Shuttle launch canceled due to broken valve

— -- A stuck fuel valve prompted NASA to call off the scheduled launch of the space shuttle Discovery during fueling earlier today.

Space shuttle managers and engineers immediately went into troubleshooting mode, trying to understand why a valve that worked just fine during a countdown 24 hours earlier suddenly stopped working Tuesday night. They have not yet reset the launch date and a decision on when to try again might not come until late tonight. Early indications are there will be no attempt Thursday and possibly not for several days.

NASA must launch the shuttle by Aug. 30 or wait until mid-October because of conflicts with other space station missions launching from Russia and Japan in the coming months. It's unclear whether the valve could be replaced or repaired with Discovery on the launch pad. All of those questions were being assessed Tuesday evening.

The valve in question is critical to dumping excess liquid hydrogen rocket fuel from the spaceship once it reaches orbit. A build-up of highly-flammable hydrogen in the rear end of the spaceship would present an explosive hazard for the shuttle orbiter and crew.

Discovery and seven astronauts were to launch on a mission to deliver supplies and a new crewmember to the International Space Station.

The shuttle's most prominent payload is NASA's new $5 million treadmill, which is named after Comedy Central's Stephen Colbert. He said in a recorded message that he couldn't be prouder that his treadmill soon will be installed at the space station "to help finally slim down all those chubby astronauts."

"Let's face it, being weightless is mostly just a desperate bid to get away from that bathroom scale every morning," Colbert said. "But you guys and gals are ambassadors to the universe. Don't make us look bad. Put down the astronaut ice cream, tubby. Tubby, tubby, two-by-four, couldn't fit through the air lock door."

Colbert campaigned earlier this year to have a space station room named after him. He won the online vote, but NASA went with Tranquility, the name of the dry lunar sea in which Neil Armstrong and Buzz Aldrin landed 40 years ago this summer. As a consolation prize, Colbert got the treadmill. It's full name is Combined Operational Load Bearing External Resistance Treadmill; it will fly up in more than 100 pieces and won't be put together until sometime next month.