X-15

The North American X-15 is a hypersonic rocket-powered aircraft operated by the United States Air Force and the National Aeronautics and Space Administration (better known as NASA) as part of the X-plane series of experimental aircraft. The X-15 set speed and altitude records in the 1960s, crossing the edge of outer space and returning with valuable data used in aircraft and spacecraft design. The X-15's highest speed, , was achieved on 3October 1967, when William J. Knight flew at Mach6.7 at an altitude of , or 19.34miles. This set the official world record for the highest speed ever recorded by a crewed, powered aircraft, which remains unbroken. During the X-15 program, 12pilots flew a combined 199flights. Of these, 8pilots flew a combined 13flights which met the Air Force spaceflight criterion by exceeding the altitude of , thus qualifying these pilots as being astronauts; of those 13flights, two (flown by the same civilian pilot) met the FAI definition of outer space. The 5Air Force pilots qualified for military astronaut wings immediately, while the 3civilian pilots were eventually awarded NASA astronaut wings in 2005, 35years after the last X-15 flight. Design and development The X-15 was based on a concept study from Walter Dornberger for the National Advisory Committee for Aeronautics (NACA) of a hypersonic research aircraft. The requests for proposal (RFPs) were published on 30December 1954 for the airframe and on 4February 1955 for the rocket engine. The X-15 was built by two manufacturers: North American Aviation was contracted for the airframe in November 1955, and Reaction Motors was contracted for building the engines in 1956.