How does a Magnetohydrodynamic drive work?
Magneto Hydrodynamic drives work by passing an electric current through a fluid in the presence of a magnetic field.
Magneto Hydrodynamic drives are being investigated for both ocean going ships and for spacecraft.
For a ship there is a tube running the length of the ship through which sea water flows. An electric current is passed through the salt water which is electrically conductive. A strong magnetic field is applied to the water which is at right angles to the electric current. The magnetic field and the electric field interact to apply a force to the water which ejects it from the rear of the ship.
The advantages of Magneto Hydrodynamic drives are that they have no propellors of other moving parts. They are much quieter as a result.
The problem with Magneto Hydrodynamic drives is that they require a generator to generate the electric current which needs to be driven by an engine or reactor of some type. Strong magnetic fields would require superconducting magnets, which require expensive and bulky cooling.
In the case of spacecraft plasma would replace the sea water as the conducting propellant.
With current technologies Magneto Hydrodynamic drives are more expensive and slower than conventional propulsion systems. Technological advances are required to make it more cost effective.