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Ionize air and repell away from it with magnetic fieldHelpful Member!(2) 

lestu (Computer) (OP)
5 Jul 12 3:10
Question from a complete layman:

Would it be possible to build a propulsion system that continually ionizes air with a laser or high voltage und uses a strong magnetc field to push itself away from the ionized air?

If the ionization rate of "new" air is high and quick enough, this should work in a way similar to the rotor of a helicopter, no?

- lestu
Helpful Member!  MiketheEngineer (Structural)
5 Jul 12 14:33
Been done - in the 1960's And it does work but the force is so small as to be impractical
DHambley (Electrical)
12 Jul 12 18:55
What you described is called an ion thruster. They are used for station-keeping and for long-term constant thrust. An ion thruster made by Aerojet succesfully lifted a military satellite towards geosynchronous orbit last year after it's main thruster failed. Due to the low thrust (several ounces) it took almost one year to gt into orbit.
YoungTurk (Mechanical)
13 Jul 12 14:51
Ion thrusters on spacecraft don't use air, they use an onboard gas as a fuel (typically something heavy, like xenon.) These are highly efficient but very low thrust.

The relative amount of thrust to electric field requirement makes ion thrust impractical for flight due to the weight required to generate the electric field.

Using ionized air for aerodynamic purposes in the atmosphere has been discussed here and you'll find some links if you look.
lestu (Computer) (OP)
13 Jul 12 16:32
Thanks for your answers.

So it is possible to barely lift the propulsion system itself, but not any significant payload. Unless there were "unlimited" amounts of energy available and more efficient ways to create strong magnetic fields with lighter materials.

It could work sometime in the future?
IRstuff (Aerospace)
13 Jul 12 16:41
No, ion engines only work well in space, and that's only because the engines are only tweaking the forward velocity that's already there. There's no way to deadlift a payload into orbit from the ground with only an ion engine. You can do the math; mass*gravity*orbit height <= total integrated thrust

FAQ731-376: Forum Policies

Helpful Member!  btrueblood (Mechanical)
13 Jul 12 18:16
Well, yeah, unless the power source is on the ground, i.e. power delivered to the payload body via UV, free-electron laser, or focussed microwaves. Latter has been demonstrated, and can acheive a zero-speed liftoff, but it's not dependent on magnetic or electrostatic or electromagnetic forces. Link

FWIW, magnetic forces alone (i.e. without some kind of electrostatic or E-M intereaction) don't give propulsion, just torque. Magnetic fields react against the Earth's magnetic field to do so - see: magnetic torque bars.. EM or electrostatic forces can couple to plasma to give improvements in net thrust, or specific impulse. see Link

MiketheEngineer (Structural)
16 Jul 12 16:18
If I remember - it took a lot of DC power and a couple of grids to make this work - but I designed one for a Science Fair and when my Dad saw the DC voltage required - he freaked. End of project!! Probably a good decision!!

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