Space Shuttle Discovery rolls toward Launch Pad 39B.

Space Shuttle Discovery rolls toward Launch Pad 39B. The shuttle rests on the mobile launcher platform, which is being carried by the crawler-transporter underneath. First motion of the shuttle leaving NASA's Vehicle Assembly Building 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/Dimitri Gerondidakis