Workers prepare to transfer the external tank from the checkout cell for attaching on the mobile launch platform in highbay 3 for mission STS-116.

Inside the Vehicle Assembly Building, workers prepare to transfer the external tank from the checkout cell for attaching to its twin solid rocket boosters on the mobile launch platform in highbay 3 for mission STS-116. The gigantic, rust-colored external tank is the largest element of the Space Shuttle system at 27.6-feet wide and 154-feet tall. STS-116 will be mission no. 20 to the International Space Station and construction flight 12A.1. The mission payload is the SPACEHAB module, the P5 integrated truss structure and other key components. Launch is scheduled for no earlier than Dec. 7. Photo credit: NASA/Jack Pfaller