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0 pointsncmncm4y ago0 comments

Yet, integrating over the lifetime of Ariane 5, the overwhelmingly largest single cause of loss-of-vehicle failures was a software bug that would not have occurred with a different implementation language.

Spacecraft failures that can be blamed on failings of a particular language are very rare. There was a planetary space probe that failed arguably because it was coded in Fortran.

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pyjarrett4y ago· 2 in thread

I don't agree with your point.

Leaving in debug code, especially for an entire part of the launch that doesn't exist anymore by bringing in reused and untested code, seems like the real problem. I'm pretty sure integer overflow in this case would be undefined behavior, so you don't know what the compiler would do, especially since things were a lot more wild on the hardware side in 1996. Your point sounds like arguing that preferring Objective-C would prevent all those pesky `NullPointerException`s in Java since it allows sending messages to nil (null), but that's success by coincidence.

If you read the ESA's report [1], there were a lot of things which failed before you even get to the language. This software failure is the only one in the entire Ariane series of rockets. Considering that this is 1996, the list of languages to pick from was pretty slim, e.g. this predates C++ initial standardization (1998), `enum class` and other modern C++ features.

Even using just Ada 83 (of which 95, 2005, 2012, and 2022 succeeded and improved), I would argue that its forward looking features of preventing mixed mode arithmetic having properly typed checked enums and other features (like being strong typed) probably prevented a significant number of failures should other available languages at the time been used.

[1]: http://sunnyday.mit.edu/nasa-class/Ariane5-report.html

ncmncmOP4y ago

You miss that all the Ariane 4s were launched with the same flaw: any of them would have blown up for the same reason, if their vibration had peaked a bit beyond expected amplitude.

pyjarrett4y ago

It wasn't a flaw in Ariane 4 because it used a very different rocket flight path. This means the BH value which caused the error was physically impossible.

> The value of BH was much higher than expected because the early part of the trajectory of Ariane 5 differs from that of Ariane 4 and results in considerably higher horizontal velocity values.

> o) In Ariane 4 flights using the same type of inertial reference system there has been no such failure because the trajectory during the first 40 seconds of flight is such that the particular variable related to horizontal velocity cannot reach, with an adequate operational margin, a value beyond the limit present in the software.

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