Earlier in the day, it had been moved off the launching pad for repair of a hydrogen leak.

However, a hydrogen leak in one of the orbiter's main engines was discovered.

Atlantis also was found to have a hydrogen leak, but in a different spot.

Instead, the hydrogen leak was detected in the shuttle's rear engine compartment.

The Columbia's astronomy mission has been delayed four times, mostly because of the hydrogen leaks.

Twice before, they had encountered a hydrogen leak while loading fuels.

"With the hydrogen leak resolved, we're ready to extend our knowledge of the universe."

An entry by Virginia Tech developed hydrogen leaks and other problems.

The announcement came after a hydrogen leak reappeared during a test.

Columbia, like Atlantis, has been grounded for months by hydrogen leaks.