Atlantis Shuttle Crew Ready for Mission, Launch Rehearsal

With lessthan three weeks remaining before they rocket toward the International SpaceStation (ISS), six astronautsare looking forward to climbing inside their Atlantis shuttle Thursday for a launch dressrehearsal at NASA's Florida spaceport.

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

"We'relooking forward to a good practice countdown tomorrow," Jett told reportersWednesday at Atlantis' Pad 39Blaunch site at NASA's Kennedy Space Center (KSC) in Cape Canaveral.

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

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

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

NASA plansabout 15 shuttle flights to complete the ISS, where orbital construction hasbeen stalled since late2002 following the 2003Columbia tragedy, before retiring the remaining three orbiters - Atlantis, Discoveryand Endeavour- in 2010.

With threeplanned spacewalks - two of them back-to-back - alongside shuttle heat shieldinspections and the deployment of new solar panels outside the ISS, Atlantis' 11-daymission promises to be a challenging one for its astronaut crew.

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

NASAmanagers have called the STS-115 mission the most challenging to date for theshuttle program, though subsequent flights are expected to only increase incomplexity.

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

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