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CAPE CANAVERAL, Fla. – Inside the Vehicle Assembly Building at NASA's Kennedy Space Center, technicians replace a valve on Atlantis’ external tank after small dings were found on the sealing surface of the quick disconnect system that handles liquid-hydrogen fuel for the shuttle’s three main engines. The tank will be attached to the twin solid rocket boosters on Aug. 3 for the STS-125 mission, the fifth and final shuttle servicing mission to NASA’s Hubble Space Telescope. During the mission, the crew will install new instruments on the telescope, including the Cosmic Origins Spectrograph and the Wide Field Camera 3. A refurbished Fine Guidance Sensor will replace one unit of three now onboard. Mission specialists will also install new gyroscopes, batteries and thermal blankets on the telescope. Launch is targeted for Oct. 8. Photo credit: NASA/Kim Shiflett