I'm not an engineer and I don't have a scientific background. When I consider the time frame Orion has been in development and when I look at that devastating report, I'm curious how the Apollo engineers managed to do this with less experience, less advanced tools and in a shorter period of time. Or was it simply the 10x higher budget that was available back then?
10x budget and engineering that relied much more heavily on physical testing and verification than computational simulation. They flew over a dozen missions on the Saturn IB and two of the full Saturn V stack before flying crews, testing nearly all the systems under flight conditions. That 10X budget really wasn't extravagant as they really had no alternative than to flight test everything back then. Hardware is expensive. And even still, we lost the crew of Apollo 1 and had the Apollo 13 incident.
Even with modern computer modeling and simulation, your results are only as good as your inputs and physics models. Just because a computer spits out an answer doesn't mean it's correct. Apparently there was some parameter in the Artemis thermal modeling that was incorrect and they only discovered that after they had the test flight. Computer modeling is not a substitute for actual test data. But computer simulations are far cheaper, so there is a tendency to lean on those results vs. doing more physical testing. But computer simulations must be validated against test data, otherwise it is nothing more than a best guess.
diogom said:
Not excusing the necessity of understanding why this happened, but I thought they also had an intentionally harder re-entry than a crew would have? Specifically to push the heatshield and systems.
They did a free-return with a low perilune on Artemis I like planned for Artemis II. Unless they actually burned prograde when on return to increase their kinetic energy it should have been a representative test of a nominal Artemis II re-entry.
If they forced it to undergo a reentry say 120% harder than the intended mission reentry and the heat shield came through flawlessly, they could be very confident in that heat shield. But if they proof to 120% and the heat shield picks up all sorts of unexpected damage, what does that tell us? The damage would tell us that there is something that isn't understood about the physics, and the fact that it survived doesn't necessarily mean there is any safety margin - it could just mean that they got damned lucky.
The shuttle experienced lots of debris damage on the TPS for many years and many flights, and NASA management took that as a sign that it was not a safety concern. What they unwittingly did with this decision was play Russian roulette on each flight until a particular piece of foam hit a particular sensitive spot when the Columbia was lost. Doing analysis beforehand costs a lot of money and schedule, but relying on luck costs nothing ... except lives, when the luck invariably runs out.