NASA’s experimental X-59 plane is one step closer to making faster-than-sound flight quiet after the aircraft flew supersonic for the first time on June 5, reaching a peak speed of 713 miles per hour at an altitude of 43,400 feet—equivalent to Mach 1.1.
“Flying at supersonic speeds is a major milestone for the X-59 team,” said Cathy Bahm, project manager for the program at NASA, in a statement in late May, before the flight. “Completing the first mission-conditions flight is especially meaningful—it’s the moment where we begin validating the aircraft in the environment it was designed for.”
The flight lasted 81 minutes and was based at Edwards Air Force Base; NASA pilot Jim Less flew the milestone sortie.
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“Supersonic” is a slippery term, given that the speed of sound depends on the temperature and pressure of the local atmosphere. Mach 1 represents the local speed of sound, above which movement is considered supersonic; Mach 5 marks the transition to even faster “hypersonic” speeds. When objects travel faster than the speed of sound, the pressure waves they produce are funneled to their rear and produce a cone; if the object is flying low enough for this cone to hit Earth, the result is a loud noise called a sonic boom.
These booms—as well as a massive price tag—prompted the 2003 retirement of the only supersonic passenger plane, the Concorde, which ferried passengers starting in 1976. The plane reached cruise speeds of 1,350 mph and could fly from New York City to London in less than three hours under good conditions.
For nearly a decade, NASA has been working to engineer a plane that can fly faster than the speed of sound without resulting in disruptive sonic booms. The vehicle’s long nose is designed to disperse the shock waves so that flight produces merely a “quiet supersonic thump,” as the agency described it in the late May statement, somewhere between distant thunder and a car door shutting 20 feet away.
The result is the X-59, which first flew in October 2025 and has made more than a dozen flights to date. Now that the X-59 has gone supersonic, the test flight program continues, with planned speeds reaching Mach 1.6 (1,218 mph) and altitudes reaching 60,000 feet, although the plane will also make less superlative flights to provide its engineers with ever more data.
“These flights not only deepen our confidence in the X-59’s performance—they mark our progression toward the future phases of the mission that will ultimately help shape the future of supersonic travel,” Bahm said in the late May statement.
Once this round of test flights is complete, NASA will begin a second phase of tests that focuses on the noise the plane makes, determining whether it produces the planned “quiet supersonic thump” or something more akin to the unacceptable sonic booms of other high-speed vehicles. The final phase will relocate these tests over communities, with NASA surveying residents on their impressions of the airplane’s noise.
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