This is a bit of a take on an ion thruster. Install a backwards facing coil gun on a satellite, and fire small iron projectiles in rapid succession, in the opposite direction of the desired trajectory. Newton's 3rd law says it will accelerate. The iron projectiles will have more mass than the xenon in ion thrusters, but still not much so shooting a lot of them quickly will be required for significant acceleration. Also a lot of power will be required, meaning a nuclear generator of some sort.
I haven't really thought about the pros & cons of this yet, have at it!-- DIYMatt, Jun 08 2010 Required reading http://en.wikipedia...ki/Specific_impulseSpecific impulse, understanding this will go some way to explaining why this isn't comparable to an ion drive [Custardguts, Jun 08 2010] See link for information about specific impulse. Basically you'll have a lot of trouble accelerating the iron slugs to relativistic speeds, thus (per gram of ejecta) you'll get less impulse from this method than from a xenon ion drive.
Specific impulse isn't the be-all and end-all. Ultimately, you need a combination of high specific impulse (which in the field of rocketry is I suppose a measure of mass-eficiency) and also total thrust (which is more about power, ie how much push you get, needed for escaping gravity wells, and getting anywhere before you die of old age).
At this stage, to my knowledge, ion engines are very high specific impulse, but very low total thrust.-- Custardguts, Jun 08 2010 Also heavily pre-heated in situations where iron is readily available. FE thrust engines are common in science fiction or practical scientific speculation on how to get around the asteroid belt and how to shift asteroid ore inwards for use in terrestrial orbit.-- MechE, Jun 08 2010 Why not an iron ion drive?
<goes off whislting "any ore ion, any ore ion, any any any ore ion">-- coprocephalous, Jun 08 2010 //have to worry about a having a wrinkly space-suit..// Until, of course, you run out of fuel!-- gnomethang, Jun 08 2010 //Until, of course, you run out of fuel!// - then you use the trouser press. It all fits into place.-- pocmloc, Jun 08 2010 Why not just use one large chunk of iron (such as an anvil) and tie a length of string to it so you can get it back and use it again.
I know, I know.....-- Twizz, Jun 09 2010 Maybe if you just pull it back really really slowly...-- RayfordSteele, Jun 09 2010 elastic?-- pocmloc, Jun 09 2010 For added practicality, use a really long length of string and aim the anvil at a convenient asteroid etc from which it can bounce back, or even slingshot it round a nearby planet (careful not to get the string tangled).-- Twizz, Jun 09 2010 Much cheaper: a lead thruster six-shooter, ie, a Colt 45.-- ldischler, Jun 09 2010 of note is that Fe can indeed burn with a sufficient temperature and oxidant. The most common being Iron and Aluminum oxide also known as thermite. At very low pressures you might be able to get gaseous iron from the reaction and make a high temperature fe rocket.
The only thing about any sort of reaction mass engine is that you have a finite source of fuel AND you have to haul all that fuel with you at the start of the flight. I can't imagine launching ton's of iron into space would be cheap, unless you talk about mining asteroids or the moon.-- metarinka, Jun 10 2010 random, halfbakery