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KENNEDY SPACE CENTER, FLA. - In the Operations and Checkout Building at NASA Kennedy Space Center, STS-115 Mission Specialist Steven MacLean signals "go" for another attempt at liftoff. MacLean is with the Canadian Space Agency. The launch attempt on Sept. 8 was scrubbed due to an issue with a fuel cut-off sensor system inside the external fuel tank. This is one of several systems that protect the shuttle's main engines by triggering their shutdown if fuel runs unexpectedly low. During the STS-115 mission, Atlantis' astronauts will deliver and install the 17.5-ton, bus-sized P3/P4 integrated truss segment on the station. The girder-like truss includes a set of giant solar arrays, batteries and associated electronics and will provide one-fourth of the total power-generation capability for the completed station. This mission is the 116th space shuttle flight, the 27th flight for orbiter Atlantis, and the 19th U.S. flight to the ISS. STS-115 is scheduled to last 11 days with a planned landing at KSC. Photo credit: NASA/Kim Shiflett