Discovery, NASA’s oldest and most journeyed space shuttle, is poised to launch on Thursday on its final mission, wrapping up a near three-decade legacy of orbital travel.
When the storied spacecraft lifts off at 4:50 pm (2150 GMT), it will mark the beginning of the end of the US space shuttle programme, with Discovery the first of the remaining three shuttles headed for retirement this year.
The closure of the US shuttle programme will forge a gaping hole in the American space mission, and leaves astronauts to rely on the Russian Soyuz space capsule for transport to the orbiting International Space Station.
But concerns for the future were brushed aside as excitement mounted at Kennedy Space Center for Discovery’s mission, with technical checks moving along smoothly and no hint of the fuel tank woes that delayed the launch in November.
“Everything is on track and going beautifully with the countdown,” said mission management team director Mike Moses. “We’re really looking forward to a very action-packed, successful mission.”
Cracks on Discovery’s external fuel tank emerged just before launch more than three months ago, causing engineers to puzzle for many weeks over the cause and how to fix it.
The six-member crew of astronauts headed to bed at 11 pm (0400 GMT) and were to awaken at 7:00 am (1200 GMT) for the launch Thursday, NASA said.
The loading of the external fuel tank was to begin at 7:25 am (1225 GMT). The astronauts were expected to board the shuttle at around 1:35 pm (1835 GMT).
The mission will be led by commander Steven Lindsey, pilot Eric Boe and astronauts Alvin Drew, Michael Barratt, Steve Bowen and Nicole Stott.
Astronaut Tim Kopra was scratched from the crew list after a bicycle accident in January. He was replaced by Bowen.
The crew plans to deliver the Permanent Multipurpose Module, with extra storage space and an area for experiments, as well as some spare parts and the Express Logistic Carrier, an external platform for large equipment.
The shuttle is also to bring the first humanoid robot to the ISS. The Robonaut 2, or R2, is a joint project of General Motors and NASA and will stay behind when Discovery leaves as a permanent resident of the ISS.
The weather forecast - clear skies, sunshine and a mild breeze - was considered exceptionally good with only a 20-percent chance of conditions that could delay the launch, NASA weather officer Kathy Winters said.
Discovery first flew in 1984. Final flights for the other two remaining in the fleet, Atlantis and Endeavour, are scheduled for later this year.
Endeavour is set for its final takeoff on April 19 and a last mission for Atlantis is scheduled for June 28, though funding for Atlantis remains in question.