Space Shuttle Atlantis is poised inside the Vehicle Assembly Building to begin its slow rollout to Launch Pad 39A.

Space Shuttle Atlantis is poised inside the Vehicle Assembly Building to begin its slow rollout to Launch Pad 39A. A shuttle comprises the orbiter, external tank and twin solid rocket boosters. The 3.4-mile trip along the crawlerway will take about 6 hours. The mission payload aboard Space Shuttle Atlantis is the S3/S4 integrated truss structure, along with a third set of solar arrays and batteries. The crew of six astronauts will install the truss to continue assembly of the International Space Station. Launch is targeted for March 15. Photo credit: NASA/Kim Shiflett