GoKawiilArtemis II Is Not Safe to Fly
“Our test facilities can’t reach the combination of heat flux, pressure, shear stresses, etc., that an actual reentering spacecraft does. We’re always having to wait for the flight test to get the final certification that our system is good to go.”—Jeremy VanderKam, deputy manager for Orion’s heat shield, speaking in 2022
On Wednesday, NASA will attempt to send four astronauts around the moon on a mission called Artemis II. This will be second flight of NASA’s SLS rocket, and the first time the 20-year-old Orion capsule flies with people on board.
The trouble is that the heat shield on Orion blows chunks. Not in some figurative, pejorative sense, but in the sense that when NASA flew this exact mission in 2022, large pieces of material blew out of Orion’s heat shield during re-entry, leaving divots. Large bolts embedded in the heat shield also partially eroded and melted through.
NASA’s initial instinct was to cover up the problem. In early press releases, they stressed that both rocket and spacecraft had performed exceptionally, while declining to publish the post-flight assessment review. The first mention of heat shield damage came from Orion program manager Howard Hu on a call with reporters in March of 2023. Hu said: “we observed there were more variations across the heat shield than we expected; some of the expected char material that we would expect coming back home ablated away differently than what our computer models and what our ground testing predicted.”
Asked by a journalist to quantify the char loss in a January 2024 phone call, Moon-to-Mars Deputy Administrator Amit Kshatriya said: “it was very small localized areas. Interestingly, it would be much easier for us to analyze if we had larger chunks and it was more defined”. A Lockheed Martin representative on the same call added that "there was a healthy margin remaining of that virgin Avcoat. So it wasn’t like there were large, large chunks.”
It wasn’t until May 2024, when the Office of the Inspector General released photographs of the heat shield, that the extent of the damage became clear. The problem wasn’t char loss or excessive ablation, but deep gouges and holes in many of the Avcoat blocks that comprise the heat shield.
The Avcoat material is not designed to come out in chunks. It is supposed to char and flake off smoothly, maintaining the overall contours of the heat shield. But Orion is a fat and heavy spacecraft, about twice as heavy as the Apollo command module it is modeled after. And the Avcoat heat shield is an experimental design. No one has flown a segmented heat shield like this at lunar return speeds, let alone on a spacecraft this heavy.
The substance of the OIG report was as alarming as the pictures. The OIG identified three issues that could potentially kill the crew on Artemis II:
Heat shield spalling. This is the technical term for all those divots. Since spalling leaves voids and gaps in the heat shield material, it can expose the unprotected body of the capsule and lead to burnthrough. Spalling also changes the pattern of hypersonic airflow around the capsule, creating the potential for localized hot spots and cascading effects. Impact from heat shield fragments. When spalling sends pieces of heat shield into the hypersonic airstream, they can strike the top of the capsule, damaging the parachute compartment. Whether this happened on Artemis I is unknown. As the OIG report pointed out with some frustration, NASA failed to recover either the parachutes or the parachute cover, despite making elaborate plans to do so. Any evidence of debris impact is now at the bottom of the Pacific Ocean. Bolt erosion. The OIG report noted erosion and melting in four large separation bolts that sit embedded in the heat shield. These bolts are packed with a heat-resistant material and are supposed to be rugged enough to survive re-entry. But three of the four bolts had melted through, due to a flaw in the heating model NASA had used in designing them. The report further noted: ”separation bolt melt beyond the thermal barrier during reentry can expose the vehicle to hot gas ingestion behind the heat shield, exceeding Orion’s structural limits and resulting in the breakup of the vehicle and loss of crew.”
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