As the Discovery heads to a docking at the International Space Station, NASA announced late Wednesday afternoon that it is grounding its entire shuttle fleet because the foam debris that caused the damage that brought down Columbia in 2003 remains a risk.

The announcement came after NASA officials reviewed images of the launch of the Discovery Tuesday and determined that a sizable chunk of foam insulation that came flying off the Discovery's fuel tank during liftoff.

The debris did not hit the orbiter and does not pose a risk to the seven astronauts, but it was a problem NASA thought it had fixed.

"We won't be able to fly again" until that hazard is removed,” Shuttle program manager Bill Parsons told reporters.

"Obviously we have some more work to do,” he said.

Discovery astronauts spent part of the day using a 90-foot robotic arm to inspect the outer portion of the shuttle for possible launch damage as part of the new safety processes put into effect after the intensive review of the shuttle program that followed the disintegration of Columbia during reentry high over Texas more than two years ago.

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