Analysis Of Ariane 5 Launch, The Software Failure

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During Ariane 5 launch, the software failure occurred when an attempt to convert a 64-bit floating point number to convert a 64-bit floating point number representing the horizontal velocity to a signed/fixed 16-bit integer caused the number to overflow (become too big). The floating point number was too large to be represented in 16-bit (i.e. Ariane 4 software) and this hence caused a numeric overflow. The maximum value that can be represented in 16-bit is 32768. And the horizontal velocity which was being measured by sensors was greater than this, and hence the number overflowed. Moreover, Ariane 5 software did not have an exception handler for numeric overflow and as a consequence it defaulted overall runtime exception handling for the programming language used (i.e. ‘Ada’) and this default behavior in the event of NULL exception handler was to shut the system down. Since the backup system was running the same software code, exactly the same thing happened.
Famous author and software engineer, Ian Sommerville has defended the argument where software designed for Ariane 4 was reused. According to Ian, in fact the developers of Ariane 5 software developers followed the good systems engineering practice. They decided to reuse the software because the inertial reference system (IRS) was exactly the same as installed in Ariane 4 (i.e. very reliable system). The part of the system that failed was actually not required because particular calculation being carried out there was

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