SpaceX and Elon Musk suspected that the upper stage Starship's forward flap could catch fire during today's flight, according to previously unreleased footage shared by YouTube creator Tim Dodd on X earlier today. Dodd's channel interviewed Musk ahead of today's test flight as part of a series where Musk provides updates and shares details about SpaceX's activities in its Starbase facilities in Texas. SpaceX's fully stacked Starship rocket took to the skies earlier today, and the test met all primary objectives that SpaceX had set before launch.
SpaceX's Second Stage Starship Fire Could Be Due To Hot Gas Making Its Way In A Gap
One of the hardest systems on a rocket or a spacecraft is a heat shield since engineers are unable to test full scale models at the conditions that a vehicle faces on reentry while the ship is on Earth. This means that heat shield development often extends late into a spacecraft's developmental cycle. SpaceX's first crewed Dragon launch in 2020 surprised engineers due to anomalous damage, and NASA's Orion spacecraft also suffers from cavitation.
Similarly, the second stage Starship could not survive atmospheric reentry during its third flight. The ship's heat shield design sees SpaceX using thousands of tiles to cover its wind-facing surface and fins, and any gaps in the tile application can have untoward consequences.
During Starship's launch earlier today, the ship's forward flap, which is located on top of the rocket, caught fire. This provided unique visuals of a rocket on fire while traveling thousands of kilometers per hour in the upper regions of the Earth's atmosphere.
In his interview with Everyday Astronaut, Musk shared that SpaceX had anticipated the issue beforehand. According to him, the hinge between the flap and Starship is one of the most vulnerable areas during reentry. This is due to hot gas that can flow in this gap, destroying not only the stainless steel body but also the ceramic heat shield tiles.
The night before #Starship's 4th flight, @elonmusk described one of the main concerns about Starship's heat shield. He turned out to be right as it was the exact spot that burned through. More video to come! pic.twitter.com/NTfw9Cw944
— Everyday Astronaut (@Erdayastronaut) June 6, 2024
"Sealing that hinge gap and not having hot gas just go flowing super fast through the interface" of the flap hinge is crucial to ensuring that the gas does not "cook anything, including the tiles," according to Musk. Throughout today's test flight, SpaceX shared multiple camera views from the second stage Starship. These cameras showed the forward and aft flaps, and after the forward flap caught fire, SpaceX stuck with its camera view for the remainder of Starship's flight.
According to Musk, SpaceX placed a "hot gas seal at the forward and rear flap hinge" and the test checked whether these seals worked. Surprisingly for Starship, even though its flap had caught fire, Starship completed its atmospheric reentry thanks in no small part to SpaceX's decision to use steel as the rocket's build material.
While initially, SpaceX had chosen stainless steel grade 301 to build Starship, Musk shared in another post that the firm has since moved to an internally developed alloy called SX300. This is because 301 steel could not withstand the extremely cold temperatures that Starship has to endure because of its cryogenic propellants. The propellants, methane, and liquid oxygen are super cooled before launch to improve fuel capacity and rocket performance.
On the flaps, Musk added that future Starships will feature upgraded flaps. According to him, an upgraded Starship will have "a newer version of Starship has the forward flaps shifted leeward" to "improve reliability, ease of manufacturing and payload to orbit."
Starship's leeward side is the region that points to the sky and away from the atmosphere during reentry. Following the Super Heavy's successful soft splashdown, Musk remained optimistic for his rocket and hinted that SpaceX might try to catch the rocket with the launch toward in the fifth flight.
About the author: Ramish is a seasoned technology writer and editor with more than a decade of experience. He specializes in semiconductor fabrication and market analysis. With a background in finance and supply chain management - via his bachelors in Finance and a micromasters in supply chain management from MIT - Ramish combines financial rigor with deep industry insight to deliver accurate and authoritative coverage.
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