Artemis II fault tolerance

tcp_handshaker

For the Airbus they used different CPUs because CPUs have bugs too...

WorkerBee28474

> Orion utilizes two Vehicle Management Computers, each containing two Flight Control Modules, for a total of four FCMs. But the redundancy goes even deeper: each FCM consists of a self-checking pair of processors. Who sits down and determines that 8 is the correct number? Why not 4? Or 2? Or 16 or 32?

MiracleRabbit

Interesting. In safety components we are using Lockstep Microcontrollers which are doing something similar in a much smaller scale. https://en.wikipedia.org/wiki/Lockstep_(computing) Example: https://www.st.com/resource/en/datasheet/spc574k72e5.pdf

y1n0

What I would like to see is the fault data. Also a graph of the # of in sync FMCs over time and how well did it correlate with predictions. I other words, how over engineered is it.

_whiteCaps_

I'm a big fan of Dissimilar Redundancies (but didn't know that was the term until today) for building system software. Build for various Linux distros, and some of the BSDs. You'll encounter weird compile errors or edge cases that will pop up. Often times I've found that these will expose undefined behaviour or incorrect assumptions that you wouldn't notice if you were building for a single platform.

m3kw9

The training the astronauts need must be a lot

ranger207

> 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. How does a pair determine which of the pair did the calculation correctly?

methodical

Candidly, while I understand the need for some amount of redundancy, I'm curious what this level of redundancy adds in terms of complexity to the system of a whole and whether or not that complexity-add almost outweighs the higher redundancy. I'm sure NASA has calculated the trade off, but I'd be curious to see the thoughts behind that. I feel in a similar vein when learning of certain aircraft accidents over the years, where it feels like the redundancy of certain systems and the complexity it adds has been the indirect cause of accidents instead of preventing them. I suppose there's not really a way to quantify the accidents that it's prevent to be able to compare them directly.

arscan

I interned at a company called Stratus which did hardware fault tolerant computers in the 80s/90s. I think they called it a “Pair and spare” approach, where every component had 3 copies running and comparing state every cycle. If one component’s state stopped matching the other 2, the failing component would be taken offline and the system would call home for a replacement to be fedexed overnight. I think just about every component was hotswappable too. Pretty cool, but expensive, and other architectures for improving availability, or mitigating impact from loss of availability, won out (except for a handful of exotic use cases).

Nevermark

The most significant redundancy, is the decisive N rockets for N launches, hedge against any and all operational degradation.