1. integer. When Ariane 5 was launched the stand

1.     Ariane 5 explosion Software Failure

                     
i.           
What
is the source of your example?

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https://www.around.com/ariane.html

https://en.wikipedia.org/wiki/Cluster_(spacecraft)

http://sunnyday.mit.edu/accidents/Ariane5accidentreport.html

http://iansommerville.com/software-engineering-book/case-studies/ariane5/

 

                    
ii.           
What
is the name of the software?

Ariane 5 ‘s Primary/Backup Inertial reference system
software which is reused from Ariane 4 which is also called as Inertial
navigation system.

 

                  
iii.           
When
did the failure happen?

On 4 June 1996
at altitude of 3700m, at 36.7 Secs from its launch the software failure is occurred.

 

                  
iv.           
What was the software Failure?

The Inertial
navigation system which will look after altitude and trajectory and velocity had
failed due to software error by which Ariane 5 lost control after 36.7 secs from
its launch and changed its axis and exploded at 39 secs from its launch.

 

                    
v.           
What was the software error that caused the
failure?

The design of Inertial reference system was taken directly from Ariane 4
which has a primary inertial reference system and a backup inertial reference
system (which will support primary inertial system). So, there is no need to do
it again. But, there is a problem Arian 5 has got the high horizontal velocity
than Ariane 4. Inside Inertial navigation system there is software to convert
64bit float to 16bit integer. When Ariane 5 was launched the stand by system
did the 64bit to 16bit conversion and had an overflow because of the high horizontal
velocity at that point (36.7 secs after its launched). The system fault
consideration was that the hardware could fail but the software works properly
because there is no exception handling for overflow instead the exception
handling mechanism will shut down the inertial reference system whenever there
is an exception occurred. So, when the stand by recognized the overflow it
determined that it was a hardware failure and it shuts itself off and the
primary system continues the operation. However, both the systems were of same
software and are placed in the same rocket. So, the primary system experienced
the same overflow with high horizontal velocity and shuts off without noticing
the backup system has shut down too. Due to no guidance incorrect signals were
sent to engines which changed its axis and imposed high stress on rocket and
was exploded.