Ensuring the sound of loud launches don’t destroy buildings and spacecraft
These days it’s possible to see an abundance of rocket launches from the comfort of our own homes, offices, or even street corners, if you feel like watching a broadcast from your phone. Launches are covered with cameras on the ground and even on the rockets themselves, letting us experience some of these exciting events like never before. One key aspect of a rocket launch that isn’t being fully translated through YouTube is the sound though, which is a very good thing. The amount of energy to create 650,000 pounds of thrust leads to some very powerful vibrations, loud enough to not only blow out your ear-drums, but even destroy buildings or the rocket itself if left unchecked.
The typical launch these days peaks at about 195 decibels, but this is by no means the record holder. The Saturn V rockets from the late 60s were observed blasting at 204 decibels, well beyond what would be safe for a human body. At that magnitude, the sound is less of an audio experience as and more of a shock-wave, creating waves of energy strong enough to damage structures as well as the spacecraft trying to take off. In effect, it’s almost like a an earthquake made out of sound and air. Buildings near launch areas are insulated with buffering panels to help absorb some of these vibrations, but to really reduce the amount of engine noise during a launch, NASA turns on the sprinklers.
Very wet sound dampening
We don’t normally think of spraying water as quieting, but the droplets are actually quite good at absorbing energy and breaking up the massive sound waves so they don’t become dangerously intense. Supplied by a 300,000 gallon tank, water is sprayed at two locations during a launch— in a trench below the engines for when they first fire, and higher up from 12-foot “rainbird” nozzles as the spacecraft leaves the ground. Over 900,000 gallons are sprayed per minute, which is enough interference to bring the overall volume levels within a spacecraft’s payload bay down to 142 decibels, 8 decibels quieter than a close encounter with a jet engine, and more importantly, 3 decibels below the structural threshold of a spacecraft like the now retired space shuttle.
With even larger engines slated to go into use in the next year or so, NASA has been conducting tests of this sound-suppression system. Rather than risk damaging sensitive and expensive equipment, tests are performed with functional models around 11 feet tall. The engines are fired and model lifted to no more than seven-and-a-half feet, which simulates 150 feet of lift in the real thing. This allows for measurements from hundreds of microphones, all to make sure that the future Space Launch System (SLS) spacecraft can withstand the noise of its own engines at liftoff. In the mean time, the rest of us can crank up our sub-woofers and safely pretend to go along for the journey, doing no more damage than annoying our neighbors with the sound.
Source: NASA's Next Rocket Is So Big, the Sound of It Launching Could Damage Buildings by Amy Shira Teitel, Motherboard