During the X-15 program, 13 flights by eight pilots met the Air Force spaceflight criterion by exceeding the altitude of 50 miles (80 km), thus qualifying these pilots as being astronauts . The Air Force pilots qualified for astronaut wings immediately, while the civilian pilots were eventually awarded NASA astronaut wings in 2005, 35 years after the last X-15 flight. The only Navy pilot in the X-15 program never took the aircraft above the requisite 50 mile (80 km) altitude and thus never earned astronaut wings.  
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