing up "refueling"payloads or extracting residual fuel frompayloads about to be deorbited into a planetaryatmosphere.For this scenario, we assumed that, whenloaded with a payload, the EarthWhip andMarsWhip tethers were rotating with a tethertip speed of V T = 2,000 m/s. The length of eachtether arm was chosen as L=400 km in order tokeep the acceleration on the payload, G=V T2 /L,near one gee. We also assumed that the totalmass of the Whips are 15,000 kg for a 1000 kg26