The North American X-15 rocket-powered aircraft was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, the NASA, and the USN . The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design.
During the X-15 program, 13 flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80.47 km), thus qualifying the pilots for astronaut status; some pilots also qualified for NASA astronaut wings.
Of all the X-15 missions, two flights (by the same pilot) qualified as space flights, per the international FAI definition of a spaceflight by exceeding the 100 kilometre (62.137 mi, 328,084 ft) mark.
