Ariane 5

Learn about the Ariane 5 Case!

when

4th June 1996

when crashed

40 seconds after flight sequence initiation

when launched

09:33:59 local time

how high

3700m

what happened

failure of backup inertial reference system (SRI) followed by failure of active SRI

why

operand error - data conversion from 64-bit floating point to 16-bit signed integer caused SRI 2 malfunction because floating point had a greater value than what could be represented in 16 bit signed

why 2

value of horizontal bias (BH) was much higher than expected because early part of trajectory of Ariane 5 is different to Ariane 4 and results in higher horizontal velocity values but the software was reused

issue 1

despite SRI being “rigorously” tested, no test was performed to verify that it would behave correctly under the count-down, flight time sequence and trajectory of Ariane 5

note

possible to do ground testing by injecting simulated accelerometric signals in accordance with predicted flight parameters - if this had been done, the failure mechanism would have been found

issue 2

overall review process - limitations of SRI were not fully analyzed, also not realised that test coverage was too inadequate to even expose those limitations

why 3

SRI transmitted diagnostic info to OBC but was interpreted as flight data and used in calculations due to failure. caused booster and main engine nozzles to make a large correction for an altitude deviation that had not occurred

why 4

rapid change of altitude occurred causing the launcher to disintegrate due to aerodynamic forces