Why sonic booms from the most powerful rocket ever built have some scientists worried

By Jackie Wattles, CNN

(CNN) — A SpaceX Super Heavy rocket booster as tall as a 20-story building reappeared in the skies over South Texas minutes after blastoff in October, blazing up its engines to slow its fall back toward Earth. In an unprecedented feat, the booster wowed audiences with a precision midair landing in the arms of its launch tower.

The stunning spectacle — part of a test flight of SpaceX’s Starship, the most powerful rocket system ever constructed — was a moment many viewers witnessed via live stream and broadcast. But only those physically located near the launch site actually experienced the thunderous noise of the event.

As the Super Heavy booster made its way back to a pinpoint landing, an earsplitting sonic boom rang out.

“It truly was one of the loudest things I’ve ever heard or experienced,” said Noah Pulsipher, an applied physics undergraduate at Brigham Young University in Provo, Utah, and a coauthor of a recent study about the noise associated with the Starship launch.

The sound, detectable miles away at a popular tourist destination, was as loud as a gunshot at close range, according to the study that published in November in the journal JASA Express Letters.

Similar sonic booms are expected to ring out each time SpaceX returns a Super Heavy booster back to its Starbase launch site, which lies near Brownsville, Texas, on the Mexican border at the state’s southernmost tip. So far, the company has conducted six test flights of a fully stacked Starship rocket from the area, but so far only the October flight — Flight 5 — has had a Super Heavy booster return for landing.

Federal regulators have already green-lit the next test flight, Flight 7, that could see the Super Heavy booster head back for a landing.

As the lower stage of the Starship system, the booster initially vaults the Starship spacecraft, the rocket’s upper stage, toward orbit before heading back to the launchpad.

The sonic booms associated with that maneuver could raise new environmental concerns for a rocket development program already mired in them.

Sonic boom-related issues may include potential hearing damage or result in minor structural issues for buildings in the area near the Gulf of Mexico.

SpaceX did not respond to a request for comment for this article, but CEO Elon Musk has downplayed recent reports about sonic boom risks.

“Starbase is an area that experiences storms and hurricanes that are far more serious than Starship launches,” Musk posted on X, the social media platform formerly known as Twitter that he purchased in 2022. He added that he believes reports about the phenomenon should say, “Starship Launches Cause No Damage.”

But while no instances of property destruction were publicly reported after the Super Heavy’s first soft landing in October, researchers said they need more data to understand the risks fully.

“I think this has to be carefully watched,” said Dr. Victor Sparrow, a professor and director of the graduate program in acoustics at Penn State who was not involved in the study. “Some people are more sensitive (to noise), and for those sensitive people, this could be a problem for them.”

And if SpaceX makes good on its intention to launch dozens, if not hundreds, of Starship flights per year, it raises questions about how the local community surrounding the company’s launch site might react — and whether the mega rocket could elicit the same pushback as other high-profile vehicles that have sparked sonic boom controversy.

The booster’s boom

Sonic booms became part of the public consciousness during the advent of supersonic air travel in the mid-20th century.

The sharp clap of noise occurs when an object travels faster than the speed of sound, which varies due to factors such as air temperature but is typically around 767 miles per hour (1,235 kilometers per hour).

The phenomenon is widely considered to be one of the key reasons for the downfall of the Concorde, the supersonic British-French passenger jet that cut transatlantic flight times in half but discontinued service in 2003.

SpaceX’s rocket launches are now bringing sonic boom conversations back to the fore.

SpaceX is the only company in the world that routinely guides its rockets back to a pinpoint landing after launch, the maneuver that triggers a startling sonic boom. The company mastered that technique over the course of a decade flying its workhorse Falcon 9 rockets.

Lead study author Kent Gee found in his experience measuring sonic booms after Falcon 9 launches in Florida and California that some residents there have grown weary of the jarring noises.

“Some people love it. Some people don’t love it,” said Gee, chair of Brigham Young’s department of physics and astronomy. “Some people loved it at the beginning, and now they don’t love it.”

SpaceX is looking to do the same with its Starship system — guiding the Super Heavy booster that launches the Starship spacecraft toward orbit back to a landing on terra firma.

And because Super Heavy is nearly twice the size of a Falcon 9 booster, the sonic boom it can emit is much louder.

The Brigham Young researchers estimated that Starship gives off the noise equivalent of 10 Falcon 9 launches.

Their analysis was informed by data the team collected at the October 13 test flight as well as earlier research the team conducted at Falcon 9 launches.

“You almost feel it more than you hear it,” Pulsipher said. “It pushes you back almost.”

Sonic booms occur because an object traveling at supersonic speeds compresses the air in front of it, and the quick compression of air molecules creates a shock wave that triggers a sudden increase in air pressure. Humans experience this as an “overpressure event ” — which can be heard and felt.

“It set off car alarms,” Pulsipher said of the sonic boom emitted during SpaceX’s Flight 5 Starship test flight when the Super Heavy booster landed back at its launchpad.

From Pulsipher’s vantage point during the flight — looking on from the small beach community of Port Isabel about 6 miles (9.7 kilometers) from the launchpad — the overpressure event he experienced clocked in at roughly 9 pounds per square foot, a unit of pressure that measures the strength of the shock wave from a sonic boom.

An instrument set up on the roof of the Margaritaville Beach Resort on South Padre Island, a popular tourist destination across the water from SpaceX’s facilities, measured 11 pounds per square foot.

“So you can just imagine a 10-pound dumbbell, and you put that on your chest — that’s kind of the experience that we’re talking about,” Pulsipher said.

Potential risks

Researchers and regulators are working to assess further what risks these sonic booms may present to the surrounding area, Gee said.

“Anytime you have a sharp sound exceeding 140 decibels, there is a non-negligible risk of hearing loss,” he said.

The sonic boom from the October Starship launch measured up to 146 decibels in some areas.

“That’s like being a few feet away from a gunshot without hearing protection,” Gee said.

He added that the pressure and noise levels the Brigham Young researchers recorded indicate that the sonic boom reached levels in some areas that previous research has shown is capable of breaking windows — particularly old, damaged or single-pane ones.

“Is it loud enough to knock your house down? No … but you’re starting to have risk of structural damage,” Gee said.

Overall, Gee noted, while the threat to people and property is likely small, exactly how sonic booms might affect the South Texas communities around Starship’s launch site is not yet clear.

More data about the sonic booms — and how weather patterns might affect their impact — is desperately needed, he said.

“Right now, we essentially have one data point,” Gee said, referring to SpaceX’s October test flight of Starship so far being the only successful attempt to bring a Super Heavy booster back to a ground landing.

Still, Gee said he is occasionally hesitant to discuss these issues because of pushback. He said fans of the company have accused him of trying to slow SpaceX down or paint Starship in a bad light.

“That’s not my goal. Our goal is to provide data (about Starship’s sonic booms) so that we can have rational conversations. Without the data, you’re just guessing,” Gee said. “Everything has a trade-off, and I will be the first to say this is always a nuanced discussion.”

Boca Chica Village

The Brigham Young researchers collected their data via instruments placed between 6 and 22 miles (9.7 and 35.4 kilometers) away from the launch site.

But there are structures much closer to the Starship launchpad at a site that SpaceX calls Starbase. The “strongest effects (from sonic booms) will be localized” there, SpaceX acknowledged in a July blog post.

The Starbase area largely consists of wildlife refuges and land privately owned by SpaceX. There’s also a neighborhood, called Boca Chica Village, which is less than 2 miles (3.2 kilometers) from the launchpad. SpaceX bought out most of the homes in that community years ago.

But private residents still own at least a few properties, according to public records.

“(The) FAA requires SpaceX to maintain insurance in the event a sonic boom results in claims of structural damage,” according to a launch license update the Federal Aviation Administration published in October ahead of the first Super Heavy booster landing. “Property owners may contact SpaceX directly to submit claims and evidence in support of the damage claim.”

Risk to wildlife

The recent study didn’t address the impact on wildlife, but past research has documented an array of effects that sonic booms may have on pets and wild animals.

They include startle and stress responses, such as one Pulsipher described witnessing near SpaceX’s launch site in October. “Dogs were barking. We saw some deer running around kind of startled,” he said. “It’s really startling if you don’t know that it’s happening.”

One 1972 study documented “occasional trampling, moving, raising head, stampeding, jumping, and running” among animals exposed to sonic booms.

“Avian species occasionally run, fly, or crowd. Reactions vary from boom to boom and are not predictable,” the study reported.

Responses can also vary wildly depending on the species, and it’s not yet clear whether sonic booms may have a long-term impact on the wildlife at the reserves surrounding SpaceX’s Starship launch site.

The US Fish and Wildlife Service said that it does not have sonic boom monitoring equipment near the Starship launch site in Texas, but the agency does collect data about sonic booms emitted from Falcon rockets launching from Florida and California.

In the latter state, sonic booms and noise associated with rocket launches are one reason local officials said they moved to limit the number of launches SpaceX carries out in California. The company responded with a lawsuit alleging the state commission involved in the matter had exhibited “naked political discrimination.”

Mitigation measures

Sonic booms are top of the mind for some at the FAA as it evaluates whether to approve SpaceX’s request to carry out up to 25 Starship flights per year from South Texas. (Currently, the company is permitted to launch up to five.)

SpaceX Chief Operating Officer Gwynne Shotwell has also said the company aims to carry out as many as 400 Starship flights in the next four years.

In a statement to CNN, the FAA said, “(I)f an environmental assessment concluded that sound levels would rise to the level of significance,” it would prompt the agency to issue an environmental impact statement — a lengthy regulatory process almost certain to slow down SpaceX’s ambitious goals for ramping up Starship development.

It’s unclear how Musk may approach the FAA in his new role within President-elect Donald Trump’s transition team. The SpaceX CEO has called for FAA leadership to resign, and more broadly he’s promised to slash regulations in his role as cochair of Trump’s proposed Department of Government Efficiency. (FAA Administrator Michael Whitaker recently announced he will step down in January, giving Trump the opportunity to appoint a new agency chief.)

Five public comment meetings for the FAA’s draft environmental assessment of Starship are scheduled for January.

The FAA was not involved in the Brigham Young study on Starship launch noise.

However, SpaceX is instructed to “monitor sonic boom levels of up to three successful authorized operations that involve a Super Heavy booster landing,” according to the agency’s emailed statement to CNN, and the company is required to “provide the monitoring data to the FAA within 15 days of the launch for review with other post-launch reporting.”

Still, the FAA “does not regulate a particular sound level with a commercial space operator,” the agency said in a statement.

But if an environmental impact statement found that “sound levels (from a Starship launch) would rise to the level of significance” that they posed a risk to property, “the FAA would identify mitigation measures, which the applicant could implement to avoid, minimize, or compensate for the damage.”

Mitigating the noise that a Super Heavy rocket booster emits as it heads back in for landing at supersonic speeds, however, would be difficult.

New supersonic aircraft with bodies designed to dampen the boom they emit are under development, hoping to learn from the lesson of the failed Concorde.

But similar design changes likely are not possible for rockets — as the vehicle’s size and structure is already carefully tailored for the difficult task of escaping Earth’s gravitational pull, noted Sparrow, the Penn State sonic boom researcher.

“You could put the launch site further and further from habitable areas,” Sparrow said. “But that’s it” as far as mitigation measures go.

The arrival of the future

For its part, SpaceX has attempted to rally public support for Starship, emphasizing that the rocket will aim to one day carry the first human to Mars. NASA also intends to use Starship to return humans to the moon for the first time in five decades.

SpaceX has indicated it hopes sonic booms will be associated with those ambitious goals in the public consciousness.

“Sonic booms announce the return of rockets and spacecraft built to be reused,” a blog post from the company reads. “With Starship, they’ll signal the arrival of a rapidly reusable future in spaceflight to travel to Earth orbit, the Moon, Mars, and beyond.”

Sparrow added that — if SpaceX weren’t developing a massive launch vehicle for interplanetary travel — another company would attempt to do so.

“I don’t think it’s SpaceX’s fault,” he said. “If they didn’t develop these technologies, somehow, someone eventually is going to develop this technology — and they’re going to have exactly the same issues.”

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