The crew of Discovery's mission arrive to take part in the Terminal Countdown Demonstration Test or TCDT.

The crew of space shuttle Discovery's STS-124 mission arrive at NASA Kennedy Space Center's Shuttle Landing Facility to take part in the Terminal Countdown Demonstration Test, or TCDT. Here, Commander Mark Kelly (center left) and Mission Specialist Greg Chamitoff (center right) are greeted by Shuttle Launch Director Mike Leinbach (far left) and NASA Flow Director for Discovery Stephanie Stilson. TCDT is a rehearsal for launch that includes practicing emergency procedures, handling on-orbit equipment, and simulating a launch countdown. On the STS-124 mission, the crew will deliver and install the Japanese Experiment Module – Pressurized Module and Japanese Remote Manipulator System. Discovery's launch is targeted for May 31. Photo credit: NASA/Kim Shiflett