Stock Photo - The second X_15 rocket plane 56_6671 is shown with two external fuel tanks which were added during its conversion to the X_15A_2 configuration in the mid_1960´s. After receiving an ablative coating to protect the craft from the high temperatures associated with high_Mach_number supersonic flight, the X_15A_2 was then covered with a white sealant coat. This ablative coating and sealant and the additional fuel would help Air Force Col. William J. Pete Knight fly the 2 X_15 to a world record speed of 4,520 mph Mach 6.7. The famed X_15 rocket planes were flown at NASA´s Dryden Flight Research Center, Edwards, California, from 1959 through 1968. The X_15 was developed to provide data on aerodynamics, structures, flight controls and the physiological aspects of high speed, high altitude flight. The joint NASA/U.S. Air Force/North American Aviation X_15 hypersonic flight research program is still considered to be one of the most successful NASA aeronautical research programs ever flown. One of the most advanced aeronautical tools of its day, the X_15 carried almost 600 instruments and sensors to record flight data. A wide range of experiments flown by the three X_15s during the 199_flight program helped advance the development of vital aeronautic and space flight systems.