Feb 21, 2011 7:01 PM by Greg Boyce
CAPE CANAVERAL, Fla. (AP) - NASA's countdown clocks are ticking again for space shuttle Discovery's final launch. Discovery is supposed to blast off Thursday afternoon to the International Space Station. The flight should have taken place four months ago. But the countdown was halted in the final hours by
a hydrogen gas leak. Then fuel tank cracks cropped up.
The countdown picked up again Monday afternoon. Mission commander Steven Lindsey says the cracking problem was probably one of the most difficult technical challenges NASA has faced in recent years. He says the other challenge for the crew was the loss of the mission's lead spacewalker.
Astronaut Timothy Kopra was replaced last month after being hurt in a bicycle crash.
Good launch weather is forecast.