CAPE CANAVERAL — After a four-month grounding of the space shuttle fleet, NASA's countdown clocks started ticking again Monday for Discovery's final ride into orbit.
Discovery is scheduled to blast off Thursday afternoon to the International Space Station. Forecasters put the odds of good weather at 80 percent.
When NASA tried to launch Discovery in early November with supplies and a humanoid robot for the space station, the countdown never got past the fueling phase. A hydrogen gas leak halted everything, then a more insidious problem cropped up: cracks in the external fuel tank.
The shuttle team went into overdrive to fix all the cracks in the metal struts, located on the tank's central portion, and to reinforce the rest of the area. The problem increased the risk of broken insulating foam, which doomed Columbia in 2003.
"Discovery has been a really remarkable vehicle for us," NASA test director Jeff Spaulding told reporters Monday. "She still has a few more miles to go before she sleeps, though. She's taken us on many amazing journeys throughout the years, and we expect this flight to be no different than any of those."
Commander Steven Lindsey and his crew expressed gratitude for the unprecedented repairs. After arriving at Kennedy Space Center over the weekend, Lindsey called the cracking problem "probably one of the most difficult, technical challenges we've faced in recent years."
The other challenge for the six-person crew, he noted, was the loss of the mission's lead spacewalker.
Astronaut Timothy Kopra was replaced last month after he was hurt in a bicycle crash. Stephen Bowen, an experienced spacewalker, took over.
Following this 11-day mission, Discovery will be retired and sent to a museum. Its final destination is expected to be the Smithsonian Institution. It is the oldest of the surviving space shuttles.