Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

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Tethers Unlimited, Inc.Appendix R: MERITT ArchitectureMars-Earth Rapid Interplanetary Tether Transport(MERITT) ArchitectureRobert L. Forward 1 , Gerald D. Nordley 21 Tethers Unlimited, Inc. 8114 Pebble Court, Clinton, WA 982362 Consultant, 1238 Prescott Avenue, Sunnyvale CA 94089-2334Phone: +1- 360-579-1340 Email: forward@tethers.comAbstract. Routine travel to and from Mars demands an efficient, rapid, low cost means of two-way transportation. Toanswer this need, we have invented an architecture consisting of two spinning tether systems in highly elliptical orbitsabout each planet. At Earth, a payload is picked up near periapsis and tossed a half-rotation later, still near periapsis, at avelocity sufficient to send the payload on a high-speed trajectory to Mars. At Mars, it is caught near periapsis and isreleased a short time later on a suborbital reentry trajectory. The system works in both directions and is reusable. Energyand momentum lost by the throwing tethers can be restored either by catching incoming payloads or by propellantlesstether propulsion methods. Tethers with tip velocities of 2.5 km per second can send payloads to Mars in as little as 90days if aeroslowing is used at Mars. Tether-to-tether transfers without aeroslowing may be accomplished in about 130 to160 days. Tether systems using commercially available tether materials at reasonable safety factors can be as little as 15times the mass of the payload being handledINTRODUCTIONThe idea of using orbiting spinning tethers to pick up and toss payloads has been in the tether literature for decades(Cosmo and Lorenzini, 1997). Forward (1991) and Hoyt (1997) have combined a number of spinning tetherconcepts to show that such tethers could move payloads from a suborbital trajectory just above the Earth'satmosphere to the surface of the Moon and back again, without any use of rockets except to get out of the Earth'satmosphere. Forward and Nordley (1999) then showed in their paper "Mars-Earth Rapid Interplanetary TetherTransport (MERITT) System", that orbiting spinning tethers would also provide two-way transport between Earthand Mars. Work on the Earth-Moon and Earth-Mars systems is continuing under a $500,000 grant from the NASAInstitute for Advanced Concepts, and the presentation at the meeting will cover the latest results from that study.MERITT ARCHITECTURE DESCRIPTIONThe Mars-Earth Rapid Interplanetary Tether Transport (MERITT) Architecture consists of two essentially identicalrapidly spinning tether facilities in highly elliptical orbits: EarthWhip around Earth and MarsWhip around Mars. Apayload capsule is launched from Earth into a low orbit or suborbital trajectory. The payload is picked up by agrapple system on the EarthWhip tether as the tether nears perigee and the tether arm nears the lowest part of itsswing. It is tossed later when the tether is still near perigee and the arm is near the highest point of its swing. Thepayload thus gains both velocity and potential energy at the expense of the tether system, and its resulting velocity issufficient to send it on a high-speed trajectory to Mars with no onboard propulsion needed except for midcourseguidance. At Mars, the incoming payload is caught in the vicinity of periapsis by the grapple end of the MarsWhiptether near the highest part of its rotation and greatest velocity with respect to Mars. The payload is released laterwhen the tether is near periapsis and the grapple end is near the lowest part of its swing at a velocity and altitudewhich will cause the released payload to enter the Martian atmosphere. The system works in both directions. TheMERITT system can give shorter trip times with aerobraking at Mars because the incoming payload velocity is notlimited by the maximum tether tip velocity and thus payloads can use faster interplanetary trajectories.R-1
Tethers Unlimited, Inc.Appendix R: MERITT ArchitectureDETAILED MERITT EXAMPLEThere are a large number of variables in the MERITT system concept, and many of those variables can be freelychosen at the start of the system design. We have carried out dozens of complete round-trip scenarios under variousdifferent assumptions, such as: aerobraking before tether catch versus direct tether-to-tether catch; sub-, circular, andelliptical initial and final payload orbits; 1.5, 2.0, 2.5 and higher tether tip velocities; large, small and minimumtether central facility masses; etc. We will present here just one of the many possible MERITT scenarios usingfinite mass EarthWhip and MarsWhip tethers, but do it in extensive detail so the reader can understand where thebroad assumptions are, while at the same time appreciating the accuracy of the simulations between the broadassumptions. In most cases, the matches between the payload trajectories and the tether tip trajectories are accurateto 3 and 4 decimal places.The scenario we will describe uses EarthWhip and MarsWhip tethers of near minimum mass made of Spectra2000 with a tip speed of 2.0 km/s. Because they have small total masses, the toss and catch operations significantlyaffect the tether rotation speed, center of mass, and orbital parameters, all of which are taken into account in thesimulation. The payload is assumed to be initially launched from Earth into a suborbital trajectory to demonstrate tothe reader that the MERITT system has the capability to supply all of the energy and momentum needed to move thepayload from the upper atmosphere of the Earth to the upper atmosphere of Mars and back again. We don't have askthe payload to climb to nearly Earth escape before the MERITT system takes over. In practice, it would probably bewise to have the payload start off in an initial low circular orbit. The energy needed to put the payload into a lowcircular orbit is not that much greater than the energy needed to put the payload into a suborbital trajectory with anapogee just outside the Earth's atmosphere. The circular orbit option also has the advantage that there would beplenty of time to adjust the payload orbit to remove launch errors before the arrival of the EarthWhip tether. In theexample scenario, the payload, in its suborbital trajectory, is picked up by the EarthWhip tether and tossed fromEarth to Mars. At Mars it is caught by the MarsWhip tether without the use of aerobraking, and put into a trajectorythat enters the Martian atmosphere at low velocity. Since this scenario does not use aerobraking, the return scenariois just the reverse of the outgoing scenario.Payload MassWe have chosen a canonical mass for the payload of 1000 kg. If a larger payload mass is desired, the masses of thetethers scale proportionately. The scenario assumes that the payload is passive during the catch and throwoperations. In practice, it might make sense for the payload to have some divert rocket propulsion capability toassist the grapple during the catch operations. In any case, the payload will need some divert rocket propulsioncapability to be used at the midpoint of the transfer trajectory to correct for injection errors.Tether MassBoth the EarthWhip and MarsWhip tethers were assumed to consist of a robotic central station, two similar tethers,two grapples at the ends of the two tethers, and, to make the analysis simpler, one grapple would be holding adummy payload so that when the active payload is caught, the tether would be symmetrically balanced. The tethercentral station would consist of a solar electric power supply, tether winches, and command and control electronics.There may be no need to use center of mass rocket propulsion for ordinary tether operations. Both tethers can beadequately controlled in both their rotational parameters and center-of-mass orbital parameters by "gravity-gradient"propulsion forces and torques generated by changing the tether length at appropriate times in the tether orbit. TheEarthWhip tether would also have a small conductive portion of the tether that would use electrodynamic tetherpropulsion, where electrical current pumped through the tether pushes against the magnetic field of the Earth to addor subtract both energy and angular momentum from the EarthWhip orbital dynamics, thus ultimately maintainingthe total energy and angular momentum of the entire MERITT system against losses without the use of propellant.The grapple mechanisms are assumed in this scenario to mass 20% of the mass of the payload, or 200 kg for a1000 kg payload. It is expected, however, that the grapple mass will not grow proportionately as the payload massincreases to the many tens of tons needed for crewed Mars missions. In the scenario presented here, it is assumedthat the grapples remain at the ends of the tethers during the rendezvous procedure. In practice, the grapples willcontain their own tether winches powered by storage batteries, plus some form of propulsion. As the time forR-2
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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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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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Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

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