The X-15 Hypersonic Aircraft One of the three X-15s under its B-52 mothership, ignition of the rocket engine, launch, and flight as viewed from the B-52 and X-15 - View of Test Flight from Onboard Camera Three X-15s made 199 flights during a research program which lasted from 1960 through 1968. It was a daring, yet highly successful program that resulted in hundreds of technical reports. It made contributions to the NASA space program of the 1960s and also on the design and flight of the Space S