Ariane 501 Inquiry Board Reports

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For Immediate Release

Number 96-04, July 24, 1996

On June 4th, 1996 the maiden flight of the Ariane 5 launcher ended in a failure. Only about 40 seconds after initiation of the flight sequence, at an altitude of about 3700 meters, the launcher veered off its flight path, broke up and exploded. The following information has been excerpted from an ESA News Release made public at European Space Agency Headquarters in Paris, France on July 23, 1996.

Immediately after the failure, Mr. Jean-Marie Luton, ESA Director General, and Mr. Alain Bensoussan, CNES Chairman, set up an independent Inquiry Board (see ESA-CNES Press Release of 10 June 1996), which has now submitted its report.

The report begins by presenting the causes of the failure, with analysis of the flight data having indicated:

A chain of events, their inter-relationships and causes have been established, starting with the destruction of the launcher and tracing back in time towards the primary cause. These provide the technical explanations for the failure of the 501 flight, which lay in the flight control and guidance system. A detailed account is given in the report, which concludes:

The failure of Ariane 501 was caused by the complete loss of guidance and attitude information 37 seconds after start of the main engine ignition sequence (30 seconds after lift-off). This loss of information was due to specification and design errors in the software of the inertial reference system. The extensive reviews and tests carried out during the Ariane 5 development program did not include adequate analysis and testing of the inertial reference system or of the complete flight control system, which could have detected the potential failure.

Despite the series of tests and reviews carried out under the program, in the course of which thousands of corrections were made, shortcomings in the system approach concerning the software resulted in failure to detect the fault. It is stressed that alignment function of the inertial reference system, which served a purpose only before lift- off (but remained operative afterwards), was not taken into account in the simulations and that the equipment and system tests were not sufficiently representative.

Without implicating the system architecture, the report makes a series of recommendations for ensuring that the launcher's software operates correctly. The Ariane 5 program will be taking action in line with all these recommendations, as follows:

More specifically, the following corrective measures will be applied:

In addition, the following general measures will be taken:

The ESA Director General and CNES Chairman will be making a joint presentation of the plan of action put into effect and its programmatic consequences at a press conference in September.

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