The STS-115 crew walks out of the Operations and Checkout Building to head for Launch Pad 39B.

The STS-115 crew walks out of the Operations and Checkout Building to head for Launch Pad 39B. From left are Mission Specialists Heidemarie Stefanyshyn-Piper, Steven MacLean, Joseph Tanner and Daniel Burbank, Pilot Christopher Ferguson and Commander Brent Jett. They are taking part in a simulated launch countdown as part of the preparation for the liftoff of Space Shuttle Atlantis on mission STS-115, scheduled to take place in a window that opens Aug. 27. The mission crew has been at KSC for Terminal Countdown Demonstration Test (TCDT) activities, which include emergency egress training and the simulation. During their 11-day mission to the International Space Station, the crew will continue construction of the station and attach the payload elements, the Port 3/4 truss segment with its two large solar arrays. Photo credit: NASA/Cory Huston