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posted by CoolHand on Thursday May 07 2015, @07:03AM   Printer-friendly
from the not-as-promoted-as-y2k-bug dept.

A surprisingly simple bug afflicts computers controlling planes, spacecraft and more – they get confused by big numbers. As Chris Baraniuk discovers, the glitch has led to explosions, missing space probes and more.

Tuesday, 4 June 1996 will forever be remembered as a dark day for the European Space Agency (Esa). The first flight of the crewless Ariane 5 rocket, carrying with it four very expensive scientific satellites, ended after 39 seconds in an unholy ball of smoke and fire. It's estimated that the explosion resulted in a loss of $370m (£240m).

What happened? It wasn't a mechanical failure or an act of sabotage. No, the launch ended in disaster thanks to a simple software bug. A computer getting its maths wrong – essentially getting overwhelmed by a number bigger than it expected.

How is it possible that computers get befuddled by numbers in this way? It turns out such errors are answerable for a series of disasters and mishaps in recent years, destroying rockets, making space probes go missing, and sending missiles off-target. So what are these bugs, and why do they happen?

Imagine trying to represent a value of, say, 105,350 miles on an odometer that has a maximum value of 99,999. The counter would "roll over" to 00,000 and then count up to 5,350, the remaining value. This is the same species of inaccuracy that doomed the 1996 Ariane 5 launch. More technically, it's called "integer overflow", essentially meaning that numbers are too big to be stored in a computer system, and sometimes this can cause malfunction.

Such glitches emerge with surprising frequency. It's suspected that the reason why Nasa lost contact with the Deep Impact space probe in 2013 was an integer limit being reached.

And just last week it was reported that Boeing 787 aircraft may suffer from a similar issue. The control unit managing the delivery of power to the plane's engines will automatically enter a failsafe mode – and shut down the engines – if it has been left on for over 248 days.

 
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  • (Score: 2) by c0lo on Thursday May 07 2015, @12:38PM

    by c0lo (156) Subscriber Badge on Thursday May 07 2015, @12:38PM (#179869) Journal

    because microcontrollers like that can be had for almost literally a dime a dozen in this day and age.

    I can't believe a Boeing 747 can't afford a modern CPU (pricewise or energywise). What's going to add on the price of the aircraft, a few hundred dollars?
    Is the ass of the free market fairy that tight? (even after the banksters abused it repeatedly?)

    the large quantities of memory that are required for arbitrary precision arithmetic

    A 64bit uint=1.84e+19 - let's put down some numbers for comparison:

    Why would one need arbitrary precision arithmetic for the usual time/distances/speeds to fly in Earth's vicinity is beyond me.

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  • (Score: 2) by Reziac on Sunday May 10 2015, @02:16AM

    by Reziac (2489) on Sunday May 10 2015, @02:16AM (#180940) Homepage

    Regardless of what it runs on, it should be restarted before every flight as part of the pre-flight check. Why would it run for 248 days in the first place??

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