The code that exploded a rocket

In 1996 a very expensive (but fortunately non-fatal!) rocket explosion became a teachable moment in computer science, when the debut launch of the ESA's shiny new Ariane 5 rocket spectacularly failed less than a minute after lift off.

This video was produced for a University of Sydney online course called "NaN: Numbers And Numerics".

Credits:
Ariane 5 launch videos: ESA, Arianespace, CNES
Mission Control flight desk image: NASA
Ariane 4 & Ariane 5 images: ESA, Arianespace, CNES

[hoocna]

I feel kinda bad for laughing so hard at how you animated the content.
EXCELLENT job hahahah

[sovietmudkip]

I'm so glad this channel got randomly mentioned in a Reddit post. The content is excellent

[simonnielsen]

A very good description of the accident. My CS 101 professor gave a very similar presentation of the problem back in 1996, when the post mortem report first came out.

[ryanhamstra]

You mentioned the code ran for 40 seconds then shut down, and on the old rocket it was fine but this one was going faster. My favorite part is the issue happened at 38 seconds into flight, so they didn’t even have to fix the software, they would have just had to do the math and know and shut it down at 35 seconds instead and it would have been fine

[RAJATHRAJRK]

You can host history lessons or science classes with such a cool sound

[gawayne]

I love the reaction of the flight director.

[Rk]

A very nice video, in ‘easy to understand’ English!

Thank you for the video!

I have seen a talk from Matt Parker, with him explaining this disaster. And it is a small addition to this story.

On the Ariana 4, there were indeed a lot of sensors which the guidance system monitored.
(Including the sensor that was still sending data, when it could have been turned off after launch).

Some sensors would send 16 bits of data, and some sensors would send 64 bits.
For the sensors that could send 64 bits, there was a small checksum that would check the amount of bits. But some sensors never send more than 16 bits. And for these sensors, the checksum never initiated.

To save memory and computer power, they would allocated a 16 bit part of the memory in the guidance system for the sensors that wouldn’t exceed a 16 bit data block.
(Why reserve a space of 64 bits, when only 16 bits are coming in)?

And this worked just fine.
For the Ariana 4.

But when the Ariana 5 launched, and like this video explaines, this particular sensor suddenly went beyond the 16 bits of data and send 64 bits of data. But because there were only 16 bits allocated for this sensor in the guidance system’s memory bank, the guidance system crashed and send this error message to the flight computer.

And like this video brilliantly explained, the flight computer interpreted this message as navigation data.

[logarhythmic]

"Why test the code? It worked on the other rockets"

It's not nearly as costly or as serious, but it kind of reminds me of the Venera probes that landed on Venus. In Venera 9-12, either one or both lens caps failed to release from the camera, and then Venera 14 had the lens cap release, but it landed right under where another instrument was supposed to take measurements of the surface, thus blocking the measurements.

[MichaelPohoreski]

@2:10 Standard *2's complement* means negative values have the sign bit *set* so -1 is 1111 1111 1111 1111, and -32768 is 1000 0000 0000 0000.

[Daresco]

Very nice content, very well explained. Thumbs up!

[dnielDayZContent]

The last 40 secs of this video left me speechless.

[SteevyMathew]

You should really voice an audiobook... Or a podcast... Or just record yourself reading a scientific journal or even a dictionary.

[PRCA-zwxo]

Outstanding video. Thank you so much. Will be showing to my class.

[stighenningjohansen]

its a flaw in their system. No quality control going on? or guidelines, reviews, testing to failiure? This a sign of weakness in the ESA organisation. An embarrassing one

[lucassousa]

What a great video! Thank you very much for this. You've got an amazing voice, by the way hahaha

[waqarmehdi]

Inadvertently I am watching this on a 4th of June 24 years later.

[jamskinner]

Why convert from float to int anyway? And why only a 16 bit int? How old is this hardware?

[alexfigueroa]

I don't know why this was recommended from YT but, wow!

[charlesbyrne]

The most expensive firework in history!

[AW-xjun]

Excellent description of something that was born of laziness and incompetence.