From Halopedia, the Halo wiki
Impulse drives are a form of sublight propulsion system used by the Forerunners and later by the Covenant. Forerunner monitors possess impulse drives for long-distance travel, while Sentinels use an exotic form of the impulse drive to fly. Otherwise, both monitors and Sentinels use teleportation grids for transport. The Covenant would later adapt this technology as a form of maneuver drive for their space-capable craft.
Powered by a small pinch fusion reactor, the Covenant's impulse drives convert energy and a small amount of exotic matter into thrust. This process creates a vivid stream of virtual neutrons and protons as a byproduct. Power can be redirected from the craft's other systems to temporarily boost acceleration. As craft fitted with impulse drives are capable of accelerating and decelerating at bone-crushing rates, the crafts require inertial dampers to keep occupants safe.
The Covenant used impulse drives as propulsion systems on their Ren shuttles, Type-27 Banshees, Type-28 Ticks, Type-29 Vampires, Phantom dropships, insertion pods, and Type-56 Lichs. Uztet'sKelln fighters, one of the earliest models of the Banshee, were equipped with twin impulse drives. The Type-31 Seraphs are equipped with an impulse drive, with the tail serving as a thrust vectoring system to direct the exhaust to increase maneuverability.
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