Emergency impulse power
Emergency impulse power was a form of emergency power for impulse engines.

In 2267, with no warp power, Lieutenant Commander Spock ordered the activation of emergency impulse power to break free from the planet killer's tractor beam and stay ahead of the pursuing doomsday machine. The  was fast enough to stay ahead but doing so would exhaust their fuel supplies in less than a day. ()

See also
Emergency warp
Energy
Propulsion technology
Energy technology