The crew practices rendezvous and docking with the International Space Station in the Systems Engineering Simulator at NASA s Johnson Space Center in Houston June 28, 2011.

The STS-135 crew practices rendezvous and docking with the International Space Station in the Systems Engineering Simulator at NASA?s Johnson Space Center in Houston June 28, 2011. NASA astronaut Chris Ferguson, commander, is at back left, and astronaut Rex Walheim, mission specialist, is at back right; and astronaut Doug Hurley, pilot, is at center. The session marked the crew's final scheduled training in the "Dome" in preparation for the final mission of the Space Shuttle Program. Photo credit: NASA photo/Houston Chronicle, Smiley N. Pool