Slicing through the atmosphere at 55,000 feet, NASA’s experimental X-59 reached a vital milestone on Friday, June 12, by hitting Mach 1.4 (roughly 924 mph).

Hitting these exact numbers is a huge deal. Mach 1.4 at 55,000 feet represents the identical speed and cruising height the aircraft will use when it eventually flies over populated American towns.

“Each flight brings NASA one step closer to flying the X-59 over communities and gathering feedback that could help shape the future of commercial supersonic flight over land,” NASA stated. 

Achieving flight conditions

For over fifty years, international aviation regulators have strictly banned civilian supersonic flights over land due to the deafening, window-rattling disruption of sonic booms. 

Established in 1973, this absolute ban has locked commercial air travel to standard subsonic speeds to protect populated areas on the ground.

Developed in partnership with Lockheed Martin, NASA’s X-59 is an experimental aircraft designed for supersonic flight.

In a rapid sequence of testing milestones, NASA test pilot Jim “Clue” Less first flew the X-59 to Mach 1.1 (713 mph) at 43,400 feet during an 81-minute flight from Edwards Air Force Base on June 5. 

Just one week later, on June 12, the experimental craft successfully pushed its performance envelope even further, accelerating to Mach 1.4 at even higher altitude.

How does the plane bypass the classic explosion? It comes down to design. Standard supersonic jets create air-pressure ripples that quickly clump together into a single, massive shockwave.

The X-59 is built like a needle. Its ultra-long, slender shape separates those air-pressure waves and prevents any combination from occurring. Rather than a loud boom, people on the ground should theoretically hear a gentle, car-door-like “thump.”

Currently, pilots are steadily pushing the aircraft through a battery of complex maneuvers, varying speeds, and diverse altitudes to find its absolute physical performance limits.

Engineers will thoroughly measure the aircraft’s supersonic acoustic signature using ground microphone arrays to confirm that the quiet thump is performing exactly as intended.

Eventually, NASA will take the X-59 out of isolated test spaces and fly it directly over several U.S. communities to openly survey real public perception of the sound.

The F-15 companion

Right now, verifying the plane’s actual acoustic signature is a bit tricky. During these early test flights, the X-59 is trailed closely by a NASA F-15 research fighter jet.

The trailing jet is about to become a critical scientific tool. In upcoming tests, engineers will mount a specialized, shock-sensing probe to the F-15’s nose. This will let researchers fly directly into the wake of the X-59, mapping out its invisible pressure waves and gathering real-time data on its low-boom performance.

Once the data from the community overflights has been fully gathered, NASA plans to hand the findings to international regulatory boards. The hope is to replace the decades-old speed limits with a new, noise-based standard. 

If the public agrees that the X-59 is quiet enough, the aviation industry could see a cutting of cross-country commercial flight times squarely in half.

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