Comment by russdill
4 days ago
I mean, that's how these heat shields work. They aren't reusable, you can't test them and then use them again. Or do you mean the design? We already did Artemis I.
4 days ago
I mean, that's how these heat shields work. They aren't reusable, you can't test them and then use them again. Or do you mean the design? We already did Artemis I.
See this recent blog post about it (I am not the author): https://idlewords.com/2026/03/artemis_ii_is_not_safe_to_fly....
It says that it is not safe to fly. They are sending humans without having tested in real conditions that their design was sound, GIVEN that the first time they did that (without humans), it turned out that their design was unsafe.
An article written by a "Polish-American web developer, entrepreneur, speaker, and social critic" says it's not safe to fly. And? What do the astronauts flying on board with significantly more information say?
There is also an old article written by a professional bongo player about the Challenger explossion. He has other hobbies, but he was not a Rocket Scientist https://www.nasa.gov/history/rogersrep/v2appf.htm
The takeaway, is that the software was fine, but other systems like the main engine used too much cutting edge technology and have a lot of unexpected failure modes and too many problems like partialy broken parts that should no get partialy broken. [For a weird coincidence, Artemis II uses the same engines.] He concluded that when you consider all the possible problems the failure rate was closer to 1/100, but management was underestimating them and the official value that was 1/100000. [Anyway, the engines didn't fail in Columbia, it was one of the other possible problems.]
The articles explain that the shield has problems but management is underestimating them again. Let's hope the mission goes fine, but in case of a explosion it would be like a deja vu.
4 replies →
Did you read it? They're prolific here and the essence of the post is a bunch of citations and quotes from Nasa's own staff and literature.
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I mean the design.
They've changed the AVCOAT to be less permeable and altered the re-entry profile.
One of the findings of Artemis I is that lack of permeability led to trapped gas pockets which expanded and blew out pieces of heat shield. The reason for the change to be less permeable is to make it easier to perform ultrasonic testing, not to improve performance.
They altered the re-entry profile on the theory that the skip period contributed to spalling, but Charles Camarda disagrees in this doc: https://docs.google.com/document/d/1ddi792xdfNXcBwF8qpDUxmZz...
> Another chart which the Artemis Tiger Team did not intend to show on Jan. 8th, was the figure showing the spallation events as a function of time during the skip entry heating profiles (Figure 6.0-4 of NESC Report TI-23-0189 Vol. 1). In this figure, it was quite clear that the Program narrative they were feeding to the press, that it was the dwell time during the skip which allowed the gases generated to build up and cause the delta pressures which caused most of the spallation was, again, patently false. In fact, during the first heat pulse (t ≈ 0 to 240 sec), approximately 40-45% of all the medium to large chunks of ablator spalled off the Artemis I heatshield.
> Hence, varying the trajectory would do little to prevent spallation during Artemis II. I was never shown the new, modified trajectory at the Jan. 8th meeting.
your point about gas pockets making the shield blow out made me curious
I found this visual schematic of the spalling helpful - https://vectree.io/c/the-physics-of-ablative-spalling-in-ori...
It finally makes sense why the gas needs to leak out... if it gets trapped behind the burnt outer crust, the pressure just blows pieces of the shield off like a tiny bomb
We already did Artemis I and the heat shield lost a lot more material than it was supposed to on that flight. "Specifically, portions of the char layer wore away differently than NASA engineers predicted, cracking and breaking off the spacecraft in fragments that created a trail of debris rather than melting away as designed. The unexpected behavior of the Avcoat creates a risk that the heat shield may not sufficiently protect the capsule’s systems and crew from the extreme heat of reentry on future missions."
Fixes have been made to the design, but they haven't been tested in flight.
Also the fixes weren’t made on this capsule, since it was already built with the old design.
So that means this capsule will fly a different re-entry profile to attempt to avoid the issue and Artemis IV will fly with untested fixes for lunar return.
And the different re-entry profile has more velocity and temperature stress. So if their reasoning is wrong (that the failure was due to do lower pressure during the skip) it will very likely fail.
The heat shield is a bit different, and the reentry profile is a bit different as well.
I suppose "this will be the first time we can test this slightly modified heat shield in the slightly different pressures and temperatures that it will have to endure." isn't quite as eye catching.
With humans on board? Even if they are not necessary for the actual mission?
Yeah, that's what "untested" means in spaceflight.
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I mean, sure. But that's like equipping a sub with a screen door and claiming that in the grand scheme of things, it's a slightly different door with slightly different permeability characteristics.