Covenant starships use Repulsor Engines for low-level propulsion. Little is known about its mechanisms, other than that they produce quantum fluctuations that can affect personnel within range of them, and they leave a wake that can affect starships. It's possible that Repulsor Engines could be a form of "reactionless drive" that makes use of negative matter. Negative matter would have negative mass and would have a "repulsive" effect with the normal matter if placed behind the ship.
- The name suggests a similarity to the Star Wars repulsor-lifts.