Discovery Mission Specialists Doug Wheelock and Stephanie Wilson are in their assigned seats for the launch countdown or TCDT.

Inside space shuttle Discovery, STS-120 Mission Specialists Doug Wheelock and Stephanie Wilson are in their assigned seats for the simulated launch countdown, culmination of the prelaunch terminal countdown demonstration test, or TCDT. 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