The countdown has started for the launch of the Discovery space shuttle. At 4:50pm Eastern time Thursday, Discovery will lift off and head for the International Space Station after a delay of more than three months.
NASA said Tuesday that liquid oxygen and liquid hydrogen will be loaded into Discovery's Power Reactant Storage and Distribution (PRSD) system today. The system, used in the shuttle's three fuel cells, allows the shuttle to produce electricity in space, pressurizes the shuttle's crew cabin, and produces water.
"Shuttle crews visiting the International Space Station routinely fill up bags with the water for use by station residents," NASA said.
Liquid oxygen and liquid hydrogen are also used by the space shuttle's main engines at lifotff, but the propellants for that job go into the 15-story-tall external fuel tank and are not loaded until launch day.
Before liftoff, Commander Steve Lindsey and Pilot Eric Boe will practice landing approaches in a Gulfstream II jet modified to simulate a shuttle's cockpit, motion, and handling. The rest of the crew will be reviewing orbiter ingress procedures.
For those who want to watch live, NASA will air the launch on NASA TV. The agency said the launch will also be available for viewing on the iPhone and iPad. If you miss it, NASA said it will post reruns on NASA's Web site and YouTube.
Space Shuttle weather officer Kathy Winters predicted an 80 percent "go" forecast for Discovery's launch, NASA tweeted on Monday. A successful launch would cap off several months of delays thanks to weather, leaks, and cracks.
After Discovery, NASA has two additional shuttle launches on the schedule before retiring the fleet. The Shuttle Endeavor is scheduled for April 19; the crew for that flight includes astronaut Mark Kelly - husband of Rep. Gabrielle Giffords. The final flight, Shuttle Atlantis, is scheduled for June 28.
The Discovery crew is pictured below at NASA's Kennedy Space Center in Florida. From left are Nicole Stott, Michael Barratt, Steve Bowen and Alvin Drew, pilot Eric Boe, and Commander Steve Lindsey.
