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There’s rarely time to write about every cool science story that comes our way. That’s why we’re posting a special series of Twelve Days of Christmas again this year, in which we highlight one scientific story every day from December 25 to January 5 that fell through the cracks in 2022. Today: Debunking the popular myth that the Saturn V launch was loud enough to melt concrete.
The 1967 Apollo 4 mission was an unmanned flight to test the Saturn V rocket as a viable launch vehicle for future crewed missions. The test was a resounding success and a critical step in the US space program. But the Saturn V was also incredibly loud – so loud that there was a rumor that the acoustic energy was enough to melt concrete. That’s not the case, according to an August paper published in a special educational issue of the Journal of the Acoustical Society of America (JASA).
“The Saturn V has taken on a kind of legendary, apocryphal status,” said study co-author Kenneth Gee of Brigham Young University. “We felt that as part of the JASA special issue on education in acoustics, it was an opportunity to correct misinformation about this vehicle.” In addition to the authors’ analysis, the paper includes several problems for students to solve related to the event, including an ironic problem involving the use of acoustic temperature to make a grilled cheese sandwich.
German rocket scientist Wernher von Braun, who helped build the V-2 rocket, came to work for NASA in 1945 as part of Operation Paperclip. His job was to share his accumulated knowledge with the Army’s missile division. But when the Soviets launched Sputnik 1 in 1957, the priority shifted and von Braun’s team was tasked with developing an equivalent American missile. Juno 1 launched the first US satellite in January 1958 and served as a prototype for the Saturn series for deployment in Earth orbit and lunar missions.
The Apollo 4 mission was launched on a Saturn V on November 9, 1967 at 7 a.m. EST. When the five F-1 engines ignited eight seconds before launch, the sound pressure produced was so powerful that the waves pounded the vehicle assembly building, launch control center and press buildings, even though the launch pad was more than three miles long. away. CBS reporter Walter Cronkite and his producer had to hold onto their trailer’s observation window when ceiling tiles fell to the floor, fearing it would shatter from the noise. Cronkite later claimed it was the most terrifying space mission he had taken. As one Saturn V launch observer described it:
“It’s like a continuous thunder, and when you think it can’t get any louder, it gets louder anyway. I remember the vibration seemed to pierce my bones… The bird takes off, the flames spew and the thunder goes on, increasing in pitch, it climbs and finally disappears in a sound like a billion sheets of heavy paper being torn lengthwise for a minute.
Something memorable would no doubt have inspired a few exaggerated claims and unsubstantiated rumors in the ensuing decades. Gosh et al. conducted a survey of online forums and discussion forums, and were baffled by the amount of misinformation that had spread about them. In addition to claims that the noise level was sufficient to melt concrete, there were claims that it ignited “grass ablaze more than a mile away” and was powerful enough to “ignite bystanders’ hair” and “create rainbows to blow out of the air”. According to the authors, “Such claims inspire awe at the power of the vehicle that propelled humans to the moon, but are nonetheless based on a flawed understanding of the true acoustic environment.”
Their analysis of that acoustic environment includes NASA footage of the Apollo 17 launch — digitized by the Discovery Channel for a 2008 documentary — in which sound waves can actually be seen shortly after engine ignition due to the humid atmosphere and backlight. Their physics-based model pegged the acoustic level at 203 decibels. Per Gee, 170 dB is equivalent to ten aircraft engines, while 200 dB is equivalent to 10,000 aircraft engines.
Since the human pain threshold is around 130 dB, that’s pretty loud. It just wasn’t loud enough to melt concrete or set grass on fire. Gosh et al. think the myth arose from confusion between sound power (similar to the wattage of an incandescent light bulb) and sound pressure (similar to the brightness of an incandescent light bulb). This would lead to erroneous attempts to calculate the acoustic power of a Saturn V launch. If reports of burning grass or melting concrete turn out to be confirmed, it’s more likely to be caused by radiant heat from the plume or debris — not the noise from the Saturn V.
DOI: Journal of the Acoustical Society of America, 2022. 10.1121/10.0013216 (About DOIs).
