WASHINGTON - Even as NASA engineers debated possible damage, a flight director e-mailed Columbia's astronauts to say there was "absolutely no concern" that breakaway foam that struck the space shuttle might endanger its safe return. The shuttle's commander cheerily replied, "Thanks a million!"Flight director J.S. "Steve" Stich conveyed his assurance to Columbia's commander and pilot on Jan. 23, according to documents disclosed Monday. At the time, engineers inside NASA continued to debate and study whether insulating foam that smashed against Columbia's wing on liftoff might have fatally damaged materials protecting the shuttle during its fiery descent.Such materials included the gray-colored...