How do you fly faster than sound without a sonic boom?

On 28 October 2026, a year to the day after its first flight, NASA’s X-59 left California on its first cross-country trip, stopping at El Paso and Fort Worth on the way to Kennedy Space Center. It is a strange-looking jet: 99.7 feet long, almost a third of it nose, with its engine on top. It is built to fly faster than sound, about Mach 1.4 at 55,000 feet, without the sonic boom. So how do you fly faster than sound without a sonic boom?

▶ Try it yourself in Quiet Boom Lab: stretch a jet’s nose, change its speed and height, and watch its shock waves merge into a boom or stay apart as a thump.

Every bump makes a shock

A jet flying faster than sound can’t warn the air ahead that it is coming. Every place where it pushes air aside, the nose, the canopy, the inlet, the wings, the tail, starts its own pressure wave, and close to the jet each one is a separate shock. Our Sonic Boom Lab shows how those waves trail behind the jet as a cone that sweeps the ground below.

Why ordinary jets boom twice

The stronger part of a pressure wave travels a little faster than the weaker part. Over the long way down, about 17 km from 55,000 feet, the shocks at the front catch up with each other and merge into one big shock, and the ones at the back do the same. What reaches the ground is an N-wave: a sudden jump in pressure, a steady fall, and a sudden jump back. You hear it as a sharp double boom. In the tool’s model, an ordinary 19.5 m jet at Mach 1.4 and 55,000 feet arrives as an N-wave of about 0.8 pounds per square foot, each jump taking about a millisecond: about 92 on the model’s loudness scale.

Stretch the nose

The X-59 is shaped so its shocks stay weak and far apart, too far apart to catch up before they reach the ground. The long, slender nose spreads the front of the wave over many metres instead of one sharp point; the engine sits on top, where the wing shields the ground from its inlet’s shock; and the lift is spread from the small canard to the T-tail. NASA designs the shape backwards from the sound it wants on the ground. In the tool, the X-59’s shape arrives as five small steps that build the pressure over about 15 milliseconds instead of one: a soft thump.

Seventy-five, not a hundred and five

NASA rates booms in perceived decibels (PLdB), a scale built for short, sharp sounds. Its target for the X-59 is about 75 PLdB on the ground, which NASA has compared to a car door closing. Concorde’s boom was about 105 PLdB, NASA says. That 30 dB gap is the whole point. Booms got civil supersonic flight banned over US land in 1973, and the ban still stands; in July 2026 the FAA proposed replacing it with a limit of 0.11 pounds per square foot on a boom’s pressure at the ground, which is not final. Next, after acoustic tests, NASA plans to fly the X-59 over US towns and ask people what they hear.

The tool is a simplified model, not a CFD result: Whitham’s theory of supersonic flow, with the waves aging on the way down through the standard atmosphere. Both jets weigh an assumed 24,000 lb (Lockheed Martin gives the X-59’s take-off weight as about 25,000 lb, other sources up to about 32,300 lb), and the loudness scale is set so the X-59 shape at Mach 1.4 and 55,000 feet reads NASA’s 75 PLdB target. The film uses short clips of the X-59 landing at and taking off from Fort Worth, filmed by spotter @LensOfMae, and NASA’s schlieren image of two T-38s and their shock waves (NASA Armstrong), credited on screen; the jets, shock waves and numbers are drawn from the model.

Sources: NASA, How is the X-59 designed to quiet the boom?; NASA, Low-Boom Flight Demonstrator lithograph; NASA, NASA awards contract to build quieter supersonic aircraft (2018); NASA Armstrong, Sonic boom heads for a thump; NASA Quesst blog, X-59 completes record six flights in one week (Mach 1.53); AIN, X-59 heads to Florida as NASA marks first-flight anniversary; DLA Piper, Proposed FAA rule would allow civil supersonic flight.