Mission Specialist Tracy Caldwell tests the fit of her helmet and launch a dress rehearsal for launch.

STS-118 Mission Specialist Tracy Caldwell tests the fit of her helmet and launch and entry suit during Terminal Countdown Demonstration Test (TCDT) activities, a dress rehearsal for launch. TCDT activities include the M-113 training, payload familiarization, emergency egress training at the pad and a simulated launch countdown. The STS-118 payload aboard Space Shuttle Endeavour includes the S5 truss, a SPACEHAB module and external stowage platform 3. The mission is the 22nd flight to the International Space Station and is targeted for launch on Aug. 7. NASA/George Shelton