Joseph A. Walker's Flight Into Space

Two weeks before Soviet cosmonaut Yuri Gagarin rode Vostok 1 into space to become the first human to complete a full orbit around the Earth, NASA test pilot American Joseph A. Walker took the hypersonic rocket-powered airplane, the X-15, to the edge of space, becoming the first person to cross the stratosphere.

The North American X-15 program was one of the most ambitious aeronautical research programs in history. The program was designed to answer fundamental questions about flight at extreme speeds and altitudes. In doing so, it quietly laid the groundwork for much of modern spaceflight.

Joe Walker with the X-15, 1961. Credit: Wikimedia Commons

The X-15 was conceived in an era when the boundaries between aviation and astronautics were still uncertain. Engineers and scientists wanted to understand what would happen to an aircraft and its pilot when pushed to unprecedented speeds and into the fringes of space. Conventional wind tunnels and simulations could not provide all the answers. The solution was to build a piloted, rocket-powered research aircraft capable of flying higher and faster than anything before it.

Developed by North American Aviation under the joint management of NASA (then NACA), the U.S. Air Force, and the U.S. Navy, the X-15 looked unlike any airplane that had preceded it. It had stubby wings, a thick wedge-shaped tail, and a fuselage designed to endure temperatures that would melt ordinary aluminium. Its structure was built largely from a nickel-based alloy called Inconel X, chosen for its strength at extreme heat.

Unlike conventional aircraft, the X-15 did not take off from a runway. Instead, it was carried aloft beneath the wing of a modified B-52 bomber and released at high altitude. Once dropped, the pilot ignited the aircraft’s rocket engine, most famously the XLR99, which produced up to 57,000 pounds of thrust and burned for only a few minutes. In that brief window, the X-15 accelerated with astonishing force, climbing steeply and crossing into regimes of flight no human had previously experienced.

Boeing NB-52B takeoff with X-15 mounted under the wing. Credit: Wikimedia Commons

At its peak, the X-15 reached speeds exceeding Mach 6.7 (more than 8,000 km per hour) and altitudes above 350,000 feet. At such heights, the atmosphere was so thin that conventional aerodynamic control surfaces became ineffective. Pilots relied instead on small reaction-control thrusters, similar to those later used by spacecraft, to orient the aircraft in near-vacuum conditions. After the rocket engine burned out, the X-15 flew a ballistic trajectory into the upper atmosphere and carried out a controlled re-entry, gliding down and landing on Rogers dry lake bed at Edwards Air Force Base. The total free flight time was roughly 10 minutes.

The X-15 was flown by a small group of elite test pilots drawn from NASA, the Air Force, and the Navy. Among them were figures who would later become legends, including Neil Armstrong, who would go on to command Gemini 8 and become the first person to walk on the Moon.

One of the program’s most notable pilots was Joseph A. Walker, a NASA research pilot who flew the X-15 higher than anyone else. In 1963, Walker reached an altitude of 354,200 feet, officially qualifying as an astronaut under U.S. standards. His flights, and others like them, blurred the distinction between pilot and astronaut at a time when the definition of “space” itself was still being debated.

The X-15A-3 rocket plane flies over Edwards Air Force Base during a mission in the 1960s. Credit: Wikimedia Commons

Joseph Walker was born in Washington Pennsylvania. He earned his Bachelor of Arts degree in physics from Washington and Jefferson College in 1942, before entering the United States Army Air Forces. During World War II, Walker flew the Lockheed P-38 and F-5A photo aircraft on weather reconnaissance flights. After World War II, Walker joined the National Advisory Committee for Aeronautics (NACA) and became a test pilot. He flew in several pioneering research projects such the D-558, X-1, X-3, X-4, and X-5 before being assigned chief X-15 pilot.

Walker first flew on the X-15 on 25 March 1960 attaining an altitude of 48,630 and a speed of Mach 2. He was the first NASA pilot to fly the X-15, and only the second X-15 pilot, following Scott Crossfield, the manufacturer's test pilot. On his first X-15 flight, Walker did not realize how much power its rocket engines had, and he was crushed backward into the pilot's seat, screaming, "Oh, my God!". Then, a flight controller jokingly replied "Yes? You called?".

Walker’s first flight into the mesosphere was on 30 March 1961. Walker was launched from Hidden Hills on an envelope expansion flight. The flight was intended to reach only 45 km but Walker overshot and reached 51 km, breaching the stratosphere and into the mesosphere. It was the first time a human has achieved such altitude. This human altitude record lasted only about two weeks, until Yuri Gagarin became the first man in space on Vostok 1 on April 12, 1961.

Walker in 1955. Credit: Wikimedia Commons

Walker continued flying the X-15 and would himself surpass the 100 km altitude, the internationally accepted boundary where space begins. This historic flight took place on 19 July 1963. Walker and the X-15 were airdropped from the Boeing NB-52B Stratofortress over Smith Ranch Dry Lake, Nevada. Walker fired the XLR99-RM-1 rocket engine and over the next 84.6 seconds the engine’s 60,000 pounds of thrust drove the X-15 upward. The engine’s thrust on this flight was higher than expected, shutdown was 1.6 seconds late, and Walker’s climb angle was 1½° too high, so the X-15 overshot the predicted maximum altitude and its ballistic arc peaked at 347,800 feet (106,010 meters). The maximum speed was Mach 5.50 (5,977 kilometres per hour). On this flight, Joe Walker became the first American civilian to fly into Space, and the second civilian overall, after Soviet Union's cosmonaut, Valentina Tereshkova.

Walker would fly again into space, this time achieving an altitude of 354,200 feet (107,960 meters), which is the highest altitude of the entire X-15 program. It was also Walker’s last X-15 flight.

Walker died when an F-104N Starfighter he was piloting collided with an XB-70 when attempting a tight formation during a publicity photoshoot. The F-104 exploded killing Walker immediately.

Walker's F-104 tumbles in flames following the midair collision. Credit: Wikimedia Commons