(02/09/1999) -- In the transfer aisle of the Vehicle Assembly Building, Atlantis awaits a vacancy in one of the Orbiter Processing Facility bays. Seen behind the right wing is an external tank being raised to a vertical position. The largest and heaviest element of the Space Shuttle, an external tank contains the liquid hydrogen fuel and liquid oxygen oxidizer for the three Space Shuttle main engines (SSMEs) in the orbiter during liftoff and ascent. When the SSMEs are shut down, the external tank is jettisoned, breaking up as it enters the Earth's atmopshere and impacting in a remote ocean area. It is not recovered