Tethering to a large mass is an efficient way to change spacecraft velocity.
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The retrieved literature indicates that momentum transfer tethers and spinning tether systems can be effectively used for space transportation missions, such as placing vehicles into transfer orbits or facilitating Earth-Moon and Earth-Mars travel.
<div class="htmlview paragraph">The Earth orbiting tether, is based in part on the elevator into space idea that was described by Arthur C. Clark in his book, <i>The Fountains of Paradise</i>. That particular space transportation concept consisted of hanging a cable from geostationary orbit down to the surface of the Earth and moving people and freight from the Earth into space on an elevator which would ascend and descend along the cable.</div> <div class="htmlview paragraph">The tether concept used in this transportation system is an intermediate version of that idea which can be built with existing materials. It works by starting from a much lower altitude orbit and hanging the tether down to just above the Earth's atmosphere. The length of the lower half of the tether is selected such that a suborbital shuttle, built using existing technology, can fly to the lower end of the tether without the need for any additional stages or drop-off external propellant tanks. The length of the upper half of the cable is chosen so that its endpoint is traveling at slightly less than escape velocity for its altitude. This is done so that an Earth-Moon transfer vehicle, upon being released from the upper end of the tether, can be placed in a lunar bound orbit with only minimal use of its onboard propellant.</div> <div class="htmlview paragraph">The transportation system consists of 4 major components:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">a reusable single-stage suborbital shuttle that carries people and cargo to the lower end of the tether.</div> </li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">a vertically-oriented, Earth-orbiting tether with a lower endpoint terminal for receiving cargo from the suborbital shuttle, and an upper endpoint terminal for launching and receiving the Earth-Moon Transfer Vehicles.</div> </li> <li class="list-item"> <span class="li-label">3.</span> <div class="htmlview paragraph">an Earth-Moon Transfer Vehicle that carries people and cargo back and forth between the tether and lunar orbit.</div> </li> <li class="list-item"> <span class="li-label">4.</span> <div class="htmlview paragraph">and a reusable, single-stage Lunar Lander that transfers people and cargo between the lunar surface and lunar orbit.</div> </li> </ol> </div>
Dynamic analysis and motion control of spinning tether system during its Earth to Mars flight
The dynamic analysis and motion control of a spinning tether system for an interplanetary mission to Mars is considered. The space system consists of two spacecraft connected by a tether with thrusts to control its movement. The movements of the tether system in the sphere of action of the Earth, on the interplanetary trajectory and in the sphere of action of Mars are consistently analyzed. In near-Earth orbit, the transfer of the system into rotation with the help of jet engines installed on the end spacecrafts is considered. The spin of the system is used to create artificial gravity during the interplanetary flight. The tether system spins in the plane perpendicular to the plane of the orbital motion of the center of mass of the system. To describe spatial motion of the system, a mathematical model is used, in which the tether is represented as a set of material points with viscoelastic unilateral mechanical connections. When calculating the movement of the system, an approach based on the method of spheres of action is used. Spacecrafts are considered as material points.
The Space Mission Design Example Using LEO Bolos
Four sample space launch missions were designed using rotating momentum transfer tethers (bolos) within low Earth orbit and a previously unknown phenomenon of “aerospinning” was identified and simulated. The momentum transfer tethers were found to be only marginally more efficient than the use of chemical rocket boosters. Insufficient power density of modern spacecrafts was identified as the principal inhibitory factor for tether usage as a means of launch-assistance, with power densities at least 10 W/kg required for effective bolos operation.
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