NASA stands for the National Aeronautics and Space Administration because they do more than just space rockets.

In fact, before NASA went to orbit with the Mercury capsule in February 1962, they went to near space – and actual space – with the X-15 hypersonic research plane. The X-15 program was run with the United States Air Force, which had an interest in hypersonic flight for different, less wholesome reasons.

The program started flights in 1959 and conducted 199 flights until its end in 1968. Instruments gathered data on hypersonic flight, in particular how the extreme heat and pressure affected an aircraft’s structure. They also gathered data on the upper atmosphere and the space environment. Finally, the program showed how humans would react to flying at these incredible speeds and what kind of flight controls would be needed to control a spacecraft.

To reach the speeds needed, the X-15 used a liquid propellant rocket engine instead of a jet engine like a normal plane. The XLR-99 engine used alcohol and liquid oxygen, producing 260 kilonewtons of thrust. In addition to normal aircraft controls, the X-15 had small rocket thrusters to point the plane when it was above enough atmospheric pressure for the regular controls to work. The rocket engine meant that the plane could not take off on its own and do the mission, so the X-15 was carried to altitude on the wing of a B-52 bomber and dropped, after which the engine started, and the plane climbed toward space.

The X-15 was piloted by a small group of NASA and Air Force pilots, many of whom would go on to become NASA astronauts, including Neil Armstrong. Those pilots flew one of two general flight profiles in the program’s 199 flights: one for altitude, and the other for speed.

On an altitude flight, the vehicle pitched up steeply shortly after engine ignition, aiming for the highest apogee possible. Two of these flights made it to space, passing the 100-kilometer Kármán Line.

On a speed fight, the X-15 flew straight and level while firing the engine to achieve maximum velocity.

X-15 flight 59 was a speed flight that set the program’s first speed record on June 27th, 1962.

Pilot Joe Walker was in the cockpit of X-15 number one that day, and it was his thirteenth flight in the aircraft. The mothership’s flight profile was to take off from Edwards Air Force Base and go far away to drop the X-15 so that the X-15 could land back at Edwards at the end of its mission. The B-52 mothership took off at noon local time and was at the drop zone an hour later. The drop took place at 13:08 local time. During the flight, the aircraft reached a speed of 1,834 meters per second, which is just shy of Mach 6 (six times the speed of sound) and an apogee of 38 kilometers. The engine fired for 88 seconds. By the 572-second mark, the X-15 had traveled 223 kilometers over the ground before landing back at Edwards.

The 1,834 meters per second velocity was an unofficial speed record for the time and would end up the third-fastest X-15 flight during the entire program. Joe Walker would fly a total of twenty-five X-15 flights before going on to fly the Lunar Landing Research Vehicle, a test rig for the planned Apollo Lunar Module.

In all, three X-15s were built. One was destroyed in flight, but the other two survived. Today you can find one in the Smithsonian National Air and Space Museum in Washington, DC, while the other is at the National Museum of the United States Air Force in Riverside, Ohio, near Dayton.

More Information

Proceedings of the X-15 First Flight 30th Anniversary Celebration (NASA)

PDF: The X-15 Rocket Plane (Michelle Evans)