VASAMR thrusters.

[SirusKing]

I suggest a new thruster for rocketry construction, the VASIMR (Variable Specific Impulse Megnetoplasma Rocket) is an electric propulsion engine that is being designed for Space station (On the ISS) and trans-orbital use.

How it works IRL.

The VASIMR Engine is fairly simple, it first pumps a noble gas (IRL Argon, but in KSP Xenon) through a series of electromagnetic coils (while inside a tube) to constantly confine the gas, It is then put through a Helicon Antenna to Ionize it into plasma, then the gas is heated to a few Million degrees kelvin then out of a magnetised Nozzle. Because during the process the plasma never actually touches any of the interior, this ion engine's life is much longer then most. This engine is also capable of doing its namesake, as in either operating in a High Thrust but low ISP mode or Low Thrust but High ISP mode.

Unfortuantly, it does of course have some downsides. Because of the ejection of plasma, it tends to overheat quite easily, especially in atmospheres. Additionally, When in atmospheres, the magnetic field is disrupted by the magnetosphere and causes the engine to.. uh... "wobble" an awful lot. It also uses a ton of power :S

A recent diagram, according to Wikipedia.

How it might work in KSP.

In KSP, the engine would consume Xenon of course. The engine itself would be about the size of an LV-T30 Liquid Fuel Engine but thinner. It would have two modes, switchable by right clicking on it:

Low ISP, High Thrust, at max throttle:

Consumes ~0.4 Xe/s and ~25 E/s

Outputs 75 kN and 70 ISP (in vacuum).

High ISP, Low Thrust, at max throttle:

Consumes ~0.2 Xe/s and ~50 E/s

Outputs 1kN and 5250 ISP (in vacuum).

Note, I haven't really done the math

Downsides:

Can overheat quite easily.

Requires a ton of energy (You would need a whole bunch of generators/batteries, like IRL, they are Planning to use small fission reactors on the ISS to power it)

If used in an atmosphere, it may cause large unexpected Torque. If this occurs, something you have done broke the warranty. Just trust on that, okay?

[WhiteWeasel]

http://forum.kerbalspaceprogram.com/threads/52042-0-23-Near-Future-Propulsion-Pack-%28updated-20-12-13-new-panel-23-compatibility%29

[SirusKing]

Well NVM then xD