In the Operations and Checkout Building at NASA's Kennedy Space Center Pilot Ken Ham tries on his helmet.

In the Operations and Checkout Building at NASA's Kennedy Space Center, STS-124 Pilot Ken Ham tries on his helmet. The suit fit is part of the simulated launch countdown. The simulation is the culmination of the launch dress rehearsal called the terminal countdown demonstration test. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. 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