A technology whose origin remains the subject of heated debate, the hyperdrive is an engine - powered by fusion generators - which allows a spacecraft to enter hyperspace, an alternate dimension where travel at many times the speed of light ceases to be an impossibility. Journeys that would require months or years in normal or "realspace" zip by in a matter of weeks or hours, making distant star systems easily accessible.
Travel through hyperspace is a serious and very delicate operation. Objects in realspace cast a hyperspace shadow, acting as obstacles in hyperspace as well. While the pilot of a starship hurtling through realspace might have enough time to react to a planet or asteroid in his craft's trajectory, the incredible speeds reached by a spacecraft in hyperspace render human reflexes absolutely useless. Hyperspace-travelling starships are thus equipped with a nav computer or an astromech droid, whose job is to calculate with the utmost precision the entry and exit coordinates, as well as the speed and duration of the trip, based on hyperspace maps. Should a previously uncharted space body show up on the ship's itinerary, mass shadow sensors would detect its hyperspace shadow and automatically shut down the hyperdrive, bringing the ship back into realspace.
Ships that have their hyperdrive damaged or disabled risk ending up stranded in deep space, unable to reach a spaceport or inhabited planet before they run out of supplies. In such a situation, a hyperdrive backup can mean the difference between life and death. Although most backups are very slow, their performance is still far ahead of the most powerful sublight drives.
The hyperdrives of Han Solo's ship, the Millennium Falcon have been greatly modified to make it a dangerously fast space transport; but as a result the hotrod starship is highly prone to engine failure.