Atlantis Shuttle Crew Ready for Mission, Launch Rehearsal

The STS-115 crew gets instructions about using the slidewire baskets for emergency egress from the space shuttle on the pad on Aug. 9, 2006. CREDIT: NASA/Cory Husten.

With less than three weeks remaining before they rocket toward the International Space Station (ISS), six astronauts are looking forward to climbing inside their Atlantis shuttle Thursday for a launch dress rehearsal at NASA's Florida spaceport.

Flight controllers began counting down toward a mock liftoff at 8:00 a.m. EDT (1200 GMT) today, with Atlantis' STS-115 commander Brent Jett and his crewmates eager to practice the final hours of their upcoming launch.

"We're looking forward to a good practice countdown tomorrow," Jett told reporters Wednesday at Atlantis' Pad 39B launch site at NASA's Kennedy Space Center (KSC) in Cape Canaveral.

Jett, STS-115 pilot Chris Ferguson and mission specialists Joseph Tanner, Heidemarie Stefanyshyn-Piper, Daniel Burbank and Steve MacLean - of the Canadian Space Agency - are going through a multi-day training session at KSC known as the Terminal Countdown Demonstration Test (TCDT). The session allows the astronauts, pad workers and flight controllers to practice flight and emergency escape procedures for the STS-115 crew's planned Aug. 27 launch.

During their mission, the STS-115 astronauts will deliver a 17-ton, two-segment addition for the space station's truss backbone, as well as a pair of new solar arrays to be installed on the orbital laboratory's port side.

"This mission marks the restart of the [ISS] assembly sequence," Jett said. "But it's just that, it's just one of the assembly missions we have to get done."

NASA plans about 15 shuttle flights to complete the ISS, where orbital construction has been stalled since late 2002 following the 2003 Columbia tragedy, before retiring the remaining three orbiters - Atlantis, Discovery and Endeavour - in 2010.

With three planned spacewalks - two of them back-to-back - alongside shuttle heat shield inspections and the deployment of new solar panels outside the ISS, Atlantis' 11-day mission promises to be a challenging one for its astronaut crew.

"I think the most challenging thing for us on this flight is going to be our timeline," Jett said. "It's probably the most aggressive timeline that's been flown on the shuttle ever. We think we're ready for it, we've been training for it for four and a half years."

NASA managers have called the STS-115 mission the most challenging to date for the shuttle program, though subsequent flights are expected to only increase in complexity.

"Every crew likes to say that 'Boy this is one of the most complex missions that we've ever flown,'" Jett said. "They're all that way, and they will be that way until we stop flying in 2010."

• Atlantis Astronauts Arrive at NASA Spaceport for Launch Rehearsal
• VIDEO: Shuttle Commander Brent Jett
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• Complete Space Shuttle Mission Coverage
• NASA's STS-115: Shuttle Atlantis to Jump Start ISS Construction