Rex Walheim and Sandy Magnus pause for a photo before boarding space shuttle Atlantis through the crew hatch in the background.

In the White Room at Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-135 Mission Specialists Rex Walheim and Sandy Magnus pause for a photo before boarding space shuttle Atlantis through the crew hatch in the background. The astronauts are at the pad to participate in a launch countdown simulation exercise.

As part of the Terminal Countdown Demonstration Test (TCDT), the crew members are strapped into their seats on Atlantis to practice the steps that will be taken on launch day. Shuttle Atlantis and its crew are targeted to lift off July 8, taking with them the Raffaello multi-purpose logistics module packed with supplies and spare parts to the International Space Station. The STS-135 mission also will fly a system to investigate the potential for robotically refueling existing satellites and return a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Jim Grossmann