To design this "low-boom" aircraft, NASA and Lockheed Martin returned to the basic principles of aerodynamics. The result is an airplane that is both incredibly advanced and elegantly simple. 

"Those principles of physics, of aerodynamics, have been around since the beginning of time," says Lockheed Martin's X-59 program director, David Richardson. "This is what Mother Nature wants to see. Just like birds are perfectly designed, this airplane is being perfectly designed to fly supersonic as quiet as it can."

When the X-59 takes to the skies, the goal is to generate a "sonic thump" and by doing so, convince regulators like the FAA that a ban on supersonic passenger travel over land can be overturned. 

That change could open the door to a future where supersonic travel is no longer just for fighter pilots. If NASA's X-59 QueSST program succeeds, flying faster than the speed of sound may be possible again for the first time since the Concorde was retired in 2003.

The science of sound

To understand how a sonic boom works, you need to know a little something about the basic physics of sound. 

Sound is essentially a wave of compressed air -- imagine it like a pulse in a slinky, moving from point A to point B at a speed of roughly 340 meters per second. When a plane flies through the air, it pushes air out in front of it, creating those compression waves. 

But when a plane flies at supersonic speeds (above Mach 1), it's traveling faster than those waves of compressed air can move out of the way. As a result, the plane generates shock waves that travel down to the ground where they are perceived as a sonic boom. 

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When a plane flies, it pushes waves of compressed air out in all directions. When it flies at supersonic speeds (faster than the speed of sound), those waves coalesce and produce a shock wave that is heard on the ground as a sonic boom. 

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A mock-up showing the X-59 taking off.

"We want to keep [the shock waves] parallel and separated from each other so they don't combine into a loud sonic boom," says Cliatt. "So we're dragging out those volume changes, making them very gradual across the entire body of the airplane."

A new way of flying

The X-59 is so long and streamlined that its cockpit has no forward-facing window.

Instead, the pilot uses an External Vision System created by NASA to fly the plane. The XVS uses two cameras above and below the aircraft to create a real-time view of the front of the plane shown on an HD screen. But the XVS also acts as a head-up display, or HUD, showing data such as altitude, airspeed and flight path. 

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NASA test pilot Nils Larson in the X-59 flight simulator, using the same External Vision System that will be used in the final X-59 aircraft.

The sonic thump

The real test of NASA and Lockheed Martin's efforts will come when the X-59 begins testing. In 2022, Lockheed will conduct initial flight tests to make sure everything is working as expected and the plane is flying with the right speed and altitude. Then Lockheed hands the keys over to NASA, which will begin "acoustic validation" testing in 2023 to ensure the sonic boom has been satisfactorily scaled back to a sonic thump.

This second stage of testing will involve sending the X-59 up with an F-15 fighter jet that will act as a chase plane, measuring the shockwaves being produced by the aircraft midflight. And perhaps most impressive of all, NASA will capture images of the shockwaves -- a process that's known as schlieren photography. 

Photographing a plane moving faster than the speed of sound is no easy feat.

"The X-59 has to eclipse the sun because we use the sun as a backdrop," says Cliatt, theacoustic testing lead. "All of that has to happen perfectly. It's like threading a needle to get that gorgeous image."

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Schlieren images like this one can capture the shockwaves coming off supersonic aircraft midflight. 

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Getting up close to the build of the X-59 at Lockheed Martin's Skunk Works.