Florida ? NASA said Thursday it was stumped by Discovery’s foam loss during liftoff and did not expect another space shuttle to fly until at least late this year.

Bill Gerstenmaier, the space agency official leading the investigation into the foam loss, said the shuttle’s fuel tanks will need modifications, which eliminates any chance of launching in September.

The next available launch window would be November, then that would be it until next year because of strict lighting requirements needed to photograph any flyaway foam or shuttle damage.

A 1-pound slab of foam insulation broke off Discovery’s external fuel tank two minutes after liftoff on July 26 and, unlike in the case of Columbia, missed hitting the shuttle.

Discovery’s redesigned tank also lost smaller but still sizable and worrisome pieces of foam in four other areas, including the same spot where a large chunk came loose during Columbia’s doomed liftoff in 2003.