As Rockets leave Earth they generate infrasound, low-frequency sound waves that need different instruments to detect. Scientists are working on detecting them. A new study details infrasounds from 1,001 launches, including Space Shuttles, Falcon 9, Soyuz, the Ariane 5, Russian Proton, and Chinese Long March Rockets.
The recordings were made using the International Monitoring System. The network of more than 50 monitoring stations around the world was put together as a result of the 1996 Comprehensive Nuclear-Test-Ban Treaty. Built to detect nuclear explosions, the network also works well for detecting Rocket launches.
In one launch the Space Shuttle Atlantis launched from Kennedy Space Center in Florida, on 16 November 2009. Here the sound waves are sped up by 250 times so that they’re audible to humans. The instruments used by the monitoring system are tuned enough to identify the individual stages of each Rocket launch. In some cases, these Rockets travel faster than sound.
These infrasound waves can travel very long distances and could be detected by the IMS network even as far away as 9,000 kilometres. The 1,001 launches were logged as part of 7,637 infrasound signatures captured and analyzed between 2009 and 2020 at the IMS stations. Researchers were able to recognize infrasonic signatures for 733 of the Rocket launches, a little over 73%. The remainder 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.