What is required to transform the thunderous crack of a sonic boom into a mere whisper across the sky? On July 10, 2025, the solution became visible on the sun-drenched runways of Palmdale, California, as NASA’s X-59 QueSST test aircraft rolled under its own power for the first time. This slow-speed taxi test, conducted by NASA test pilot Nils Larson and a combined team from NASA and Lockheed Martin, was a milestone: the last set of ground tests prior to the X-59’s first flight.
During these early taxi tests, engineers carefully checked and double-checked important systems such as steering and braking, closely observing the plane’s performance as it rolled along the runway. These inspections are not formalities; they are the bedrock of flight safety, guaranteeing the stability and controllability of the X-59 across an entire range of flight conditions. All the systems have to work perfectly, since the plane will shortly move on from these low-speed tests to high-speed taxi tests tests that will take the X-59 to the very limit of takeoff speed.
But the X-59 is no ordinary X-plane. It is the hub of NASA’s Quesst mission, tasked with solving one of aviation’s most intractable hurdles: the disruptive sonic boom. Previously, supersonic flight over land has been closely limited by the searing shock waves that shake windows and nerves as well. The Concorde, as an example, generated sonic booms in excess of 100 perceived loudness decibels, confining its supersonic velocities largely to transoceanic routes. The X-59, on the other hand, is intended to produce a “sonic thump” no louder than 75 perceived loudness decibels a car door slamming shut, not a clap of thunder.
This bold goal is attained through a symphony of engineering innovations. The X-59’s slender, 38-foot-long nose and carefully sculpted fuselage are designed to keep shock waves from merging into a single, ground-thumping boom. Instead, these waves are transmitted along the shape of the aircraft, reaching the ground in a sequence of soft pressure fluctuations. The engine, a specially adapted F414-GE-100 similar to what is used in the F-18 Super Hornet is situated on top of the fuselage, minimizing noise transmission to the ground further. As NASA’s X-59 propulsion lead Raymond Castner witnessed following engine testing, “We had no major showstoppers. We were getting smooth and steady airflow as predicted from wind tunnel testing. We didn’t have any structural or excessive vibration issues.”
Crucial to the X-59’s functionality is the External Vision System (XVS), a forward-facing camera and display system that substitutes the conventional cockpit windshield. Not only does this eliminate the supersonic drag from the aircraft’s profile but also gives pilots augmented reality overlays to navigate and land something required due to the stretched-out nose that would otherwise obstruct the pilot’s vision.
NASA’s development of the X-59 continues a storied tradition of X-plane research. Ever since the Bell X-1 broke the sound barrier in 1947, the X-plane program has been a proving ground for advancements in materials, propulsion systems, and aerodynamics. Planes like the X-15 expanded the envelope of hypersonic flight, while others, including the X-29 and X-48, investigated extreme wing geometry and composite materials. Every project, the X-59 among them, is a reflection of the program’s mission: to “test cutting-edge aircraft designs and technologies that could push flight beyond the known limits of speed, altitude, and maneuverability”.
Assisting the X-59’s stealthy boom effort are advanced ground-based acoustic measurement systems, like the Carpet Determination In Entirety Measurements (CarpetDIEM) array. These networks of microphones, spread over vast distances, are calibrated to detect even the faintest “thumps” as low as 50 perceived loudness decibels, comparable to a refrigerator’s hum. As Larry Cliatt, NASA’s acoustic validation lead, explained, “We expect the X-59 sonic thump to be as low as about 75 perceived loudness decibels. That is a lot quieter than the Concorde, which was over 100 perceived loudness decibels.”
The X-59’s transition from taxi testing to flight represents the next phase in a several-decade pursuit of rendering supersonic travel over land practical and acceptable. As each system is certified and each hurdle cleared, the program moves toward a future where traversing continents at Mach 1.4 is not only a possibility, but imperceptible to those on the ground.
