On April 20, the most powerful rocket ever flown stood on a launch pad in Boca Chica, Texas, its stainless steel skin gleaming in the sun. Moments later, rocket and launch pad would become fiery debris. It was the first, disastrous orbital test launch of the SpaceX Starship.
Within seconds of launching, the rocket’s ferocious thrust shattered the concrete pad at SpaceX’s Texas Starbase facility, sending debris flying as far as Port Isabel, a city six miles away. The rocket caught fire. Less than four minutes after launch, it began to tumble across the sky, and then it exploded.
The Federal Aviation Administration grounded Starship, pending an investigation into the explosion, but the rocket may soon fly again. On September 8, the FAA closed its inquiry, citing 63 corrective actions SpaceX would need to take before its second attempt to send Starship to orbit.
“The FAA has approval authority on all commercial launches, and so they are the ones who grant companies launch licenses,” says Wendy Whitman Cobb, a space policy expert and instructor at the US Air Force School of Advanced Air and Space Studies. “Any time something blows up, they want to know why. Because they want to make sure that it’s safe not only to go up, but that it’s not going to harm anybody on the ground.”
SpaceX will have to demonstrate to the FAA that the company has successfully completed those 63 corrective actions and then apply for a modified launch license. “Once that is granted, they theoretically can go up whenever they want,” Whitman Cobb says. Neither FAA nor SpaceX have publicly said what those fixes are. But the actions presumably address the failures of the April launch.
There’s a lot riding on Starship’s success. It’s key to expanding SpaceX’s launch and Starlink satellite businesses. NASA plans to return humans to the moon in 2025 with a modified Starship as the lunar landing vehicle on the Artemis III mission. If SpaceX can fix the problems—and Whitman Cobb and other experts believe that’s likely—the company may put its rocket program and NASA’s moon program back on track. This investigation might also provide insights into launch pad construction that could one day help astronauts traveling to and from the moon.
Failures to launch
Starship, despite not yet reaching orbit, holds the title for most powerful rocket ever launched—a superlative it took from the Soviet N1 rocket. Meant to power Soviet cosmonauts to the moon, the N1 first stage produced 10.2 million pounds of thrust. Starship has two stages in its “stack;” the first stage alone, the Super Heavy Booster, produces 16.7 million pounds of thrust.
That record-breaking power is why it was bizarre that SpaceX chose to launch Starship from a concrete launch pad without features such as flame trenches. Those grooves are designed to divert a rocket’s plume away from the pad and the vehicle itself. SpaceX could have also used a water deluge system to flood the pad to help mitigate the rocket engines’ heat and acoustic shockwaves.
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“You would never normally launch a rocket with that much thrust without having a better designed active mitigation of the plume in the launch environment. Because you worry about the heat and the dynamic forces of the plume breaking materials and creating ejecta,” says University of Central Florida physicist Philip Metzger. ”If the ejecta had hit the launch vehicle in a way that caused the rocket to explode while it was still near the tower, it could have destroyed a lot of infrastructure that would have taken a very long time to rebuild.”
As it was, the April launch blew the launch pad apart and dug a crater “about as deep as a house,” he says.
Lessons for the moon
Metzger has been studying the Starship launch and is currently writing a paper about the results. He wants to understand what went wrong—because the way things failed is important for the design of future rockets and landing pads on the moon or other celestial bodies.
Most concepts for a lunar landing pad simply use flat concrete. “There’s no flame diverter, no flame trench, no water,” Metzger says. “I decided just because of the pure fun of solving the physics, and also because of what we might learn about lunar landing pads, that I was going to take this seriously.”
What he found was that chunks of concrete from the Boca Chica pad were flung away at more than 200 miles per hour. A cloud of hot water vapor and carbon dioxide, created by Starship’s methane- and liquid oxygen-burning Raptor engines, heaved sand skyward and carried it to Port Isobel. Metgzer realized the process must have been similar to the way pressure builds in a volcano before an eruption.
“The only explanation we could come up with was that the landing pad cracked and the high pressure of the thrust drove gas through the cracks,” he says. This increased pressure beneath the pad until it erupted. Lunar landing pads must be designed to avoid this problem, he says, by adding vents for gases to escape or by constructing stronger pads that resist fracture.
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That could be difficult on the moon, where heavy construction will be hindered by a lack of resources, machinery, and an atmosphere. But on Earth, SpaceX may have a solution—a steel plate that is actively cooled with water to keep it from melting during a rocket launch.
”That’s really a great idea,” Metzger says. “If their engineers did it correctly, it should be a complete solution to the problem.”
As for keeping the next Starship from blowing up in the sky, SpaceX says it found that leaked fuel had ignited inside the Super Heavy Booster. The resulting fires cut the booster off from the computer guiding its flight, which caused the rocket to tumble and then explode, according to an update on its website. The company has “significantly expanded Super Heavy’s pre-existing fire suppression system in order to mitigate against future engine bay fires,” the company says.
While neither the FAA nor SpaceX have said where the two are in the process, SpaceX Founder Elon Musk has suggested that his company has completed the corrective tasks, tweeting on September 5, before the FAA announcement, that ”Starship is ready to launch, awaiting FAA license approval.”
If the ball is truly in the FAA’s court and the regulator is simply reviewing the work SpaceX has done, “I don’t think it will take more than a few weeks,” Whitman Cobbs says. “That would be my best guess.” If that’s the case, she notes, then SpaceX and the FAA have moved with exceptional speed to get Starship ready for another launch attempt. Whitman Cobb contrasted SpaceX with its competitor Blue Origin, whose New Shepard rocket remains grounded more than a year after a failed launch on September 12, 2022. Blue Origin is “still in the FAA investigation mode, and have not been able to launch,” she says. “They’ve yet to apply for a modified launch license.”
Rapidly reworking Starship and its launch pad, though, doesn’t guarantee the next launch attempt will go flawlessly. But Whitman Cobb notes that SpaceX has been more willing than NASA or other rocket makers to test new spacecraft, watch them fail, and rapidly make changes. The eighth Starship prototype was destroyed in a fiery belly flop during a high-altitude test in December 2020, for instance, but the company pressed on.
“Given the ability of SpaceX to succeed and prove its critics wrong in the past few years, I have no evidence to believe they wouldn’t be able to make this work,” she says.
Metzger also notes that the person in charge of getting Starship ready to fly again is William Gerstenmaier, who, before joining SpaceX in 2020, was the former associate administrator for Human Exploration and Operations at NASA. “Gerstenmaier is a legend in the space community,” Metzger says. ”It’s in really good hands. I don’t know if there’s anybody better in the world than Bill Gerstenmaier to manage that sort of a project.”