NASA says they have found the root cause of the Orion heat shield
issues. But they're not telling us what it was. Maybe by the end of the
year.
The pitting experienced by Artemis 1 during reentry. According to the OIG report, NASA found more than 100 locations on the heat shield where material “chipped away unexpectedly”.
The End.
I'll take a stab at it.
ReplyDeleteThe secrecy is because the root problem is exactly that of the problems in the early days of the Shuttle tiles.
To admit that is itself fraught with problems; chiefly that they have forgotten that which was learned thirty years ago.
There are others, but that's the biggee.
Oops, forty years ago.
DeleteOh, how time flies.
I think it's different than shuttle tiles and more like Apollo-era ablative coating. The Ars article says, “The heat shield, made of a material called Avcoat, was supposed to gradually and evenly burn away when the Orion spacecraft plunged into the atmosphere at a velocity of more than 24,500 mph (nearly 40,000 km/h), significantly faster than a capsule returning from low-Earth orbit....
DeleteInstead, the Avcoat material cracked unexpectedly, causing charred chunks to fall off the heat shield, and leaving cavities resembling potholes. The Orion spacecraft safely splashed down, and if astronauts had been inside, they would have been fine.”
The Avcoat applied as tiles to the parabolic shape of the module. The Avcoat material is ablative.
DeleteAn additional ablative coating is applied monolithically. 3D Multifunctional Thermal Protection System (3DMAT) serves to add structural strength at the points (compression pads) where the crew and service modules attach. The 3DMAT is bedded to the crew module and penetrates through the Avcoat tiles.
The Avcoat was used beginning with Apollo.
As an aside, cracking of even a monolithic sheet can form during rapid heat gain or rapid cooling. Change of chemical composition can be induced by similar environments. I'm only saying these are some of what can happen.
(It would be book length to discuss all of what could happen in that environment.)
I'm not saying this happened on Orion. In absence of NASA saying what is the cause, I'm going with the aforementioned.
Too, since the Avcoat ablative layer is as little as one inch thick, I would consider deformation of the module itself as contributing cause. I would look at the processes in forming the parabolic shape. To this, I would want to know the tolerances in the design.
When SiG last posted about Orion heat shield, I said the joints between the tiles is my No.1 concern. In such a harsh environment as during a reentry, any 'potential weakness' will be exploited.
Maybe they don't want us to know how bad it really is. Another 30 seconds of heating during reentry might have caused a total failure, with the loss of the craft.
ReplyDeleteAs long as this subject has been talked about, they always say the same part about if it had been crewed "...they would have been fine." Pardon my skepticism but I'd like to see some data on that.
DeleteWhy did it fail? Three reasons a heat shield fails.
ReplyDelete1. Bad material design. If the material is borked or put on incorrectly, it will exhibit these problems.
2. Bad implementation. Like a bubble in the matrix will cause the blowouts. Or incorrect mixing of the shield matrix will cause weak spots and thus blowouts.
3. Bad geometry of the shield itself. The geometry of the parabolic curve on the bottom is very critical. It affects all sorts of things, like the amount of resistance the capsule meets during reentry, the amount of heat that builds up and where it builds up. Even as to the maneuverability and entry profile of the capsule.
Or a combination of bad material, bad implementation and bad design.
The bullscat line, is, as you pointed out, is "The astronauts would have been okay." Maybe, maybe not. Maybe the additional weight of the astronauts and their gear would have been enough to totally bork the reentry.
Yeah, don't trust it. And I'd be skeptical of any 'fixes' that aren't pr
And, jeez, when is 'just barely good enough' good enough? Where's the vaunted 'over-engineered' that used to be industry standard. Seriously, 'over-engineered' stuff breaks all the time in the harsh reality of spaceflight or even airspace flight or even on the friggin highway. 'Just barely good enough' isn't good enough on a critical part like a heat shield.
Hmmm... I wonder if they could mock up a heat shield and then use a rocket motor to provide the velocity and heat of a reentry?
My bet is that DEI played a MAJOR part in the problem.
ReplyDeleteTo your No.2, I wonder if the tiles were applied in a continuous fashion. That as opposed to the work spread over several days with work stops along the way. Plus, was the work space climate controlled.
ReplyDeleteYour question at the end implies arc jet testing. Samples of the finished material were tested up to 2,400°C for 600 seconds.
I reckon it would be terribly expensive to mock up a complete heat shield.
Plus, the designers of the materials used for the heat shield said they were working under a very tight schedule. Three years to design, manufacture, test, install, test a new material. The design was for flights to and from the luner gateway.
Cheaper to mock up a whole heat shield and test all the parameters, that being material, application and geometry, than to lose a crewed capsule.
DeleteBeans, I completely agree on that point. A human life is infinitely more valuable, there worth protecting at any cost.
DeleteThat the designers were under a tight schedule points to administrators interfering with engineering. Boy, doesn't that conjure memories of previous disasters.
To be fair, that game is fraught with hazards, known and unknown.
The goal is to make the unknown, known. But risk management can get so dominant that no one flies.
NASA admits heat sheild is not safe. "What we are doing now is assessing what is the appropriate approach for Artemis II, regarding the heat shield," Glaze said Monday. "We know what needs to be done for future missions, but the Artemis II heat shield is already built. So how do we assure astronaut safety with Artemis II?" Lori Glaze, acting deputy associate administrator for NASA’s Exploration Systems Development Mission Directorate.
ReplyDeleteI don't remember where I read it. Apparently the formulation of Avcoat has changed since the 1960s/70s. One of Avcoat's important constituent components has been outlawed by the Government for "health" reasons and another product substituted. The person that pointed this out believed that this change may in part be responsible for the heat shield failure.
ReplyDeleteI remember the same basic argument around the Columbia disaster. A reformulation of the foam insulation on something due to some ingredient being declared to be too toxic. (Yeah. Really specific, I know.)
DeleteThe toxic ingredient of the foam insulation was freon. You know, that icky ozone-depleting chemical that doesn't do diddly against the ozone layer and is still used in turd-world nations.
DeleteThe freon foam was very strong and very stable. Did well against the rigors of a launch.
The new non-freon foam, well, we lost a shuttle and almost lost others due to that crap. And the weight increase required no insulating paint (that also contributes to the stability of the foam) on the foam, so you get that ugly orange blob shape.
After sleeping on this I came up with the source. The source was a comment at Behind the Black to this post, NASA IG: Major technical problems with Orion remain unsolved, by Dick Eagleson.
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