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.
The Andromeda, and other large Systems Commonwealth ships use Antiprotons as a fuel because of its very high energy to mass ratio and its attainability, which further improves engine economy. The Antiprotons are stored in a fuel tank away from the engines, and are fed into the engine by an Antiproton Solenoid Valve, which regulates the flow of Antiprotons. The Antiprotons are ionized and react with hydrogen, and are then fed into an acceleration chamber. From the chamber, they are propelled out of the engine by the electromagnetic Lorenz force, resulting from the interaction between the current flowing through the plasma and the magnetic field.
The advantages are that very little fuel needs to be held, and that a great amount of speed can be available in seconds, making MPDs great for precise maneuvering such as entering Delta-v orbits, or acceleration over extreme distances. The Andromeda can reach speeds of up to 40 PSL (percent of lightspeed), or 119,917,019.2 m/s when she uses her MPD, and she can also decelerate from her top speed, and accelerate again to her top speed in less than 5 minutes.
The fuel that can be used can be anti-hydrogen and hydrogen, but it can also be nobles gases such as xenon, argon, and metals such as lithium. The advantages of the varied fuels is that all the fuels are easily found and obtained through fuel stations, or mounted Ramscoops, as well as the disassembly of an Asteroid.