Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

IAF-99-A.5.10RAPID INTERPLANETARY TETHER TRANSPORT SYSTEMSRobert P. Hoyt and Robert L. ForwardTethers Unlimited, Inc. Clinton WA USA Gerald D. NordleyConsultant, 1238 Prescott Avenue, Sunnyvale CA USAChauncey W. UphoffFortune Eight Aerospace Co., Longmont, CO USAAbstractRoutine transport to and from Luna, Mars, and the other moons and planets in the solar systemdemands an efficient, rapid, low-cost transportation system. We have invented an innovativeinterplanetary transport architecture to meet that need. It consists of two rotating tethers in ellipticalorbits, one around Earth and the other around the destination moon or planet. These two tethers, madeof commercially available polymers, suffice to move payloads back and forth without the use ofpropellant except for midcourse corrections. For airless bodies, like Luna or Mercury, the payloads canbe delivered to the s u r f a c e of the body. We will describe two such architectures in detail, a CislunarTether Transport system and a Mars-Earth Rapid Interplanetary Tether Transport (MERITT) system.The Cislunar Tether Transport scenario takes into account the full complexities of the orbital mechanicsof the Earth-Moon system, including non-spherical gravitational potentials, inclined orbit dynamics,and luni-solar perturbations. We also describe a design for the first stage of the system, a Òrotatingelectrodynamic force tetherÓ that combines the technology of electrodynamic tethers with theprinciples of rotating momentum-transfer tethers to enable multiple payloads to be boosted from LEO tohigher orbits with no propellant needed. In the MERITT system, a payload capsule in LEO is picked upby the Earth orbiting tether as the tether nears perigee and is tossed a half-rotation later, slightlyafter perigee. The velocity increment given the payload deep in the gravity well of Earth is sufficientto send the payload on an escape trajectory to Mars, where it is caught by the Mars tether and placed inlow Martian orbit. The mass of each tether system, using commercially available polymers andreasonable safety factors, including the central facility and ballast mass, can be as little as 15 times themass of the payload being handled. Tethers with tip velocities of 2.5 km per second can send payloadsto Mars in as little as 90 days if aerobraking is used dissipate some of the high relative velocity on theMars end. Tether-to-tether transfers without aerobraking take 130 to 160 days.Nomenclature & Unitsµ mMoonÕs gravitational parameter = GM m, m 3 /s 2a semimajor axis, mωθangular velocity, radians/strue anomalyC 3orbital energy, ≡ V 2 - 2µ/r , km 2 /s 2d density, kg/m 3e ellipse eccentricityE orbital energy, JF safety factorh specific angular momentum, m 2 /si orbit inclination, degreesJ 22 nd geopotential coefficientL tether arm length, ml distance from facility to systemÕs center of mass.M mass, kgN orbital resonance parameterp orbit semiparameter, = a(1-e 2 ) , mr radius, mR e Earth radius, mr pperigee radius, mT tensile strength, PaV velocity, m/sV C characteristic velocity, m/sλ argument of tether perigee w.r.t. Earth-Moon lineµ e EarthÕs gravitational parameter = GM e , m 3 /s 2˙ω Apsidal precession/regression rate, rad/s˙Ω Nodal regression rate, radians/ssubscripts:• a apoapse • p periapse• c critical • m moon• f facility • g grapple• P payload • t tetherCopyright © 1999 by Tethers Unlimited, Inc.