KENNEDY SPACE CENTER, Fla.--Running four days late, the shuttle Discovery was refueled for launch late Friday for a 13-day mission to deliver more than 7.5 tons of supplies and equipment to the International Space Station.
With forecasters predicting a 60 percent chance of good weather, Discovery was scheduled for liftoff at 11:59 p.m. EDT.
An 8-inch liquid hydrogen valve blamed for back-to-back launch delays earlier this week worked normally during fueling Friday and engineers did not have to exercise a waiver that would have permitted additional troubleshooting.
Discovery's crew--commander Frederick Sturckow, pilot Kevin Ford, flight engineer Jose Hernandez, Patrick Forrester, John "Danny" Olivas, European Space Agency astronaut Christer Fuglesang, and space station flight engineer Nicole Stott--planned to begin strapping in for launch around 8:40 p.m. EDT.
Discovery's initial launch try early Tuesday was called off due to stormy weather near the launch pad. A second attempt was called off during fueling Tuesday night for a Wednesday morning launch when one of two hydrogen fill-and-drain valves in the shuttle's engine compartment failed to indicate it was closed.
NASA flight rules prohibited engineers from cycling the valve under supercold cryogenic conditions out of a concern about a possibly unknown problem that could cause it to fail in the closed position. In that case, it would be difficult to drain the tank after a delay. As a result, launch was tentatively rescheduled for early Friday.
During tests Wednesday night, after Discovery's tank was drained, the valve and its position indicator both worked normally, cycling open and closed five times at ambient temperatures. A pressure decay test also indicated the valve closed normally.
Discovery had two launch opportunities Friday roughly 23 1/2 hours apart. NASA managers opted to pass up the first opportunity in favor of the second to give engineers more time to review the valve issue.
During a Mission Management Team meeting Friday, a waiver was processed that would have allowed engineers to cycle the valve twice during fueling, if required, to confirm closing. In addition, engineers developed plans to use alternate cues to verify the valve's position.
As it turned out, those plans were not needed. The valve and the position indicator both worked normally.
Along with replacing a 1,800-pound ammonia coolant tank in the station's main power truss during their first two spacewalks, Discovery's crew will deliver two sophisticated science racks, an experiment sample freezer, a new air revitalization rack, a crew sleep station, and a treadmill named after comedian Stephen Colbert.
The "Combined Operational Load Bearing External Resistance Treadmill," or COLBERT, received its name after the comedian launched a successful tongue-in-cheek write-in campaign to name a final station module in his honor. NASA managers declined, naming the new module Tranquility instead, but renamed the treadmill after Colbert.
"I was still honored to receive the traditional NASA consolation prize, a space treadmill," Colbert said in a taped message to NASA. "I couldn't be prouder that my treadmill will soon be installed on the International Space Station to help finally slim down all those chubby astronauts."
Along with delivering needed supplies and equipment, Stott will replace space station flight engineer Timothy Kopra, launched to the lab complex in July and returning to Earth in Stott's place.