The X-15 was an experimental spaceplane developed by North American Aviation for NASA and the U.S. Air Force, which entered space thirteen times during the 1960s. It set a number of flight records, and the pilots who entered space were subsequently awarded status as astronauts by both organizations.
– Design and Construction –
The X-15 emerged from discussions about the possibility of a rocket-powered airplane capable of attaining hypersonic speeds. Contracts to design such an aircraft were then tendered during the mid-1950s, with Reaction getting the contract for the rocket itself and North American Aviation, NASA’s later contractor of choice for the Apollo command module, designing the aircraft.
As designed, the X-15 was a long plane with only tiny, stub-like wings, relying for lift on its 57,000 pound-force liquid-fuelled rocket. It could not take off under its own power, but instead would be air-launched from the wing of a B-52 strategic bomber, make its flight, and then land with its own landing gear. At its highest altitude, the X-15 would be able to achieve suborbital space flight.
Ultimately, three of the spaceplanes were built, and the first gliding test flight took place in 1959.
– Flight History –
The three X-15s flew a total of 199 times between 1959 and 1968, with a total of twelve pilots in the cockpit, including future Apollo astronaut Neil Armstrong and space shuttle astronaut Joe Engle. By the time one of their colleagues, Joe Walker, reached the official boundary of outer space in 1963, he had already been beaten into orbit by both Soviets (led by Yuri Gagarin) and Americans (following Alan Shepard). However, Walker’s flight was the first time that a plane entered space and then descended to a controlled and recoverable landing.
Tragically, not all of the program’s flights were so triumphant. In 1967, a test flight was descending towards landing when it began to spin. Under the extreme stresses of spinning at hypersonic speeds, the plane broke apart; the pilot, Michael Adams of the U.S. Air Force, died.
The X-15 program should have involved 200 flights total; however, the final flight in November 1968 was cancelled due to poor weather and malfunctions.
– Retirement –
With the exception of the destroyed X-15-3, the X-15 aircraft survived their test flights and are now on public display. The first is located in the National Air and Space Museum, and the second in the U.S. Air Force National Museum on Wright-Patterson Air Force Base.
In addition to the three X-15 spaceplanes, the Air Force committed two of its lumbering B-52 bombers to the program. The second of these, tail number 52-008 (nicknamed “Balls 8), spent its lifetime as a NASA test aircraft, before finally being retired from research in 2004. It will eventually be put on display at Edwards Air Force Base. The other B-52 was retired in 1969, and is now located at the Pima Museum in Arizona.