CAPE CANAVERAL, Fla. -- STS-134 Pilot Greg H. Johnson signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- The STS-134 crew members pose in front of the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. From left, are Mission Specialists Greg Chamitoff, Michael Fincke, Andrew Feustel, Pilot Greg H. Johnson, Mission Specialist Roberto Vittori, with the European Space Agency, and Commander Mark Kelly. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- STS-134 Mission Specialist Michael Fincke signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- STS-134 Mission Specialist Roberto Vittori, with the European Space Agency, signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- STS-134 Commander Mark Kelly signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- STS-134 Mission Specialist Andrew Feustel signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- STS-134 Mission Specialist Greg Chamitoff signs the space shuttle wall tribute in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Kennedy employees who have supported the Space Shuttle Program throughout the last 30 years have been signing the wall as a tribute to the program. Endeavour's six crew members are at Kennedy for the launch countdown dress rehearsal called the Terminal Countdown Demonstration Test (TCDT) and related training. Endeavour is targeted to launch April 19 at 7:48 p.m. EDT on its final spaceflight mission. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett