NASA halted future shuttle flights on Wednesday after learning that a large chunk of insulating foam broke off Discovery's external fuel tank during launch, an echo of the problem that doomed sister ship Columbia and its crew two and a half years ago.

The falling debris does not appear to have hit or damaged Discovery, which took off Tuesday on a 12-day mission to the International Space Station, the agency said.

But NASA said it would launch no more shuttle flights until its engineers could review the problem of debris falling off during blastoff.

Photos taken by Discovery's crew during launch showed the chunk of foam was missing from the fuel tank, a troubling finding because a 1.67-pound piece of foam insulation fell off Columbia's external tank during its launch on Jan. 16, 2003, and hit the ship's wing.

The damage caused Columbia to break apart as it attempted to fly through the atmosphere for landing 16 days later, killing the seven astronauts aboard.

NASA spent months changing the way foam insulation was applied to the tank and had expected to see only tiny pieces of debris come off Discovery's tank during its launch.

"Obviously we have to go fix this," a NASA spokesman said.

Astronauts aboard Discovery were still inspecting their ship for damage on Wednesday while imagery experts on the ground studied thousands of pictures and videos taken during its launch.

NASA expects to know by Thursday whether engineers want additional inspections with the shuttle's new laser-scanning boom to assure Discovery is in good shape to return to Earth at the end of its 12-day flight.

Preliminary images found that part of a tile, a component of the shuttle's heat shield, also broke off from the area around the shuttle's nose wheel landing gear door.

The mission is NASA's first manned flight since Columbia. Discovery is scheduled to reach the International Space Station on Thursday to deliver critical supplies.

Atlantis had been scheduled to launch on the next shuttle mission in September, also on a visit to the International Space Station.