NASA says it doesn't expect another space shuttle mission until at least late this year because of a problem with foam loss during last month's Discovery lift-off.

A one-pound slab of foam insulation broke away from Discovery's external fuel tank shortly after it took off on July 26. Also, smaller pieces of foam broke off in four other areas.

As a result, NASA's chief investigator into the foam loss said the shuttle's fuel tanks will need more modifications. Bill Gerstenmaier said that eliminates any chance for a shuttle launch next month, which had been the intended time for Atlantis to go up.

He said the next available launch window would be in November and then, after that, missions would have to wait until next year.

Gerstenmaier said the foam problem is "an extremely difficult engineering problem to solve."

Insulation shedding from the tank is blamed for the 2003 destruction of shuttle Columbia. A piece of it fell off during launch and smashed a hole in the craft's left wing, allowing superhot gases inside during re-entry.

Discovery's mission, which ended Tuesday morning, was the first test flight since the disaster.

President George W. Bush has called for the retirement of the fleet by 2010, but the orbiters were also supposed to complete the international space station before then.