X-24 was a joint NASA/U.S. Air Force project to investigate
the use of lifting bodies for returning from space. Lifting
bodies are wingless aircraft that derive lift from their shape.
The X-24A's first flight was in 1970. The
typical flight profile was to be carried aloft and released from a
B-52. The rocket engine then boosted the X-24 to altitude and the
pilot glided the craft back to a landing.
In 1972, the X-24A was rebuilt as the X-24B with
twice the lifting surface and more stable flight characteristics.
The X-24 flight program ended in 1975.