X-15 Flight 91 was a 1963 American crewed mission, and the second and final flight in the program to achieve sub-orbital spaceflight—a flight over 100 km in altitude. It was the highest flight of the X-15 program. August 22, 1963 at 18:05 UTC · Launch Successful North American X-15 — United States Air Force, to Suborbital Edwards Air Force Base, Air launch to Suborbital flight Crew: Joseph A. Walker Program: X-15 Data: Launch Library 2, The Space Devs. Image via The Space Devs.