The MagnetoplasmaDynamic Drive (MPD), also known as an Arcjet, is an engine that creates a huge amount of thrust from the interaction between an electromagnetic field and its fuel, which is ionized. Spacefaring vessels use MPDs as their main source of sublight propulsion because of the relatively small amount of fuel required to power it, and the enormous amount of thrust (velocities up to 500,000 m/s) that is generated as a result.