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C C
Dec 30, 2019 10:44 PM
(This post was last modified: Dec 30, 2019 10:44 PM by C C.)
(Dec 25, 2019 09:58 PM)RainbowUnicorn Wrote: (Dec 25, 2019 01:37 AM)Yazata Wrote: Here's an interesting short video about the computer hardware and software that SpaceX uses.
Lots of off-the-shelf components, lots of redundancy, linux, C++ etc.
https://youtu.be/N5faA2MZ6jY
why doesn't he explain what dragon does when all 3 computers are hit by cosmic particles causing a bit flip/corruption ?
he jumps to saying there is 18 other systems on board as if the number is supposed to distract the audience from the fact he has not said how the 3 computers work when all 3 computers are hit by cosmic particles.
Hmm... I guess we're left to assume that the other 18 systems redundantly and passively carry data about what the flight computers are doing in addition to their own tasks. And that if all 3 of the flight computers suffer bit flipping, they can amazingly reboot and re-sync so fast with applicable memory recovery from the unimpaired systems (among the other 18) that Dragon has little chance to get off course or hit anything.
TRANSCRIPT:
https://www.rankred.com/what-hardware-so...s-rockets/
pertinent passage:
If one of the flight computers is hit with radiation and produces a wrong calculation, the others will spot it. When that happens the malfunctioning computer will be rebooted automatically to prevent further errors. After rebooting the computer has to perform whats called a re-sync. It has to get up to speed with what the vehicle is doing, so it copies the memory of the other two computers and runs the same programs.
A bit like rebooting your computer with the option to restore all your windows when you log back in. Dragon can even handle a situation where all three of its computers are hit by radiation at the same time although that's very unlikely to happen. Besides 3 flight computers, Dragon has 18 other systems onboard that also use triple redundancy computers. That brings the total amount of processors up to 54! And that’s just for a single Dragon capsule.
Cosmic rays flipping bits on Earth during elections
https://www.johndcook.com/blog/2019/05/2...ping-bits/
"
A cosmic ray striking computer memory at just the right time can flip a bit, turning a 0 into a 1 or vice versa. While I knew that cosmic ray bit flips were a theoretical possibility, I didn’t know until recently that there had been documented instances on the ground.
Radiolab did an episode on the case of a cosmic bit flip changing the vote tally in a Belgian election in 2003. The error was caught because one candidate got more votes than was logically possible. A recount showed that the person in question got 4096 more votes in the first count than the second count. The difference of exactly 212 votes was a clue that there had been a bit flip. All the other counts remained unchanged when they reran the tally."