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Aug 21, 20234 min read

This Day in History: The X-15 Hypersonic Plane

On this day in 1963, a NASA test pilot soars into space. Joseph A. Walker was then flying an experimental spaceplane, the X-15. The trip made him the first to twice pass the Kármán line, the internationally accepted altitude where outer space begins.


Do you know about the X-15 hypersonic plane? Three were built, then piloted by NASA and U.S. Air Force pilots. From 1959 to 1968, these planes would conduct 199 different missions in Earth’s upper atmosphere.


“The North American Aviation X-15 rocket planes,” a NASA website concludes, “designed to explore the problems of atmospheric and space flight at supersonic and hypersonic speeds . . . contributed directly to the success of the Apollo lunar missions.”


In some ways, the X-15 was more rocket than plane. For starters, it didn’t take-off as a conventional plane would. Instead, it was attached to a modified B-52 bomber, then released at an altitude of 45,000 feet. Once released, the pilot would fire up the X-15’s rocket engines and start climbing to higher altitudes.


The X-15’s unofficial speed record ultimately hit 4,520 mph (Mach 6.7).


In March 1960, Walker became the first NASA pilot to make the trip. He couldn’t believe the forceful acceleration when the rocket engine roared to life.


“Oh, my God!” he yelled inadvertently. The flight controller was in a jovial mood, joking back: “Yes? You called?”


Other X-15 pilots had similar experiences. “[The launch] was a surprise no matter how many times I went through it,” pilot Milt Thompson wrote. “It felt as if the X-15 exploded off the hooks.”


Walker is perhaps best known for the three space flights he made in 1963. Two made him the only X-15 pilot to cross the Kármán line, which requires an altitude in excess of 62 miles.


Walker’s first flight came in January, when he flew to an altitude of 271,000 feet. The trip was a spaceflight by U.S. standards, but it fell short of the Kármán line. Nevertheless, he had just a few minutes to take in the view. “Some kind of searchlight was shining in the right-hand side of the cockpit instead of the left,” he later described, “and I discovered it was the moon.”


Later that year, a July 19 flight put him more than 65 miles above the Earth’s surface, well past the Kármán line. A later flight on August 22 reached an altitude of 354,200 feet, more than 67 miles above Earth.


The August 22 flight established an altitude record that would not be broken until 2004.


But the trip was about more than just gaining altitude. The descent was extraordinarily dangerous. “[A]s the pilot switched from thruster control to traditional ‘stick-and-rudder’ flying,” a NASA website explains, “the X-15 became a 15,000-pound unpowered hypersonic glider glowing red-hot as it decelerated from 4,000 mph to 200 mph. With only one shot at landing, there was simply no room for error.”


“By the time they got the aircraft back on the ground it was not the same airplane that it had been when it left the base. There were holes burned in from the heat,” adds NASA historian Christian Gelzer.


Walker’s days as a pilot unfortunately came to an end on June 8, 1966. He was flying an F-104 Starfighter in formation with a XB-70 Valkyrie bomber in what was supposed to be a publicity photo, but he got caught in a vortex coming off the larger plane’s wing.


“He died doing what he always wanted to do—fly,” a newspaper tribute concluded.


Today, we remember a tragedy—but we also remember our heroes. Daring and intrepid pioneers such as Walker fill the pages of American history. Their relentless determination has always made our country great!

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