Discovery's final countdown: Space shuttle launch signals NASA transition

After 27 years and more than 143 million miles, the space shuttle Discovery is poised for her final countdown.

The orbiter and its crew of six astronauts are scheduled to lift off from the Kennedy Space Center in Florida at 4:50 p.m. local time – with a packed cargo bay.

The ship is carrying an Italian-built cargo carrier re-engineered to provide extra storage space on the International Space Station. In addition, the orbiter is lofting some 5 tons of supplies and Robonaut 2, which designers envision as an eventual humanoid helpmate for future space-station crews.

Discovery's launch marks the first of three curtain calls – one for each of the remaining vessels in the shuttle fleet – as NASA's human spaceflight program enters a period of profound transition.

NASA is handing off the responsibility of ferrying goods and US astronauts to and from the station to private launch companies.

NASA can then focus on preparing to send human explorers beyond the space station's confines in low-Earth orbit, possibly to asteroids, the moon, and Mars.

Such missions, however, likely would be launched in the 2020s, depending on how agreeable successive administrations are to the current blueprint.

Discovery's last launch

As with the end of any long-running production, the cast and support crew behind Discovery's launch are finding this a bittersweet moment.

"She's been an amazing machine; she's done everything we've asked of her," says Michael Leinbach, the shuttle launch director.

For now, the entire team is focused on successfully completing the mission, he says.

But "landing day is going to be tough," he added during a prelaunch briefing Wednesday. "You'll see a lot of people on the runway who will probably choke up some."

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