STS-119 Mission Specialist Richard Arnold gets ready to enter space shuttle Discovery behind him.

In the White Room on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-119 Mission Specialist Richard Arnold gets ready to enter space shuttle Discovery, behind him. The White Room provides access into Discovery. Arnold and other crew members will conduct a simulated launch countdown as part of the prelaunch preparation known as Terminal Countdown Demonstration Test. The TCDT also includes equipment familiarization and emergency egress training. Discovery is targeted to launch on the STS-119 mission Feb. 12. During the 14-day mission, the crew will install the S6 truss segment and solar arrays to the starboard side of the International Space Station, completing the station's truss, or backbone. Photo credit: NASA/Jim Grossmann