North American Aviation X-15 56-6670 at the National Air And Space Museum Published on June 10, 2012 in 10 June 1969Full resolution (794 × 533) Next → North American Aviation Inc./U.S. Air Force/NASA X-15A 56-6670 hypersonic research rocketplane on display at the National Air and Space Museum. (Photo by Eric Long, National Air and Space Museum, Smithsonian Institution)