The STS-115 crew walk out of the Operations and Checkout Building, heading for Launch Pad 39B. From the left are Mission Specialists Heidemarie Stefanyshyn-Piper, Steve MacLean, Joseph Tanner and Daniel Burbank, and at the front of the lines are Pilot Christopher Ferguson and Commander Brent Jett. The crew walkout is part of a simulated launch countdown in preparation for the upcoming mission on Space Shuttle Atlantis. Credit: NASA