Rocket launches are noisy affairs, for sure, but the sounds they produce aren’t all audible to the human ear. As rockets leave Earth they generate infrasound, low-frequency sound waves that require special instruments to detect.
And scientists have indeed been detecting them. A latest study details infrasounds from 1,001 rocket launches, including Space Shuttles, Falcon 9 rockets, Soyuz rockets, the Ariane 5, Russian Proton rockets, and Chinese Long March rockets.
These recordings were made using the International Monitoring System (IMS), a network of quite 50 monitoring stations round the world put together as a results of the 1996 Comprehensive Nuclear-Test-Ban Treaty. Built to detect nuclear explosions, the network also works well for detecting rocket launches.
You can hear one such launch below – the spacecraft Atlantis launching from Kennedy Space Center in Florida, on 16 November 2009. Here the sound waves are sped up by 250 times in order that they’re audible to humans.
The instruments used by the IMS are finely tuned enough to spot the individual stages of every rocket launch in some cases – though because these rockets travel faster than sound, within the example above you hear the splashdown of the boosters within the ocean before the roar of the take-off.
Researchers hope that recordings like this may enable them to assess the success of individual rocket launches and to spot any problems which may have happened along the way. In rocket launches that do not go as planned, infrasonic signatures could help scientists compute why.
These infrasound waves can travel very long distances and might be detected by the IMS network whilst distant as 9,000 kilometers (5,592 miles). The 1,001 rocket launches were logged as a part of 7,637 infrasound signatures captured & analyzed between 2009 and 2020 at the IMS stations.
Researchers were ready to recognize infrasonic signatures for 733 of the rocket launches, a little over 73%. the reainder had thrusts that were too small for them to be identified, or they were launched during atmospheric conditions that didn’t allow the sound waves to travel far enough in enough detail.
Adrian Peter, a professor of computer engineering and sciences at the Florida Institute of Technology, wasn’t directly involved within the study but has studied the infrasonic signatures of rockets before. Peter says it’s good to ascertain the IMS getting used for other purposes, which the collected data could have many various applications in coming future.
“Now we’re leveraging it for other scientific applications,” says Peter. “The ability to detect differing types of rockets might be helpful.”
The research has been published in Geophysical Research Letters.