Researchers: Starship pad destruction could hold lessons for lunar landings

By Paul Brinkmann|January 29, 2024

Analysis of April launch also determined particles did not pose a health hazard

This story has been updated to include additional information about NASA and SpaceX’s plans for operating Starships on the lunar surface.

If a SpaceX Starship spacecraft attempted to touch down or launch from the moon, it could kick up a cloud of debris similar to the one created in April during the launch of the first fully stacked Starship-Super Heavy, according to analysis by a team of researchers from the University of Central Florida and Rice University in Texas.

NASA has contracted SpaceX to develop a lunar lander variant of its Starship design, which utilizes the same kind of engines as those that power the Super Heavy boosters that send the spacecraft to orbit. During the April launch from Boca Chica, Texas, the ignition of most of the 33 Super Heavy engines pulverized the launch pad of reinforced concrete and gravel, spewing debris for up to 10 kilometers at speeds of 90 meters per second.

Among the dozens of “corrective actions” that FAA directed SpaceX to complete before launching another Starship-Super Heavy, SpaceX last year made “significant reinforcements to the pad foundation” and installed what it described as a water-cooled steel “flame deflector.” The modifications appeared to do the trick in November during the second test flight: Starship and Super Heavy exploded minutes apart over the Gulf of Mexico shortly after separating, but the launch pad remained intact and no debris cloud was generated.

While these repairs were underway, UCF planetary physicist Phil Metzger decided that the April launch provided a chance to study the impact that such a powerful rocket had on underlying soil and ground material, as an early step toward modeling launches and landings on the lunar surface from some form of rudimentary pad.

“If you’re trying to lift off from the moon and you get hit by chunks of concrete traveling that fast, that would be loss of vehicle or loss of crew,” Metzger told me, adding that in the reduced lunar gravity, such objects could travel distances up to 6 kilometers.

For NASA’s Artemis moon program, plans do not call for Super Heavy boosters to touch down on or launch from the lunar surface. Rather, astronauts would be ferried from lunar orbit to the surface and back in Starship landers. SpaceX did not respond to a request for comment about Metzger’s paper, but the company has said in the past that it intends to design the lander so that the thrusters are positioned higher up on the vessel, so as to mitigate the amount of lunar dust and debris stirred up when the Starships touch down and take off again.

Metzger and his co-author, doctoral candidate Brandon Dotson, plan to present their findings in a paper in April at the American Society of Civil Engineers Earth and Space Conference to be held in Miami. Ahead of that presentation, Metzger provided me with a draft copy of the paper, “A new launch pad failure mode: Analysis of fine particles from the launch of the first Starship orbital test flight,” and spoke to me about the findings.

He said the space community has long known that a pad can be destroyed if not properly built, but the Starship mishap went beyond mere pad damage. “This was an explosion — what they had was an explosion comparable to a volcanic eruption, where it blew chunks of concrete at 90 meters per second,” Metzger told me. This cloud of debris and dust — and, in some cases, what appeared to be water droplets created by “water vapor from the rocket exhaust,” the paper reads — reached a height of about 260 meters following the launch.

Satellite and drone imagery taken after the launch show that this explosion created a large crater underneath the pad: “Application of mechanical stress and thermal stress resulted in concrete fractures that grew until they spanned the pad’s thickness, allowing hot, high pressure gas to penetrate beneath its surface,” the authors wrote in the paper. “The shallow groundwater was vaporized by the hot gas, lowering the temperature but increasing the pressure.”

As Starship lifted off, the exhaust plumes mixed “with turbulent ambient gas reducing impingement pressure on the pad, which would further exaggerate the pressure imbalance above versus below the concrete until failure occurred.”

Along with determining how far the debris traveled from Boca Chica, another question the researchers set out to answer was whether the particles posed any health risks to residents of surrounding towns. So they studied pieces of gravel, sand and other materials from the launch that was sent to them by volunteers, who collected it from cars, patio furniture and other outdoor locations near Port Isabel, about 8.5 kilometers from SpaceX’s launch site.

The majority of the particles were about the size of a grain of sand — too large to be inhaled and prompt respiratory problems such as asthma, so they concluded that “there are little negative health or environmental impacts from the fine particle material,” the paper reads. “Natural storms or wind processes can routinely transport material with similar particle sizes as observed in this study.”

With all this information in hand, Metzger and Dotson are now working on the lunar portion of the question — specifically, what effect Starship’s engines could have on lunar regolith, calculated for lunar atmosphere and gravity, Dotson told me.

“We need to do a bit more analysis of this [Starship] level of thrust but on the moon, and maybe do some modeling,” he said.