An member crawls through the hatch after the countdown culmination of the prelaunch terminal countdown demonstration test.

In the white room on Launch Pad 39A, an STS-120 crew member crawls through the hatch after the simulated launch countdown, culmination of the prelaunch terminal countdown demonstration test, or TCDT. The crew will also practice emergency egress from the pad. The TCDT at NASA's Kennedy Space Center provides astronauts and ground crews an opportunity to participate in various launch preparation activities, including equipment familiarization and emergency training. The STS-120 mission will deliver the U.S. Node 2 module, named Harmony, aboard space shuttle Discovery to the International Space Station. Discovery is targeted to launch on its 14-day mission at 11:38 a.m. EDT on Oct. 23. Photo credit: NASA/Kim Shiflett