Space shuttle Endeavour is towed by a diesel-powered tractor toward the Orbiter Processing Facility, or OPF, at NASA's Kennedy Space Center in Florida. After landing in California to end the STS-126 mission, Endeavour returned to Kennedy on a piggyback flight atop a shuttle carrier aircraft. In the OPF, Endeavour will begin preparations for its next mission, STS-127, targeted for May 2009. Photo credit: NASA/Jack Pfaller