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Redundancy in hardware is one problem. But then all those CPUs still run the same software. After Ariane 5 crashed spectacularly due to a software error that a

by Nitramp 15y ago

Redundancy in hardware is one problem. But then all those CPUs still run the same software. After Ariane 5 crashed spectacularly due to a software error that affected the two on board computers and the ground control unit likewise (http://en.wikipedia.org/wiki/Ariane_5_Flight_501 http://en.wikipedia.org/wiki/Ariane_5_Flight_501), there had been talk about having the same software be developed by multiple, independent teams, and then use the different versions for error correction. Sounds like a crazy idea and probably won't work, but I don't really know of a better solution either.

deleted 15y ago
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mfenniak 15y ago
The Space Shuttle had a design like this, with a separate backup flight control system that used independent hardware and software. http://en.wikipedia.org/wiki/Space_Shuttle#Flight_systems http://en.wikipedia.org/wiki/Space_Shuttle#Flight_systems I wonder though -- in this case, the backup software was never used. In my experience, redundant systems tend to fail more often the less frequently they're used... I wonder how they maintained testing the backup flight system to ensure that it the transition would operate correctly.
gnaffle 15y ago
http://en.wikipedia.org/wiki/N-version_programming http://en.wikipedia.org/wiki/N-version_programming It's used in Airbus planes, for instance. Of course, it's useless if the specification is wrong, and the assumption that the differing versions will fail in different ways seems to not hold water.
joelhaasnoot 15y ago
Wouldn't that just make it worse? "Oh it failed, let's see if the other team had a better idea... [5 minutes later] Nope, they used the same algorithm but it can't talk to this algorithm"
adavies42 15y ago
IIRC, that's more or less how the DNS root servers are managed--they're not just in different locations, they're running different server software on different OS's, to minimize the chance that any one problem could take all of them out.

by Nitramp 15y ago

deleted 15y ago

[deleted]

mfenniak 15y ago

The Space Shuttle had a design like this, with a separate backup flight control system that used independent hardware and software. http://en.wikipedia.org/wiki/Space_Shuttle#Flight_systems http://en.wikipedia.org/wiki/Space_Shuttle#Flight_systems I wonder though -- in this case, the backup software was never used. In my experience, redundant systems tend to fail more often the less frequently they're used... I wonder how they maintained testing the backup flight system to ensure that it the transition would operate correctly.

gnaffle 15y ago

http://en.wikipedia.org/wiki/N-version_programming http://en.wikipedia.org/wiki/N-version_programming It's used in Airbus planes, for instance. Of course, it's useless if the specification is wrong, and the assumption that the differing versions will fail in different ways seems to not hold water.

joelhaasnoot 15y ago

Wouldn't that just make it worse? "Oh it failed, let's see if the other team had a better idea... [5 minutes later] Nope, they used the same algorithm but it can't talk to this algorithm"

adavies42 15y ago

IIRC, that's more or less how the DNS root servers are managed--they're not just in different locations, they're running different server software on different OS's, to minimize the chance that any one problem could take all of them out.