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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.2//EN"><HTML><HEAD> <TITLE>ARIANE 5 Failure - Full Report</TITLE> <META NAME="GENERATOR" CONTENT="Mozilla/3.0b5aGold (X11; I; SunOS 5.5 sun4c) [Netscape]"></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#FF0000"><DIV ALIGN=right><P>Paris, 19 July 1996</P></DIV><CENTER><P><B><FONT SIZE=+1>ARIANE 5</FONT></B></P></CENTER><CENTER><P><B><FONT SIZE=+1>Flight 501 Failure</FONT></B></P></CENTER><CENTER><P>Report by the Inquiry Board</P></CENTER><CENTER><P>The Chairman of the Board :</P></CENTER><CENTER><P>Prof. J. L. LIONS</P></CENTER><H3>FOREWORD</H3><P>On 4 June 1996, the maiden flight of the Ariane 5 launcher ended ina failure. Only about 40 seconds after initiation of the flight sequence,at an altitude of about 3700 m, the launcher veered off its flight path,broke up and exploded. Engineers from the Ariane 5 project teams of CNESand Industry immediately started to investigate the failure. Over the followingdays, the Director General of ESA and the Chairman of CNES set up an independentInquiry Board and nominated the following members :</P><P>- Prof. Jacques-Louis Lions (Chairman) Academie des Sciences (France)<BR>- Dr. Lennart Lbeck (Vice-Chairman) Swedish Space Corporation (Sweden)<BR>- Mr. Jean-Luc Fauquembergue Delegation Generale pour l'Armement (France)<BR>- Mr. Gilles Kahn Institut National de Recherche en Informatique et enAutomatique (INRIA), (France) <BR>- Prof. Dr. Ing. Wolfgang Kubbat Technical University of Darmstadt (Germany)<BR>- Dr. Ing. Stefan Levedag Daimler Benz Aerospace (Germany) <BR>- Dr. Ing. Leonardo Mazzini Alenia Spazio (Italy) <BR>- Mr. Didier Merle Thomson CSF (France) <BR>- Dr. Colin O'Halloran Defence Evaluation and Research Agency (DERA), (U.K.)</P><P>The terms of reference assigned to the Board requested it</P><UL><P>- to determine the causes of the launch failure, <BR>- to investigate whether the qualification tests and acceptance tests wereappropriate in relation to the problem encountered, <BR>- to recommend corrective action to remove the causes of the anomaly andother possible weaknesses of the systems found to be at fault.</P></UL><P>The Board started its work on 13 June 1996. It was assisted by a TechnicalAdvisory Committee composed of :</P><P>- Dr Mauro Balduccini (BPD) <BR>- Mr Yvan Choquer (Matra Marconi Space) <BR>- Mr Remy Hergott (CNES) <BR>- Mr Bernard Humbert (Aerospatiale) <BR>- Mr Eric Lefort (ESA)</P><P>In accordance with its terms of reference, the Board concentrated itsinvestigations on the causes of the failure, the systems supposed to beresponsible, any failures of similar nature in similar systems, and eventsthat could be linked to the accident. Consequently, the recommendationsmade by the Board are limited to the areas examined. The report containsthe analysis of the failure, the Board's conclusions and its recommendationsfor corrective measures, most of which should be undertaken before thenext flight of Ariane 5. There is in addition a report for restricted circulationin which the Board's findings are documented in greater technical detail.Although it consulted the telemetry data recorded during the flight, theBoard has not undertaken an evaluation of those data. Nor has it made acomplete review of the whole launcher and all its systems.</P><P>This report is the result of a collective effort by the Commission,assisted by the members of the Technical Advisory Committee.</P><P>We have all worked hard to present a very precise explanation of thereasons for the failure and to make a contribution towards the improvementof Ariane 5 software. This improvement is necessary to ensure the successof the programme.</P><P>The Board's findings are based on thorough and open presentations fromthe Ariane 5 project teams, and on documentation which has demonstratedthe high quality of the Ariane 5 programme as regards engineering workin general and completeness and traceability of documents.</P><DIV ALIGN=right><P>Chairman of the Board </P></DIV><H3>1. THE FAILURE</H3><H4>1.1 GENERAL DESCRIPTION</H4><P>On the basis of the documentation made available and the informationpresented to the Board, the following has been observed:</P><P>The weather at the launch site at Kourou on the morning of 4 June 1996was acceptable for a launch that day, and presented no obstacle to thetransfer of the launcher to the launch pad. In particular, there was norisk of lightning since the strength of the electric field measured atthe launch site was negligible. The only uncertainty concerned fulfilmentof the visibility criteria.</P><P>The countdown, which also comprises the filling of the core stage, wentsmoothly until H0-7 minutes when the launch was put on hold since the visibilitycriteria were not met at the opening of the launch window (08h35 localtime). Visibility conditions improved as forecast and the launch was initiatedat H0 = 09h 33mn 59s local time (=12h 33mn 59s UT). Ignition of the Vulcainengine and the two solid boosters was nominal, as was lift-off. The vehicleperformed a nominal flight until approximately H0 + 37 seconds. Shortlyafter that time, it suddenly veered off its flight path, broke up, andexploded. A preliminary investigation of flight data showed:</P><UL><LI>nominal behaviour of the launcher up to H0 + 36 seconds;</LI><LI>failure of the back-up Inertial Reference System followed immediatelyby failure of the active Inertial Reference System;</LI><LI>swivelling into the extreme position of the nozzles of the two solidboosters and, slightly later, of the Vulcain engine, causing the launcherto veer abruptly;</LI><LI>self-destruction of the launcher correctly triggered by rupture ofthe links between the solid boosters and the core stage.</LI></UL><P>The origin of the failure was thus rapidly narrowed down to the flightcontrol system and more particularly to the Inertial Reference Systems,which obviously ceased to function almost simultaneously at around H0 +36.7 seconds.</P><H4>1.2 INFORMATION AVAILABLE</H4><P>The information available on the launch includes:</P><UL><P>- telemetry data received on the ground until H0 + 42 seconds <BR>- trajectory data from radar stations <BR>- optical observations (IR camera, films) - inspection of recovered material.</P></UL><P>The whole of the telemetry data received in Kourou was transferred toCNES/Toulouse where the data were converted into parameter over time plots.CNES provided a copy of the data to Aerospatiale, which carried out analysesconcentrating mainly on the data concerning the electrical system.</P><H4>1.3 RECOVERY OF MATERIAL</H4><P>The self-destruction of the launcher occurred near to the launch pad,at an altitude of approximately 4000 m. Therefore, all the launcher debrisfell back onto the ground, scattered over an area of approximately 12 km2east of the launch pad. Recovery of material proved difficult, however,since this area is nearly all mangrove swamp or savanna.</P><P>Nevertheless, it was possible to retrieve from the debris the two InertialReference Systems. Of particular interest was the one which had workedin active mode and stopped functioning last, and for which, therefore,certain information was not available in the telemetry data (provisionfor transmission to ground of this information was confined to whicheverof the two units might fail first). The results of the examination of thisunit were very helpful to the analysis of the failure sequence.</P><H4>1.4 UNRELATED ANOMALIES OBSERVED</H4><P>Post-flight analysis of telemetry has shown a number of anomalies whichhave been reported to the Board. They are mostly of minor significanceand such as to be expected on a demonstration flight.</P><P>One anomaly which was brought to the particular attention of the Boardwas the gradual development, starting at Ho + 22 seconds, of variationsin the hydraulic pressure of the actuators of the main engine nozzle. Thesevariations had a frequency of approximately 10 Hz.</P><P>There are some preliminary explanations as to the cause of these variations,which are now under investigation.</P><P>After consideration, the Board has formed the opinion that this anomaly,while significant, has no bearing on the failure of Ariane 501.</P><H3>2. ANALYSIS OF THE FAILURE</H3><H4>2.1 CHAIN OF TECHNICAL EVENTS</H4><P>In general terms, the Flight Control System of the Ariane 5 is of astandard design. The attitude of the launcher and its movements in spaceare measured by an Inertial Reference System (SRI). It has its own internalcomputer, in which angles and velocities are calculated on the basis ofinformation from a "strap-down" inertial platform, with lasergyros and accelerometers. The data from the SRI are transmitted throughthe databus to the On-Board Computer (OBC), which executes the flight programand controls the nozzles of the solid boosters and the Vulcain cryogenicengine, via servovalves and hydraulic actuators.</P><P>In order to improve reliability there is considerable redundancy atequipment level. There are two SRIs operating in parallel, with identicalhardware and software. One SRI is active and one is in "hot"stand-by, and if the OBC detects that the active SRI has failed it immediatelyswitches to the other one, provided that this unit is functioning properly.Likewise there are two OBCs, and a number of other units in the FlightControl System are also duplicated.</P><P>The design of the Ariane 5 SRI is practically the same as that of anSRI which is presently used on Ariane 4, particularly as regards the software.</P><P>Based on the extensive documentation and data on the Ariane 501 failuremade available to the Board, the following chain of events, their inter-relationsand causes have been established, starting with the destruction of thelauncher and tracing back in time towards the primary cause.</P><UL><LI>The launcher started to disintegrate at about H0 + 39 seconds becauseof high aerodynamic loads due to an angle of attack of more than 20 degreesthat led to separation of the boosters from the main stage, in turn triggeringthe self-destruct system of the launcher.</LI><LI>This angle of attack was caused by full nozzle deflections of the solidboosters and the Vulcain main engine.</LI><LI>These nozzle deflections were commanded by the On-Board Computer (OBC)software on the basis of data transmitted by the active Inertial ReferenceSystem (SRI 2). Part of these data at that time did not contain properflight data, but showed a diagnostic bit pattern of the computer of theSRI 2, which was interpreted as flight data.</LI><LI>The reason why the active SRI 2 did not send correct attitude datawas that the unit had declared a failure due to a software exception.</LI><LI>The OBC could not switch to the back-up SRI 1 because that unit hadalready ceased to function during the previous data cycle (72 millisecondsperiod) for the same reason as SRI 2.</LI><LI>The internal SRI software exception was caused during execution ofa data conversion from 64-bit floating point to 16-bit signed integer value.The floating point number which was converted had a value greater thanwhat could be represented by a 16-bit signed integer. This resulted inan Operand Error. The data conversion instructions (in Ada code) were notprotected from causing an Operand Error, although other conversions ofcomparable variables in the same place in the code were protected.</LI><LI>The error occurred in a part of the software that only performs alignmentof the strap-down inertial platform. This software module computes meaningfulresults only before lift-off. As soon as the launcher lifts off, this functionserves no purpose.</LI><LI>The alignment function is operative for 50 seconds after starting ofthe Flight Mode of the SRIs which occurs at H0 - 3 seconds for Ariane 5.Consequently, when lift-off occurs, the function continues for approx.40 seconds of flight. This time sequence is based on a requirement of Ariane4 and is not required for Ariane 5.</LI><LI>The Operand Error occurred due to an unexpected high value of an internal⌨️ 快捷键说明
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