JSC2011-E-021705 (25 Feb. 2011) --- NASA astronauts Chris Ferguson (kneeling), STS-135 commander; Doug Hurley, pilot; Rex Walheim (left) and Sandy Magnus, both mission specialists, participate in a training session in a space station mock-up in the Space Vehicle Mock-up Facility at NASA's Johnson Space Center. Photo credit: NASA or National Aeronautics and Space Administration