What a former of the U.S. Air Force and defense expert had to say on the X-15:Before the Mercury astronauts broke the threshold of outer space, before John Glenn rode Friendship VII around the globe for three orbits, and well before Neil Armstrong and Buzz Aldrin set the Eagle lunar module down upon Mare Tranquillity, a question persisted within the aerospace community: which agency would take Americans into space? And within what type of vehicle would they ride?

The Air Force Made a Strong Case to Go Into Space

The U.S. Air Force advocated that they, rather than the newborn NACA (later NASA), should bear the responsibility of taking Americans into space. And the Air Force, experts of controlled flight, believed that their men should actually fly into space, rather than be launched into space aboard a rocket. To prove that Americans could indeed be flown into space, rather than shot spam-in-a-can style, the Air Force would need a unique machine. Something fast. Something high flying. The solution was indeed the fastest and highest-flying aircraft ever built: the North American X-15.

The X-15 is essentially a rocket with maneuverable flight surfaces and a cockpit. Initially, the X-15 used an XLR11 rocket engine, which was also used in the Bell X-1 that Chuck Yeager used to break the sound barrier for the first time. The XLR11 only lasted eleven flights, however, before being swapped for the XLR99. Developed by Reaction Motors, the XLR99 provided a stunning 57,000 pounds of thrust. Using anhydrous ammonia and oxygen as a propellant, the jet consumed fuel voraciously; the jet could burn 15,000 pounds of propellant in just one minute and twenty seconds. In the process, the X-15 set records, for speed and altitude, that remain intact today, nearly six decades later.

The X-15 Earns its Wings and Breaks a Few Records

In October of 1967, USAF pilot William J. Pete Knight flew an X-15 to 100,000 feet and gunned the throttle. Sliding past Mach 1, sliding past Mach 2, he just kept accelerating. Knight maxed out at Mach 6, an unmatched 4,520 miles per hour; fast enough to cross the continental United States in about forty minutes. No one has ever flown faster. And no one has ever flown higher than the X-15 pilots who, on 13 separate occasions, flew above 50 miles, or 264,000 feet, past the accepted boundary of outer space.

In doing so, these 13 flights qualified as space flights, confirming the USAFs belief that man could be flown into space, rather than shot into space. The pilots who crossed the 50-mile outer space boundary were given astronaut wings, just like NASA darlings Armstrong, Aldrin, Conrad, and Schmitt. The still-standing record for altitude belongs to Joseph A. Walker, who guided his X-15 to 67 miles above the Earth on August 22nd, 1963.

The X-15 did not use a runway like most planes. Rather, the X-15 was ferried into the air attached to the hardpoint of a B-52 Stratofortress. The eight-engine B-52, the biggest bomber in the USAFs inventory, was so powerful it had no problem hefting the X-15. Once aloft, the B-52 would release the X-15, which would light the candle and fly away under its own power. Before NASAs Mercury capsule was formally chosen as the vehicle to take Americans into space, the Air Force considered launching an X-15 into orbit aboard the SM-64 Navaho missile. The X-15-Navajo configuration forebode the Space Shuttle configuration that would dominate space flight in the 1980s and 90s.

The X-15 was never launched into orbit, and the space race moved on, favoring capsules to planes. However, the X-15 program gleaned information that aided space exploration. Retired in 1968, only three X-15s were ever built. The X-15 is featured prominently in First Man, where Neil Armstrong, depicted by Ryan Gosling, pilots the jet, the fastest ever.

Harrison Kass is the Senior Defense Editor at 19FortyFive. An attorney, pilot, guitarist, and minor pro hockey player, he joined the US Air Force as a Pilot Trainee but was medically discharged. Harrison has degrees from Lake Forest College, the University of Oregon, and New York University. He lives in Oregon and listens to Dokken. Follow him on Twitter @harrison_kass.

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X-15: The Mach 6 Space Plane That Broke All the Rules - 19FortyFive