Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Cislunar Tether TransportEcliptici mMoon'sEquatorialPlaneMoon'sOrbiti eλ mEarth'sEquatorialPlaneTo sunFigure 1. Conceptual illustration of the CislunarTether Transport System.Orbital Mechanics of the Earth-Moon SystemOrbital mechanics in cislunar space are madequite complex by the different and varyingorientations of the ecliptic plane, the EarthÕsequatorial plane, the MoonÕs orbital plane, andthe MoonÕs equatorial plane. Figure 2 attempts toillustrate these different planes. The inclinationof the EarthÕs equatorial plane (the Òobliquity ofthe eclipticÓ), is approximately 23.45¡, but variesdue to tidal forces exerted by the Sun and Moon.The angle i m between the MoonÕs equatorial planeand a plane through the MoonÕs center that isparallel to the ecliptic plane is constant, about1.58¡. The inclination of the MoonÕs orbit relativeto the ecliptic plane is also constant, about λ m =5.15¡. 5 The line of nodes of the MoonÕs orbitregresses slowly, revolving once every 18.6 years.As a result, the inclination of the MoonÕs orbitrelative to the EarthÕs equator varies between18.3-28.6 degrees. The MoonÕs orbit also has aslight eccentricity, approximately e m = 0.0549.Tether OrbitsAfter considering many different options,including the three-tether systems proposed previouslyand various combinations of ellipticaland circular orbits, we have determined that theoptimum configuration for the Cislunar Tethersystem is to utilize one tether in an elliptical,equatorial Earth orbit and one tether in acircular, polar lunar orbit, as illustrated in Figure1. This two-tether system will require the lowesttotal system mass, minimize the systemcomplexity and provide the most frequenttransfer opportunities. The Earth-orbit tetherwill pick payloads up from equatorial low-LEOFigure 2. Schematic illustrating the geometry of theEarth-Moon system.orbits and toss them towards one of the two pointswhere the Moon crosses the EarthÕs equatorialplane. The toss is timed so that the payloadreaches its apogee ahead of the Moon. The Moonapproaches the payload from behind, and itsgravity causes the payloads velocity to slow andthen reverse, pulling it into a hyperbolic polarlunar trajectory. As the payload approaches theMoon, it will need to perform a small ∆ Vmaneuver to set it up into the proper approachtrajectory; the size of this maneuver will varydepending upon the inclination of the MoonÕsorbit plane and launch dispersions, but under mostconditions it will only require about 25Êm/s of ∆V.In the following sections, we will first developa design for a tether facility for boostingpayloads from low-LEO orbits to lunar transferorbits (LTO). We will then develop a design for aLunavator ª capable of catching the payloads anddelivering them to the surface of the Moon. W ewill then discuss the numerical simulations usedto verify the feasibility of this systemarchitecture.Design for Incremental DevelopmentThis effort has sought to design the CislunarTether Transport System so that it can bedeveloped and deployed in an incremental,modular fashion. The first components deployedwill generate revenue by transporting materialsto the Moon to facilitate lunar base development,and this revenue will be invested in thedeployment of additional modules to increase thesystem capacity and eventually enable round triptransport between LEO and the lunar surface.Although the system will realize its fullpotential when it is capable of transporting2