Over and over, a projector at one end of a long pale-blue conference room in Building 13 of the Johnson Space Center showed a piece of whitish foam breaking away from the space shuttle Columbia's fuel tank and bursting like fireworks as it struck the left wing. In twos and threes, engineers at the other end of the cluttered room drifted away from their meeting and watched the repetitive, almost hypnotic images with deep puzzlement: Because of the camera angle, no one could tell exactly where the foam had hit. It was Tuesday, Jan. 21, five days after the foam...