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PROVO — How loud is the world's most powerful rocket when it roars to life?
A group of Brigham Young University researchers found out on Nov. 16 when NASA's Space Launch System rocket ignited, turning the night sky into day and powering the unmanned Orion crew capsule into space on a mission marking the first step toward putting humans back on the moon and beyond.
The BYU research team of undergraduate and graduate students, led by professors Kent Gee and Grant Hart from the school's Department of Physics and Astronomy, traveled a long road to complete its multipoint, high-fidelity recording of the Artemis I mission launch from Kennedy Space Center in Cape Canaveral, Florida.
A small grant helped kick-start the project which involved some 18 months of planning and preparation. Then a series of issues plagued NASA's attempts to get the Artemis I mission off the ground, including pesky fuel leaks and a pair of hurricanes that rolled over central Florida.
Why assessing rocket launch noise matters
While the path to completing the recording was rife with pitfalls, it's work that the researchers say will help inform how to manage the impacts of the massive sound emissions from an increasing number of rocket launches now taking place in the U.S. and around the world.
One recent example of the kinds of impacts created by frequent rocket launches was highlighted in a U.S. Fish and Wildlife report on SpaceX's plans to build a commercial rocket launch site in Boca Chica, Texas.
The Fish and Wildlife Service analysis determined that if SpaceX moves ahead with the proposal it would impact some species protected under the Endangered Species Act, as well as hundreds of acres of their critical habitat, although the activity would not completely wipe out those species, according to a May report from CNBC.
Of greatest concern is the company's anticipated impact to the mating, migration, health and habitat of the piping plover, red knot, jaguarundi and ocelot populations. Per CNBC, disruptions and harm can be caused by everything from regular vehicle traffic to the noise, heat, explosions and fragmentation of habitat caused by construction, rocket testing and launches.
And, a 2018 paper from Georgia Institute of Technology researchers noted that "despite the increase of rocket launches in the past years and the commercialization of their operations, little work has been published assessing the community noise impacts from rocket operations." The authors suggest further work on noise modeling studies would lead to better understanding the potential noise exposure issues for communities located near rocket launch facilities.
Here a launch, there a launch
This isn't the first time the BYU team has conducted launch recordings, with previous field outings having captured audio from rockets including the United Launch Alliance's Delta IV Heavy, SpaceX's Falcon 9 and Falcon Heavy and Firefly Aerospace's Alpha.
With an early research paper on the SLS sound recordings currently being considered for publication, Gee wasn't able to share all the data on the latest sound recordings. But he noted the launch of the world's most powerful rocket — the SLS produces 8.8 million pounds of maximum thrust, 15% more than the Saturn V rockets that powered Apollo astronauts to the moon — dwarfed the team's previous work, from a volume perspective.
"It's hard to describe the experience, the energy is so massive," Gee said. "Our recordings show that the sound energy is greatest at frequencies so low, they're below our normal range of hearing. So, you're as likely to feel the launch as much as you hear it.
"But even a few miles away, the maximum sound level was well over 120 decibels. It's similar to being at an airshow and having a military jet roar overhead … but only a few hundred feet away."
The BYU researchers captured the launch soundtrack from 14 recording stations in an array around Kennedy Space Center's launch pad 39B and placed at various distances from the site. Due to NASA safety restrictions in the blast zone, most of the stations had to be set up then left unmanned for the actual launch.
Gee said this is one of the most nerve-wracking aspects of capturing launch audio because recording performance cannot be monitored and success, or failure, isn't known until long after the rocket has left the ground.
A new definition of loud
BYU student researcher Taggart Durrant, who has participated in numerous other field recordings, said the in-person experience of the Artemis launch was one-of-a-kind.
"I was 10 miles away and it literally shook me," Durrant said. "It was so bright it felt like the sun had just risen. That low frequency rumble and high pitch crackling ... it's almost otherworldly. Watching this huge rocket the size of a skyscraper just take off and making one of the loudest noises you ever heard ... it blew me away."
And, Durrant noted, the sound energy of rocket launches reaches far beyond the experiential.
"The launch acoustics are so loud that they can damage the launch pad structure and even the payloads of the spacecraft," he said. "They can have huge impacts on wildlife species living on or near the base. And there's the community side of it, with more and more rocket launches heightening community exposures.
"We're hoping to evaluate and improve rocket noise models. Anything to better understand it, so we can quantify or mitigate these impacts."
Gee noted that launch acoustics research has been largely ignored since the end of the Apollo program some 50 years ago, but the growing number and frequency of rocket launches, in the U.S. and around the world, has been surging in recent years.
The space economy is taking off
In a report released in late November, McKinsey & Co. assessed a burgeoning global space economy, and associated rocket launch volumes, that are on an accelerated growth arc and particularly so over the past few years.
"These activities, once primarily the domain of government agencies, are now possible in the private sector because recent technological advances in manufacturing, propulsion and launch have made it much easier and less expensive to venture into space and conduct missions," McKinsey researchers wrote.
"Lower costs have opened the door to new start-ups and encouraged established aerospace companies to explore novel opportunities that once seemed too expensive or difficult. The technological improvements have also intrigued investors, resulting in a surge of space funding over the past five years."
If you launch it, they will come
The growing volume of rocket launch activity underscores the real world benefits of BYU's quest to build a deeper and more detailed understanding of the acoustic impacts of firing up those massive engines. But it's also providing growing career opportunities for students like Durrant and his colleague and fellow BYU senior Michael Bassett.
Durrant is in the process of applying to graduate schools and considers his research experience as a great addition to his curriculum vitae, as well as an invaluable part of his education experience and preparation for the job world.
"Being on the research team is definitely a great resume item but more than that, I've built a set of skills that I wouldn't have been able to without it," Durrant said. "That's one of the reasons I wanted to go into this field. We're starting a new space age where there is more opportunity than ever before. Space is not just what big governments do. It's become interesting and profitable for everyday people."
Bassett called working on research projects with Gee and his other instructors and student colleagues a "great opportunity to really understand fundamentals and their real world applications beyond classwork." And while he is still debating his next steps following completion of work on an applied physics degree, he definitely sees continued research as part of his future.
"I feel like I really enjoyed working with Dr. Gee, and the side of it that he has me working on, the research and development of the technologies to go with this acoustic recording," Bassett said. "Figuring out how to overcome the hurdles on projects like these, how to optimize equipment for the best outcomes, that might be where I could get into further research."
Gee, who also chairs BYU's Department of Physics and Astronomy, highlighted that the rocket launch acoustics research has been a student-led effort from the start and is producing amazing results while building confidence and skills for a new generation of scientists.
"It's just a tremendous experience for the students," Gee said. "They trained for this, prepared for it and executed the recordings perfectly. They were ready for the moment."