The impulse drive is a propulsion system used for sublight speeds. In Federation starships, the impulse drive is essentially an augmented fusion rocket, usually consisting of a Fusion Reactor, an accelerator-generator, a driver coil assembly and a vectored thrust nozzle to direct the plasma exhaust. The fusion reaction generates a highly energized plasma. This plasma, ("electro-plasma") can be employed for propulsion, or can be diverted through the EPS to the power transfer grid, via EPS conduits, so as to supply other systems. The accelerated plasma is passed through the driver coils, thereby a subspace field is generated that improves the propulsive effect.
By the 2270s, impulse was capable of reaching 0.8 of light speed without the warp drive even online but, due to relativity issues, this is often impractical for a ship's crew and impulse speeds are limited to approximately 0.25 c.