On November 16, 2022 at 01:47 EST, NASA’s new rocket “SLS (Space Launch System)” is the first mission using “Artemis 1” was launched. The SLS was the world’s most powerful rocket ever successfully launched, with an estimated launch power output of 39.1 million Newtons. This is 13% higher than the “Saturn V” used in the Apollo program to send humans to the moon.
Well, the Saturn V, which was launched more than half a century ago, has been plausibly whispered on the Internet as follows.The Saturn V’s firing sound was so intense that its sonic energy melted concrete and burned grass a mile (1.6 km) away., That’s what it means. However, in a study that scientifically verified this urban legend, “there can be no such phenomenon” was the conclusion.
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One of the reasons why such an urban legend has been whispered for many years is that there have been almost no launches of large rockets comparable to the Saturn V in the last half century, and the sound at launch is modern and modern. This is because there were no observational examples.
[▲ Figure 1: SLS just before liftoff (Credit: NASA)]
![【▲ Figure 2: At the moment when the sound emitted from the SLS rocket engine occurs, you can see that a white “cloud” that was not generated in Figure 1 appears. This is caused by extremely loud noises. (Image credit: NASA)]](https://sorae.info/wp-content/uploads/2023/03/3d2b5298101bc2e5040dcd638d6e4fd0.jpg)
【▲ Figure 2: At the moment when the sound emitted from the SLS rocket engine occurs, you can see that a white “cloud” that was not generated in Figure 1 appears. This was caused by an extremely loud sound (Credit: NASA)]
A research team such as Kent L. Gee of Brigham Young University reported the first report on the launch sound measured at the launch of Artemis 1 in a paper.
Artemis 1 launched at midnight local time, and it was a humid day. Together with the light shining on the launch pad in such an environment, the sound waves are easier to see visually. In layman’s terms, sound waves come from changes in the density of air, and when extremely loud sounds occur, such as the sound of a rocket launching, pressure changes create “clouds.” In fact, the video of the launch of Artemis 1 shows such “clouds”.
[▲Figure3:Picturesoffivestations(redpinsinFigurea)andmicrophonesinstalledatthestations(FigurebandFigurec)Thistimeitbecameclearthattheloudnessatallpointswashigherthanthepredictedloudness(Credit:Geeetal)】
In this study, the launch sounds recorded by five microphones placed 1.5 km to 5.2 km away from the launch pad were analyzed. The SLS launch uses four liquid hydrogen-liquid oxygen engines and two solid-fuel rocket boosters, and the primary source of the sound was presumed to be the solid-fuel rocket boosters. The loudest recorded sound was approximately 136 dB at 1.5 km from the launch pad, and the farthest recorded sound at 5.2 km was approximately 129 dB.
Interestingly, at all five recording locations, the sound was louder than previously predicted. Before SLS development began, NASA was developing another rocket, the Ares V, which was about 40 percent more powerful than SLS. An environmental assessment to predict the impact of rocket launches on the environment predicted that the Ares V launch sound would be below 110 dB at a distance of 4.5 km from the launch site. However, the SLS launch sound measured this time was about 20 dB louder than the predicted value for the Ares V, which was supposed to be a rocket with higher output than the SLS.
The evaluation of sound depends on various factors such as the waveform and frequency of the sound, as well as the weather and atmospheric conditions of the day, so it cannot be easily predicted. It suggests that there is room for improvement.
The recording also showed other interesting data. How a sound sounds to the human ear depends on its frequency characteristics. In the case of noises such as rocket launches, it is important how to characterize the sound. For example, when analyzed using a technique called “A-weighted frequency weighting” (*characteristics that weight the frequency range that can be perceived by human hearing), the noise level at a point 5.2 km away from the launch pad is similar to the chain saw or lock at hand. It indicates that noise equivalent to that of a concert venue was generated.
Also recorded was the high-frequency sound colloquially described as “crackling” emanating from the high-powered engine. While crackling is sometimes recorded in military jet engines, it has not been recorded in rocket engines and has been little studied. The measurements suggest that it recorded a crackling sound that was 40 million times louder than the sound of a bowl of cereal crunching.
Research on extremely loud sounds has not progressed much due to the rarity of their sources. This paper is an early-stage analysis of rocket launch sounds, and it can be said that many mysteries still remain. Further analysis of recorded sounds and additional data obtained from subsequent SLS launches may have a certain impact on future rocket development.
Source
Text: Riri Ayae
