TIMING UNCERTAIN FOR RETURN OF TROUBLED SHUTTLE

Astronauts turned into plumbers Sunday in an effort to fix space shuttle Columbia's stopped-up toilet and continue their mission until Tuesday, but NASA said it still could be cut short a day by a new problem: bad weather. The National Aeronautics and Space Administration said a cold front was approaching shuttle Columbia's landing field at Edwards Air Force Base, Calif., bringing with it clouds, rain and gusty winds forecast to be outside safety limits for the scheduled touchdown.