The North American X-15's Flight 188 on October 3, 1967, was a record-setting flight. William J. Knight took the X-15A-2 hypersonic rocket-powered aircraft to 102,100 feet (31,120 meters) over Mud Lake, Nevada when flight 188 reached a record-setting top speed of 4,520 mph (7,274 km/h), Mach 6.70.