Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Cislunar Tether TransportMoon once per month. 8A third method is to choose the tether orbitssuch that their precession rates are nearlyharmonic with the MoonÕs orbital rate, so thatthe line of apsides lines up with the MoonÕs nodesonce every several months.LEO⇒GTO Payload TransferThe same Tether Boost Facility can, bychanging its initial orbit and rotation rate, boost2,500 kg payloads from a 308 km circular orbit togeostationary transfer orbit. To perform thisLEO⇒GTO boost operation once per month, thesystem must have a 150 kW solar power array,and expend the collected energy at a rate of 450kW during perigee passes. The Control Stationshown in Figure 5 is sized with a 200 k W(beginning of life) solar array.System ModularityThe Tether Boost Facility concept has beendesigned to enable it to be grown incrementally.After the initial facility, capable of tossing 1000kg to LTO and 2,500 kg to GTO, has been deployedand tested, a second module of nearly identicalhardware can be launched and combined in aparallel fashion with the first module, asillustrated in Figure 7. This will increase thesystemÕs capacity to 2,000 kg to LTO and 5,000 kgto GTO. The parallel construction will provideredundancy to the system, reducing the need forredundancy within each module. Cross-linkingbetween the two parallel tethers could be addedto increase their redundancy. Additional modulescan be launched to increase the system capacityfurther.Design of a Lunavator ª Compatiblewith Minimal-Energy Lunar TransfersThe second stage of the Cislunar TetherTransport System is a lunar-orbit tether facilitythat catches the payloads sent by the Earthorbittether and deposits them on the Moon withzero velocity relative to the surface.Background: MoravecÕs Lunar SkyhookIn 1978, Moravec 9 proposed that it would bepossible to construct a tether rotating around theMoon that would periodically touch down on t h elunar surface. MoravecÕs ÒLunar SkyhookÓ wouldhave a massive central facility with two tetherarms, each with a length equal to the facilityÕsorbital altitude. It would rotate in the samedirection as its orbit with a tether tip velocityequal to the orbital velocity of the tetherÕscenter-of-mass so that the tether tips wouldperiodically touch down on the Moon with zerovelocity relative to the surface (to visualize this,imagine the tether as a spoke on a giant bicyclewheel rolling around the Moon).As it rotates and orbits around the Moon, t h etether will capture payloads from Earth as theyreach perilune and then set them down on t h esurface of the Moon. Once round-trip traffic isestablished, the tether could simultaneously pickup payloads to be returned to Earth, and later tossthem down to LEO.Lunavator ª DesignIn order to minimize the ∆V requirementsplaced upon the Earth-orbit portion of theCislunar Tether Transport System and therebypermit the use of a single Earth-orbit tether witha reasonable mass, we have developed a methodfor a single lunar-orbit tether to capture apayload from a minimal-energy lunar transferorbit and deposit it on the tether surface withzero velocity relative to the surface.Moon-Relative Energy of a Minimum-Energy LTOA payload that starts out in LEO and is injectedinto an elliptical, equatorial Earth-orbit with anapogee that just reaches the MoonÕs orbital radiuswill have a C 3 relative to the Moon ofapproximately 0.72 km 2 /s 2 . For a lunar transfertrajectory with a closest-approach altitude ofseveral hundred kilometers, the payload willhave a velocity of approximately 2.3 km/s a tperilune. As a result, it would be moving tooslowly to rendezvous with the upper tip ofFigure 7. Tether Boost Facility with two modules, capable of tossing 2000 kg to LTO. (Tether length not to scale)7