NASA Stumped By Cracks In Space ShuttleNASA Stumped By Cracks In Space Shuttle

Space shuttle Discovery will lift off on its final mission no earlier than late February, NASA said Friday, as engineers are still uncertain about what caused cracks to develop in the spacecraft's external fuel tank during a launch effort in November.

Space Shuttle Discovery

"Progress continues to be made in understanding the most probable cause of cracks discovered on Discovery’s external tank mid-section, known as the intertank, where small cracks developed during the Nov. 5, 2010, launch attempt," NASA officials said in a statement.

"Four additional small cracks were found during thorough X-ray of the backside of the tank after Discovery was returned to the Vehicle Assembly Building before Christmas," NASA said. The space agency is now studying the feasibility of a Feb. 24 launch, but said it needs more time to determine why the cracks developed and how best to fix them before a final decision is made.

The shuttle program will wind down this year as NASA, under a directive from President Obama, turns launches to the International Space Station over to private contractors such as Space Exploration Technologies Corp. Obama has said the plan will cut costs while allowing NASA to focus on long-term goals such as a manned mission to Mars, but critics say it could cost jobs and leave the U.S. lagging in the space race.

Discovery's current mission, officially known as STS-133, is scheduled to be its last. When it finally lifts off from Florida's Kennedy Space Center bound for the ISS, it will carry a six-member, all-U.S. crew.

The team is led by Commander Steve Lindsey, 50, of Temple City, Calif., and pilot Eric Boe, 45, of Atlanta. Also on board will be mission specialists Alvin Drew, 47, of Washington, D.C., Tim Kopra, 47, of Austin, Texas, Michael Barratt, 51, of Camas, Wash., and Nicole Stott, 47, of Clearwater, Fla.

Discovery entered service in 1984, and is one of three remaining shuttles of the six originally built. Atlantis and Endeavour remain in service, while Challenger and Columbia were lost in 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.

The shuttle Endeavour will make the final flight of the program when it takes to the skies later this year.