Warp nacelle

A warp nacelle is a feature of Star Trek starships that is a component of the warp drive. The nacelles generate the subspace field that allows the ship to exceed lightspeed.

Warp nacelles draw a substantial amount of power (usually from a warp core) in the form of plasma. This makes them a vulnerable part of the ship, as the plasma can escape violently if the nacelle is damaged. Such an event can potentially feed back into the warp core and destroy the ship (TNG "Cause and Effect").