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How NASA built Artemis II’s fault-tolerant computer

cacm.acm.org

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Re: How NASA built Artemis II’s fault-tolerant computer

#171

Post by anymouse123456 »

dmk wrote: post #3

The quote from the CMU guy about modern Agile and DevOps approaches challenging architectural discipline is a nice way of saying most of us have completely forgotten how to build deterministic systems. Time-triggered Ethernet with strict frame scheduling feels like it's from a parallel universe compared to how we ship software now.

Some of us still work on embedded systems with real-time guarantees.

Believe it or not, at least some of those modern practices (unit testing, CI, etc) do make a big (positive) difference there.

Re: How NASA built Artemis II’s fault-tolerant computer

#173

Post by dojopico »

I did VOS and database performance stuff at Stratus from 1989-95. Stratus was the hardware fault tolerant company. Tandem, our arch rivals, did software fault tolerance. Our architecture was “pair and spare”. Each board had redundant everything and was paired with a second board. Every pin out was compared on every tick. Boards that could not reset called home. The switch from Motorola 68K to Intel was a nightmare for the hardware group because some instructions had unused pins that could float.

Re: How NASA built Artemis II’s fault-tolerant computer

#174

Post by sippeangelo »

randomNumber7 wrote: post #167
georgehm wrote: post #58

>Effectively, eight CPUs run the flight software in parallel. The engineering philosophy hinges on a >“fail-silent” design. The self-checking pairs ensure that if a CPU performs an erroneous calculation >due to a radiation event, the error is detected immediately and the system responds. >“A faulty computer will fail silent, rather than transmit the ‘wrong answer,’” Uitenbroek explained. >This approach simplifies the…

For errors due to radiation the probability is extremely low, since it would need to flip the same bit at the same time in two different places.

Then why 8 instead of 3?

Re: How NASA built Artemis II’s fault-tolerant computer

#175

Post by anymouse123456 »

dgb23 wrote: post #163
weli wrote: post #130

Earlier quoted context omitted.

Mises never claimed that the free market produced the most optimal solutions at a given moment. In fact Mises explicitly stated many times that the free market does indeed incur in semi-frequent self-corrections, speculations and manipulations by the agents. What Mises proposition was - in essence - is that an autonomous market with enough agents participating in it will reach an optimal Nash equilibrium where both o…

Many intellectuals have this problem. They make interesting, precise statements under specific assumptions, but they get interpreted in all kinds of directions. When they push back against certain narratives and extrapolations they usually don’t succeed, because the same mechanism applies here as well. The only thing they can do about it, is throwing around ashtrays.

What a great visual. I haven't heard that phrase before.

Re: How NASA built Artemis II’s fault-tolerant computer

#176

Post by ToucanLoucan »

randomNumber7 wrote: post #166
ToucanLoucan wrote: post #41

Earlier quoted context omitted.

Wild shit to be advising other people to be humble whilst talking directly out of your ass about technology you clearly do not understand and engineers you have no respect for. Perhaps self-reflect.

How do you know that op doesn't know what he is talking about? I have written code for real time distributed systems in industrial applications. It runs since years 24/7 and there never was a failure in production. I also think nasa is full of shit.

Well for one, if you follow their profile and a few more clicks, you get to their resume, and while it's an impressive one and I'm sure they know a lot of shit I don't, what's notably missing is anything even remotely close to Aerospace, rocketry, guidance systems, positioning, etc.

For another, if an engineer has an axe to grind with a public facing project, I would expect them to just grind the thing, not echo a bunch of the same lame and stale talking points every layperson does (bureaucracy bad, government bad, old tech, etc.). I'm not saying NASA in general and Artemis in particular are flawless, I'm just saying if you're going to criticize it, let's hear it. Otherwise you just sound like another contrarian trying to get attention, like a 14 year old boy saying Hitler had some good points.

Re: How NASA built Artemis II’s fault-tolerant computer

#177

Post by ragebol »

Davidbrcz wrote: post #160
huxleyFiddler wrote: post #154

[flagged]

> Dissimilar redundancy eliminates that risk. A completely different OS, different codebase, different development team. Not entirely true. I've heard during my uni years of a case were two independent teams used the same textbook for implementing a feature, which had an error, and thus resulting in the same failure mode.

Ha, very curious what the issue was and what textbook

Re: How NASA built Artemis II’s fault-tolerant computer

#179

Post by Cthulhu_ »

JumpCrisscross wrote: post #102
themafia wrote: post #61

Earlier quoted context omitted.

In the Shuttle they would use command averaging. All four computers would get access to an actuator which would tie into a manifold which delivered power to the flight control surface. If one disagreed then you'd get 25% less command authority to that element.

> In the Shuttle they would use command averaging I think the Shuttle, operating only in LEO, had more margin for error. Averaging a deep-space burn calculation is basically the same as killing the crew.

Sure, but these maneuvers aren't done realtime and aren't as time-sensitive; a burn is calculated and triple checked well in advance. If there was an error, there's always time to correct it.

In the case of moon landings, the only truly time-critical maneuvers are the ones right before landing... and unfortunately, a lot of fairly recent moon probes have failed due to incorrect calculations, sensor measurements, logic errors, etc.

Re: How NASA built Artemis II’s fault-tolerant computer

#180

Post by Schlagbohrer »

"High-performance supercomputers are used for large-scale fault injection, emulating entire flight timelines where catastrophic hardware failures are introduced to see if the software can successfully ‘fail silent’ and recover."

I assume this means they are using a digital twin simulation inside the HPC?

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