NASA decided Dec. 3 to postpone the launch of Space Shuttle Discovery’s final mission until February, the latest in a long string of delays that have kept the spacecraft grounded for more than a month.

Discovery is now slated to launch no earlier than Feb. 3, giving NASA engineers more time to complete work to analyze why small cracks developed in the shuttle’s external fuel tank. The cracks — which appeared on U-shaped aluminum brackets called stringers — have since been repaired, but NASA wants to make sure similar issues do not pose a future concern.

Because of the delay, NASA now expects to launch Space Shuttle Endeavour no sooner than April 1 on its mission to deliver the $2 billion Alpha Magnetic Spectrometer to the international space station. That mission had been scheduled for Feb. 27. Launch of NASA’s final planned shuttle mission, the congressionally mandated STS-135 flight, remains targeted for no sooner than June.

Shuttle program managers met Dec. 2 to evaluate the repairs made to Discovery’s 15-story tall fuel tank following five consecutive days of technical- and weather-related launch scrubs at the start of November. Engineers at NASA’s Kennedy Space Center in Cape Canaveral, Fla., have been performing tests and gathering data to try to determine what caused the cracks that were found on the metal ribs of the shuttle’s external fuel tank.

The space agency had been holding out hope for a Dec. 17 launch, but opted instead to give engineering teams more time to assess all the potential risks.

Discovery’s planned 11-day mission will deliver a storage room and Robonaut 2, a humanoid robot, to the space station. Two spacewalks are also planned.

The mission will be the 39th and last flight for Discovery.