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NASA Announcement for the Moon
- Thread starter Grendal
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TBF, Starship and Superheavy are not as far along as SLS, even though Starship has actually flown (Prototype and kinda). When they’ve actually heaved a bunch of Starlinks to orbit, then we’ll find out just how committed Nelson is to SLS.
Reviving this thread because it seems more appropriate than the ‘SLS capitulation” thread for discussing the Artemis missions, as the idea that SLS is going to go away any time soon seems fanciful.
A comment from the ars technica article comments page:
NASA still doesn’t understand root cause of Orion heat shield issue
NASA says that Artemis II won’t fly until it understands why the Orion heat shield ablated excessively and unevenly during the late 2021 mission, but 2 1/2 years later they still haven’t figured it out.
A comment from the ars technica article comments page:
They don't do it that way because they're not a rocket organization, able to launch stuff when they want to. They're a science and engineering organization, subject to tight budget restrictions. They already have test facilities that allow them to run samples of heat shield material through scale tests. They have computer simulations and engineers who know how to use them. So they use what they have.
It may be that they're simply not as good as the engineers at SpaceX, who constantly look outside the box for solutions. The NASA engineers may be quite myopic in their outlook.
Let's remember too that the NASA engineers may know exactly what's going on with the heat shield, but can't come up with a fix for it. A YouTube commentator observed that this latest approach to the heat shield is just like the 60s approach, but they install the heat shield in prefabricated blocks instead of building the whole thing in place, filling one tiny honeycomb cell at a time with the heat material. He suggests that they just go back to doing it the old way. I assume that they won't do that because of inertia; somebody wants to do the shield in blocks because of the cost savings and the opportunities such an approach offers, and they're going to keep bashing away at it until they figure out how to do it that way. In the end, it'll be a win, but for now it's dragging the timetable out.
Eric Berger:NASA says Artemis II report by its inspector general is unhelpful and redundant
The inspector general report also contained previously unreleased photos of the heavily damaged Orion heat shield after Artemis I. It looks pretty bad and I don’t think any Apollo heat shield ever looked that damaged.
And so far NASA has yet to reveal a fix and continues to say that Artemis II is a go in September 2025. Really?
NASA does not like criticism. But it is only through independent review boards that the public learned the actual cost of a single SLS/Orion mission: $4.2 billion! Which is an obscene amount of money in this age of reusable rockets.
The inspector general report also contained previously unreleased photos of the heavily damaged Orion heat shield after Artemis I. It looks pretty bad and I don’t think any Apollo heat shield ever looked that damaged.
And so far NASA has yet to reveal a fix and continues to say that Artemis II is a go in September 2025. Really?
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Nobody does, especially when it's comes from an external bureaucracy.
The bit that bothers me is the assumption that the chunks were lost during reentry. Could they have been lost on impact with the ocean? During cooling in atmosphere? I suppose that's all "reentry", except that if the thing came through the extreme phase completely intact, it wouldn't matter.
The NASA engineers are concerned that the shield wasn't ablating as they expected it to, not that it "looks bad". That is, it did something unexpected and they want to understand it. It still did its job and there would have been no danger to the capsule occupants.
If this had been SpaceX, we'd all be patting ourselves on the back at how they move fast and break things, operating on the edge of the envelope and so on.
My immediate reaction to seeing the damage is that all of it is adjacent to a block edge, except for the one that they zoomed in on. In the testing that I saw, they put a small block of the material into a simulated hot air stream, but I never saw a test of two blocks side by side in that stream, mounted as they would be on the capsule.
The one thing that they changed was moving from a monolithic shield to component blocks. If they didn't test that change, that would border on incompetence.
Just in case anyone is confused, that number was reported about a year ago. It's not something that came to light as a result of this heat shield thing.
For the curious, here's the PDF of the May 2023 report from the Inspector General's office. The following quote is reformatted for clarity.
I think your original characterization was accurate. The Orion heat shield is massively more beat up than the Apollo shields. The engineers expected damage - ablation is its job - but not in the manner, and possibly to the degree, that they saw on Orion.
I've seen some of those Apollo heat shields in person, and I think you can also tell in the pics above, and it doesn't seem as severe as those missing chunks on the Orian shield. The ablation was relatively even for the most part, and where there are missing sections, it appears the relatively thin upper layer came away, rather than a deep chunk gone. The discoloration definitely is splotchy though.
Granted that a Dragon doesn't have the same amount of stress on it compared to an Orion, but I'll bet that SpaceX's PICA-X is a decent step better than your basic PICA that Orion uses.
Orion uses an AVCOAT shield, while Dragon uses PICA. NASA started out testing with PICA, then ended up with AVCOAT. PICA was used on the Stardust mission where it survived 942 W/cm2 peak heat flux. From what I read, Orion requires greater than 1000 W/cm2. Even though it's slower on reentry than Stardust, I guess the much greater mass means that it won't slow down as quickly. So it looks like they went with AVCOAT because it can tolerate higher peak heat flux.
Note that AVCOAT is an epoxy-novolac system, while PICA is an acronym for Phenolic-Impregnated Carbon Ablator.
I'll also add that PICA-X, the SpaceX variant, is ten times less expensive to manufacture than the NASA PICA. Surprising, I know. In 2010, SpaceX started using PICA-3 with Crew Dragon.
From an article in Smithsonian Magazine about the recent NASA OIG report:
Corrected Link: https://oig.nasa.gov/wp-content/uploads/2024/05/ig-24-011.pdf
Corrected Link: https://oig.nasa.gov/wp-content/uploads/2024/05/ig-24-011.pdf
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Looks like you inadvertently used the perlite link from the other post for the article hyperlink...
Moderator's note: Thanks. The post now has the proper link attached.
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Stephen Clark on ars: NASA confirms “independent review” of Orion heat shield issue
There is going to be an independent review of the internal investigation.
There is going to be an independent review of the internal investigation.
I think the key point is that NASA has not said they have identified corrective actions.
“…set the bit…”? I don’t understand that phrase in this context. All he seems to be saying is that he has seen the damaged heat shield in person and he is very “interested” in the issue. Well, obviously.
“If”? That makes clear to me that at this time NASA does not have a solution and has not yet determined if a solution is even possible. The publicly stated launch date is NET September 2025. I know that date is generally considered to be unrealistic, though of course the NET part is a huge fudge factor. But if the heat shield that is already installed on the Orion capsule has to be physically redesigned I don’t see how Artemis II can be a crewed mission, that seems too risky for NASA. And that’s essentially what they are saying.
I think the issue is the size and mass as compared to the Apollo command modules. A quick search says the Apollo CM was ~12K lbs, whereas the Starliner is ~29K. And quick math says the Starliner's larger diameter yields 57% greater surface area on the bottom, which I undoubtedly plays in to it as well...
That having been said, I assume Avcoat is superior to the Apollo-era materials, but I don't know specifically how they compare...
I assume it's an equestrian reference, suggesting that he was all-in.
If not, he's an extreme geek, and it's a computer reference.
I think he was using a phrase that was intended to convey his confidence in the team, not to suggest how difficult the problem is. After all, he did say "set the bit", so his use of English may be slightly removed from the vernacular we're used to seeing from spaceflight companies.
They both use AVCOAT. Apollo's construction was monolithic, while Orion uses blocks that are bonded to the vehicle.
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