When the Artemis 2 Orion capsule slams into the discernible atmosphere 75 miles above the Pacific Ocean Friday, it will be traveling at 24,000 miles per hour. Within seconds, temperatures across its 16.5-foot heat shield will climb to roughly 5,000 degrees Fahrenheit — half as hot as the visible surface of the sun — as the spacecraft slows in an electrically charged fireball of atmospheric friction. Four astronauts will be inside: Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen.
NASA says the heat shield will hold. The agency has spent nearly two years proving it.
"We have high confidence in the system, in the heat shield and the parachutes and the recovery systems we put together," Amit Kshatriya, NASA's associate administrator, said Thursday. "The engineering supports it, the Artemis 1 flight data supports it. All of our ground tests support it, our analysis supports it and tomorrow, the crew is going to put their lives behind that confidence."
The confidence statement landed Friday morning — hours before re-entry — precisely because NASA knows what's at stake. The heat shield on Orion is nearly identical to the one that flew on the unpiloted Artemis 1 mission in 2022. And that shield came back damaged.
The Avcoat ablative material that makes up the heat shield developed sub-surface cracks and gas pockets during re-entry, according to Ars Technica. Chunks of the outer "char" layer blew away. It was not a catastrophic failure — the capsule landed on target and astronauts, had any been aboard, would have survived. But it was a problem NASA could not ignore before flying crew.
Engineers spent the intervening years figuring out why. Their conclusion: the Avcoat lacked permeability during a specific phase of re-entry when external temperatures were lower while internal layers were still generating extreme heat. Trapped gas built up, then blew out.
The fix was not a new heat shield — the Artemis 2 shield was already installed and replacing it would have delayed the mission 18 months or more. The fix was the trajectory. NASA redesigned the re-entry profile to a "lofted" path that eliminates the temperature and pressure swings that caused the damage.
"They did a tremendous amount of research, a lot of groundbreaking research in some facilities that we had not used before, and they discovered the root cause," Wiseman said, according to SpaceFlight Now. "They did wind tunnel testing and laser testing and hyper-velocity testing, and they determined that if we come in with this lofted profile, this heat shield will be safe for us to go fly."
NASA Administrator Jared Isaacman reviewed the analysis in January and came away convinced, calling it "full confidence" after a technical briefing. Even Isaacman allows for some anxiety. "There's no question that I'll be anxious," Kshatriya said this week, according to CBS News. "We've done the work. It's impossible to say you don't have irrational fears left. But I don't have any rational fears."
The re-entry is expected to last roughly 14 minutes, per Ars Technica. After the heat shield bears the brunt, the forward bay cover jettisons at about 35,000 feet and three small drogue parachutes deploy at around 22,000 feet. Main parachutes slow the capsule to roughly 20 mph before splashdown in the Pacific, according to CBS News.
The USS John P. Murtha is the recovery ship, per The Guardian. Under a nominal scenario, recovery crews will extract Koch first, then Glover, Hansen, and finally Wiseman. The astronauts are expected back in Houston Saturday morning.
A modified trajectory is not a guarantee. But it is an answer — and NASA wanted to be on record with that answer before the crew put their lives behind it.
