Probably because they’ve discovered some structural cracks and/or wingbox fatigue that would be difficult to repair.

NASA hasn’t said anything about that? I’ve long suspected that NASA withholds info. that the public has a right to know.

Btw, Back last August, was it, when NASA had a press conference announcing that the next Shuttle launch would be delayed, I seem to recall Mr. Gerstenmair (sp) making an obscure little comment about the launch delay not being such a bad thing because one of the Shuttles needed modifications. Did he say “modifications’ or “some work done”? I can’t recall.