Saturn V SA-506, the space vehicle for the first lunar landing mission, is rolled out of the Vehicle Assembly Building and down the 3.5-mile crawlerway to Launch Complex 39-A. Photo: NASA

Morning breaks over Launch Pad 39A following the arrival of shuttle Atlantis and Mobile Launcher Platform-2 prior to the STS-132 mission. Photo credit: NASA/Jack Pfaller

Mobile Launcher Platform-3 returns to the Vehicle Assembly Building after launch of shuttle Atlantis on the STS-135 mission. Photo credit: NASA/Kim Shiflett

Shown in front of one of the crawler's eight tread belts are, left to right, Richard L. Drollinger, Director of Engineering, Marion Power Shovel Co.; Theodor A. Poppel and Donald D. Buchanan, both of Kennedy Space Center; S. J. Fruin, Executive Vice President and Philip Koehring, Project Engineer, both of Marion; and Kurt H. Debus, Center Director at Kennedy. In July 1964, the group gathered to observe the first test at Marion, Ohio. Image credit: NASA

The crawler-transporter that carried space shuttle Discovery on its last rollout from the Vehicle Assembly Building to Launch Pad 39A moves toward the pad perimeter gate. Image credit: NASA/Jim Grossmann

Space Shuttle Atlantis began moving from the Vehicle Assembly Building at 5:02 a.m. on Tuesday, May 15, 2007. It took about six hours to reach launch pad 39A. Photo credit: NASA/Troy Cryder

The Space Shuttle Atlantis rides a crawler transporter to Launch Complex 39A on Tuesday, May 15, 2007 at NASA’s Kennedy Space Center. Photo credit: NASA/Troy Cryder

Pictured is a schematic of the crawler's design. Image credit: NASA