The mobile launcher or ML begins to move off Launch Pad 39B at NASA's Kennedy Space Center in Florida.

The mobile launcher, or ML, begins to move off Launch Pad 39B at NASA's Kennedy Space Center in Florida on Nov. 30, 2011. Data on the ML was collected from structural and functional engineering tests and will be used for the next phases of construction overseen by NASA’s 21st Century Ground Systems Program. The 355-foot-tall ML structure, which took about two years to construct, is being modified to support NASA’s Space Launch System, the heavy-lift rocket that will launch astronauts farther into space than ever before. Photo credit: NASA/Frankie Martin