CAPE CANAVERAL, Fla. – Baffled by fuel tank cracks, NASA announced another prolonged launch delay for space shuttle Discovery on Wednesday and raised the prospect of a Christmastime flight.

Shuttle managers refused to set a new launch date for Discovery's final flight, on hold since the beginning of November.

The next launch opportunity would be Dec. 17.

"We would have liked to have found a most probable cause by now" for the cracks that were found on Discovery's fuel tank, said Bill Gerstenmaier, head of NASA's space operations. "This is turning out to be a little more complicated from an analysis standpoint."

"We'll let the data drive where we're heading," he told reporters.

Hydrogen gas leaks halted the countdown for Discovery on Nov. 5. An unrelated crack later was found in the insulating foam on the external fuel tank; cracks in the actual exterior of the tank then were found beneath the flawed foam.

NASA wants to understand the cracking before launching Discovery to the International Space Station one last time. The space agency had been working toward a Dec. 3 liftoff for the 11-day mission. But that was no longer feasible given all the tests and analyses remaining.

A new space station crew is due to lift off from Kazakhstan on Dec. 15 and arrive at the orbiting complex two days later; at this point, Discovery must wait until after that.