Key Points and Summary – The X-15 was a rocket-powered research aircraft that pushed human flight to the edge of space and deep into the hypersonic regime.
-Air-launched from a B-52, three X-15s flew 199 missions between 1959 and 1968, hitting Mach 6.7 and altitudes above 350,000 feet.
-Pilots like Neil Armstrong and Joe Engle used the platform to gather critical data on aerodynamics, heating, structures, and control at extreme speeds and altitudes—directly shaping Mercury, Gemini, Apollo, and later the Space Shuttle.
-The program’s risks were real, including one fatal breakup in 1967, but its surviving aircraft now sit in museums as milestones of flight.
BONUS – National Security Journal visited the U.S. Air Force Museum back in July and took some fantastic photos of the X-15 that are included in this article.
The X-15 Hypersonic Rocket Plane
The X-15 was a rocket-powered research aircraft developed in the 1950s that achieved hypersonic speeds and reached the edge of space, serving as a bridge between atmospheric and spaceflight.
The X-15 hypersonic research program was a collaborative effort between NASA, the U.S. Air Force, the Navy, and North American Aviation Inc., spanning nearly a decade.
Launched from a B-52 bomber, it gathered critical data for future aircraft and spacecraft, including the development of the Mercury, Gemini, and Apollo spaceflight programs, as well as the space shuttle program.
X-15 Harry J. Kazianis National Security Journal Photo.
X-15 Long Shot and Engine Photo. Image Credit: National Security Journal.
North American X-15 Head On. Image Credit: National Security Journal.
The X-15 holds the record for the fastest piloted winged aircraft, reaching a maximum speed of Mach 6.7 (over 4,520 mph) and an altitude of 354,200 feet.
The X-15 Program Takes Off
On October 15, 1958, the first X-15 hypersonic rocket-powered aircraft rolled out of its factory. A joint project among NASA, the US Air Force, and the US Navy, the X-15 greatly expanded our knowledge of flight at hypersonic speeds and at near-space altitudes.
The program had 12 pilots complete 199 missions between 1959 and 1968, while gathering data on the aircraft’s aerodynamic and thermal performance as it flew to the edge of space and beyond, then returned to Earth.
Among these were Neil Armstrong, later a NASA astronaut and the first man to set foot on the Moon, and Joe Engle, later a NASA Space Shuttle commander.
Among the 12 pilots who participated in the program were five from NASA, five from the Air Force, one from the Navy, and one from North American Aviation. Pilots generally flew one of two flight profiles: a speed profile, which maintained a level altitude until descent, and a high-altitude profile, which required a steep climb to altitude before descending.
The Beginnings Of the X-15 Program
The X-15 program dates back to 1952, when the Committee on Aerodynamics of the National Advisory Committee for Aeronautics (NACA) adopted a resolution to expand its research to study flight up to altitudes between 12 and 50 miles and speeds between Mach 4 and 10.
Four companies submitted proposals, and the Air Force selected North American Aviation, Los Angeles, as the winning bidder on September 30, 1955, awarding the contract in November.
Meet The X-15 Hypersonic Rocket-Powered Aircraft
On October 1, 1958, the new National Aeronautics and Space Administration (NASA) incorporated the NACA centers and inherited the X-15 project, just two weeks before the first aircraft rolled out of the factory.
The X-15 fuselage was long and cylindrical, with rear fairings that flattened its appearance, and thick, dorsal and ventral wedge-fin stabilizers. Parts of the fuselage (the outer skin) were heat-resistant nickel alloy (Inconel-X 750).
X-15 from U.S. Air Force Museum Original Photo. Image Credit: National Security Journal.
X-15 USAF Museum Photo. Image Credit: National Security Journal.
X-15A from U.S. Air Force Museum. Image Credit: National Security Journal.
The retractable landing gear comprised a nose-wheel carriage and two rear skids. The skids did not extend beyond the ventral fin, which required the pilot to jettison the lower fin just before landing, and it was recovered by parachute.
North American produced three aircraft for the program. The first unpowered glide flight was conducted by Scott Crossfield, a North American test pilot and former National Advisory Committee for Aeronautics (NACA) pilot, on June 8, 1959.
William H. Dana of NASA piloted the final X-15 flight on October 24, 1968. All flights took place within the area known as the “High Range,” primarily east of Edwards Air Force Base and NASA’s Flight Research Center (later renamed NASA Dryden Flight Research Center).
The X-15 Power Plant
The first 24 powered flights used two Reaction Motors XLR11 liquid-propellant rocket engines, each enhanced to provide a total of 8,000 pounds-force (35 kN) of thrust.
In November 1960, Reaction Motors delivered the XLR99 rocket engine, generating 57,000 pounds-force (250 kN) of thrust.
The remaining 175 flights used XLR99 engines in single-engine configuration. The XLR99 used anhydrous ammonia and liquid oxygen as propellant, and hydrogen peroxide to drive the high-speed turbopump that delivered propellants to the engine.
The XLR99 was a thirsty engine; it would burn through 15,000 pounds (6,800 kg) of propellant in just 80 seconds. Due to the large fuel consumption of its rocket engine, the X-15 was air-launched from a B-52 at an altitude of about 45,000 feet, reaching speeds over 500 mph.
The thick wedge tail of the X-15 was designed to enable it to fly steadily at hypersonic speeds.
Fatal Accident
When pushing the boundaries of space and speed as the X-15 program did, there will be accidents. And the program suffered several, including one fatal accident.
On November 15, 1967, X-15-3 was destroyed during the 65th flight of X-15-3 and the 191st flight of the X-15 program as a result of a structural load exceedance precipitated by a loss of control. The research pilot, United States Air Force (USAF) Major Michael J. Adams, was killed.
At 10:34:54, at an altitude of 62,000 feet and with dynamic pressure exceeding 1300 psf, the fuselage catastrophically buckled, and the aircraft disintegrated into several large fragments. The pilot did not successfully eject.
The Surviving Hypersonic Aircraft Are In Museums
Once the end of the X-15 program was reached, the two surviving X-15 aircraft were sent to museums. The X-15-1 arrived at the Smithsonian Institution in Washington, D.C., in June 1969.
When the new National Air and Space Museum opened in July 1976, the X-15-1 found a prominent place in the Milestones of Flight exhibit.
The X-15A-2 went on display at the National Museum of the Air Force at Wright-Patterson AFB, in Dayton, Ohio, where it still resides.
Although the third aircraft was lost in a crash, North American built a replica of X-15-3 that was mounted outside the entrance to Dryden in 1995. Damage from winds required its removal and refurbishment, and it is currently in storage.
About the Author: Steve Balestrieri
Steve Balestrieri is a National Security Columnist. He served as a US Army Special Forces NCO and Warrant Officer. In addition to writing on defense, he covers the NFL for PatsFans.com and is a member of the Pro Football Writers of America (PFWA). His work was regularly featured in many military publications.
More Military
The U.S. Navy’s Constellation-Class Frigate Crisis Keeps Getting Worse
China’s New H-20 Stealth Bomber Might Have a 10,000 km Range
Even Mach 3 Speeds Could Not Save the Titanium SR-71 Blackbird
The U.S. Navy’s New DDG(X) Destroyer Is Sailing Into Stormy Waters
