Microphones against hypersonic missiles: how an old trick from the First World War can help against new weapons

Hypersonic missiles are a radar nightmare. They fly 5-10 times faster than sound, are enveloped in plasma, which "extinguishes" radio signals, and change their trajectory on the way to the target. But there is one caveat: they make a lot of noise. And this is exactly what a new, but essentially ancient idea is based on — to detect missiles not with radars, but with microphones.

Does that sound like a joke? But it's not. It's a return to the roots. Back in World War I, armies used arrays of microphones to determine where enemy artillery was firing from. The time difference between the sound of the shot coming to different microphones was measured, and the launch point was calculated from this difference. Today's technology just took this idea and put smart glasses on it.

Modern acoustic systems are not just microphones, but entire networks of "smart" sensors with integrated processing. They determine the direction of the sound themselves, classify it (it's a drone, it's a jet engine, it's an explosion), and immediately send the data to the command center. And they do it quickly, cheaply and without radiation, which means they are difficult to detect.

Infrasound sensors are especially powerful — they catch waves with a frequency below 20 Hz, which spread over hundreds of kilometers, almost without losing strength. Such systems are already in use: for example, the American UTAMS tracks missile launches, mines and shelling by sound. And in Ukraine, the Zvook network operates — thousands of acoustic sensors that use artificial intelligence to analyze noise and help air defense to find drones, Grads and helicopters. It's not a replacement for radars, but it's a great addition, especially when the enemy uses silencers and low-profile targets.

So can such a "microphone shield" stop a hypersonic missile?

Partly— yes, but not in the way it seems.  

While the rocket is at launch, during takeoff, it emits a powerful engine roar and an explosion — this can be detected. Acoustic networks can record the moment of launch and orient other systems: satellites, IR sensors, radars. That is, the microphones here are not the main character, but the "starting whistle".

But as soon as the rocket goes into the stratosphere, the sound lags behind. A sound wave travels at 340 m/s, while hypersound travels at 1,700 m/s or higher. In addition, the air is thin at high altitude, and sound does not spread well. Therefore, acoustics are powerless in the terminal phase of flight.

The real "hunters" of hypersound are: 

- Satellites with infrared sensors that see the fire plume from the engine;  

- Powerful AFAR radars capable of operating in interference conditions;  

- Over-the-horizon systems that track missiles beyond radio visibility;  

- And most importantly, data fusion systems that combine information from all sensors into a single picture.

So microphones are not a panacea, but a valuable element of the mosaic. They are cheap, easy to deploy, and work great in the near-term. In the fight against hypersound, they will not replace space systems, but they can provide those very first seconds that decide the outcome of an attack. And in war, as you know, every second counts.