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Electric propulsion is driven by power. Are there any theoretical limitations to the amount of power that can be used for electric propulsion? If limits do exist, do they rule out electric propulsions as a launch mechanism? For simplicity, in talking about a vertical launch.
The perfect answer would also give details on power storage/production and if this rules out the method for launch.
Clarifying statement: My intension for the question was ion engines.
Edit: on second thought, you're probably referring to an ion drive instead of firing the spacecraft out of a rail gun.
You could use a rail gun on a spacecraft as a mass driver: gun fires a rock out the back end, and the reaction force drives the ship.
If you're talking about firing the spacecraft out of a rail gun: the main limits to this are common to all gun launch methods:
Rail guns exist. The US Navy is experimenting with one that will fire a 3-kg projectile at 2.5 km/s. The most difficult part of this is getting the gun to not destroy itself. This gun works by placing a conductive dart on top of two parallel rails. The current goes up one rail, through the dart and down the other. The rails are heated by the huge current needed (on the order of 1 MA), to the point where they initially had to swap out the rails after a few shots. You're also setting up huge EM fields around the projectile.
There are other electromagnetic gun principles, e.g. you can place coils in series and pulse current through them to propel a metal projectile. I used to have fun firing metal pins from a coil scavenged from a set of toy train points.
Thrust is thrust and its effects are the same no matter where it comes from. In theory, yes electric propulsion such as hall effect thrusters, electrostatic ion thrusters and magnetoplasmadynamic (MPD) thrusters can be used to launch a satellite from the surface of the earth to orbit. However, due to the very high exhaust velocity of electric propulsion systems they have a very high specific impulse, which is a nice way of saying that in theory they can produce a large change in spacecraft velocity for a small amount of propellant.
While a higher specific impulse may sound advantageous, the gravity and atmospheric drag at Earth's surface can counteract the effects of the high specific impulse. By re-arranging the equations of motion and the equation for kinetic jet power we can see that as the specific impulse of an engine increases, the amount of power required to produce a pound of thrust also increases at a near logarithmic rate. Because of this increase in the ratio of power to thrust, electric propulsion systems would require an enormous power source to produce enough thrust to accelerate against gravity and minimize drag losses. Unfortunately, the specific mass of contemporary power systems (chemical, solar and nuclear) is too low to allow for this type of launch system.
So in summary, if we could build power sources that could produce an enormous amount of power for a very low structure mass (~3 kg/kWe or less), that were also compact then yes, it is possible to use electric propulsion systems for launch vehicle applications. However, this is beyond the current state of the art for power systems.
