The space station delivery mission is now off until the end of February. NASA had been aiming for an early February liftoff, but managers decided Thursday to take more time to complete repairs to Discovery's external fuel tank.
Following a failed launch attempt in early November, cracks were found in metal struts of the massive tank. More cracks were discovered last week, after the shuttle was returned to its hangar. NASA is considering reinforcing all 108 struts on the central part of the tank for extra safety, NASA spokesman Allard Beutel said Friday.
The initial cracks were so big that the insulating foam on top of the damaged struts, or so-called stringers, split open. That's NASA's main concern: Cracking could cause foam to break away during liftoff and slam into Discovery. Columbia ended up being destroyed in 2003 after a slab of foam gouged a wing.
Engineers are still trying to figure out why the cracking occurred; a manufacturing flaw is suspected.
Discovery is loaded with supplies for the International Space Station, as well as a humanoid robot that will be tested in orbit. The late February launch window opens on the 27th, but Beutel said NASA might be able to try a few days earlier than that.
As of now, the mission is the next-to-last for NASA's 30-year shuttle program. Another flight may be added this summer, however, which would mean a total of three remaining, one per shuttle.
NASA is under direction from the White House to retire the shuttle fleet this year, turn over space station taxi flights to private companies, and focus on eventual expeditions to asteroids and Mars.