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Leaving on a Jet PlaneShortly after sunrise Tuesday, the powered-down space shuttle Discovery began its ride into the sunset atop a Boeing 747. NASA's longest-serving shuttle, shown above Florida's Kennedy Space Center, was carried north to Virginia's Dulles International Airport, pausing for a victory lap over Washington, D.C. On Thursday Discovery will roll to its final resting place, a Smithsonian Institution facility near the airport.(See Space Shuttle Discovery in extreme detail: exclusive new pictures.)Even before NASA's final space shuttle mission—an Atlantis expedition last July—workers had begun making Discovery safe for the National Air and Space Museum's Steven F. Udvar-Hazy Center, draining toxic fluids, disabling flammable fuel cells, and removing other dangers.In its time Discovery marked a series of space milestones. The shuttle was the first to dock with Russia's Mir space station, carried NASA's first African-American mission commander as well as the first woman to pilot a spacecraft—and executed the first "return to flight" missions after the Challenger disaster.—With reporting by Ker Than

Photograph courtesy Glenn Benson, NASA