electromagnetic flight?

In one plain word NO!

Hey HiTek,

Mind if I wade in?

For a moment let's assume the air in front of the craft is completely ionized. It is worthwhile to note that this may not actually be the case in practice, by the way; meaning that there might also be a sizable population of neutral particles (both atoms and molecules) present. Also, by saying 'completely' ionized, I'm speaking in terms of ionization by removal of valence electrons only and not about naked nuclei stripped of all electrons. Nevertheless, we will have a plasma consisting of equal numbers of free electrons and positive ions. If we were dealing instead with a homogenous plasma; one consisting exclusively of either electrons (ie, an electron 'gas'), or one exclusively of ions, our problem would be considerably simplified. But all is not lost.

Left on its own, our plasma will quickly neutralize; the electrons will quickly rejoin with the ions resulting once more in a neutral gas. One conceptual complication introduced by our heterogenous plasma is twofold: a varying magnetic field will indeed induce currents in the plasma, but there will be two opposing currents: the electron current, flowing one direction; and the ion current, flowing the opposite direction. Furthermore, as electrons are far more mobile than their comparatively massive ionic counterparts, they'll tend to respond to external fields more quickly and you may tend to segregate the two species rather quickly. And although the two currents are in opposite directions, the charges involved are also opposite which means that each current will generate a magnetic field of its own, and both will contribute to a field in the same direction.

But here's the kicker: the resulting magnetic fields will always counter the applied field no matter what! So instead of "pulling" the craft through the air as hoped, the plasma and craft will repel each other with the net effect of that the ionized layer is simply pushed away from the far more massive craft - without affecting its speed in any way. Moreover, even if the craft were attracted to the plasma, the forces involved are exclusively between the plasma and the craft; not between the craft and its more general surroundings. And the fact that the plasma is outside the confines of the craft makes no difference to the fact that both are in the same inertial frame of reference - outside of there being any "outside" at all! You would get the same effect, for example, if a person inside the craft pulled or pushed against against a bulkhead. As you probably well know this wouldn't affect the vehicle's speed in any way - but it might tire you out!

Plasma physics is far more complicated than I've let on here, and so I've left out a bunch of stuff: things like self-shielding effects on a particle scale (google Debye radius for an example of particle self-shielding), how plasmas tend "freeze" embedded magnetic fields within themselves, and other ways plasmas tend to muck with external magnetic fields in the most interesting ways.

Is this clear as mud?

Finally, there's a simple experiment you can perform which demonstrates this repelling action due to induced currents: Slide a magnet down a smooth sheet of aluminum or copper (copper's better), or if you have access to it, a sheet of pure silver. A sheet 20-40 cm wide by 1 m long is great if you can get it.

Tilt the sheet at a 45-60° angle, place the magnet at the top and let it slide down on its own. Use as powerful a magnet as you can get, but not one weighing more than 30 grams (~1 oz) nor one less than a few grams. Rare-earth magnets are the best; especially samarium-cobalt magnets. If you have an old 5 1/4" hard drive laying around that you don't mind sacrificing in the name of science, remove its "voice-coil" assembly and remove one of the magnets. These are typically of the rare-earth type and are about the right size for what you need.

Metals are electrically conductive because, in bulk, a metal atom's outer electrons tend to leave the parent atom and wander freely about within the volume of metal. You can think of these electrons as forming a kind of 'electron gas' filling the interstices of the metal's atomic lattice which gives the metal its rigidity. An electron gas is every bit a plasma as one formed in free space except that it is confined within the metal's volume. And so you have, in a sense, a ready-made plasma at your fingertips. It's different than the heterogenous plasma of your craft's ionized shock wave, but the same principles apply.

When you perform this experiment, you will notice right away that the magnet just "creeps" down the incline instead of sliding freely. If you want to assure yourself that the effect is not due to friction, pit the magnet in a race with another object of similar size and weight. The magnet will lose every time.

Sorry to rain on your parade, but I hope you found this to be somewhat more informative than "NO!"

-e

you make the mistake thinking I care. Buit even if I did the answer is the very same.NO. Your experiment does not transfere across.

I appreciate the feedback.

Since this is a thought experiement,and costs nothing, lets try this.Guide the ionized air around the vessel, using a magnetic field to protect the vessel and to help shape the ion field.At the trailing end, introduce some chemicals that enhance ionization, such as salt, and use a magnetic field to "push" the ionized air away at an accellerated speed, thus giving thrust to the vessel. Would this be any more efficient than present methods?

Hey HiTek,

Although we're pushing against the ionized gas, we're not actually ejecting it per se. We're not generating thrust, if this is what you have in mind. But your proposal brings up an interesting thought: rather than manipulate a plasma on the outside of a craft, where conditions are extremely variable and hard to control, put all the thrust-generating goodies inside a 'thruster' of sorts, where it's more or less at your mercy. And besides, other means already protect craft from an ionized shock wave - the primary one being the shock wave itself. Only the leading edges of a craft really experience heating to a significant degree, and this is due to friction. The plasma is a side-effect of this heating, actually, and doesn't actually come into contact with the vehicle at points much beyond the leading edge that generates it. From Schlieren photographs of supersonic shock fronts, you've probably noticed that the shock front propogates outward at a sharp angle from the craft (or projectile) in all cases.

Something that might prove to be very beneficial is that if one could completely ionize the air in front of a leading edge - before it even reaches the edge - and to divert the resulting plasma away from the edge so that frictional heating is reduced or eliminated entirely. It will have to be one hellacious field for sure, because it will have to hold its shape while withstanding the formation of a hypersonic shock front. It's one thing to slice through air at hypersonic speeds with honest-to-Bog matter, but quite another to do the same thing with a comparatively 'squishy' magnetic field. If you could do it without the requisite field strength screwing up every other subsystem on your vehicle (including the toilet facilities), you might be able to eliminate the ablative heat shields and glass tiles used now to protect hypersonic vehicles (spacecraft on reentry, for the most part - and the legendary, pulse-jet-powered Aurora?). Protecting leading edges from frictional heating would be the far greater breakthrough, IMO. Even more so than a magnetohydrodynamic air-breathin' thruster.

Your take?

-e

If we accellerate the ionized gas via magnetic repulsion,there has to be a resultant opposite effect, accelleration of the vessel.I realize the pulse would have to be VERY fast, because the ionization will quickly dissipate, and the field will not work on ordinary air.With the ionized air moving past at say mach6,and the magnetic field formed by a series of coils, spaced the length of the rear half of the vessel , being energized in RAPID succession(faster than the ionized air), the result should be a repulsion of the ionized air at a greater speed than the vessel.I realize this would take a lot of energy, but for thought experiments, it is free and unlimited.

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