The sound an orbital rocket generates during lifting-off is so loud that it is still deafening, and its vibrations are felt, shaking the ground three miles away. It raises the question of exactly how loud a rocket gets.
An orbital rocket can reach noise levels as high as 200 decibels during its launch. The acoustic energy is powerful enough to cause substantial damage to both the launch structure and vehicle and will also be fatal to any human too close to the epicenter of the launch site during this period.
An employee of NASA once commented after watching the Space Shuttle lift off from a safe distance: “Standing a few miles away, you could feel every organ in your body vibrating.” The sound an orbital launch vehicle produces during a launch is indeed that powerful.
The first stage of the Saturn V rocket (used during the Apollo Program of the 1960s and 70s to carry astronauts to the Lunar Surface) generated sound waves that registered 205 decibels during testing. The Space Shuttle generated around 194 decibels during liftoff.
To put this into context, a normal human conversation takes place at around 65 decibels, an approaching train in a subway at 100 decibels, and a jet airplane taking off at approximately 136 decibels.
(It has to be noted that decibels do not increase in a linear fashion but exponentially. For example, an increase of 10 decibels means the sound is ten times louder, while an increase of 20 decibels means the sound is 100 times louder.)
These extremely high noise levels will not only result in permanent hearing loss if a human being is too close to the launch location, but it can also have much more severe consequences, as the following section will illustrate.
Why The Noise Generated By Rockets Are So Dangerous
Sound travels through the air as waves, which disturb the air molecules they travel through. This essentially creates a pressure wave (sometimes referred to as a shockwave), which causes the air particles to vibrate and produce energy.
The bigger the sound, the bigger the pressure wave and the extent to which the air molecules vibrate and release energy. At close to 200 decibels, the sound of a rocket lifting off produces a pressure wave so strong it can flatten structures in the immediate vicinity.
The acoustic energy released is also capable of severely damaging the launch structure, and the pressure wave reflecting off the launchpad can also damage the launch vehicle itself.
(During the launch of the Space Shuttle Columbia in 1981, 16 thermal tiles got dislodged, and another 148 were damaged due to the reflected acoustic energy.)
The impact of this pressure wave is not limited to launch vehicles and structures, though. Any human in the immediate vicinity of a rocket launch will also be severely injured, to the extent that it may even result in almost instantaneous death.
The sudden and violent change in air pressure will most probably rupture an individual’s lungs but, at the very least, cause the blood vessels in it to form air bubbles, which will inadvertently travel to the heart. In either case, the end result will be fatal.
As a result, launch facilities have put several measures in place to protect launch vehicles, the surrounding structures, and crew & personnel, as the following section illustrates.
Measures To Reduce Rocket/Suppress Noise
NASA recognized the power and potential damage the sound generated by its orbital launch vehicles could cause very early in the United States Space Program. They addressed the problem by using a sound suppression system still widely used today.
The sound suppression system uses nozzles placed on the launchpad, which start to spray large volumes of water at high velocities between the rocket nozzles and launch platform just before & during the launch, significantly reducing the effect of the acoustic energy.
(The billowing clouds of white “smoke” observers typically see expanding rapidly from a launchpad as a rocket lifts off are, in fact, clouds of steam forming as the heat from the rocket thrusters vaporizes the thousands of gallons of water sprayed onto the launchpad.)
The jets of high-speed waterdrops can absorb and suppress the effect of the shockwave to a large extent. The sound suppression system works so well that it can reduce the noise level from 200 decibels to a more manageable and less damaging 142 decibels.
This method of sound suppression was used during the Apollo missions of the 1960s and 70s to reduce the acoustic energy produced by the first stage boosters of the gigantic Saturn V rockets and is still used today for virtually every orbital rocket launch.
(One can learn more about the sound suppression systems used during orbital launches and the role the familiar tall water towers play in these systems in this article.)
To protect the ground crew and other personnel, the area in and around the launch complex is vacated up to three hours before the rocket lifts off. Spectators that choose to attend a live launch event are kept at a safe distance of at least 5 kilometers (3 miles).
Conclusion
The deafening sound an orbital rocket produces is not only capable of causing permanent hearing loss more than a mile away, but it can also cause severe damage to the launch vehicle and launchpad, as this article illustrated.
As a result, the measures implemented to suppress the sound generated are not only practical but crucial to protect the launch structure, vehicle, and ground crew.
This article was originally published on headedforspace.com. If it is now published on any other site, it was done without permission from the copyright owner.
