Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Rapid Interplanetary Tether Transport SystemsIAF-99-A.5.10periapsis and its tip at the zenith of its swing. Inone approach to this model, these tetherconditions are used to set the periapsis velocityand radius of the incoming orbit. This, in turn,defines the relative velocity at the patch point,and the origin planet injection angle can beiterated to produce a Sun frame orbit thatproduces that relative velocity at thedestination planet patch point.Aerobraking Payload CaptureIn the case of using aerobraking in theplanetary atmosphere, the injection angle can beoptimized for minimum transfer time. As shownin Figure 22, the radius at which the atmosphereof the destination planet is dense enough tosustain an aerodynamic trajectory is used todefine the periapsis of the approach orbit; thereis no velocity limit.In a similar manner, the tether tip at anestimated capture position and velocity, togetherwith the radius at which the outgoing payloadresumes a ballistic trajectory define an exit orbitwhich results in tether capture. The difference inthe periapsis velocity of this orbit and theperiapsis velocity of the inbound trajectory is thevelocity that must be dissipated during theaerodynamic maneuver. For Mars boundtrajectories, this aerobraking ∆V is on the orderof 5 km/s, as compared to direct descent ∆VÕs of 9km to 15 km/s. Also, payloads meant to bereleased into suborbital trajectories already carryheat shields, though designed for lower initialvelocities.After the tether tip and the incomingpayload are iteratively matched in time,position and velocity, the center of mass orbit ofthe loaded tether is propagated to the releasepoint. This is another free choice, and theposition of the tether arm at release determinesboth the resulting payload and tether orbit. Inthis preliminary study, care was taken to ensurethat the released payload did enter the planet'satmosphere, the tether tip did not, and that thetether was not boosted into an escape orbit.Initial Planet Whip AnalysisWe first carried out analyses of a number ofMERITT missions using a wide range ofassumptions for the tether tip speed and whetheror not aerobraking was used. The trip times forthe various scenarios are shown in Table 4. As canbe seen from Table 4, the system has significantc = capturer = releaseDestinationbodyorbitTethercenterof massorbitγ r∆qrδu∆uPayloadon Tetherδucqγ ccuTcπ TuxcTether centerof mass orbitπ xTether orbitperiapsisAerobraking∆ω, ∆vPayload orbitafter release.Periapsisentry optionTo Sunω TωxωiPayload Incoming trajectoryAi-u i ∞DestinationbodyorbitPayload hyperbolicasymtoteFigure 22. Aerobraking Tether Capture.23