The Rocket That Exploded Because Of One Number
In 1996, Ariane 5 self-destructed 37 seconds after launch because old code tried to fit a 64-bit number into a 16-bit space.
The script
This rocket took ten years to build... and thirty-seven seconds to destroy itself.
June fourth, nineteen ninety-six. Ariane five lifts off.
Thirty-seven seconds in, its navigation computer crashed... then the backup, the exact same way.
The rocket swung sideways and blew itself apart.
You see, the code was reused from the older, slower Ariane four.
It stored the rocket's sideways speed in a box that only fit numbers up to thirty-two thousand.
Ariane five was so fast, the number didn't fit.
The code worked perfectly... just on the wrong rocket.
And that one number is why...
The facts, checked
- Ariane 5 Flight 501, 4 June 1996. About 37 seconds after liftoff both inertial reference systems failed. The rocket veered and broke up, and self-destructed.
- A 64-bit floating-point value tied to horizontal velocity was converted to a 16-bit signed integer (max 32,767) and overflowed. The backup ran the same software and failed the same way.
- The code was reused from Ariane 4, whose slower trajectory never produced values that large. The programme took about a decade; the loss is usually quoted at about $370 million (some sources say $500 million).
