3 of NASA's Vehicle Assembly Building Space Shuttle Discovery begins its slow journey via the crawlerway.

From high bay 3 of NASA's Vehicle Assembly Building, Space Shuttle Discovery begins its slow 4.2-mile journey via the crawlerway to Launch Pad 39B. The shuttle rests on a mobile launcher platform that sits atop a crawler-transporter. First motion was at 12:45 p.m. EDT. The rollout is an important step before launch of Discovery on mission STS-121 to the International Space Station. Discovery's launch is targeted for July 1 in a launch window that extends to July 19. During the 12-day mission, Discovery's crew will test new hardware and techniques to improve shuttle safety, as well as deliver supplies and make repairs to the station. Photo credit: NASA/Kim Shiflett