The North American X-15 was developed in the late 1950’s, as a joint effort between North American Aviation, who created the airframe, and Reaction motors, who developed the engines. It was a rocket-powered aircraft capable of hypersonic speeds in excess of Mach 6 (4,500 MPH). It broke the record for the fastest speed ever achieved by a manned, powered aircraft and also pushed the boundaries of altitude flying too. During its development there were thirteen flights, undertaken by eight different pilots that met the Air Force criteria for space flight by flying higher than 50 miles. Those eight pilots were awarded astronaut wings for their acheivements and the X-15 became the World’s first operational Spaceplane. United States Air Force test pilot, Major Michal Adams was killed in November 1967 when his X-51 went into a spin while descending, the plane broke up under enormous G-forces as it plummeted from the sky and wreckage was spread over a 50 square mile area. The X-51 was retired early the following year.