FOR MORE THAN SEVEN DECADES, speed has been the hallmark of commercial aviation. But while we have the capability to push those speeds from around 500 miles per hour to even greater extremes thanks to faster-than-sound supersonic flight, doing so comes with a stiff penalty: ear-splitting, glass-rattling, baby-waking sonic booms. These pesky perturbations occur when the air molecules around an object traveling above the speed of sound compress faster than they can get out of the way, creating a shock wave that travels out in all directions—along with a thunderous acoustic blast.

Sonic booms effectively killed the elegant Concorde supersonic airliner in the 1970s. The fleet-footed aircraft could reach 1,354 miles per hour (or Mach 2), enough speed to rocket it from Paris to New York in just 3.5 hours versus the eight hours a conventional airliner takes. But the acoustic battering left in its wake meant that the Concorde could only ever fly over water, a rule still in place today for any proposed new supersonic commercial aircraft.

That is, unless a new design could dispense with the sonic boom. Enter NASA’s latest—and by far sleekest—experimental aircraft, the X-59. The 100-foot-long, 29-foot-wide X-59 is the centerpiece of a NASA mission dubbed Quesst (“Quiet SuperSonic Technology”) that has been nine years in the making, a partnership between Lockheed Martin’s legendary Skunk Works and NASA’s four aeronautical research centers. The project aims to develop an aerodynamic solution that could mute sonic booms to barely perceptible thumps while traveling at up to Mach 1.4 or 925 miles per hour.

The design includes a long, sharp nose and additional lifting surfaces to stretch out the air-compression region, preventing the shock waves from coalescing. The resulting airframe is visually stunning, with a needle-nose profile and top-mounted engine inlet that also helps reduce the intensity of shock waves. If the X-59 successfully muzzles its sonic boom, it could change commercial aviation forever, allowing transportation agencies to consider lifting the speed limits over land—and airlines to hot-foot it around the globe without disturbing folks on the ground.

First, though, NASA’s bird has to get off the ground. Originally intended to fly by 2021, delays have pushed back the X-59’s first flight to sometime in mid-2025.

x59 aircraft on ramp with sunset in the background

There are multiple reasons for the slow start. For one, the X-59 uses a variety of parts from other aircraft to keep costs down, including landing gear from an F-16 fighter, engine inlets from a U-2 reconnaissance airplane, the canopy and ejection seat from a T-38 military trainer, and a General Electric F414-GE-100 engine from an F-18 fighter. Integrating this hodgepodge collection of borrowed components has been a challenge, according to Jay Brandon, NASA’s chief engineer on the project. But the silver lining is that this hurdle has allowed the team to focus its resources—both financial and mental—on the core problem of quieting the sonic boom.

“For a one-off airplane, it is not cost effective to have to design everything custom,” Brandon says. “The demonstrators are typically purpose-driven vehicles. They exist to hopefully prove some new advance in technology. The philosophy of reusing heritage parts keeps costs down and enables quicker development of the X-planes. Things don’t have to be optimized for a wide mission capability for X-planes.”

Brandon adds that, in addition to getting these outsourced aircraft systems to “play together nicely,” pandemic-related supply chain issues also slowed down some of the X-59 team’s progress.

Developing the overall design for the plane came with its own stumbling blocks, too. Muting the sonic boom has been a massive engineering challenge for decades, but there have only been a few concrete attempts to get it right. Most notably, NASA ran a two-year test beginning in 2003 that featured a modestly effective but awkwardly re-designed adaptation of Northrop Grumman’s F-5E fighter jet, a lightweight supersonic aircraft that first took to the skies in 1972. By reshaping the F-5E’s nose to be shorter and thicker, the aircraft dropped the acoustic impact of the sonic boom by about one-third—helpful, but not quite good enough to permit overflight of populated areas. Though the X-59 does indeed beg, borrow, and steal a few essential components from a variety of other airplanes, they’re mostly discrete systems unrelated to the aerodynamics–it remains overwhelmingly a clean-sheet design.

computational fluid dynamics simulation of the x59 aircraft concept during supersonic flight

There’s nothing in the U.S. fleet now or in the past that truly resembles this airplane. It has a top-mounted engine nestled in an aerodynamic nest of sorts directly behind the wing, and no fewer than three additional horizontal lifting surfaces beyond its primary delta-shaped wing—one at the top of the vertical stabilizer at the rear, a conventional elevator also in back, and a canard in front of the cockpit. It has a perilously long nose that constitutes one-third of the airplane’s total length. That proboscis completely blocks the pilot’s forward view, which prompted the development of a camera system, dubbed the eXternal Vision System, that will generate the forward view on a 4K monitor inside the cockpit.

The elongated snout is central to the X-59’s boom-muffling design strategy. According to NASA, sonic booms generally happen when shock waves from an object traveling through the air faster than the speed of sound merge together before reaching the ground. The resulting blast could reach 110 decibels, similar to a loud thunderclap nearby. Engineers thus created a design that seeks to redistribute and stretch out those shock waves–hence the long nose and multiple, smaller lifting surfaces, among other design choices. Early simulations conducted over the last decade during the development of the final design suggest the strategy will work. Now, it’s time to see if the engineers are right.

The delays in getting the plane off the ground come from piecing all this engineering together. “Once we start the final design processes, there are a lot of mundane but serious challenges,” Brandon explains. “How do you make several miles of wire fit in the airplane? How do you ensure all those wires go to the right places, and they are routed so that current in one wire does not adversely affect signals being carried by another wire? How do you fit all the systems within the confines of the airplane? Unlike other airplanes, we don’t have the luxury of being able to change the outer lines to accommodate actuators or other components, since shape is the technology we are demonstrating to reduce the sonic boom noise.”

Fortunately, that process is mostly complete, and there has been significant recent progress toward first flight, including firing of the engine for the first time in October. Test pilots are now working on simulations and strategies that will progressively step up the X-59 toward full capability. This will include ground tests, taxi tests, low-speed flight, and finally breaking through the sound barrier. When that happens, engineers and volunteers on the ground beneath the airplane’s flight path will generate data on the loudness of the boom.

If the program is successful, the potential payoff could be significant for both passengers and the airlines carrying them. There is skepticism, of course, that even a successful demonstration could turn into a financially feasible product.

“I’m not sure that anyone could make the business case for supersonic transport,” says Richard Aboulafia, an aviation analyst at AeroDynamic Advisory, a consulting firm based in Ann Arbor, Michigan. He notes that challenges of engine efficiency, manufacturing costs, and maintenance costs could keep such ambitions out of reach, even though companies like Boom Supersonic and Spike Aerospace have been working for years to overcome them. “You really have to use a military fighter engine, and military engines on commercial jets make for truly God-awful economics, he says.”

Aboulafia does feel that the research is still valuable in broadening our understanding of the physics involved in sonic boom suppression. And, he says, the potential applications for low-boom designs in military use cases are in some ways even more compelling than commercial uses. (After all, sonic booms are a pretty good giveaway that you’re in the area, and military leaders would love to eliminate them.)

Nonetheless, the traveling public has been enamored with supersonic flight since the dawn of the jet age, and it’s likely interest—and investor dollars—will spike massively if NASA’s tests pay off.

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Eric Adams is a writer and photographer who focuses on technology, transportation, science, travel, and other subjects for a wide range of outlets, including Wired, The Drive, Gear Patrol, Men's Health, Popular Science, Forbes, and others.

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Avenging the Concorde: Inside NASA’s Quest to Break the Sound Barrier and Hush the Sonic Boom