Space shuttle Endeavour is towed to the Kennedy Space Center landing facility in Cape Canaveral, Fla., on Friday. John Raoux/AP Photo hide caption

itoggle caption John Raoux/AP Photo

The space shuttle Discovery is loaded onto the back of a modified 747 at Kennedy Space Center on April 15. The plane will ferry the shuttle to Washington, D.C., on April 17, where it will be permanently installed at the Smithsonian National Air and Space Museum. Kim Shiflett/NASA hide caption

itoggle caption Kim Shiflett/NASA

Every space shuttle mission had its own mission emblem, designed and worn by the crews. Centered in this photo are the embroidered patches for the first and last missions, STS-1 and STS-135. The STS-1 emblem is a rare version, produced only for the astronauts and NASA employees. The souvenir edition was slightly different. collectSPACE.com hide caption

itoggle caption collectSPACE.com

Atlantis lifts off from Kennedy Space Center on its final flight on July 8. There are plans for a next-generation space vehicle, but some space experts aren't sure if the vehicle will ever be completed. Tony Gray and Tom Farrar/NASA hide caption

itoggle caption Tony Gray and Tom Farrar/NASA

A large section of Discovery's nose, called the forward reaction control system, which helped steer the shuttle while in orbit, was removed in March. The spacecraft will be cleaned and detoxified before being put on display in museums. Jim Grossmann/NASA hide caption

itoggle caption Jim Grossmann/NASA

The International Space Station as seen from the space shuttle Atlantis after it undocked from the outpost in November 2009. Despite an end to the space shuttle program, NASA says scientific work is just getting into full gear on the space station. NASA hide caption

itoggle caption NASA

A worker tests components on a model of the space shuttle before wind tunnel testing. NASA hide caption

itoggle caption NASA

The San Andres Mountains and pieces of construction equipment are reflected in the glass windows of Spaceport America near Upham, N.M., in May. Despite construction delays and difficult working conditions in a remote area of the desert, state officials say New Mexico is committed to seeing the project succeed. Susan Montoya Bryan/AP hide caption

itoggle caption Susan Montoya Bryan/AP

Seventh-graders Sophie Maloro (left) and Unity Bowling "fly" a mission to Mars, part of a summer program at the MathScience Innovation Center in Richmond, Va. Larry Abramson/NPR hide caption

itoggle caption Larry Abramson/NPR

The Virgin Galactic VSS Enterprise spacecraft is seen before its first public landing during the Spaceport America runway dedication ceremony near Las Cruces, N.M., on Oct. 22. Virgin Galactic is one of a handful of private companies that plan to fly paying customers into space. Mark Ralston/AFP/Getty Images hide caption

itoggle caption Mark Ralston/AFP/Getty Images