The move follows a series of launch delays due to cracks on the fuel tank as well as other mechanical glitches, including a dangerous hydrogen leak.
If delays continue, Discovery might not make it off the ground before the scheduled launch of Endeavor, which is scheduled for Feb. 27, 2011. That flight is meant to mark the end of the shuttle program.
NASA has repaired the latest problem -- cracks on two, 21-foot support brackets, called stringers, that are part of Discovery's external fuel tank. Engineers determined that the foam on the stringers cracked during initial loading operations for Discovery's STS-133 mission to the International Space Station (ISS) on its flight originally scheduled for Nov. 5.
NASA wants to give time for engineers to fully determine exactly why the cracks occurred, which is why additional testing time is needed, said Bill Gerstenmaier, associate administrator for space operations, during a press conference about the delay Friday.
Specifically, the agency wants to replicate two scenarios -- one to look at how loading operations may have caused the problem, and the other to look at how loading conditions on the pad could have created it, he said.
NASA had delayed the Discovery flight until Nov. 30 and then pushed it to no sooner than Dec. 17. The latest delay came after a NASA review board responsible for evaluating the flight-worthiness of the craft met Thursday to assess repair work. The space shuttle entered service in 1984, and is one of three remaining shuttles of the six originally built. Atlantis and Endeavour remain in service, while NASA lost Challenger and Columbia in separate accidents that claimed the lives of their crewmembers. The first shuttle, Enterprise, was a test vehicle that was retired shortly after its initial series of suborbital flights in 1977.
When Discovery finally makes it off the ground, it will bring a series of components to improve the International Space Station (ISS). They include the Permanent Multipurpose Module, which was converted from the multipurpose logistics module Leonardo to provide additional storage for station crew, as well as a place for astronauts to experiment.
The space shuttle also will deliver some unique cargo to the ISS -- a humanoid robot called Robonaut 2 co-developed by NASA and General Motors.
Once it arrives at the station, the robot will become a permanent resident, performing mundane tasks and setting up work sites for astronauts to eliminate some of their busywork.