Mike Leinbach, the launch director, said: "On behalf of all the manufacturing, processing and flight launch teams who worked on Atlantis since March of 1980, we wish you good luck and godspeed have a little fun up there."
After this mission, only two more shuttle launches remain - one in September for Discovery and the final blast off for Endeavour in November.
The 32nd and final voyage for Atlantis, first launched in 1985, will take six astronauts to the International Space Station (ISS), delivering an integrated cargo carrier and a Russian-built mini research module.
Atlantis will be retired upon its safe return home after a 25-year career, a poignant moment for Nasa as the agency begins a countdown towards the end of an era in human spaceflight.
"Twelve days, three (spacewalks), tons of robotics. We are putting on spares that make us feel good about the long-term sustainability of the ISS, replacing batteries that have been up there for a while, and docking a Russian-built ISS module," said John Shannon, the space shuttle programme manager.
"This flight has a little bit of everything, and it's been a great preparation for the team."