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Dynamics of binary asteroids
Today the news is that the rediscovered Hermes asteroid may be a
binary of roughly equal masses. Makes me wonder if there is some way to exploit the energy of this rotating system, tether perhaps, to fling the two masses apart--putting one of the masses into a more advantageous orbit (for whatever purpose), letting the other one go as "exhaust." I'm not an engineer so bear with me... If you tether two masses and winch the tether in, I suppose the total energy of the system doesn't change, but the angular velocity goes up, right? If you then cut the tether, will the masses merely fly out to their previous orbits, or will they fly apart? Tether the two masses, winch them closer, and increase the energy with tangentially firing rockets of some sort? Maybe using propellants mined from the asteroids themselves. Then cut the tether at the right moment. Does this give an energy advantage over just sticking the engines on a single asteroid and making it a big conventional rocket? Patrick |
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Dynamics of binary asteroids
In article ,
Patrick Underwood wrote: I'm not an engineer so bear with me... If you tether two masses and winch the tether in, I suppose the total energy of the system doesn't change, but the angular velocity goes up, right? Not quite correct. Angular momentum -- mass times radius times (linear) velocity -- is conserved. Energy is not: you're putting energy into the system with your winch, doing work against centrifugal force. If you then cut the tether, will the masses merely fly out to their previous orbits, or will they fly apart? Hmm, depending on details, the winching could add enough kinetic energy to the system to exceed the gravitational binding energy. (Escape velocity rises as the radius shrinks, but conservation of angular momentum makes the linear velocity rise too, and faster.) Otherwise they'll end up in elliptical orbits. ...Then cut the tether at the right moment. Does this give an energy advantage over just sticking the engines on a single asteroid and making it a big conventional rocket? As above, you may not need engines. If you do, the energy advantage is probably small. If you don't, it's considerable, because the winching will probably be much more energy-efficient. And unlike a rocket, it doesn't throw mass away. (Well, if you don't count the other half of the asteroid, which probably doesn't end up anywhere useful.) -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
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