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1. COMSATS INSTITUTE OF INFORMATION TECHNOLOGY
VEHARI CAMPUS
DEPARTMENT OF COMPUTER SCIENCE
Subject Name:
SOFTWARE ENGINEERING
Topic:
“REASON WHY ARIANE 5 FAILED”
Submitted to:
SIR QAIZAR JAVED SB
Submitted by:
FAISAL SHEHZAD
Roll: No:
SP17-MCS-020
Section:
MCS-B12-A
Date of Submitting:
26TH SEPTEMBER 2017
Assign.
No: 01

2. What Is Ariane 5?
Ariane 5 is a European heavy-lift launch vehicle that is part of the Ariane rocket family,
an expendable launch system used to deliver payloads into geostationary transfer
orbit (GTO) or low Earth orbit (LEO).
Ariane 5 rockets are manufactured under the authority of the European Space
Agency (ESA) and the Centre National d'Etudes Spatiales. Airbus Defence and Space is the
prime contractor for the vehicles, leading a consortium of other European contractors.
Ariane 5 is operated and marketed by Arianespace as part of the Ariane programme. The
rockets are launched by Arianespace from the Guiana Space Centre in French Guiana.
Ariane 5 succeeded Ariane 4, but was not derived from it directly. Ariane 5 has been
refined since the first launch in successive versions, "G", "G+", "GS", "ECA", and most
recently, "ES". ESA originally designed Ariane 5 to launch the Hermes spaceplane, and thus
intended it to be human rated from the beginning.
The Ariane 5 Launcher Failure
June 4th 1996
Total failure of the Ariane 5 launcher on its maiden flight
Ariane 5
➢ A European rocket designed to launch commercial payloads (e.g. communications
satellites, etc.) into Earth orbit
➢ Successor to the successful Ariane 4 launchers
➢ Ariane 5 can carry a heavier payload than Ariane 4

3. Launcher Failure
➢ Approximately 37 seconds after a successful lift-off, the Ariane 5 launcher lost
control.
➢ Incorrect control signals were sent to the engines and these swivelled so that
unsustainable stresses were imposed on the rocket.
➢ It started to break up and was destroyed by ground controllers.
➢ The system failure was a direct result of a software failure. However, it was
symptomatic of a more general systems validation failure.
The Problem Occurred In Ariane 5
➢ The attitude and trajectory of the rocket are measured by a computer-based inertial
reference system. This transmits commands to the engines to maintain attitude and
direction.
➢ The software failed and this system and the backup system shut down.

4. ➢ Diagnostic commands were transmitted to the engines which interpreted them as
real data and which swivelled to an extreme position resulting in unforeseen
stresses on the rocket.
Reasons of Failure
Software Failure
➢ Software failure occurred when an attempt to convert a 64-bit floating point
number to a signed 16-bit integer caused the number to overflow.
➢ There was no exception handler associated with the conversion so the system
exception management facilities were invoked. These shut down the software.
➢ The backup software was a copy and behaved in exactly the same way.
Avoidable Failure?
➢ The software that failed was reused from the Ariane 4 launch vehicle. The
computation that resulted in overflow was not used by Ariane 5.
➢ Decisions were made
• Not to remove the facility as this could introduce new faults;
• Not to test for overflow exceptions because the processor was heavily
loaded. For dependability reasons, it was thought desirable to have some
spare processor capacity.
➢ The designer’s of Ariane 5 made a critical and elementary error.
➢ They designed a system where a single component failure could cause the entire
system to fail.
➢ As a general rule, critical systems should always be designed to avoid a single point
of failure.
Validation Failure
➢ As the facility that failed was not required for Ariane 5, there was no requirement
associated with it.
➢ As there was no associated requirement, there were no tests of that part of the
software and hence no possibility of discovering the problem.
➢ During system testing, simulators of the inertial reference system computers were
used. These did not generate the error as there was no requirement.

5. Ariane 5 Specifications
Ariane 5 ES with ATV-4 on board on its way to the launch pad
Function Heavy launch vehicle
Manufacturer Airbus Defence and Space for
ESA, Arianespace and CNES
Country of origin 20 ESA member states
Cost per launch $165–220M
Size
Height 46–52 m (151–171 ft)
Diameter 5.4 m (18 ft)
Mass 777,000 kg (1,713,000 lb)
Stages 2
Capacity
Payload
to LEO(260 km
(162 mi) circular,
51.6°)
G: 16,000 kg (35,000 lb)
ES: over 20,000 kg (44,000 lb)
Payload to GTO
• G: 6,950 kg (15,320 lb)
• G+: 6,950 kg (15,320 lb)
• GS: 6,100 kg (13,400 lb)
• ECA: 10,500 kg (23,100 lb) (effective
record 10,865 kg (23,953 lb) on 1 June
2017