Engineers started the shuttle Columbia's countdown Thursday with all systems "go" for blastoff Sunday, just 12 days after the shuttle Atlantis glided back to Earth to wrap up a military mission.

Carrying a $150 million battery of high-tech telescopes, Columbia and its seven-man crew are scheduled for launch on the 38th shuttle mission at 11:28 p.m. MST Saturday, six months behind schedule because of a series of crippling fuel leaks.At the controls will be commander Vance Brand, 59, and co-pilot Guy Gardner, 42. Their crewmates are John "Mike" Lounge, 44, Robert Parker, 53, Jeffrey Hoffman, 46, and civilian astronomers Ronald Parise, 39, and Samuel Durrance, 46.