Boeng employees Rick Koger (left) and Brian To (cq) infront of wall bearing the names of shuttle contractors from the past two years as NASA space shuttle Atlantis is prepared on the Vehicle Assembly Building floor at the Kennedy Space Center May 18, 2011 in Cape Canaveral, Florida. (Photo by Roberto Gonzalez/Getty Images)

Detail of the protective tiles on NASA space shuttle Atlantis as its prepared on the Vehicle Assembly Building floor at the Kennedy Space Center May 18, 2011 in Cape Canaveral, Florida. (Photo by Roberto Gonzalez/Getty Images)

NASA space shuttle Atlantis is prepared on the Vehicle Assembly Building floor at the Kennedy Space Center May 18, 2011 in Cape Canaveral, Florida. The space shuttle program ends with Atlantis mission STS-135 scheduled for early July. Space shuttle Atlantis will carry the Raffaello multipurpose logistics module to deliver supplies, logistics and spare parts to the International Space Station. Atlantis also will fly a system to investigate the potential for robotically refueling existing spacecraft and return a failed ammonia pump module. (Photo by Roberto Gonzalez/Getty Images)