As we approach the flight of Artemis II to the moon...

We've entered into the mental landmark that we're within four weeks of the start of the Artemis II mission to loop around the moon and, as every story says, the first time astronauts have gone beyond Earth Orbit since the end of the Apollo 17 mission in December 1972. Launch is currently scheduled for NET Friday, February 6, at 9:45 PM EST. That is one day later than I've been listing for months. 

Something that was going on without mention in the emails I get or sites I check regularly is that NASA’s new administrator, Jared Isaacman, called together a review of the Orion heat shield issues that showed up after the first Artemis mission. Afterward, Isaacman said he has “full confidence” in the space agency’s plans to use the existing heat shield to protect the Orion spacecraft during its upcoming lunar mission.

“We have full confidence in the Orion spacecraft and its heat shield, grounded in rigorous analysis and the work of exceptional engineers who followed the data throughout the process,” Isaacman said Thursday.

The Artemis I mission was in November of 2022, so just over 3 years ago, and the agency was roundly criticized for how it handled the heat shield issues. The pictures of the heat shield with chunks of ablative material blasted out of it didn't surface until nearly a year and a half after the mission.

The inspector general’s report, released on May 1, 2024, included new images of Orion’s heat shield. Credit: NASA Inspector General

After taking the job in Washington, DC, Isaacman asked the engineers who investigated the heat shield issue for NASA, as well as the chair of the independent review team and senior human spaceflight officials, to meet with a handful of outside experts. These included former NASA astronauts Charles Camarda and Danny Olivas, both of whom have expertise in heat shields and had expressed concerns about the agency’s decision-making.

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Convened in a ninth-floor conference room at NASA Headquarters known as the Program Review Center, the meeting lasted for more than three hours. Isaacman attended much of it, though he stepped out from time to time to handle an ongoing crisis involving an unwell astronaut on orbit. He was flanked by the agency’s associate administrator, Amit Kshatriya; the agency’s chief of staff, Jackie Jester; and Lori Glaze, the acting associate administrator for NASA’s Exploration Systems Development Mission Directorate. The heat shield experts joined virtually from Houston, along with Orion Program Manager Howard Hu.

Isaacman made it clear at the outset that, after reviewing the data and discussing the matter with NASA engineers, he accepted the agency’s decision to fly Artemis II as planned. The team had his full confidence, and he hoped that by making the same experts available to Camarda and Olivas, it would ease some of their concerns.

To help ensure transparency, Isaacman added two independent reporters to the mix, Eric Berger of Ars Technica and Micah Maidenberg of The Wall Street Journal. They were allowed to report on the discussions but required to not quote participants directly by name to encourage a full and open discussion.

Perhaps the most striking revelation was what the NASA engineers called “what if we’re wrong” testing.

At the base of Orion, there are 186 blocks of a material called Avcoat, individually attached to provide a protective layer that allows the spacecraft to survive the heating of atmospheric reentry. Returning from the Moon, Orion encounters temperatures of up to 5,000° Fahrenheit (2,760° Celsius). A char layer that builds up on the outer skin of the Avcoat material is supposed to ablate, or erode, in a predictable manner during reentry. Instead, during Artemis I, fragments fell off the heat shield and left cavities in the Avcoat material.

Work by Saucedo and others—including substantial testing in ground facilities, wind tunnels, and high-temperature arc jet chambers—allowed engineers to find the cause of gases becoming trapped in the heat shield, leading to cracking. This was due to the Avcoat material being “impermeable,” essentially meaning it could not breathe.

After considering several options, including swapping the heat shield out for a newer one with more permeable Avcoat, NASA decided instead to change Orion’s reentry profile. For Artemis II, it would return through Earth’s atmosphere at a steeper angle, spending fewer minutes in the environment where this outgassing occurred during Artemis I. Much of Thursday’s meeting involved details about how the agency reached this conclusion and why the engineers deemed the approach safe.

A test block of Avcoat undergoes heat pulse testing inside an arc jet test chamber at NASA’s Ames Research Center in California. The test article, configured with both permeable (upper) and non-permeable (lower) Avcoat sections for comparison, helped to confirm an understanding of the root cause of the loss of charred Avcoat material on Artemis I. Credit: NASA

The Avcoat blocks, which are about 1.5 inches thick, are laminated onto a thick composite base of the Orion spacecraft. Inside this is a titanium framework that carries the load of the vehicle. The NASA engineers wanted to understand what would happen if large chunks of the heat shield were stripped away entirely from the composite base of Orion. So they subjected this base material to high energies for periods of 10 seconds up to 10 minutes, which is longer than the period of heating Artemis II will experience during reentry.

What they found is that, in the event of such a failure, the structure of Orion would remain solid, the crew would be safe within, and the vehicle could still land in a water-tight manner in the Pacific Ocean.

“We have the data to say, on our worst day, we’re able to deal with that if we got to that point,” one of the NASA engineers said.

After more than two years of testing and analysis of the char loss issue, the NASA engineers are convinced that, by increasing the angle of Orion’s descent during Artemis II, they can minimize damage to the heat shield. During Artemis I, as the vehicle descended from about 400,000 to 100,000 feet, it was under a “heat load” of various levels for 14 minutes. With Artemis II, this time will be reduced to eight minutes.

This may seem contradictory, but despite all this testing, the heat shield being accepted, and everyone feeling it's not exceptionally risky to ride it for reentry, there also seems to be a widespread feeling that they would rather not fly on it. I read that as saying there's nothing that shows extreme danger, but they're just not comfortable that they've tested every condition they should test. What if there were conditions that were encountered in Artemis I that didn't show up in the tests they've done? Nature isn't that cooperative - maybe there's noise, some sort of random fluctuations, and testing with the systems they're using doesn't exactly match what the heat shield might encounter on its flight? 

The Orion heat shield as seen after the Artemis I flight. Credit: NASA