The mobile launcher ML rolls out to Launch Pad 39B a distance of 4.2 miles.

On the crawlerway at NASA's Kennedy Space Center in Florida, the mobile launcher (ML) rolls out aboard a crawler-transporter from next to Kennedy's Vehicle Assembly Building to Launch Pad 39B, a distance of 4.2 miles. Rollout began at about 9:15 a.m. EST. Data on the ML will be collected from structural and functional engineering tests and 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 (SLS), the heavy-lift rocket that will launch astronauts farther into space than ever before. SLS will also create high-quality jobs here at home, and provide the cornerstone for America's future human space exploration efforts. Photo credit: NASA/Charisse Nahser