Torsion plate

Torsion plates are a form of slower-than-light maneuver drive system employed almost ubiquitously aboard Forerunner starships. The plates convert harvested vacuum energy into a form of inertia-less thrust (presumably torsion fields), and are considered so simple and widely applicable they are near-universally used across the Forerunner fleet. Other forms of propulsion are used, though they are generally used for an extremely specific niche or aesthetic purposes. Stores of exotic matter may be used as reaction mass by torsion plates, allowing them to accelerate at a higher rate.

Supernal Spiral-class keyships such as Anodyne Spirit are equipped with torsion drivers, as are more terrestrial (though still floating) structures such as skydocks. The accuracy and precision required of atmospheric maneuvering makes torsion plates practically a required feature for any atmospheric flight.

The Wings of Malygus, the maneuver drives of Forerunner origin used to move the city-station High Charity around, were likely torsion plates - owing to the city-station's construction around the remains of a derelict Fortress-class vessel. The Covenant's own repulsor engines and boosted gravity propulsion drives are considered a rudimentary step between standard fusion drives and fully-utilising torsion drives.