Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

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Tether Boost Facility Design AIAA 2000-3866Figure 7. LEFT: Tether Boost Facility initial orbit (yellow ellipse) and payload initial orbit (red circle). RIGHT:Tether Facility orbit after payload boost (inner yellow ellipse) and Payload GTO (red outer ellipse).Simulation of Electrodynamic ReboostAs the Tether Boost Facility catches and tosses apayload into GTO, its orbit drops, as illustrated inFigure 7. The apogee drops 2340 km, and the perigeedrops 16 km. To restore the orbit, the tether systemmust increase the facilityÕs orbital energy by 54 GJ, andit will do so by performing electrodynamic thrustingwhile the tether is within the dense portion of the ionospherenear the perigee of its orbit. Because the tether isrotating, the direction of the current must be alternatedas the tether rotates to produce a net thrust on the facility.Using the TetherSim ª program, we have modeledreboost of a rotating tether system to investigate theefficiency of the reboost, and to develop methods forcontrolling the electrodynamic thrust to achieve thedesired final orbit.Method:To study the performance of electrodynamic reboostof the tether facility, TetherSim ª was used to simulatereboosting of the orbit of the Tether Boost Facilitydescribed in Table 1 over a period of two days. TetherSim ªis a numerical simulation tool that includesmodels for tether dynamics, orbital mechanics, electrodynamics,thermal behavior, geopotential, geomagneticfield, ionospheric density variations, neutral gas densityvariations, and other relevant physics.In the simulations, thrusting was performed when thetether facilityÕs altitude was under 2000 km. The electrodynamictether system had hollow-cathode plasmacontactors at both ends of the conducting tether, so thatit could carry current in both directions. The thrustingwas performed at a maximum power of 450 kW. TheControl Station contained a 150 kW solar power supply,a 8500 A¥hr (120 V) battery system. Peak tethercurrent levels were limited to 20 A, with typical currentsvarying between 15 and 20 A. In addition, thrustingwas performed only when the tether was within ¹/4of vertical.ResultsReboost SimulationsFigure 8 shows the orbit semimajor axis, and Figure9 shows the orbit eccentricity during the two days ofboosting simulated. The semimajor axis increases at52 km/day. Note that if the electrodynamic boost systemadds energy to the orbit at a constant rate, the rateof semimajor axis increase will accelerate due to theinverse relation between orbital energy and semimajoraxis. The eccentricity increases at 0.0034/day. Notethat the eccentricity change rate will also vary duringreboost. Figure 10 shows the apogee altitude increase.Thrust Efficiency:The thrust efficiency is shown in Figure 12. Thegraph shows that the thrust efficiency varies cyclicallyduring each day; this variation is due to the fact thatthe Earth, and its magnetic field, are rotating inside thefacilityÕs orbit, and thus the angle between the geomagneticfieldÕs axis and the orbit plane varies once perday. In addition, not readily apparent on this timescale,the thrust efficiency varies with altitude and withthe angle of the tether relative to local vertical. Overthis one day period, the average thrust efficiency is 40µN/W (thrust efficiency calculated using the power inputto the electrodynamic tether).Reboost Time:Since the rate of semimajor axis increase varies duringthe reboost operation, the best way to estimate the timeneeded to reboost the orbit is to assume that the rate atwhich the orbital energy of the system is increased isrelatively constant during the reboost period. To reboostthe orbit from 391x6105 km to 407x8445 km,the electrodynamic system must restore 54 GJ of energyto the tether facilityÕs orbit. In the 2-day simulation,the electrodynamic thrusting restored the facilityÕsorbital energy at a rate of 2.7 GJ/day, as illustrated inFigure 11.7
Tether Boost Facility Design AIAA 2000-3866Semimajor Axis (km)97209700968096609640962096000 10 20 30 40Time (hours)Figure 8. Semimajor axis during the first two daysof the reboost operation.Energy (GJ)-490-492-494-496-498-5000 10 20 30 40Time (hours)Figure 11. Orbital Energy.0.3180Eccentricity0.3050.30.295Thrust Efficiency (µN/W)7060504030200.290 10 20 30 40Time (hours)Figure 9. Orbit eccentricity.Apogee Altitude (km)63006250620061506100605060000 10 20 30 40Time (hours)Figure 10. Apogee altitude1000 10 20 30 40 50Time (hours)Figure 12. Thrust efficiency.Current (A)20151050-5-10-15-202.2 2.4 2.6 2.8 3Time (hours)Figure 13. Current driven through the electrodynamictether during a perigee pass.8
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Tethers Unlimited, Inc.MMOSTT Final
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Page 16 and 17: Tethers Unlimited, Inc.MMOSTT Final
Page 24 and 25: NIAC Funded Tether Research• Moon
Page 26 and 27: Electrodynamic Reboost• Power sup
Page 28 and 29: Cislunar Tether Transport System•
Page 30 and 31: MXER Tethers Included in NASA’sII
Page 32 and 33: 5mt Payload Tether Boost Facilityfo
Page 34 and 35: LEOGTO Boost Facility• Initial Fa
Page 36 and 37: Tether Boost FacilityControl Statio
Page 38 and 39: LEOGTO Boost Facility• TetherSim
Page 40 and 41: Rendezvous• Rapid AR&C Capability
Page 42 and 43: Proposed RETRIEVE TetherExperiment
Page 44 and 45: µTORQUE on Delta IV• Delta-IV Se
Page 46 and 47: Opportunities for NASATechnology De
Page 48 and 49: AIAA 2000-3842COMMERCIAL DEVELOPMEN
Page 50 and 51: --Commercial Tether Transport AIAA
Page 52 and 53: -Commercial Tether Transport AIAA 2
Page 54 and 55: Commercial Tether Transport AIAA 20
Page 56 and 57: Commercial Tether Transport AIAA 20
Page 58 and 59: Momentum Exchange/Electrodynamic Re
Page 60 and 61: DESIGN AND SIMULATION OF A TETHER B
Page 62 and 63: Tether Boost Facility Design AIAA 2
Page 70 and 71: Tethers Unlimited, Inc.Cislunar Tet
Page 82 and 83: Interim Report Outline- Configurati
Page 84 and 85: Mission Definition¥ Payload Capaci
Page 86 and 87: Baseline Control Station DetailsTET
Page 88 and 89: Baseline Grapple AssemblyCAPTURES A
Page 90 and 91: LEO Facility System ArchitectureGRA
Page 92 and 93: Payload Adapter Assembly Subsystems
Page 94 and 95: Potential Reeling FunctionsReeling
Page 96 and 97: LEO Control Station Weights16
Page 98 and 99: Payload Adapter Assembly Weights18
Page 100 and 101: Tether Boost FacilityRequired Power
Page 102 and 103: Electrical Propulsion Voltage´ Spe
Page 104 and 105: Potential Reeling FunctionsReeling
Page 106 and 107: Preliminary Reeling AnalysisθθAss
Page 108 and 109: Tether Boost FacilitySystem Require
Page 110 and 111: Table of Contents1 Scope ..........
Page 112 and 113: 2 ReferencesThis section lists docu
Page 114 and 115: 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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Incremental Development Path1. TORQ
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LEOGTO Boost Facility• TetherSim
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Tether Boost FacilityControl Statio
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Modular Design• Design Components
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Payload Accommodation AssemblyConfi
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Electrodynamic Thrusting• Drive c
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Tether Facility Reboost• Use Elec
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Rendezvous• Rapid Automated Rende
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Rendezvous Method: Preparation• P
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Development Issues• Automated Ren
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Potential Flight Experiments• Hig
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Opportunities for NASATechnology De
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Acknowledgements• Boeing/RSS - Jo
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IAF-99-A.5.10RAPID INTERPLANETARY T
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Rapid Interplanetary Tether Transpo
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IAF-00-S.6.04TETHER SYSTEMS FOR SAT
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IAF-00-S.6.04controlled very precis
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IAF-00-S.6.04Perigee Altitude (km)3
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IAF-00-S.6.04The LEO⇒GTO Tether B
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IAF-00-S.6.04AcknowledgmentsThis re
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Tethers Unlimited, Inc.Appendix K:
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Tethers Unlimited, Inc.at a rate of
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Tethers Unlimited, Inc.Appendix L -
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Tethers Unlimited, Inc.Appendixm M:
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Appendix N. MXER Tether for Deployi
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Electrodynamic Thrustingto Reboost
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100000 95000 90000 85000 80000 7500
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Momentum Exchange/Electrodynamic Re
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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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Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

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