Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Rapid Interplanetary Tether Transport Systemsenough total mass so that it will not be driveninto an escape orbit from Mars.The final orbit for the tether is found to havea periapsis radius of 4078 km (676 km altitude sothat the tether tip never goes below 253 kmaltitude), a periapsis velocity of 4,503 m/s, anapoapsis radius of 115,036 km, an eccentricity of0.931, and a period of 6.65 sol. The tether remainswithin the gravity influence of Mars and is in itshigh energy state, ready to pick up a payloadlaunched in a suborbital trajectory out of t h eMartian atmosphere, and toss it back to Earth.Elapsed TimeThe total elapsed transit time, from captureof the payload at Earth to release of the payloadat Mars, is 157.9 days. This minimal massPlanetWhip scenario is almost as fast as moremassive PlanetWhip tethers since, although thesmaller mass tethers cannot use extremely high orlow eccentricity orbits without hitting theatmosphere or being thrown to escape, the timespent hanging on the tether during those longerorbit counts as well and the longer unbalancedgrapple arm of the lightweight tether lets i tgrab a payload from a higher energy tether orbit.SummaryWe have developed tether system architecturesfor Earth-Luna and Earth-Mars payloadtransport. Our analyses have concluded that theoptimum architecture for a tether systemdesigned to transfer payloads between LEO andthe lunar surface will utilize one tether facilityin an elliptical, equatorial Earth orbit and onetether in low lunar orbit. We have developed apreliminary design for a 80 km long Earth-orbittether boost facility capable of picking payloadsup from LEO and injecting them into a minimalenergylunar transfer orbit. Using currentlyavailable tether materials, this facility wouldrequire a mass 10.5 times the mass of thepayloads it can handle. After boosting apayload, the facility can use electrodynamicpropulsion to reboost its orbit, enabling thesystem to repeatedly send payloads to the Moonwithout requiring propellant or return traffic.When the payload reaches the Moon, it will becaught and transferred to the surface by a 200 kmlong lunar tether. This tether facility will havethe capability to reposition a significant portionof its ÒballastÓ mass along the length of thetether, enabling it to catch the payload from aIAF-99-A.5.10low-energy transfer trajectory and then Òspin-upÓso that it can deliver the payload to the Moonwith zero velocity relative to the surface. Thislunar tether facility would require a total mass ofless than 17 times the payload mass. Bothequatorial and polar lunar orbits are feasible forthe Lunavator ª . Using two different numericalsimulations, we have tested the feasibility ofthis design and developed scenarios fortransferring payloads from a low-LEO orbit tothe surface of the Moon, with only 25 m/s of ∆ Vneeded for small trajectory corrections. Thus, i tappears feasible to construct a Cislunar TetherTransport System with a total on-orbit massrequirement of less than 28 times the mass of thepayloads it can handle, and this system couldgreatly reduce the cost of round-trip travelbetween LEO and the surface of the Moon byminimizing the need for propellant expenditure.Using similar analytical techniques, we haveshown that two rapidly spinning tethers inhighly elliptical orbits about Earth and Mars canbe combined to form a similar system thatprovides rapid interplanetary transport from asuborbital trajectory above the Earth'satmosphere to a suborbital trajectory above theMartian atmosphere and back.AcknowledgmentsThis research was supported by a Contract07600-011 from NASAÕs Institute for AdvancedConcepts, Dr. Robert A Cassanova, Director; andin part by the Tethers Unlimited, Inc. IR&Dprogram.References1. M.L. Cosmo and E.C. Lorenzini, Tethers In SpaceHandbook - Third Edition, prepared forNASA/MSFC by Smithsonian AstrophysicalObservatory, Cambridge, MA, Dec 1997.2. Paul A. Penzo, "Tethers for Mars Space Operations,"The Case For Mars II, Ed. C.P. McKay, AAS Vol. 62,Science and Technology Series, pp. 445-465, July1984.3. Paul A. Penzo, "Prospective Lunar, Planetary, andDeep Space Applications of Tethers," Paper AAS 86-367, AAS 33rd Annual Meeting, Boulder, CO, Oct1986.4. Carroll, J. "Preliminary Design for a 1 km/s TetherTransport Facility," NASA OAST Third AnnualAdvanced Propulsion Workshop, JPL, Pasadena, CA,30-31 Jan 1992.5. Forward, R. L., ÒTether Transport from LEO to theLunar Surface,Ó AIAA paper 91-2322, July 1991.30