Chris Johnson, Index
Ariane 5 Case Study
- Problems in requirements/safety analysis.
n) During design of the software of the inertial reference system used for Ariane 4 and
Ariane 5, a decision was taken that it was not necessary to protect the inertial system
computer from being made inoperative by an excessive value of the variable related to the
horizontal velocity, a protection which was provided for several other variables of the
alignment software. When taking this design decision, it was not analysed or fully
understood which values this particular variable might assume when the alignment
software was allowed to operate after lift-off.
