Washington  - NASA technicians on Wednesday removed three fuel valves from the space shuttle Discovery that they feared could break off and damage the craft during launch.

The valves control the flow of hydrogen from the engines to the external fuel tank. NASA planned to replace the valves with models that had flown on fewer missions, after a piece broke off a similar valve on the space shuttle Endeavour in November. There was no damage, but the incident raised fears that shuttles could be damaged in the future.

Since the space shuttle Columbia disintegrated on re-entry in 2003 after it was damaged during takeoff, the US space agency has been extremely cautious about preventing possible damage.

Concern about the valves has delayed Discovery's launch several times and a new target launch date has not yet been set. Officials are to meet Wednesday to discuss safety issues before rescheduling a review to set a new launch target.

Discovery is to deliver the final solar panel to the International Space Station. (dpa)