Two shuttle training aircraft or STAs wait to taxi onto the runway at the Shuttle Landing Facility.

Two shuttle training aircraft, or STAs, wait to taxi onto the runway at the Shuttle Landing Facility. STS-118 Commander Scott Kelly and Pilot Charlie Hobaugh are each piloting one of the STAs for landing practice. The practice is part of Terminal Countdown Demonstration Test, or TCDT, activities that include a simulated launch countdown. The STA is a Grumman American Aviation-built Gulf Stream II jet that was modified to simulate an orbiter's cockpit, motion and visual cues, and handling qualities. In flight, the STA duplicates the orbiter's atmospheric descent trajectory from approximately 35,000 feet altitude to landing on a runway. The STS-118 mission is the 22nd flight to the International Space Station and is targeted for launch on Aug. 7. The mission payload aboard Space Shuttle Endeavour includes the S5 truss, a SPACEHAB module and external stowage platform 3. NASA/George Shelton