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KENNEDY SPACE CENTER, FLA. - STS-121 Commander Steven Lindsey is helped with his boot during suitup before heading to Launch Pad 39B and the third attempt at liftoff on mission STS-121. The launch of Space Shuttle Discovery on mission STS-121 is the 115th shuttle flight and the 18th U.S. flight to the International Space Station. During the 12-day mission, the STS-121 crew will test new equipment and procedures to improve shuttle safety, as well as deliver supplies and make repairs to the International Space Station. Photo credit: NASA/Kim Shiflett