Space Shuttle Discovery
The space shuttle Discovery rests atop Boeing 747 known as shuttle carrier aircraft

Nasa's oldest and most travelled space shuttle, Discovery, has embarked on its final journey piggybacking on a Boeing 747 to the Smithsonian National Air and Space Museum in Washington.

The shuttle, which first flew in 1984, has flown more number of times than any other in the fleet during its 27-year career. It will become the first of Nasa's three space shuttle orbiters, which all completed their final trips to space in March 2011.

The shuttle has started its journey from Nasa's Kennedy Space Center in Florida, and will land midmorning at the Dulles International Airport outside Washington. The shuttle carrier plane will make a loop around Washington DC before touching down at the airport.

Spot the Shuttle gatherings are being planned on rooftops, balconies and at outdoor restaurants to spot the shuttle when it flies around Washington. According to the schedule, it will reach the washington airspace between 10:00 am and 11:00 am (1400 and 1500 GMT). Spectators are expected to witness a low flyover of Discovery and its aircraft carrier as it pass through nation's capital, marking a historic flight over some of its landmarks, reported the Space web site.

Once it reaches Dulles International Airport, the shuttle will be taken to its new home nearby Steven F. Udvar-Hazy Center in Chantilly, Virginia, an annex of the Smithsonian's National Air and Space Museum.

The crew was supposed to mount the shuttle on Saturday, but high winds forced them to call off the operation until Sunday. Discovery will replace the Space Shuttle Enterprise, which is currently on display at the Smithsonian. The Space Shuttle Enterprise will be taken to the Intrepid Sea, Air & Space Museum in New York City.

"It's sad to see this happening," Reuters quoted Nasa astronaut Nicole Stott, a member of Discovery's final crew, as saying.

"But you look at it and you just can't help but be impressed by it. That's my hope now, that every time someone looks at that vehicle they are impressed, that they feel that this is what we can do when we challenge ourselves," she added.

The orbiter's other two retired sister spacecraft, Atlantis and Endeavour, will be put on public display at the Kennedy Space Center's Visitors Center and the California Science Center in Los Angeles, respectively.