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KENNEDY SPACE CENTER, FLA. - Workers in the mobile service tower on Pad 17-B, Cape Canaveral Air Force Station, check the progress of the Boeing Delta II Heavy second-stage engine as it descends toward the first stage. The Delta is the launch vehicle for the MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) spacecraft, scheduled to lift off Aug. 2. Bound for Mercury, the spacecraft is expected to reach orbit around the planet in March 2011. MESSENGER was built for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.