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Mass drivers


Kerbface

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I was reading the Wikipedia article on these and I may seem dumb for saying this but it didn't seem entirely clear on how they work. It says they catapoult loads, but the way it's described seems more like a cannon. Is that how it works, a big tube that uses an electromagnetic charge to repel a similarly charged payload out? I couldn't find any good diagrams of the inner workings of one either. Is this a plausible option for use in the future on, say, the moon?

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Yes, it's a cannon. The difference is that instead of a expansion of gasses caused by detonation pushing the projectile out of the barrel, the projectile is accelerated through some other means. This is usually a series of electomagnets around the barrel that switch on sequentially, which pushes the (magnetic) projectile out of the barrel.

Edited by Nibb31
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Coilgun is just one of several kinds of linear accelerators. Coilguns are very efficient at low velocities, but they lose their edge if you want high acceleration or high final speed. Both of these are a factor for a mass driver, so a railgun does seem like a better option.

Particle accelerators use a slightly different principle.

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The point is that you can design a mass driver so that what it accelerates is a magnetic bucket. You load the bucket with rocks, used baby diapers, belly-button lint, old AOL CD-ROMs, or whatever spare mass you have. The bucket is magnetically accelerated coilgun fashion. At the end of the driver, the bucket is braked to a halt, and the bucket contents go whizzing off into space.

When used for propulsion, typical figures I've seen say a representative model would require about 350 megawatts, engine mass about 150 metric tons, thrust about 20,000 newtons, specific impulse about 3,000 seconds.

The attractive part is that you can use any mass for propellant. So an asteroid miner could land one on a valuable asteroid, and use the mass driver to alter the asteroid's trajectory. Naturally the astromilitary of the various spacefaring nations will have their warships closely monitoring this, so no evil person or nation covertly alters an asteroid's orbit to strike Earth (or Kerbin) or to take out a space station or something.

Mass drivers can also be used for transport, this was how they were designed originally. You site one at a mine on Mün which produces titanium or aluminium. You use the mass driver to send blocks of ore into orbit to the future site of a huge L5 orbital colony. A "catcher" at the site intercepts the ore, which is then refined into structural members for the colony. You go to all this trouble instead of sending the structural members up from Kerbin because of the insanely high delta-V cost to boost into orbit.

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