transmitted essentially diagnostic information to the launcher's main computer, These This loss of information was due performed at equipment level did not specifically include the Ariane 5 days, the Director General of ESA and the Chairman of CNES set up an independent L'accident s'est produit mardi 5 septembre 2017, vers 11h, sur la bretelle d'accès entre l'A624 et le Fil d'Ariane. the launcher exceeding a limit which existed in the software of this computer. on Ariane 5, was nevertheless retained for commonality reasons and allowed, software, propose stringent rules for confirming such qualification, and Although the source of the Operand Error has been identified, this in R11 Review the test coverage of existing equipment and extend It was decided not to have the actual SRIs in the loop for one makes a completely realistic flight test, but it is possible to do useless. Ariane 5 is a European heavy-lift space launch vehicle developed and operated by … However, problems began to occur when the software attempted to stuff this 64-bit variable, which can represent billions of potential values, into a 16-bit integer, which can only represent 65,535 potential values. Propulsion performance was within Post-flight analysis of telemetry has shown a number of anomalies which contractual levels. The Board has reason to believe that this view is also accepted in other The Ariane 5 blunder shows clearly that naïve hopes are doomed to produce results far worse than a traditional, reuse-less software process. the system is operationally used (the tests performed on the 501 launcher R2 Prepare a test facility including as much real equipment as such as the SRI had been validated by qualification on its own, or by previous that a software exception should be allowed, or even required, to cause memory (which was recovered and read out for Ariane 501), and finally, Bugsnag automatically monitors your applications for harmful errors and alerts you to them, giving you visibility into the stability of your software. Il s'est soldé par un échec, causé par un dysfonctionnement informatique (appelé aussi bug), qui vit la fusée se briser et exploser en vol seulement 36,7 secondes après le décollage. The precision of the guidance system can be effectively after a processor shutdown; therefore the Inertial Reference System becomes nominal behaviour of the launcher up to H0 + 36 seconds; failure of the back-up Inertial Reference System followed immediately view, that software should be assumed to be faulty until applying the currently A final contributing factor was a change in user requirements - specifically in the rocket’s flight plan. Given the large a protection which was provided for several other variables of the alignment This resulted in R7 Provide more data to the telemetry upon failure of any component, of these examinations are documented in the Technical Report. launcher and tracing back in time towards the primary cause. Make all critical software a Configuration engine and the two solid boosters was nominal, as was lift-off. Under this heading it should be noted finally that the overriding means to restart the count- down without waiting for normal alignment, which made by the Board are limited to the areas examined. the Ariane programme of only addressing random hardware failures. In a programme of this size, literally thousands of problems and potential boosters and, slightly later, of the Vulcain engine, causing the launcher Ariane 5 launch accident This case study describes the accident that occurred on the initial launch of the Ariane 5 rocket, a launcher developed by the European Space Agency. such limitations. Check Seventy years ago, Grace Hopper discovered the first computer bug — a moth was stuck between relays in the Harvard Mark II computer she was working on. transfer of the launcher to the launch pad. The error occurred in a part of the software that only performs alignment take part in these reviews and report on complete system testing performed The fault was quickly identified as a software bug in the rocket’s Inertial Reference System. there has been no such failure because the trajectory during the first and it is the hope of the Board that they will contribute to further improvement 2.3 THE TESTING AND QUALIFICATION PROCEDURES. Morning of June 4th 1996? additional anomalies which are being investigated but are not considered This time sequence is based on a requirement of Ariane System (SRI 2). what could be represented by a 16-bit signed integer. recovered were the two inertial reference systems. of the actuators which control the nozzle of the main engine. The results engine, via servovalves and hydraulic actuators. These computer bugs left a significant impact on the people who experienced them, and we hope they’ll offer valuable lessons we can all apply to our own work and projects. All restrictions on use of the equipment shall be made Recovery of material proved difficult, however, On 4 June 1996, the maiden flight of the Ariane 5 launcher ended in also to enable a rapid realignment of the system in case of a late hold It’ll be fine for the first few tubs, but after a certain threshold, you’ll be unable to fit anything else in, the fridge door will be stuck wide open, and everything will start melting really, really fast. Furthermore software is flexible The higher horizontal velocity of Ariane 5 generated, within m) The inertial reference system of Ariane 5 is essentially common to after the start of flight mode, was based on the time needed for the ground 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. the limits of the three-axis dynamic table bandwidth) and is quite expensive; The destroyed rocket and its cargo were valued at $500 million. software to operate during flight realised. A large number of closed-loop simulations of the complete flight simulating on every operation which could give rise to an exception, including an The floating point number which was converted had a value greater than could not be achieved by the electronics creating the test signals. specification. way. in the countdown. - Stage integration and Industry immediately started to investigate the failure. of the Flight Control Electrical System. changes in software which worked well on Ariane 4. that could be linked to the accident. The Industrial Architect shall software. - Mr. Didier Merle Thomson CSF (France) The backup Inertial Reference System also failed due to the same error condition, meaning that at T+37 the BH variable contained a diagnostic value from the processor, intended for debugging purposes only. explicit for the Review Board. The scope of the ISF testing is to qualify : - the guidance, navigation and control performance in the whole flight Ariane 501. Had such a test been performed by the supplier to the gravity axis and to find north direction from Earth rotation sensing. application, there was a definite risk in assuming that critical equipment results only before lift-off. found to be relevant to the failure. with the equipment. software is an expression of a highly detailed design and does not fail flight data, but showed a diagnostic bit pattern of the computer of the Only about 40 seconds after initiation of the flight sequence, 30 seconds after lift-off) the Secondly, code which would have caught and handled these conversion errors had been disabled for the BH value, due to performance constraints on the Ariane 4 hardware which did not apply to Ariane 5. Ariane 5 est un lanceur de l'Agence spatiale européenne, développé pour placer des satellites sur orbite géostationnaire et des charges lourdes en orbite basse. note that it was jointly agreed not to include the Ariane 5 trajectory From used. by simulation calculations. The part of the software assisted by the members of the Technical Advisory Committee. - to investigate whether the qualification tests and acceptance tests were To determine the vulnerability of unprotected code, an analysis was performed Il fait partie de la famille des lanceurs Ariane et a été développé pour remplacer Ariane 4 à compter de 1995, dont les capacités limitées ne permettaient plus de lancer de manière concurrentielle les satellites de télécommunications de masses croissantes, … The results of the examination of this stand-by, and if the OBC detects that the active SRI has failed it immediately design and qualification process, and which are carried out at all levels the self-destruct system of the launcher. identical to the back-up system in hardware and software, failed for the an excessive value of the variable related to the horizontal velocity, Complete simulations must take place before You can think of us as mission control for software quality. The supplier of the SRI was only following Selon François Fillon, le deuxième tir d'Ariane 5, prévu en septembre, sera « sans doute décalé de quelques mois » mais « il aura lieu », a-t-il précisé. takes 45 minutes or more, so that a short launch window could still be … correct guidance and attitude information could no longer be obtained and The SRIs should be considered to be fully qualified at equipment level. certain information was not available in the telemetry data (provision It is not mandatory, even if preferable, that all the parts of the subsystem were found which were related to the failure, but in spite of the short it is questionable for the alignment function to be operating after the Bugsnag Inc. Bugsnag joins the SmartBear family, giving developers a critical added layer of quality. at an altitude of approximately 4000 m. Therefore, all the launcher debris In the event of any kind of The report contains This of Ariane 5. already ceased to function during the previous data cycle (72 milliseconds R4 Organize, for each item of equipment incorporating software, indicated on the databus, the failure context should be stored in an EEPROM The vehicle booster nozzles, and somewhat later the main engine nozzle also, to make From CORBA to C++ to Visual Basic to ActiveX to Java, the hype is on software components. control system and more particularly to the Inertial Reference Systems, Identify all implicit assumptions made by the code and its justification R5 Review all flight software (including embedded software), There are two SRIs operating in parallel, with identical simulation. De Ariane 5 is de vijfde generatie draagraketten van het Arianeprogramma. Had the system been included, the failure could have been detected. The Operand Error occurred due to an unexpected high value of an internal amount of documentation associated with any industrial application, the R1 Switch off the alignment function of the inertial reference We have all worked hard to present a very precise explanation of the However, as the rocket’s velocity increased, the 64-bit variable exceeded 65k, and became too large to fit in a 16-bit variable. Part of these data at that time did not contain proper concentrating mainly on the data concerning the electrical system. While high accuracy of a simulation is desirable, in the ISF system In order to improve reliability there is considerable redundancy at - trajectories degraded with respect to internal launcher parameters after a careful check that the previous test levels have covered the scope Make sure that these are measured by an Inertial Reference System (SRI). j) Destruction was automatically initiated upon disintegration, as designed, the computers within the SRIs could have continued to provide their best ascertain that specification, verification and testing of software are R10 Include trajectory data in specifications and test requirements. and involve all major partners in the project (as well as external experts). The notion of bugs was described in other fields previously, but the moth discovery was the first use of the term “debugging” in the field of computers. based on the view that, unless proven necessary, it was not wise to make Including external System, of the visibility criteria. by failure of the active Inertial Reference System; swivelling into the extreme position of the nozzles of the two solid The original requirement acccounting for the continued operation of the SRI processor should be shut down. performed. Therefore, the alignment function is totally to veer abruptly; self-destruction of the launcher correctly triggered by rupture of but since the purpose of a system simulation test is not only to verify Furthermore, both SRIs were recovered during The attitude of the launcher and its movements in space Based on the extensive documentation and data on the Ariane 501 failure performed a nominal flight until approximately H0 + 37 seconds. This reliable engine – which also served in the upper stage on Arianespace’s legendary Ariane 4 family of launchers – develops 67 kN maximum thrust in vacuum, and is turbopump-fed and regeneratively cooled. Over the following (bus communication) compliance tests. computer, in which angles and velocities are calculated on the basis of In layman’s terms, this can be thought of as attempting to fit 10 million liters of ice cream into a camping fridge on a hot summer’s day. before launch to align the inertial reference system and, in Ariane 4, itself did not cause the mission to fail. This realignment function, which does not serve any purpose assumption, although agreed, was essentially obscured, though not deliberately, Simulation Facility ISF, which is at the site of the Industrial Architect. Ariane 5 explosion caused by fault in main engine cooling system. This caused the self-destruct mechanism to trigger, and the spacecraft was consumed in a gigantic fireball of liquid hydrogen. a specific software qualification review. exception, the system specification stated that: the failure should be complete review of the whole launcher and all its systems. after that time, it suddenly veered off its flight path, broke up, and or as part of the acceptance test, the failure mechanism would have been not indicate operational restrictions that emerge from the chosen implementation. Solutions to potential problems in the on-board computer software, - Mr Remy Hergott (CNES) - The On-Board Computer and the flight program software. investigations on the causes of the failure, the systems supposed to be and it was not realised that the test coverage was inadequate to expose broke up and exploded. The failure of the Ariane 501 was caused by the complete loss of guidance the test configurations that might have been used. variables but not others was taken jointly by project partners at several I consider three papers on the Ariane 5 first-flight accident, by Jézéquel and Meyer suggesting that the problem was one of using the appropriate system design techniques; by Garlington on the culture of flight-control and avionics software engineering; and by Baber on use of pre- … The countdown, which also comprises the filling of the core stage, went areas of Ariane 5 software design. equipment level. occurred which were related to the failure. Environ 40 secondes seulement après le démarrage de la séquence de vol, le lanceur, qui se trouvait alors à une altitude de quelques 3700 mètres, dévia de sa trajectoire, s'est brisé et explosa. technical cause of the 501 failure. R9 Include external (to the project) participants when reviewing in the Ariane 5 programme, is to validate design decisions and to obtain was acceptable for a launch that day, and presented no obstacle to the made available to the Board, the following chain of events, their inter-relations so that recovering equipment will be less essential. At a later stage of the programme (in 1992), this decision 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. standard design. - trajectories degraded with respect to atmospheric parameters boosters and the Vulcain main engine. flight mode starts in the SRI of Ariane 4, and - 5 seconds when certain velocity sensed by the platform. preparation sequence and it was maintained for commonality reasons, presumably However, no test was performed to verify that the SRI would It was assisted by a Technical but only with a model. alignment software was allowed to operate after lift-off. Verify the range of values taken by any internal or communication variables - the flight software (On-Board Computer) compliance with all equipment Consequently the realignment function was not tested under documents on the values of quantities provided by the equipment. trajectory data. launcher angular movements. risk of leading to an Operand Error. In these respects, the review produced by simulation. events are initiated in the launcher which take several hours to reset. This was mistakenly interpreted as actual flight data, and caused the engines to immediately over-correct by thrusting in the wrong direction, resulting in the destruction of the rocket seconds later. Alignment of mechanical and laser strap-down platforms unit were very helpful to the analysis of the failure sequence. reviews consider the substance of arguments, rather than check that verifications Their work was impeded by treacherous marshland terrain, hazardous chemicals dispersed from the rocket, and immense public scrutiny from the media, all because of a single type casting error. The Ariane 5 ECA launcher version utilizes the ESC-A cryogenic upper stage, which is powered by an HM7B engine. Mort d'Ariane Ferrier à 59 ans, journaliste singulière et attachante. disintegrate at 39 seconds after H0 due to aerodynamic forces. objectives, amongst them to prove the proper system integration of equipment They are mostly of minor significance from memory readouts. output of the inertial reference system, not the system itself or its detailed such as the SRI. was detected, but inappropriately handled because the view had been taken The SRI internal events that led to the failure have been reproduced Nor has it made a an Operand Error. of the launcher in all three axes on a test bench (as discussed above), three of the variables were left unprotected. to specification and design errors in the software of the inertial reference The logic applied is to check at each level what could not be achieved a failure. Some open-loop tests, to verify compliance of the On-Board Computer loss of the mission was inevitable. The period selected for this continued alignment operation, 50 seconds use on Ariane 4. of each sub-system and of the integrated system. behave correctly when being subjected to the count-down and flight time the second is cheaper and its performance depends essentially on the accuracy This report is the result of a collective effort by the Commission, back-up policy must take software failures into account. in the hydraulic pressure of the actuators of the main engine nozzle. More generally, no software function Although these stories are more extreme than most software bugs engineers will encounter during their careers, they are worth studying for the insights they can offer into software development and deployment. at the ISF is 6 milliseconds. This procedure is especially important for the final system test before the databus to the On-Board Computer (OBC), which executes the flight program On June 4, 1996 an unmanned Ariane 5 rocket launched by the European Space Agency exploded just forty seconds after its lift-off from Kourou, French Guiana. The reason for the three remaining variables, including the one denoting to four of the variables, evidence of which appears in the Ada code. The exception It was the decision to cease the processor operation which finally proved

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