Destiny

Destiny is a ship in the Ancient fleet constructed millions of years before Atlantis. The Ancients launched the automated ship millions of years ago to seed Stargates throughout many galaxies, with a second ship planned to follow it up and explore those planets. But, because they got busy with ascension, they never followed through on the plan.

Earth discovered that the Stargate's mysterious ninth chevron can be utilized to gate directly to the Destiny, opening up literally the whole universe to explore. But because the ship is on a programmed course, the team discovered that they have no way back to Earth.