Pathfinder's priority inversion problem, discovered and fixed on Mars (1998) | Hacker News Reader

Pathfinder's priority inversion problem, discovered and fixed on Mars (1998)

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61 pointsjimktrains210 comments

I remember first day doing some work as consultant with JPL for Cassini and a sim finished just before lunch and my collaborator says “huh, that’s interesting, the bug we have been reproducing for the last week suddenly disappeared! Case closed! Well let’s go...”. Being a naive youngster I say “wait, don’t we want to rerun the sim?? Maybe we need to tweak the parameters, etc, etc”

He shakes his head knowingly, says something to the effect of “no time for all that, son” and off we go.

In the end he was right, Cassini performed wonderfully, proof in the pudding and all that...but still can’t help think that it was in many ways a lot of lucky coin tosses!

The proof of the pudding is in the eating.

Not a bad group of people figuring in this story:

Glenn Reeves is now Chief Engineer of the division of JPL that designs spacecraft systems.

Mike Jones now appears to work on the notion of Identity on the internet (https://www.microsoft.com/en-us/research/people/mbj/).

And Dave Wilner is one of two co-founders of Wind River, which developed vxWorks, the OS used on Pathfinder.

Also, previously:

https://news.ycombinator.com/item?id=5993080

https://news.ycombinator.com/item?id=9764297

I love stories like this one. It gives me sooo much motivation to dig deeper into CS (I'm in college, studying CS while working as a developer).

Often I feel CS isolates me from the world around me which stops me from digging deeper in CS. But articles like this reinforce the thought that this might just be a question of the right environment.

It has always been a childhood dream of mine to work on (or in) space. I won't make it to NASA (they only take Americans) unfortunately. But hopefully I'll make it to ESA or one of the other private companies that are going to exist in the EU in the future.

Thanks for posting this <3

If you want to work _on_ space then anecdotally I don't believe it's true that you have to be American citizen to work at NASA/JPL (you need a work visa etc.). However ESA and others are doing plenty of cool things also!

I was looking up the 1553 bus mentioned and it turns out the Military replaced it with IEEE 1394 also known as: FireWire.

FireWire is the main bus for F-35 and other advanced US/Nato weapon systems.

The Ruskies also used the same buses for their MiG fighters, which makes sense for standardization and maintenance.

https://en.wikipedia.org/wiki/MIL-STD-1553

https://en.wikipedia.org/wiki/IEEE_1394

MIL-STD-1553 is still alive and well in a lot of places, including newly-designed DoD aircraft.

I've not seen the presentation/summary that prompted this email, but it sounds like someone wanted to dunk on JPL and tossed a few stones they shouldn't have.

The RAX bug is another good story along the same lines:

https://www.youtube.com/watch?v=_gZK0tW8EhQ

Henry S F Cooper Jr.'s book The Evening Star: Venus Observed describes a similar problem, remote debugging of a race condition (and some other things) of a spacecraft orbiting Venus.

Recommended reading for both space and computer geeks (well, there is a lot of overlap...).

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