NASA Ground Tests Ion Engine

herda05 writes "New Scientist reports from a press release by NASA on a successful ground test of the HiPEP (High Power Electric Propulsion) ion engine, which is the first 'major milestone' for Project Prometheus. Also some pictures and more info on the HiPEP engine."

Comments

Re:Am I interpreting this correctly?

[jerde]

Ion propulsion works very differently than any other type of normal rocket. The idea with ion engines is that they're able to take individual atoms of their "propellant" and accelerate them to high velocities, using electricity as the energy, rather than some sort of chemical reaction.

Rockets in space work by taking some mass and throwing it in the opposite direction you want to go. Imagine yourself floating in space holding a bowling ball. You wouldn't have to push the ball away from you very hard to get yourself moving, since it's very heavy. But what if you only had a ping-pong ball: to get yourself moving quickly, you'd have to "throw" the ping-pong ball away from you very very very fast, to make up for its very small mass.

Chemical rockets take some combination of chemicals that react strongly together, creating heat. The result is a hot gas at high pressure, which blows out in the direction of the rocket nozzle, providing thrust the other direction.

The xenon ion engine takes xenon gas at very very low pressure, ionizes the atoms so that they're electrically charged, and then uses electric force to fling them at VERY high speed out into space. The velocity is much higher than in any chemical rocket. But ion engines aren't very strong -- the process works with just a little tiny bit of xenon at a time, so the engine as a whole winds up giving just a very gentle push. But since not much xenon is used up, the xenon that you have will last a LONG time.

That's the "specific impluse": a measure of how much a rocket can push you "per pound" of fuel. This page says that the space shuttle's chemical engines have a specific impulse of 460. This latest ion engine has a specific impulse of 6000!

So with the same weight of fuel, the ion engine would get you going about 13 times faster by the time you used up the fuel.

- Peter