Case Study: Investigating the 1996 Ariane 5 Rocket Launch Failure

This case study examines the 1996 Ariane 5 rocket explosion, which occurred approximately 40 seconds after launch. The investigation revealed that the failure stemmed from a flaw in the backup Inertial Reference System, triggered by the failure of the active system. This led to incorrect nozzle swiveling in the solid boosters, causing the rocket to deviate from its intended trajectory. Further analysis uncovered a software exception related to the alignment of the Strap-Down inertial platform, where an operand error occurred due to an unexpectedly high horizontal velocity value. The report details the sequence of events, highlighting the role of the flight control system and the ultimate self-destruction of the rocket, with debris scattered across a wide area. The study concludes that the incident was a result of a combination of software and hardware vulnerabilities, offering valuable lessons for future aerospace engineering projects. Desklib provides access to similar solved assignments and past papers for students.

Running Head: EXPLOSION OF THE ARIANE 5 (1996)
EXPLOSION OF THE ARIANE 5 (1996)
Name of the Student
Name of the University
Author’s Note

1EXPLOSION OF THE ARIANE 5 (1996)
Table of Contents
Introduction......................................................................................................................................2
Discussion........................................................................................................................................2
Purpose of the assignment...........................................................................................................2
Article summary..........................................................................................................................2
Conclusion.......................................................................................................................................5
References........................................................................................................................................6

2EXPLOSION OF THE ARIANE 5 (1996)
Introduction
On 4th of June in 1996, a maiden flight named Ariane 5 launcher had met a serious
accident after only 40 seconds of its take off. It exploded at the height of 3700m. The rocket
went out of its desired way and unexpectedly exploded. The engineers involved in the Ariane
project immediately verified the problem that had occurred the failure. Within few days, ESA’s
director general along with the chairperson of CNES had setup an Inquiry Board (Schelestow,
Troncoso & Torres, 2017). Various members were nominated such as chairperson, vice
chairperson and some more professionals who were involved in the project. This report discusses
the main purpose of the report. It further discusses regarding the summary of the article chosen
and the issues that caused the explosion and the outcomes.
Discussion
Purpose of the assignment
The article chosen for proceeding with this assignment is “Failure of flight feathers under
uniaxial compression” (Schelestow, Troncoso & Torres, 2017). This assignment aims in
discussing the problems occurred in the rocket, which lead to the explosion. Some weaknesses
that were involved in the system will also be discussed in this report. It would further discuss
regarding the findings after the failure.
Article summary
The rocket was launched from a launch site at Kourou. The weather in the morning at the
site was quite pleasant for the launch. The weather did not create any problem while the launcher
was transferred to the launch pad. The strength of electric field was found to be negligible and

3EXPLOSION OF THE ARIANE 5 (1996)
hence there was no chance of lightening (Schelestow, Troncoso & Torres, 2017). This made the
team realize the failure might have caused due to some loopholes in meeting the criteria of the
rocket that was manufactured. Until H0-7 the countdown also went smoothly, it was found that
the core stage of fulfilling the criteria was met. The launch was kept on hold. After some more
investigation, it was found that the visibility criteria were not fulfilled at the launch window
opening (Johnson, Bak & Drager, 2015). As the launch and forecast was initiated, the visibility
improved. After the launch was made, the rocket had a normal flight until around HO + 37
seconds. Suddenly after that, it went off its track and exploded. A detailed investigation showed
that the failure occurred in the backup Inertial Reference System that had occurred just after the
active Inertial Reference System failed. The reason for the rocket to change its launch path was
the swiveling in its crucial part of the solid boosters’ nozzles. After that, the Vulcain engine
caused the vehicle to change it path without warning. The rupture of links among the core stage
and the solid boosters caused the destruction of the launcher. Thus, it was found that the
explosion caused due to the ignorance of the flight control system and especially because of the
Inertial Reference System.
The self-destruction of rocket caused around the launch pad at a height of 4000m. As a
result, the debris of the vehicle fell on the ground. They spread over the area of around 12 km
towards east (Nguyen, Hoque & Bak et al., 2018). The recovery of lost material was found
difficult because the area where they fell was savanna and mangrove swamp. The analysis
carried out after the flight showed number of anomalies that was reported to Board.
Numerous chains of events were reported to the Board. These events were analyzed
based on extensive documentation and information regarding the failure of Ariane 501 that was
available to the Board. The events were as follows

4EXPLOSION OF THE ARIANE 5 (1996)
 The rocker started to fail at around H0 + 39 seconds. This was caused due to the heavy
aerodynamic load because of the attack angle, which was around 25 degrees. This
resulted in a separation of boosters from its actual stage (Wei, Jiao & Zhao, 2017). This
as a result triggered the self-destruction of the rocket.
 Angle of the attack was due to the deflection of the nozzle of solid boosters as well as the
main engine of the Vulcain.
 Based on the information transferred by active Inertial Reference System the deflection
of those nozzles was commanded by software of On-Board Computer(Wei, Jiao & Zhao,
2017). A part of these data did not have appropriate data regarding the flight but showed
the diagnostic pattern of computer of SRI 2.
 The OBC was not able to get access to the backup SRI 1. This is because the particular
part had already denied to function during the previous data cycle.
 The unit announced the cause of failure to be a software exception. This is the reason that
the active SRI 2 did not send appropriate data.
 The part of the software where error had occurred was the one that performs an alignment
of Strap-Down inertial platform (Wei, Jiao & Zhao, 2017). The module calculates proper
results before the vehicle takes off. When the vehicle takes off the function has no
purpose.
 Operand error took place because of the high value of the result of internal alignment
function.
 Alignment function operates for about 50 seconds after the vehicle takes off. After the
vehicle takes off, the function works for around 40 seconds of the flight. The time
sequence is decided according to the requirement of the vehicle (Wei, Jiao & Zhao,

5EXPLOSION OF THE ARIANE 5 (1996)
2017). It is not necessary that the sequence that had been decided for Ariane 4 would also
be used for Ariane 5.
 The value of the BH was comparatively greater that the value that had been expected.
This is because previous part of the trajectory of Ariane 4 differes from the Ariane 5.
This resulted in a greater value of horizontal velocity.
Conclusion
From this above report, the overall incident is clear along with the reasons for which the
explosion of vehicle occurred. The report also discusses various events, which also contributed
in the failure of the launch. The article gives a clear idea of the accident. It was found out that
during the preparation of the launch, no incident took place, which could indicate the failure. The
meteorological conditions were acceptable during the launch. No external factor was found
responsible for the failure.

6EXPLOSION OF THE ARIANE 5 (1996)
References
Johnson, T. T., Bak, S., & Drager, S. (2015, April). Cyber-physical specification mismatch
identification with dynamic analysis. In Proceedings of the ACM/IEEE Sixth
International Conference on Cyber-Physical Systems (pp. 208-217). ACM.
Nguyen, L. V., Hoque, K. A., Bak, S., Drager, S., & Johnson, T. T. (2018). Cyber-Physical
Specification Mismatches. ACM Transactions on Cyber-Physical Systems, 2(4), 23.
Schelestow, K., Troncoso, O. P., & Torres, F. G. (2017). Failure of flight feathers under uniaxial
compression. Materials Science and Engineering: C, 78, 923-931.
Wei, Q., Jiao, J., & Zhao, T. (2017). Flight control system failure modeling and verification
based on SPIN. Engineering Failure Analysis, 82, 501-513.