Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Appendix Q: SMART White PaperAPPLICATION OF SYNERGISTIC MULIPAYLOAD ASSISTANCE WITH ROTATING TETHERS(SMART) CONCEPT TO OUTER PLANET EXPLORATION. Gerald David Nordley 1 , Robert L. Forward 2and Robert P. Hoyt 2 , 1 Consultant , 2 Tethers Unlimited, Inc., 19011 36th Ave. W, Suite F,Lynnwood, WA 98036 [www.tethers.com].Introduction: We propose an innovative approachto outer planet exploration using the Synergistic MultipayloadAssistance with Rotating Tethers (SMART)concept invented by Gerald David Nordley. The basicconcept can be implemented in many different ways toaccomplish many different types of planetary missions,especially missions to the outer planets.SMART Concept: A pair of spacecraft are connectedby a tether, set to rotating about their commoncenter of mass, and injected into a hyperbolic orbitaround a massive planet. The tether is caused to separateas the combined system approaches the periapsisof the hyperbolic orbit. The spacecraft which is rotating"backward" relative to the hyperbolic flight pathreceives a velocity decrease at separation which causesit to go into a lower energy orbit, typically an ellipticalcapture orbit about the planet. The spacecraft thatis rotating "forward " with respect to the hyperbolicflight path gets a velocity increase which will cause itto exit the gravitational field of the planet with ahigher velocity than it entered. In effect, each payloadacts as the reaction mass for the other. Because thevelocity increments obtained from the tip speed of thetether take place deep in the gravity well of the massiveplanetary body, they are "amplified" by the highperiapsis velocity to produce significant changes in thefinal trajectories of the two separated bodies.Combined Pluto/Europa Mission: Figure 1 illustratesthe use of the SMART concept to carry outboth the Pluto Flyby mission and the Europa Orbiter/Landermission with one launch. The combinedsystem arriving from Earth is moving 5.6 km/s slowerthan Jupiter. The velocity of the incoming systemreaches 42.5 km/s at a periapsis of two Jupiter radii.With the tether giving the Pluto payload a 1 km/s increasein this velocity, the Pluto payload reaches ahyperbolic excess velocity with respect to Jupiter of10.9 km/s, almost double what it had as it enteredJupiter's gravity field. Adding this velocity to Jupiter'sorbital velocity gives a velocity of 23.9 km/s forthe Pluto injection velocity. For the Europa payload,a ∆V of only 400 m/s from the tether is sufficient toprovide capture into an elliptical orbit about Jupiter.Table I shows the results on the parameters of the twomissions of using different tether tip speeds.Table I - Post-Periapsis Payload TrajectoriesTether Tip Capture Pluto Inj. Pluto Trip TetherVelocity Orbit Velocity Time Mass(km/s) (days) (km/s) (years) Ratio0.0 ∞ 18.7 11.6 -0.4 1473 21.2 10.2 0.050.6 102 22.2 9.3 0.120.8 41 23.1 8.6 0.221.0 24 23.9 8.0 0.36The tether mass ratio was determined using the wellknowntether mass ratio formulas for fail-safe interconnectedmultistrand tethers [1] and assuming a 50%improvement in tether strength in the coming years.Other Outer Planet Applications: The SMARTconcept can be used in many other ways than a dualmission. Either the Pluto mission or the Europa mission,or any other mission to any other planet coulduse the dead mass of the Earth escape injection stage asreaction mass. Any mission putting a payload intoorbit around Jupiter could retain a conductive portionof the tether and use it to obtain both power and propulsion.With the tether available to provide the instantaneousthrust at periapsis, any mission could beredesigned to use efficient electric propulsion andcompletely eliminate the need for chemical propulsion.Comparison With Rocket Assist: The mass ofthe tether necessary to obtain the necessary ∆V at periapsisin the SMART concept is typically comparableto the mass of the storable propellant and tanks neededto obtain a comparable ∆V. Detailed analyses will berequired to determine the exact mass comparison numbersfor each mission example. Rockets have moreflight heritage, but one would think that the reliabilityand accuracy of a tether system that imparts all if itsexactly known mechanical energy at a single point intime by the action of a simple mechanical separationsystem would be better than the release of an uncertainamount of chemical energy over a long burn time initiatedby a complex ignition sequence.CFIG. 1 - SMART CONCEPT USED FORDUAL PLUTO/EUROPA MISSIONPLUTO PAYLOADGO ES ON TO PLUTOTETHER CUT ±1 km/s ∆VORBITAL MOTIONEUROPA PAYLOAD CAPTURED INTO ELLIPTICAL ORBITD UAL PROBE FROMI NNER SOLAR SYSTEMReferences:[1] Forward, R.L. and Hoyt, R.P., "The Hoytether:A Failsafe Multiline Space Tether Structure", Proceedingsof the Tether Technology Interchange Meeting,Huntsville, AL (9-11 Sept 1997).Acknowledgements: This work was partiallysupported by the NASA Institute for Advanced Concepts,Robert Cassanova, Director .Q - 2