The X-15 program is widely considered the most successful research aircraft program in U. S. history, leaving a legacy of scientific data and aeronautical firsts that remains unparalleled. Between June 8, 1959, and Oct. 24, 1968, a dozen pilots flew three rocket-powered X-15 research vehicles 199 times. The program contributed to numerous advances in aerospace technology, including those in materials, hypersonic aerodynamics, astronomy and spaceflight. Researchers generated more than 760 technical reports and earned numerous awards and honors for the X-15 team. Launched from beneath the wing of a modified B-52, the X-15 was the first piloted aircraft to exceed Mach 4, 5 and 6, and ultimately attained a maximum speed of Mach 6.7 (4,520 mph). Eight of the pilots earned astronaut wings for flight above 50 miles altitude. NASA research pilot Joseph A. Walker achieved the highest flight, with a maximum altitude of 354,200 feet (roughly 67 miles). The X-15 vehicles exceeded design specifications and yielded a treasure trove of data of great value to the design of future aerospace vehicles. They have also provided many lessons for future flight research, many of which could not have been anticipated at the time the project was initially approved and funded. Technological contributions of the program include experience afforded in the design, fabrication, and welding of titanium and Inconel X, a nickel-chromium alloy from which the X-15 was constructed to withstand extreme aerodynamic heating. Advanced titanium and nickel alloys and structures were subsequently employed throughout the aerospace industry in aircraft and spacecraft, including those used in the Apollo lunar exploration program. Lessons learned from X-15 turbulent heat-transfer studies contributed to the design of the Apollo capsule after designers found they could build lighter-weight vehicles with less thermal protection than was previously thought possible. The X-15 program also produced a wealth of biomedical data that paved the way for humans to travel in space and helped spacesuit designers refine protective garments. In addition, the project pioneered mission control techniques that are useful for coordinating successful spaceflight and aeronautical research missions. Photo Description The X-15 in flight. U.S. Air Force Photo
