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SpaceX Starship's Sonic Boom Creates Risk of Structural Damage, Test Finds

An independent researcher found that noise recorded miles away from the site of a recent test flight was equal to standing 200 feet from a Boeing 747 during takeoff.

SpaceX's new Starship rocket far exceeds projected maximum noise levels, generating a sonic boom so powerful it risks property damage in the densely populated residential community near its South Texas launch site, new data suggests.

The measurements — of the actual sound and air pressure generated by the rocket during its fifth test launch last month — are the most comprehensive publicly released to date for Elon Musk's Starship, the largest and most powerful rocket ever constructed.

Starship, as tall as a 30-story building, is so large that it generates 10 times as much noise as the Falcon 9 rocket that SpaceX now uses to get cargo and astronauts to orbit, the new data shows. SpaceX plans another test this week.

For residents of South Padre Island and Port Isabel, which are about six miles from SpaceX's launch site in South Texas, the noise during the October test flight was the equivalent of standing 200 feet from a Boeing 747 plane during its takeoff, said Kent L. Gee, an independent acoustics engineer who conducted the monitoring.

Dr. Gee is the chairman of the physics and astronomy department at Brigham Young University in Provo, Utah, as well as a researcher helping NASA study ways to reduce noise impacts generated by supersonic planes. The test results were published on Friday in The Journal of the Acoustical Society of America.

The Federal Aviation Administration and SpaceX did not respond to requests for comment.

When supersonic Concorde jets were still in service, the United States banned them from flying over domestic land "so their resulting sonic booms won't startle the public below or concern them about potential property damage," according to NASA.

The Starship flight test in October was about 1.5 times as loud on the ground as the Concorde sonic boom, the test results showed.

The loudest noise during the test came not during the Starship liftoff, as the giant rocket powered by 33 engines rose into the sky. Rather, the test data indicated that the peak noise was generated by the sonic boom about 6.5 minutes after liftoff, as the first-stage booster returned to the site for its self-landing at the launchpad.

During liftoff, the city of Port Isabel's sound impact reached a maximum of 105 decibels, the data shows. That is roughly equal to the noise level emitted during an average rock concert or use of a chain saw. As the first-stage booster returned, the maximum perceived noise level in Port Isabel and South Padre Island was about 125 decibels, which is equivalent to a gunshot at close range.

As that sound hit the community, it briefly created an overpressure event exceeding 11 pounds per square foot, compared with the maximum eight pounds per square foot in South Padre Island that the F.A.A. had projected in October.

Separate tests were conducted last month by a sound consultant, Terracon of Houston, hired by city officials in Port Isabel. Officials there have been increasingly concerned that the SpaceX launches might be damaging homes in the small city of about 5,000 residents.

Terracon found a peak sound pressure level of 144.6 decibels as the rocket descended, which is also higher than Port Isabel expected, said the city manager, Jared Hockema.

"We are all for economic development and the work SpaceX is doing," Mr. Hockema said. "We just want economic development that takes place in a manner that follows the law and does not hurt existing residents or the environment."

Modest property damage, such as cracks in plaster or breaks in "older and weakened, or poorly mounted windows," can start to occur when the pressurization level hits 10 pounds per square foot, according to the F.A.A., particularly if this type of level occurs repeatedly during launches. But this remains unlikely until the level hits about 20 pounds per square foot, the agency says.

In the October flight test, car alarms went off on the streets where the technicians were doing the sound monitoring. And Mr. Hockema said the city received a series of reports from residents of minor damage during the SpaceX launches, although no data has been collected on the total count.

Dr. Gee and his team set up testing devices in eight locations from six miles out — on the rooftop of the Margaritaville Hotel in South Padre Island, a resort community — to 22 miles out, at a private home in Brownsville, the closest large city.

No tests were conducted closer to the launch site, even though there are dozens of homes in Boca Chica village, less than two miles from the launchpad, and in rural areas nearby. The area is also surrounded by a national wildlife refuge and state park that are home to several endangered or threatened birds and turtles, which may also be harmed by the noise.

There has been extremely limited public data about the actual noise impact from the five full-scale Starship launch tests so far.

U.S. Fish and Wildlife Service employees last year expressed frustration that they did not have the money to buy devices to do such measurements on their own.

"It is clear we don't have the proper equipment for this (multiple devices, environmental condition sensors, software, etc.)," Stephanie Bilodeau, a wildlife refuge specialist at the agency, wrote to one of her colleagues last year, in an email obtained by The New York Times through an open records request.

The Times reported this year that SpaceX had harmed the environment around the launch site in a variety of ways. At times SpaceX disregarded promises it had made when it first proposed building a launchpad in South Texas in 2012, as it vowed to have a "small, eco-friendly footprint."

The data Dr. Gee collected last month did have some inconsistencies. When measuring just in the frequencies that humans typically hear — ignoring certain low and high frequencies — the Starship test launch in October had lower levels at all the test sites than the F.A.A. had projected.

These questions about the sound impact of the Starship are important as SpaceX is planning, once the tests are complete, to launch this rocket from two sites near the Kennedy Space Center in Florida as well as from South Texas.

"I would not be surprised if we fly 400 Starship launches in the next four years," Gwynne Shotwell, SpaceX's chief operating officer, said at a conference last week in New York.

Dr. Gee and his team will be measuring noise again during the test planned for Tuesday. Weather and wind conditions can affect how noise travels, so the results could be different, he said.