How exactly does Ion Drive work?

[Obnoxious]

They said it was a revolutionary type of engine that out performs the standard chemical drive on those little space ships that they send up, just how does it work?

[ydoaPs]

um...very slowly. it isn't really all that new. basically, a gas is charged and electric plates shoot the plasma out the back, iirc. it is a slow acceleration, but a constant one as opposed to the fast, short acceleration of a conventional rocket.

[Dave]

That's the idea. You get a constant stream of ionized particles ejected out of the back of the engine. So the principle is the same as the conventional rocket, just a lot slower.

[5614]

The 1st post here:

http://www.scienceforums.net/forums/showthread.php?t=5914

Is quite good.

[gisburnuk]

I'm not sure whether I am talking about the same engine here. I heard about NASA producing a engine that works when xenon atoms are ionised when electrons are forced through the xenon atoms (using the Hall effect). The consequence of this is that the xenon atoms are fired out of the exhaust producing a slow yet effiecient thrust.

[5614]

umm, did you even look at the link I posted?

 

(Hint: 1st post, the big picture attachment with step-by-step instructions)

[Janus]

The trick to all this is the rocket equation.

 

v_f = v_ex ln( M_i/M_f)

 

The part within the parenthesis is known as the mass ratio, and is the ratio of the fully fueled rocket to the rocker empty of fuel.

 

for any given mass ratio, the final velocity of the rocket depends on the exhaust velocity. the higher the exhaust velocity the greater final speed your rocket can achieve with the same amount of fuel. In other words, higher exhaust velocity leads to better efficiency.

 

The ion rocket is more efficient that the chemcal rocket because it is capable of producing higher exhaust velocity. The downside is that Ion drives produce a "thin" exhaust (The total amount of exhaust it can produce in a given amount of time is low), this leads to low thrust and slow acceleration.

 

Falling somewhere between is a system under development called a VASIMR (VArible Specific Impulse Magnetohydrodynamic Rocket)

 

It is more efficient than chemical rockets, while producing more thrust than ion rockets. It is also adjustable so that you can choose either the highest efficiency or the most thrust, depending on the what you need at the moment.