NASA wants to know how the launch industry's chic new rocket fuel explodes - Ars Technica

Overview

NASA wants to know how the launch industry’s chic new rocket fuel explodes

“We put fuel in a rocket, blow it up in a remote location, and measure how big the boom is.”

Details

For more than 60 years, nearly every large rocket used some combination of the same liquid and solid propellants. Refined kerosene was favored for its easy handling and non-toxicity, hydrazine for its storability and simplicity, hydrogen for its efficiency, and solid fuels for their long shelf life and rapid launch capability.

About 15 years ago, rocket companies started serious development of large methane-fueled engines. Space X and Blue Origin now build the most powerful of these new engines—the Raptor and BE-4—each capable of generating more than half a million pounds of thrust. Space X’s Starship rocket and its enormous booster are powered by 39 Raptors, while Blue Origin’s New Glenn and United Launch Alliance’s Vulcan rockets use a smaller number of BE-4s on their booster stages.

Burning methane in combination with liquid oxygen, these “methalox” engines have several advantages. Methane is better suited for reusable engines because they leave less behind sooty residue than kerosene, which Space X uses on the Falcon 9 rocket. Methane is easier to handle than liquid hydrogen, which is prone to leaks and must be stored at staggeringly cold temperatures of around minus 423 degrees Fahrenheit (minus 253 degrees Celsius). Methane is also a cryogenic liquid, but it has a warmer temperature closer to that of liquid oxygen, between minus 260 and minus 297 degrees Fahrenheit (minus 162 to minus 183 degrees Celsius).

A Chinese rocket became the first methane-fueled launcher to reach orbit in 2023. In the United States, Rocket Lab, Stoke Space, and Relativity Space are also developing methane-fueled engines for their next-generation launch vehicles.

But rockets sometimes blow up. The US Space Force and NASA, the agencies responsible for range safety at America’s federally owned spaceports, want to better understand how the hazards from an exploding methalox rocket might differ from those of other launchers. This is important as launches become more routine, with companies foreseeing multiple flights per day from launch pads that are, in some cases, just 1 or 2 miles apart.

“We just don’t have the analysis on those to be able to say, ‘Hey, from a testing perspective, how small can we reduce the BDA and be safe?'” said Col. Brian Chatman, commander of the Eastern Range at Cape Canaveral Space Force Station in Florida, at a roundtable with reporters last year.

Space X’s 11th Starship flight climbs away from Starbase, Texas, in October 2025.

Launch pads for methalox rockets are now operational or under construction on government property at Kennedy Space Center and Cape Canaveral Space Force Station in Florida, Vandenberg Space Force Base in California, and NASA’s Wallops Flight Facility in Virginia. Space X currently launches Starship test flights from South Texas on private property. The Federal Aviation Administration has jurisdiction for public safety there.

Federal safety officials require the evacuation of blast danger areas around each launch pad as rockets are fueled for flight, and some companies have raised concerns that Space X, which has the largest of the methalox rockets, could disrupt their operations on neighboring launch pads. The ongoing explosive yield tests are meant to help officials fine-tune their hazard analyses to determine the proper size of the danger areas for methalox rockets.

The concept is simple. “We put fuel in a rocket, blow it up in a remote location, and measure how big the boom is,” said Jason Hopper, deputy manager for the methalox assessment project at NASA’s Stennis Space Center.

“For many of the tests, the barrier separating the two propellants is intentionally ruptured to simulate a catastrophic failure scenario,” NASA said in a statement. “As the mixing fluids are detonated, instruments located on the test articles, and throughout a test field, measure the intensity of the blast wave at certain prescribed distances.”

High-speed cameras on the test range capture how fast and where debris fragments travel after the explosion and measure the blast’s thermal potency.

“This type of testing only comes around once every few decades,” Hopper said in a NASA press release. “With so many rockets launching now, this will contribute to public safety, site safety, and all the risk involved with the work.”

A methane test article awaits its demise at Eglin Air Force Base in Florida.

The tests began in January with two baseline explosions using C-4 with well-known blast characteristics. In February, they added methane and liquid oxygen, with four tests involving unmixed propellants. The next step will involve mixing the propellants in an environment more characteristic of an actual launch failure scenario, initially with 2,000-pound test articles, then scaling up to 20,000 pounds. The tests will examine two failure modes—a transfer tube failure and a failure of the shared wall between the two propellant tanks.

Engineers will extrapolate the results to assess the explosive potential of a huge rocket like Space X’s Starship, which contains more than 10.8 million pounds of propellant at liftoff.

NASA provided more details on how engineers are conducting the tests in a post to the agency’s website Thursday. The testing is scheduled to conclude in June.

“The findings are expected to help shape launch site planning, safety protocols, and safety requirements for years to come,” NASA said.

For now, the Space Force will treat any methalox rocket with “100 percent TNT blast equivalency” and maintain a “maximized keep-out zone” for the safety of the public and workers at the spaceport, Chatman said in November. He said initial studies show the required keep-out zone will get smaller, but officials won’t know how much until the test results are in.

Liquid oxygen and methane are highly miscible, meaning they mix together easily, raising the risk of a “condensed phase detonation” with “significantly higher overpressures” than rockets with liquid hydrogen or kerosene fuels. Small-scale mixtures of liquid oxygen and liquified natural gas have “shown a broad detonable range with yields greater than that of TNT,” NASA wrote in 2023.

Space X has conducted its own methalox detonation testing. The company said the government is relying on “highly conservative approaches to establishing blast danger areas, simply because they lack the data to make refined, accurate clear zones. In the absence of data, clear areas of LOX/methane rockets have defaulted to very large zones that could be disruptive to operations.”

Industry data suggests that the government should set its TNT blast equivalency to no greater than 25 percent, a change that would greatly reduce the size of keep-out zones around launch pads, according to the Commercial Space Federation, a lobbying group whose members include Space X, Blue Origin, and other companies with methane-fueled rockets.

In written testimony to Congress in 2023, the federation urged the government to use “existing industry data” to understand the explosive yield of methane and liquid oxygen rather than spending federal dollars on an independent test campaign. In the end, NASA, the Space Force, and the FAA decided their own tests were worth the money.

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Key Takeaways

• NASA wants to know how the launch industry’s chic new rocket fuel explodes

• “We put fuel in a rocket, blow it up in a remote location, and measure how big the boom is

• For more than 60 years, nearly every large rocket used some combination of the same liquid and solid propellants

• About 15 years ago, rocket companies started serious development of large methane-fueled engines

• Burning methane in combination with liquid oxygen, these “methalox” engines have several advantages