The next space shuttle launch has been pushed back again due to lingering safety concerns stemming from the last shuttle mission in November. NASA needs more time to analyze and possibly conduct further testing on the three flow-control valves that regulate the flow of hydrogen gas from the main engines to the external fuel tank, the space agency announced late Friday. Before the postponement, Discovery had been scheduled to depart on its servicing mission to the International Space Station as early as Friday, which was itself a pushback from an original launch date of February 12.

The safety issue came to light after the Endeavour mission in November, when engineers discovered that one of the valves had been damaged in flight. NASA removed and inspected the valves on Discovery but has been working to identify why Endeavour's valve broke and what safety risks a similar occurrence might pose to the Discovery mission.

Shuttle officials told the Associated Press that they believe there is "a realistic shot" to launch Discovery before mid-March, but no launch date has been set. A new target date could come as early as Wednesday, when program managers will meet to discuss their options for addressing the valve issue.

Photo of Discovery on launch pad at Kennedy Space Center in Florida by NASA/Troy Cryder