USA. California. Trial of X-15. 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 was based on a concept study from Walter Dornberger for the NACA for a hypersonic research aircraft. 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.1959