Extremely powerful device in Ancient city-ship design, allowing the gargantuan vessels to traverse the vacuum of space at faster-than-light speeds. In combination with an active shield, the stardrive permits space travel for the city of Atlantis, enabling it to even span the gaps between entire galaxies.
Atlantis, utilizing its star drive, was able to travel from the Milky Way Galaxy to the Pegasus Galaxy, a distance of between 3.26 and 3.5 million light years. It is not known how long it took the ship to ferry through the void. Whether the stardrive was augmented with other shortcuts is not known. Ancient hyperdrives were extremely sophisticated, so it is doubtful it took an extended period. (The modern Daedalus-class cruiser can traverse the space in 18 days, shorter, if the engines are pressed.)
Inertial dampeners work in conjunction with the stardrive. As a pre-launch measure, the dampeners require a half hour to energize.
Critical Mass - McKay is horrified when the inertial dampeners of Atlantis come online, a precursor to the initialization of the stardrive. When it reaches a critical capacity, the Zero Point Module will explode.
The Tower - McKay powers the stardrive of an Ancient city ship to drain the power of the Z.P.M. running it, effectively ending the rule of the dubious Lord Protector.
Progeny - The Asurans fire up their stardrive to bring their own city-ship to attack Atlantis.
First Strike - Under attack from the Asurans, the team uses Atlantis's stardrive to flee the planet where the Ancient city laid dormant for ten millennia.
Adrift - Atlantis drifts through space after the drive fails, and after a new Z.P.M. is installed eventually comes to rest on the surface of a new world.
Enemy At the Gate - The team takes Atlantis into space again and all the way to Earth, where the city-ship defends the planet from a Wraith assault in orbital combat.