Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

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Rapid Interplanetary Tether Transport SystemsIAF-99-A.5.10TetherPeriapsisafterincomingrelease(ready foroutboundpickup)∏ rTether Periapsis at capture∏ c(following last outbound releaseand maneuvers)Periapsis of∏ x aerobraking∆ω r-u Tc exit orbit∆u (aerobraking)Tc∆ω a ∏u xc i Periapsis ofincoming orbit-u inf (om di - π/2)= π - (A 2 - u inf )Planetorbit∏ rω iA 2Tether Orbit Inbound StateLow energy, periapsis nearantisolar pointTether Orbit Outbound StateHigh energy, periapsis rotatedcounter-clockwiseHyperbolicasymptoteof outboundpayloadorbitToSunOutboundtrajectoryInboundtrajectoryvi 2 = v u2 + v r2Hyperbolicasymptoteof inboundpayloadorbitv r(sun) = v r(orbit)- v r(planet)Trajectory of patch pointv u(orbit)A 22π + A 1v u(planet)v u(rel) = v u(orbit) -v u(planet)Figure 23. "Planet"Whip showing catch and toss states using aerobraking.The scenario we will describe usesEarthWhip and MarsWhip tethers of nearminimum mass made of Spectra ª 2000 with a tipspeed of 2.0 km/s. Because they have small totalmasses, the toss and catch operationssignificantly affect the tether rotation speed,center of mass, and orbital parameters, all ofwhich are taken into account in the simulation.The payload is assumed to be initially launchedfrom Earth into a suborbital trajectory todemonstrate to the reader that the MERITTsystem has the capability to supply all of theenergy and momentum needed to move thepayload from the upper atmosphere of the Earthto the upper atmosphere of Mars and back again.We don't have ask the payload to climb to nearlyEarth escape before the MERITT system takesover.In practice, it would probably be wise to havethe payload start off in an initial low circularorbit. The energy needed to put the payload intoa low circular orbit is not that much greater thanthe energy needed to put the payload into asuborbital trajectory with an apogee just outsidethe Earth's atmosphere. The circular orbit optionalso has the advantage that there would beplenty of time to adjust the payload orbit to25
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
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Tethers Unlimited, Inc.MMOSTT Final
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NIAC Funded Tether Research• Moon
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Electrodynamic Reboost• Power sup
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Cislunar Tether Transport System•
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MXER Tethers Included in NASA’sII
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5mt Payload Tether Boost Facilityfo
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LEOGTO Boost Facility• Initial Fa
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Tether Boost FacilityControl Statio
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LEOGTO Boost Facility• TetherSim
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Rendezvous• Rapid AR&C Capability
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Proposed RETRIEVE TetherExperiment
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µTORQUE on Delta IV• Delta-IV Se
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Opportunities for NASATechnology De
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AIAA 2000-3842COMMERCIAL DEVELOPMEN
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--Commercial Tether Transport AIAA
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-Commercial Tether Transport AIAA 2
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Commercial Tether Transport AIAA 20
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Commercial Tether Transport AIAA 20
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Momentum Exchange/Electrodynamic Re
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DESIGN AND SIMULATION OF A TETHER B
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Tether Boost Facility Design AIAA 2
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Tethers Unlimited, Inc.Cislunar Tet
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Interim Report Outline- Configurati
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Mission Definition¥ Payload Capaci
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Baseline Control Station DetailsTET
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Baseline Grapple AssemblyCAPTURES A
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LEO Facility System ArchitectureGRA
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Payload Adapter Assembly Subsystems
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Potential Reeling FunctionsReeling
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LEO Control Station Weights16
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Payload Adapter Assembly Weights18
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Tether Boost FacilityRequired Power
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Electrical Propulsion Voltage´ Spe
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Potential Reeling FunctionsReeling
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Preliminary Reeling AnalysisθθAss
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Tether Boost FacilitySystem Require
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Table of Contents1 Scope ..........
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2 ReferencesThis section lists docu
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The system shall measure and contro
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4 Ground Rules & AssumptionsThis se
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Appendix F: Tether Boost Facility D
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Appendix F Tether Boost Facility De
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Appendix F Tether Boost Facility De
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Appendix L: Tether Boost Facility D
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Tethers Unlimited, Inc.Tether Rende
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Ongoing Tether Work Under NIAC Fund
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Cislunar Tether Transport System•
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Rapid Earth-Mars Transport• Reusa
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EarthMars Launch Windows• MMOSTT
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Page 278 and 279: IAF-00-S.6.04The LEO⇒GTO Tether B
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NOMENCLATURESymbol MeaningA payload
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DepartureangleA = 1.5π - (ω + u
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Tether material has a "characterist
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Rendezvous of Grapple with PayloadT
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adius vector to the new center of m
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days from payload pickup at one pla
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"JupiterandBeyond"Tether cut CUT:<
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Tethers Unlimited, Inc.Appendix Q:
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Tethers Unlimited, Inc.Appendix R:
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