X-15 Program

The X-15 was a rocket-powered research plane that flew faster and higher than any aircraft of its time, skimming the edge of space. Flown by the United States in the 1960s, it bridged the worlds of aviation and spaceflight and gave engineers priceless data for the space programs to come.

Quick facts

• Flew: 1959 to 1968, in a joint program by NASA, the US Air Force, and the US Navy.
• Type: a piloted, rocket-powered experimental aircraft, not a spacecraft.
• Top speed: about Mach 6.7, roughly 7,270 km/h (4,520 mph), still a record for a crewed, winged, powered aircraft.
• Top altitude: over 100 km (62 miles) on its highest flights, above the internationally recognized edge of space.
• Launched from: beneath the wing of a B-52 bomber, then dropped and rocket-fired.

How it worked

The X-15 did not launch from the ground. A B-52 carried it to high altitude and released it, after which the pilot lit a powerful rocket engine and climbed steeply, sometimes arcing so high that the sky turned black and the controls had to switch from normal air surfaces to small thrusters, because the air was too thin to steer against. After the engine burned out, the pilot glided the plane back down to a dry lakebed landing.

Why it mattered

The X-15 explored the unknown territory of high-speed, high-altitude flight, teaching engineers about extreme heating, control without air, and how pilots cope at the boundary of space. Several of its flights went so high that their pilots earned astronaut wings, and one of them was Neil Armstrong before he joined NASA’s astronaut corps. The lessons fed directly into the design of spacecraft and later the Space Shuttle, making the X-15 a crucial stepping stone from aviation into the space age.