The hype today about hypersonic flight and suborbital human flights to the lower edges of space seems to go on without reference to an important data point: we did these things before, and we did them with slide rules and 60-year-old technology. The X-15 rocketplane was the the highest-performance aircraft ever built. In many ways, it still is. It first touched the sky in an unpowered test flight from its B-52 carrier aircraft on this date in 1959.
The X-15s (three built, one destroyed) were sponsored by the Air Force and the National Advisory Committee on Aeronautics (NACA, which became NASA in October 1959) and built by North American Aviation.
In 199 flights, X-15s pushed the speed record for piloted aircraft to Mach 6.7 and the altitude record, rather symmetrically, to 67 miles (not on the same flight). A 200th flight at the end of the program was scheduled but postponed and eventually canceled. Proposals to modify the X-15 to carry a satellite-bearing rocket, or even to go into space itself, were not pursued. (I have serious doubts about whether the orbital version could have survived, although test pilots would of course have lined up to try it.) Five U.S. Air Force pilots broke 50 miles, the altitude recognized the USAF as the boundary of space, and were awarded astronaut wings. The 12 pilots also included men from the Navy and NASA and a legendary civilian test pilot, Scott Crossfield, who worked for North American.
It wasn't an easy program to carry out. It pushed almost every area of technology, and the engine alone ended up costing more than the initial projection for the entire effort. It certainly wasn't easy to fly: the initial configuration included three joysticks for the two-handed pilot. (I know women who claim male fighter pilots have at least four hands, but that's neither here nor there.)
The X-15 was a unique beast. It was beautiful in a brutal kind of way, with short thick wings and a massive wedge of a vertical stabilizer. It made countless contributions to air and space technology. Historian Roger Bilstein wrote,
"The X-15’s survival encouraged extensive use of comparatively exotic alloys, such as titanium and Inconel-X, which led to machining and production techniques that became standard in the aerospace industry. . . . prompted development of the first practical full-pressure suit for pilot protection in space. The X-15 was the first to use reaction controls for attitude control in space; re-entry techniques and related technology also contributed to the space program." (from the book Testing Aircraft, Exploring Space: An Illustrated History of NACA and NASA,[2003].
As I said, the program gets overlooked today. When I worked on maneuverable hypersonic reentry craft for Air Force Space Command some years ago, the officer in charge of that branch of the Requirements section didn't even know we'd flown anything sizable in that regime before. But we did. Consider Neil Armstrong, one of whose X-15 flights appears in the movie First Man. (The bit where he actually sees the metal underneath his rudder pedals glow is dramatic license, though.)
You can still see the X-15 for yourself. The highest-performance airframe, modified to a configuration designated the X-15A-2, is in the National Museum of the U.S. Air Force in Dayton Ohio. My first impression on seeing it there was that it looked like it was going supersonic even when it was standing still. The other surviving plane is in the Smithsonian, although it's off exhibit during renovations.
Truly an American aerospace first.
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