The Shuttle Carrier Aircraft are two modified Boeing 747s.

While the project was seriously considered, it proved impractically large, and the Shuttle Carrier Aircraft was developed instead.

Shuttle Carrier Aircraft - Two 747s were modified to carry the Space Shuttle.

The An-225's original mission and objectives are almost identical to that of the United States' Shuttle Carrier Aircraft.

The aircraft would be able to "piggyback" a spacecraft, similar to the Boeing 747 Shuttle Carrier Aircraft (however much larger).

Columbia was returned to Kennedy Space Center from California on 28 April atop the Shuttle Carrier Aircraft.

Columbia returned to KSC on 20 December on the Shuttle Carrier Aircraft.

The Shuttle Carrier Aircraft and Space Shuttle Discovery remained at Barksdale over night.

NASA's own most notable application of wingtip devices is on the Boeing 747 Shuttle Carrier Aircraft.

Pig iron was used as ballast on the NASA Boeing 747 Shuttle Carrier Aircraft.

Boeing Sevenforty-seven Shuttle Carrier Aircraft carrying Orbiter Enterprise-One-oh-one.

It also tows yet another vehicle that hauls the orbiter, the shuttle carrier aircraft - a plane that transports the shuttle around the country and the world.

In 1974 the company proposed the Conroy Virtus to NASA for use as a Space Shuttle carrier aircraft.

In preparation for the anticipated relocation, engineers evaluated the vehicle in early 2010 and determined that it was safe to fly on the Shuttle Carrier Aircraft once again.

Shuttle carrier aircraft two modified 747s used to fly the shuttles back to KSC when they landed at Edwards AFB.

Intrepid was, at the time of incident, being prepared for the flyover of the Shuttle Carrier Aircraft with the Space Shuttle Enterprise later that morning.

After Edwards landings, the orbiter was flown back to KSC on the Shuttle Carrier Aircraft, a specially built Boeing 747.

Visits by NASA Shuttle Carrier Aircraft (SCA)

One former JAL 747SR is now being used as a NASA Shuttle Carrier Aircraft.

After landing at locations other than Kennedy Space Center, the shuttle is ferried back to Florida on a modified Boeing 747 Shuttle Carrier Aircraft.

Several were retired earlier; NASA acquired one of the early retired aircraft, N905NA, in 1974 and has since used it as a Shuttle Carrier Aircraft.

August 12 - The Space Shuttle Enterprise makes its first flight, a test glide in the atmosphere after detaching from a Boeing 747 Shuttle Carrier Aircraft.

This MDD was used to hoist a Space Shuttle orbiter onto a Shuttle Carrier Aircraft for the flight back to Florida.

This is where the Orbiter was mated on top of a modified Boeing 747, known as the Shuttle Carrier Aircraft, for the return flight to KSC.

For the first time ever, NASA's two highly modified Boeing 747 Shuttle Carrier Aircraft briefly flew in formation over the Edwards Air Force Base.