NASA astronaut George Zamka, the commander of the February 2010 Endeavour space shuttle mission, peers out of the newly installed cupola—a sort of observation deck—that the shuttle delivered to the International Space Station. (See more pictures of the space station observation deck.)
As the final space shuttle to be built, Endeavour initially featured new and updated hardware not present in the other orbiters, including improved plumbing and electrical connections for longer missions as well as updated flight systems.
"Challenger and Columbia were built first, and they had 1970s technology at best—and in some cases, 1960s technology. With Endeavour being built last, NASA was able to update a lot of that technology," said Roger Launius, a spaceflight historian at the National Air and Space Museum in Washington, D.C.
"It's mostly things like electronics that are behind the panels, not necessarily things that you see when you walk into the spacecraft, but that enable it to perform more effectively and also lighten it a lot."
(Also see "Space Shuttle Discovery: Final Flight in Pictures.")