Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Rapid Interplanetary Tether Transport SystemsIAF-99-A.5.10origin planetÕs orbital velocity about the Sun.This vector is done in polar coordinates, and theangle portion of this vector in the origin planetframe is, at this point, a free choice. For now, anestimate or ÒguessÓ of this quantity is made. Theresulting vector is then converted into Sun frameorbital elements and propagated to the patchpoint near the orbit of the destination planet.There, it is transformed into the destinationplanet coordinates.Tether-Only Incoming Payload CaptureFor the tether-only capture scenario, thevelocity and radius of the tip of the tetherorbiting the destination mass are calculated anditeratively matched to the velocity of thepayload on an orbit approaching the destinationplanet, as shown in Figure 21.The distance of the patch point and therelative velocity there provide the energy of theorbit. The radius and velocity of the tether tipprovide another pair of numbers and this issufficient to define an approach orbit when theymatch. There are a large number of freeparameters in this situation with respect to thetether orbit which can be varied to produce acapture. There is a good news/bad news aspect tothis. The difficulty is that the problem is notself- defined and to make the model work, somearbitrary choices must be made. The good news isthat this means there is a fair amount ofoperational flexibility in the problem andvarious criteria can be favored and trades made.In this work, we have generally tried toselect near-resonant tether orbits that might beÒtiedÓ to geopotential features so that theyprecess at the local solar rate and thus maintaintheir apsidal orientation with respect to theplanet-Sun line. The Russian Molniyacommunications satellites about Earth and theMars Global Surveyor spacecraft use such orbits.The Sun-referenced arguments of periapsis,ω, in the figures are technically not constants, butcan be treated as such for short spans of timewhen apsidal precession nearly cancels theangular rate of the planet's orbit about the Sun .The fastest transfer times are generallyassociated with the fastest usable periapsisvelocities. These are found when the tether is a tc = captureat peripasisTether centerof mass orbitγ rr = releaseDestinationbodyorbitPayload orbitafter releaserδu∆qPayloadon Tetherurπ T-u ∞ω i = ω TDestinationbody orbitTo SunPayload periapsisentry optionTethercenter ofmassorbitPayload Incoming trajectoryAiPayload hyperbolicasymtoteFigure 21. Tether-Only Capture Scenario.22