Software Bug Destroys Rocket…
On June 4, 1996, the maiden flight of the European Space Agency Ariane 501 rocket engaged its self-destruct mechanism 39 seconds after takeoff, disintegrating itself and its four-satellite payload. The loss totaled half a billion dollars — uninsured, of course.
The cause? A software bug.
Pre-lift-off calculations that align the on-board inertial reference systems were not needed for launch and would normally cease after T-9 seconds. However, since countdown holds could shut down the inertial reference systems for several hours, the calculations continued as a contingency. These calculations included the conversion of a 64-bit integer representing the “horizontal bias” or “sideways velocity” of the rocket to a 16-bit signed integer. Only 36.7 seconds into the flight, this new rocket reported a number that exceeded 2^15, a normal number for this much faster rocket, but one that was never anticipated, and an overflow error occurred.
The overflow error reported a diagnostic error message to the on-board computer which, in turn, interpreted the data as bizarre flight data. The computer immediately sent course correction instructions to the boosters and main engine, causing the rocket to swerve violently off course. Self-destruction was triggered automatically because aerodynamic forces were ripping the boosters from the rocket.
Ka-blam!
Ironically, the calculation of the horizontal bias didn’t even matter at that point, since the rocket was already in flight and no longer needed the guidance of the inertial reference systems. Another 3.3 seconds later, the calculations would have stopped because the “contingency plan” of continuing the calculations to avoid long delays was scheduled to end 40 seconds into the flight.
Suddenly I feel a bit better about Microsoft’s Blue Screen of Death syndrome. At least my computer won’t self-destruct every time some yahoo publishes bad JavaScript code on their website! However, I’m still glad Microsoft hasn’t branched into software for the auto industry. The last thing I need is for my Saturn to experience a software failure and take it upon itself to swerve into the nearest tree.
I know this was written 6 years ago; but I thought your statement about Microsoft’s absence from the auto industry was interesting. In the last few months MS has entered the auto space with voice recognition consoles. I’m not sure if they do nav systems yet, but there may be a car coming to a tree near you when the do.