Impulse engines are the fusion-powered drives that move starships at sublight speeds, used for maneuvering within star systems and whenever warp drive is unavailable or unsafe.
Impulse engines generate thrust from fusion reactions, letting a ship accelerate to a significant fraction of light speed without forming a warp field. They are the standard propulsion for orbital work, docking, combat maneuvers and travel inside a solar system, and they often keep a ship moving after its warp systems have failed.
Because impulse travel is far slower than warp, long voyages on impulse alone take years. Some small craft, such as certain fighters and raiders, were built with sub-impulse or impulse drives only.