day flight to the international space station may be the last one for a long while. NASA grounded the shuttle fleet after a slab of insulating foam broke off Discovery's external fuel tank during liftoff _ the very thing that doomed Columbia and was supposed to have been corrected. Onboard computers would guide the shuttle's dangerous, fiery descent until about five minutes before touchdown, when commander Eileen Collins and pilot Jim Kelly will begin manually controlling the 100-ton glider. After Discovery's July 26 launch, the shuttle spent nine days hitched to the space station, where astronauts resupplied the orbiting lab and removed broken equipment and trash _ one of the main goals of the mission. Discovery was the first shuttle to visit the station since 2002. During the trip, a pair of spacewalking astronauts replaced a failed 660-pound (300-kilogram) gyroscope, which controls the orientation of the station, and restored power to another. Sunday was the first time in three years that all four of the station's gyroscopes ran simultaneously. In a third unprecedented spacewalk, astronaut Stephen Robinson went beneath Discovery's belly to gently tug out two protruding thermal tile fillers. Engineers on the ground worried the material could cause dangerous overheating during re-entry and could lead to another Columbia-type catastrophe. Those on the ground learned about the material jutting out from Discovery's fragile thermal tile belly through intense inspections of the ship using cameras and lasers. --mor 1138 Local Time 0838 GMT
