— -- 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.
Colbert poked fun at NASA's choice of Tranquility for the chamber, which will be launched early next year. "Yeah, that will scare the aliens," he said. He ended his televised message by shouting, "I am 'go' to launch me. Let's light this candle!"
In all, the space shuttle will deliver about 17,000 pounds of gear to the space station. The experiments include six mice that will remain at the orbiting outpost until the following shuttle visit in November. Part of a bone loss study, the mice will be the first mammal creatures — other than humans — to spend a prolonged period at the space station.
Three spacewalks are scheduled to be performed during the 13-day shuttle flight, to install a new ammonia tank, part of the space station's cooling system, and replace other equipment and retrieve outdoor experiments. And the station will get a new resident, Nicole Stott. She will replace an astronaut who moved in during the last shuttle flight last month. That spaceman will return to Earth aboard Discovery, as will Buzz Lightyear. The action figure toy has been in orbit for more than a year.
The Associated Press contributed to this report.