CAPE CANAVERAL, Fla. - Tugboats guide the Pegasus barge containing the external fuel tank for space shuttle Discovery's STS-133 mission through the Banana River to NASA's Kennedy Space Center in Florida. On the STS-133 mission, Discovery will deliver NASA's Permanent Multi-purpose Module, or PMM, the Express Logistics Carrier 4, and critical spare parts to the International Space Station. Launch is targeted for fall 2010. Photo credit: NASA_Jack Pfaller

CAPE CANAVERAL, Fla. - At NASA's Kennedy Space Center in Florida, the external fuel tank for space shuttle Discovery's STS-133 mission is transported from the Launch Complex 39 turn basin to the Vehicle Assembly Building across the street. On the STS-133 mission, Discovery will deliver NASA's Permanent Multi-purpose Module, or PMM, the Express Logistics Carrier 4, and critical spare parts to the International Space Station. Launch is targeted for fall 2010. Photo credit: NASA_Jack Pfaller