Endeavour crew practicing launch countdown

Endeavour's crew has boarded NASA's silver Astrovan for a ride to launch pad 39A, where they'll strap into the shuttle just as they hope to on April 19.

The six astronauts and launch teams are rehearsing the late part of a countdown, with Kennedy Space Center clocks now ticking below T minus 3 hours.

Around 2 p.m. the clock will stop four seconds before a simulated T-0, as if the countdown was aborted by a main engine shutdown, and the crew will practice emergency procedures for exiting the shuttle.

The countdown dress rehearsal culminates four days of pre-launch training known as the Terminal Countdown Demonstration Test, or TCDT.

The crew plans to head back to Houston today and return in less than two weeks for real countdown to Endeavour's final flight.

IMAGE: During a simulated launch countdown, the STS-134 crew walks out of the Operations and Checkout Building to the waiting Astrovan at Kennedy Space Center. From front, left to right, are STS-134 pilot Greg H. Johnson, commander Mark Kelly; second row; astronaut Roberto Vittori from the European Space Agency and mission specialist Mike Fincke; third row are mission specialists Greg Chamitoff and Andrew Feustel. Photo credit: NASA/Kim Shiflett.