Shuttle managers decided Friday night to postpone liftoff until at least Feb. 27 to give engineers more time to pore over test data. The launch was originally planned for Thursday but has been pushed back twice already.
NASA wants to make sure three valves that control the flow of hydrogen gas into the external fuel tank will not endanger the shuttle and its seven-man crew if they break. A small piece of one valve cracked off on the last space shuttle flight in November.
Discovery holds the last set of solar wings destined for the space station.