Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

DepartureangleA = 1.5π - (ω + u ∞)Tether centerof mass orbitafter releaseDeparturebody orbitPatch pointu ∞ ∏ToSunωRelease: tethercenter of mass shifts in,back to unloaded stateToSunPayloadonTetherω TωPayloadLaunchTether center of massorbitsAbout 1Gm topatch pointPayload orbitafter releaseδuFigure 1. Payload pickup and release to aninterplanetary trajectory∆q ∆Uur∏Capture:tethercenterof massshiftsin toloadeddesignpoint1.51.50-.5-1ααDπCαABπ-1.5 -1 -.5 0 .5 1 1.5Astronomical UnitsTransittimesπB to C 120 deg 0.50 yearA to C 182 deg 0.64 yearB to D 160 deg 0.78 yearA to D 222 deg 0.92 yearFigure 2. Payload interplanetary trajectoriesFig. 2 shows an example of a Mars Earth Interplanetary Tether Transport (MERITT) systemtransfer orbit, approximating a launch opportunity from B to C on Sep 12 2005 with a 2 km/stether. Several orbit crossing rendezvous are possible, however the fastest trip times are generallyfound in the B-C trajectory case. An extensive discussion of the general orbit transfer problemmay be found in Bate, Mueller and White [14]Capture and Release at DestinationCapturing of an incoming payload with a tether (Fig. 3) is essentially the time reversal of theoutgoing scenario; the best place to add hyperbolic excess velocity is also the best place to subtractit. If the tether orbital period is an integral multiple of the rotation period following release of apayload, the tip will be pointed at the zenith at periapsis and the capture will be the mirror image.Capture after a pass through the destination body's atmosphere (Fig. 4) is more complex than aperiapsis capture, but involves the same principle: matching the flight path angle of the payloadexiting trajectory to the tether flight path angle at the moment of capture and the velocity to thevector sum of the tether velocity and tip velocity. Aerodynamic lift and energy management duringthe passage through the atmosphere provide propellant-free opportunities to do this.After capture, the payload swings around the tether and is released into a trajectory that eitherorbits the destination planet or intersects its atmosphere so that the payload can land. The tethercenter of mass shifts outward and its velocity increases in this process, leaving the tether orbit in ahigher energy state. It is, in some ways, as if the incoming payload had "bounced" off the tether.4