The Falcon-9 is the most-launched rocket in recent years, but a lot of what we know regarding rocket launch noise dates back to the Apollo era. In this episode, we interview Taggart Durrant about his research into the “triple boom” that the Falcon-9 produces when its booster re-enters the atmosphere.
Associated paper: Jeffrey Taggart Durrant, Mark C. Anderson, Kent L. Gee, Logan T. Mathews, and Grant W. Hart. Initial comparison of a Falcon-9 reentry sonic boom with other launch-related noise. Proc. Mtgs. Acoust. 46, 045002 (2022); https://doi.org/10.1121/2.0001579
Find out how to enter the Student Paper Competition for the latest meeting.
Read more from Proceedings of Meetings on Acoustics (POMA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
The Falcon-9 is the most-launched rocket in recent years, but a lot of what we know regarding rocket launch noise dates back to the Apollo era. In this episode, we interview Taggart Durrant about his research into the “triple boom” that the Falcon-9 produces when its booster re-enters the atmosphere.
Associated paper: Jeffrey Taggart Durrant, Mark C. Anderson, Kent L. Gee, Logan T. Mathews, and Grant W. Hart. Initial comparison of a Falcon-9 reentry sonic boom with other launch-related noise. Proc. Mtgs. Acoust. 46, 045002 (2022); https://doi.org/10.1121/2.0001579
Find out how to enter the Student Paper Competition for the latest meeting.
Read more from Proceedings of Meetings on Acoustics (POMA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
Kat Setzer (KS)
00:06
Welcome to Across Acoustics, the official podcast of the Acoustical Society of America’s Publications office. On this podcast, we will highlight research from our four publications, The Journal of the Acoustical Society of America, also known as JASA, JASA Express Letters, Proceedings of Meetings on Acoustics, also known as POMA, and Acoustics Today. I'm your host, Kat Setzer, Editorial Associate for the ASA.
So today we'll be talking to Taggart Durrant about his article, “Initial comparison of a Falcon-9 reentry sonic boom with other launch-related noise,” which appeared in the 46th volume of the Proceedings of Meetings on Acoustics and was one of five winners of the POMA Student Paper Competition for the 182nd meeting of the Acoustical Society of America, which took place this past May in Denver, Colorado. This episode is part of a five-episode series highlighting winners of the POMA Student Paper Competition. So, Taggart, congratulations, and thanks for chatting with me today. How are you?
Taggart Durrant (TD)
01:09
Thanks, Kat, and yeah, doing great. Just a little bit snowy here in Provo, we got about six inches of snow, so I'm a little cold but doing good.
KS
01:16
Are you serious? Oh my gosh. Oh, wow. That's intense. We’re recording in very early November guys. Wow. Yeah, well, snow days.
So first, tell us a bit about yourself. Where are you studying? And what do you research?
TD
01:39
Well, yeah, as I said, my name is Taggart Durrant. I'm a senior at BYU. My major is applied physics with an emphasis in aerospace engineering. So most of my research that I've been doing for the past few years is on sonic boom prediction and measurements. It's funded by some amazing people over at NASA Langley Research Center. I work with my advisor, Kent Gee. He also does a lot of research in rocket launch acoustics, which has more to do with what this paper is on. So the past couple years, I've also had a chance to measure several different rocket launches out of Vandenberg Space Force Base in California.
KS
02:12
Okay, that's awesome. So the research behind this article has to do with the noise created at rocket launches, specifically the Falcon-9 booster. Can you give us a bit of background about rocket launch noise?
TD
02:23
Yeah, so basically, we always joke that our research pretty much just means rocket launches are loud… really, really loud. Many people will assume that noise is coming from the combustion or like the mechanical movement of the rocket engine. But the dominant noise source is actually from the plume of that supersonic superheated gas that’s ejected out of the bottom of the rocket. And when that supersonic jet mixes with the ambient air, it generates a lot of noise. And that's where, like, most of it's actually coming from.
So much of the current understanding and modeling of rocket noise comes from data and measurement from the Apollo era. That was done on equipment that was available at the time, you know, so current rocket noise research aims to correct and improve our physical understanding and our ability to predict rocket noise. Because rocket noise can impact the environment, damage the launch pad, damage the vehicle payloads, and it can definitely annoy nearby communities.
KS
03:17
Yes, that all sounds very important and would be understandable why we'd want more up-to-date information than the Apollo stuff. So tell us a bit about Falcon-9. Why did your team decide to study it in particular?
TD
03:30
Well, it basically is Falcon-9 is the most-launched rocket in recent years. It's also the first rocket to launch astronauts to the ISS from American soil since the space shuttle. Like, I think they launched Bob and Doug back in 2020. They’ve done it several times since then; that's done on the Falcon-9.
And if that wasn't impressive enough, the Falcon-9 also is incredible because it lands its first stage booster back on Earth after launching its satellite to space. And it's this booster landing that creates the phenomenon that we were interested in studying for this paper—that's a sonic boom—because the booster returns to Earth and as it's falling, it's traveling at supersonic speeds, and that creates a wake that we hear as a sonic boom. The Falcon-9 booster sonic boom is also really unique and really cool in that it creates what is referred to as a “triple boom” which sounds something like a “boom ba-boom.”
KS
04:23
Yeah, and we actually have a sound file for our listeners to hear.
[sound file of Falcon-9 triple boom]
That's pretty cool, huh?
TD
04:38
Yeah, so most military aircraft great sonic booms that have only two booms, you know? Something like a “boom-boom” sound. So this unique sonic boom is definitely a thing of interest because it's super loud. And so we wanted to analyze it and compare this triple boom, you know, from a booster reentry and compare its loudness metrics to that of the launch noise, you know, kind of see how the sonic boom and launch noise compare with each other.
So another thing we also wanted to do was to clarify some misconceptions about the Falcon-9 triple boom, because there's many internet explanations, you know, that try to describe why there's a triple boom, but most of those are very misguided, and they claim all sorts of things are responsible for that triple boom. So we wanted to clarify that that sonic boom is created by the wake from the unique shape of the booster and its unique trajectory as it falls back to Earth.
KS
05:26
Oh, yeah, that's super cool. So tell us about your experimental setup.
TD
05:30
For this paper, we kept it really simple. We just used one measurement from one microphone located about eight kilometers from the launch and landing pad at SpaceX’s Launch Complex at Vandenberg Space Force Base in California. This microphone recorded for about 10 minutes, which was enough to record the launch and landing noise along with the sonic boom.
KS
05:48
So what did you end up finding out about the Falcon-9’s launch and booster reentry sounds? How do these noises compare to those of other rockets?
TD
05:56
Well, we compare the launch and sonic boom using several different metrics because there are two very different noise type types. The launch noise lasts for about half a minute or, you know, the loudest part of it's about half a minute, but the sonic boom lasts for less than one second. So when we compared the sound exposure levels, which integrates all the sound generated by the signal over a period of time, the two ended up being about the same. This means that an observer on the ground eight kilometers away, like where we placed our microphone, receives a similar sound exposure from a less-than-one-second sonic boom and the loudest 30 seconds of launch noise. And then we also compared the two signals’ peak overpressure values. The launch noise had shocks that were about as high as 45 pascals. And what that just means is that like, you know, when you're recording your pressure values, the highest pressure value we recorded during the launch was 45 pascals. But the sonic boom’s peak over pressure was 130 pascals, which is about three times higher than the launch.
KS
06:52
So sonic booms are really, really, really loud.
TD
06:56
Rocket launches are loud, sonic booms are really, really,really loud.
KS
06:59
Yeah. What is the significance of these findings?
TD
07:04
Well, these findings show that when we're analyzing rocket launch noise and its impact on communities and environments, we have to take into account the sonic boom in the landing noise. This is especially important as more and more launch vehicles are looking to land their boosters back on Earth in one way or another. Falcon-9s are going to keep launching, but there's also new vehicles like SpaceX’s Starship that could also generate large sonic booms and landing noise.
KS
07:26
Right. That's important to consider. Was there anything in your research that really excited you or stood out to you?
TD
07:31
Yeah, for me personally, one of the most exciting things was we compared the sonic booms from Falcon-9 to other noise sources, including NASA's X-59 plane that they're building right now. It's part of their quiet supersonic technology project. I've worked on that project during my time in my undergrad at BYU as well. And so it's fun to kind of see how much louder this Falcon-9 booster sonic boom was than the X-59 because X-59 is expected to be about 75 dB in perceived level, whereas the Falcon-9 booster was 115 db. So it's 40 dB louder than NASA's new quiet supersonic plane that they're building. So it was kind of fun to compare all the noise sources from, you know, the X-59 to the old Concorde that flew back, you know, like a couple of decades ago. And then now to the Falcon-9 booster sonic boom.
KS
08:24
Yeah, right. It sounds like a lot has changed with technology. And it'll be interesting to also see, like you said with the X-59, like, how things change in the future, or as we get these quiet sonic booms. So what are the next steps in your research?
TD
08:41
Our next steps, first are to expand on these results by gathering and using the data from more rocket launches. We call this paper “an initial comparison” because it only used one microphone recording. But we now have several more data sets of Falcon-9 launch and landing noise, including a recent data set where we actually got pretty close to the launch pad, so we can add that to this analysis. And we can measure more types of rockets, to compare all of it to the Falcon-9 and see how the sonic boom changes, you know, at different distances. We can then work on determining the environmental and community impact, as more and more rockets launch and generate sonic booms on their return to Earth.
KS
09:17
That is really interesting to think about how the noise from space travel will affect those of us here on the ground, especially. Especially, you know as space programs,expand. This is definitely a field with a lot of research potential. Thanks again for taking the time to speak with me today about your research.
TD
Yep. Thank you.
KS
Once again, congratulations on winning the award for POMA
TD
09:38
Thank you so much. It's an honor.
KS
09:40
For any students or mentors listening from around the time this episode is airing we're actually holding another Student Paper Competition for the most recent meeting in Nashville. So, students, if you presented at the national meeting, now's the time to submit your POMA. We're accepting papers from all of the technical areas represented by the ASA. Not only will you get the respect of your peers, you’ll win $300, and perhaps the greatest reward of all, the opportunity to appear on this podcast. And even if you don't win, this is a great opportunity to boost your CV or resume with an editor-reviewed proceedings paper. The deadline is January 8, 2023. We'll include a link to the submission information on the show notes for this episode.
Thank you for tuning into Across Acoustics. If you would like to hear more interviews from our authors about their research, please click subscribe or find us on your preferred podcast platform.