Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Tethers Unlimited, Inc.Cislunar Tether TransportV payloadV tipV orbitalV tipV orbitalCentral FacilityCenter-of-MassCounterbalanceMassL cm,1L ω LOrbitalf 0cm,2VelocityωL 2cm,0Central Facility"Climbs" Up TetherVTip VelocityOrbital VelocityFigure 8. Method for a lunar tether to capture a payload from a minimal-energy LTO and deposit it onthe Moon with zero velocity relative to the surface.Moravec lunar Skyhook, which would have a tipvelocity of 2.9 km/s at the top of its rotation.Consequently, the design of the lunar tethersystem must be modified to permit a tetherorbiting the Moon at approximately 1.5 km/s tocatch a payload to at perilune when thepayloadÕs velocity is approximately 2.3 km/s,then increase both the tether length and theangular velocity so that the payload can be setdown on the surface of the Moon with zerovelocity relative to the surface. Simply reelingthe tether in or out from a central facility willnot suffice, because reeling out the tether willcause the rotation rate to decrease due toconservation of angular momentum.A method that can enable the tether to catch apayload and then increase the tether rotationrate while lowering the payload is illustrated inFigure 8. The ÒLunavator ª Ó tether system iscomposed of a long tether, a counterbalance massat one end, and a central facility that has thecapability to climb up or down the tether.Initially, the facility would locate itself nearthe center of the tether, and the system wouldrotate slowly around the center-of-mass of thesystem, which would be located roughly halfwaybetween the facility and the counterbalancemass. The facility could then capture an inboundpayload at its perilune. The facility would thenuse energy from solar cells or other power supplyto climb up the tether towards the counterbalancemass. The center-of-mass of the system willremain at the same altitude, but the distancefrom the tether tip to the center-of-mass willincrease, and conservation of angular momentumwill cause the angular velocity of the system toincrease as the facility mass moves closer to thecenter-of-mass.Lunavator ª DesignUsing analyses of the orbital mechanics of thesystem, we have found the following first-orderdesign for a Lunavator ª capable of catchingpayloads from minimal-energy lunar transferorbits and depositing them on the surface of theMoon:Payload Trajectory:• mass M p = 1000 kg• perigee altitude h p = 328.23 km• Moon-relative energy C 3,M = 0.719 km 2 /s 2Lunavator ª :• tether length L = 200 km• counterbalance mass M c = 6,000 kg• facility mass M f = 6,000 kg• tether mass M t = 4,706 kg• Total Mass M = 16,706 kg= 16.7 x payload mass• Orbit Before Catch:central facility position L f = 155 kmtether tip velocity V t,0 = 0.748 km/srotation rate ω 0 = 0.00566 rad/scircular orbit altitude h p,0 = 170.5 km• Orbit After Catch :perigee altitude h p,0 = 178 km,8