Space shuttle Discovery standing ready for launch at pad 39B. The space shuttle has been revealed after retraction of the rotating service structure (RSS). Rollback of the RSS is a major preflight milestone, typically occuring during the T-11-hour hold one day before launch. On the 12-day STS-121 mission, the crew will test new equipment and procedures to improve shuttle safety, as well as deliver supplies and make repairs to the International Space Station. This mission is the 115th shuttle flight and the 18th US flight to the station. Photographed at Kennedy Space Center, on the 1st July, 2006.