The space shuttle Discovery and its six-member crew received the green light Monday for launch Wednesday afternoon to bring supplies, a new cargo-storage module, and a robotic astronaut "cadet," Robonaut 2, to the International Space Station.
The 11-day mission marks the final flight for Discovery and the penultimate scheduled launch for the 38-year-old shuttle program. The final shuttle mission is set for February, as NASA ends the program and redirects its human-spaceflight activities and tight budgets toward exploring destinations beyond low-Earth orbit, where the space station circles the planet.
"The mission's in great shape," said Michael Moses, who heads the mission management team during the shuttle's pre-launch activities. His comment at a briefing Monday follows the successful repair over the weekend of leaks that could have undercut the performance of one of two powerful engines the shuttles use to reach their final orbits, to change orbits, or to slow for reentry.
The leaks cropped up last Friday as NASA was about to begin the countdown for a Monday launch.
Both leaks were associated with one of the shuttle's two orbital-maneuvering engines, each housed in a large pod on either side of the orbiter's tail.
One leak cropped up in a fitting along a line that sends helium gas into a tank supplying fuel to the maneuvering engine. The helium keeps propellant and oxidizer in the fuel tanks under pressure so they flow smoothly to the engine.
A similar fitting sprang a leak along a nitrogen-gas line. The gas operates valves in the orbital maneuvering system. The leaks appeared in Discovery's right-hand orbital maneuvering system.
The repairs followed a fuel leak in the same pod that cropped up last month, although mission managers say the two sets of leaks are unrelated.
Despite the last-minute hitch, Discovery has proven to be the shuttle fleet's draft horse. It's logged nearly 143 million miles in space since its launch in August 1984. The orbiter has carried more people – including two US senators – than any of its stablemates.
For NASA employees who've been associated with Discovery's missions, it's a difficult time, acknowledges Michael Leinbach, the shuttle's launch director.
"There's still a certain amount of disbelief that it's really her final launch," he says. "It's difficult to accept emotionally, but rationally we all know it's coming to an end and we need to get on with it."