r bulletin 94 — may 1998

Qualification Over Ariane’s Lifetime

A. González BlázquezDirectorate of Launchers, ESA, Paris

M. EymardGroupe Programme CNES/Arianespace, Evry, France

IntroductionThe primary objectives of the qualificationactivities performed during the operationallifetime of a launcher are:– to verify the qualification status of the vehicle– to resolve any technical problems relating to

subsystem operations on the ground or inflight.

Before focussing on the European family oflaunchers, it is perhaps informative to reviewjust one or two of the US efforts in the area ofsolid and liquid propulsion in order to put theAriane-related activities into context.

Similarly, the RL10 engine on the Centaur stageof the Atlas launcher has been the subject of anongoing improvement programme. About 5000tests were performed before the first flight, and4000 during the subsequent ten years.

On-going qualification activities of a similarnature were started for the Ariane-3 and 4launchers in 1986, and for Ariane-5 in 1996.They can be classified into two maincategories: ‘regular’ and ‘one-off’.

Ariane-3/4 accompanying activitiesRegular activities These activities are mainly devoted toverification of the qualification status of thevarious launcher subsystems. They include thefollowing work packages:– Periodic sampling of engines: one HM7 and

one Viking per year, tested to the limits of thequalification domain. As an example, from1984 to 1994, 25 turbo pumps and HM7Bengines were sampled in 240 tests, totalling75 000 s of running time. Other equipment –such as onboard computers, guidanceplatforms, flight-control electronics, separa-tion thrusters, pyrotechnic components andservo-motors – was also sampled andtested up to qualification boundaryconditions.

– Detailed and systematic analysis of flightdata, to reveal any possible anomalies andalso to update and improve the variousmathematical models representing thebehaviour of the launcher (Fig. 1).

– Inspection of solid-propellant boostersrecovered after flight (Fig. 2), to detect anymanufacturing deviations and possibleweaknesses.

One-off activitiesThese activities stem from the results of flight-data analysis and launcher subsystemacceptance testing. They can be as importantas the new definition and qualification of a

In principle, the development programme for a launcher ends with thequalification phase, after which it enters operational service. Inpractice, however, the assessment of a launcher’s reliability is acontinuing process and qualification-type activities proceed, as anextension of the development programme (as is done in aeronautics),over the course of the vehicle’s lifetime. Modifications to thelauncher’s design are made whenever anomalies that might have anadverse effect on the stringent reliability requirements are detectedduring testing, to pre-empt their occurrence in flight.

The casings of the solid-propellant boosters on the Space Shuttle, for example, aresystematically recovered for technicalinspection and re-utilisation. While theeconomics of the re-utilisation can bequestioned, the technical inspections havehighlighted major anomalies not previouslydetected in ground testing, including leakage ofthe rear joint, deterioration of the interior of thenozzles, abnormal erosion of the internalthermal protection, etc. All of these anomaliescould have led to failures. The test programmefor the Shuttle’s cryogenic engine (SSME) has atesting rate higher than during the engine’sdevelopment phase. During the ten yearsfollowing the first flight, a test programmeclocking up over 300 000 s of running time wascarried out. In 1993 alone, over 37 000 s oftesting was conducted.

Figure 1. Between 500 and 800 parameters, depending on the Ariane launcher version, are measured, transmitted by telemetry andexploited after each flight. They constitute a valuable database that helps in detecting deviations and improving the mathematicalmodels that simulate the launcher system’s behaviour

ariane qualification

Figure 2. Post-flightinspection of Ariane-4 solid

boosters at the GuianaSpace Centre provides

important information thatcannot be communicated bytelemetry alone: behaviours

of thermal protection,nozzles, fields joints, etc.

© ESA/CNES/Arianespace

r bulletin 94 — may 1998 bull

pump bearing for the oxygen turbo pump onthe HM7 engine, the qualification of a newnozzle throat for the Viking engine, or thequalification of new raw materials in thebooster’s solid propellant (Fig. 3).

In addition, cases of component obsolescenceor supplier failure can arise, making itnecessary to find replacements and qualifythem for flight application. Problems of thisnature have already been encountered andsuccessfully dealt with in various areas,including electronics components, the Vikingengine regulator, and composite structuralmaterials.

Experience gainedThese accompanying activities have high-lighted several potential failure sources on theAriane-3 and 4 launchers, allowing appropriatepreventive measures to be taken:– V22 : During long-duration tests on the

Viking engine, a risk of blow-by on theregulator was detected. To eliminate it, a

procedure for in-vacuo filling of theregulation circuit was established.

– V31 : To avoid damage caused by internalover-pressurising of the water tank on theL220 first stage, an extra valve was added.

– V33 : Poor liquid-propellant booster separa-tion was observed. To correct it, the attach-ment fittings on the main stage weremodified.

– V43 : Following the ‘uncoupling’ of theHM7B engine hydrogen pump, flights weresuspended until a bleed valve preventing anypump cavitation had been qualified.

– V60 : Sampling tests on the separationrocket revealed a risk of a hot gas leakin the event of non-synchronised ignitionsequences for the redundant pyrotechnicsystems. These had to be modified toeliminate the risk.

Ariane-5 accompanying activitiesQualification of the Ariane-5 launcher is still inprogress, but the production of the first set ofoperational launchers is already well under way.Consequently, Ariane-5 accompanying activi-ties were started in 1996, based on theexperience gained from Ariane-3 and 4 andretaining the distinction between regular andone-off activities that has proved so effective.

Regular activitiesThe types of recurrent activity supporting theAriane-5 programme are similar to those forAriane-4. There are, nevertheless, key differ-ences stemming from two factors:– the higher reliability target set for Ariane-5– the development of new engines for Ariane-5.

The exceptionally high reliability requirement forAriane-5 and the aim of reducing productionand operating costs have resulted in a newlauncher configuration that differs substantiallyfrom that of the previous generations. This newconfiguration required the development of twonew liquid-propellant engines – Vulcain andAestus – and a new solid-propellant booster.

Cryogenic main stageThe two features mentioned above – highreliability and new development – are bothhighly relevant in the case of propulsion, wherea clear distinction also has to be made betweentwo cases:– integration of various items that undergo

qualification tests individually– qualification of the engine as a whole under

extreme operating conditions (Fig. 4).

To address the first case, one Vulcain enginehas been revalidated and used to test enginecomponents in a special campaign. Thesecond case is being covered by limit tests on

ariane qualification

Figure 3. Ariane-4 strap-on-booster test stand inSardinia (Italy), and a full-scale firing testsequence in 1997 to qualify a new ingredient inthe solid propellant’s composition © A. Constanzo for ESA/CNES/Arianespace

r bulletin 94 — may 1998 bull

one Vulcain engine per year. This rate of testinggives a cumulative running time over the fiveyears of the campaign through to the year 2000of about 30 000 s — nearly 1.8 times theestimated cumulative running time of flightengines (acceptance tests and flight).

Critical equipment for the stage and propulsionsystem (pressurisation/bleeding units, electro-valve units, feed valves and liquid-heliumsubsystem, flexible element, damper systems,etc.) will undergo dedicated qualificationprogrammes followed by inspection.

Storable-propellant stageThe case of the Aestus engine on the storable-propellant stage is different. It is ignited in flightand operated for about 1000 s under conditionsthat are difficult to reproduce on the ground.The ratio of cumulative running times on theground, with one test campaign a year, to thosecumulated in flight will therefore be much lowerthan that given above for the Vulcain engine.

Aestus engine testing is, however, performed ona near-annual basis, with the engine undergoingnominal acceptance testing followed by short-and long-duration tests under varying operatingconditions. The results of all of these tests serveto confirm the durability of the engine’sperformance.

Figure 4. Test firings of the Ariane-5 cryogenicVulcain engine in Vernon (France) and Lampoldshausen (Germany)© SNECMA/SEP and DLR/DASA

One-off activitiesThese can be divided into two groups:– actions to address observed anomalies– actions in cases of component or material

obsolescence.

In the case of performance deviations beingobserved in flight (or during sampling tests), theprime aim is to arrive at a thorough under-standing of the problem and thence define themost effective solution.

Experience gained under earlier Ariane launcherprogrammes has demonstrated the importanceof taking prompt action to deal with cases ofmaterial obsolescence, particularly:– the procurement of materials, ingredients,

semi-finished products and units– electronic components.

Hardware obsolescence or the withdrawal fromthe market of the relevant supplier can affectitems in either category. Moreover, the risk ofsuch obsolescence problems occurring isincreasing as a result of industrial restructuringon an international basis and the nature of thelauncher components themselves. Electronicequipment is particularly prone to suchproblems. Such changes will inevitably lead tothe need for the period substitution of certainitems, the replacements for which will alsorequire the necessary re-qualification.

ConclusionThe considerable experience acquired in thedevelopment and operation of the Ariane-1 to 4series of launchers has demonstrated that flightfailures can be prevented by conducting theaccompanying activities that have beendescribed here. With more than one hundredflights to Ariane’s credit, Ariane-4 currentlyenjoys the highest reliability record in themarket: 0.966 according to the AMSAA model.These accompanying activities are set tocontinue throughout the lifetime of Ariane-5,with the systematic analysis of flight datacombined with the sample-testing of criticalitems from the production line. The goal is toensure that Ariane-5 has an even higherreliability throughout its lifetime than itspredecessor.

AcknowledgementsThe author wishes to thank André Constanzo ofArianespace for providing the photographs thataccompany this article. r

ariane qualification

The propellant tanks and high-pressure vesselswill also undergo acceptance and destructivetesting (fracturing) for the purposes ofcomparison with the qualification margins.Other items of equipment such as thepressurisation unit and electrical servo-motorwill be subjected to their own qualificationprogrammes periodically.

Solid-booster stageAs far as the solid-booster propulsion system isconcerned, the initial development testingserves primarily to freeze the definition of theboosters and above all the casting productionprocedures and hardware acceptance criteria.The limited number of ground tests – fivedevelopment and two qualification – isinsufficient for accurate definition of theavailable margins, especially since the internalballistics are different in flight and during groundtesting. Recovery of flight specimens forinspection is therefore extremely important, asthese provide the data needed for accuratedefinition of the actual margins for the featuresconsidered most critical (thickness of thermalprotection, nozzle parts, field joints), whichcannot be determined by in-flight measure-ments alone. Moreover, despite the fact that thebooster definition is frozen on qualification,procedures and raw materials are bound toevolve over time, without it being possible to assess the impact of this on availablemargins.

The boosters from at least two Ariane-5launches per year will therefore be recovered forinspection and at least one full-scale boosterfiring will be performed on the test stand at theGuiana Space Centre.

Other launcher systemsOther launcher systems will be sample-testedon a regular basis, including:

– electrical systems: onboard computer,inertial reference unit, flight controlelectronics, etc.

– attitude control system: thrusters, tanks withmembrane, hydrazine feed valves, etc.

– pyrotechnic systems

– nozzle actuator units for the solid-propellantboosters and the cryogenic main stage.

Sampling will proceed on the basis of howcritical a given item is. Items will undergoqualification testing followed by inspections.Limit tests will be conducted on the electronicscomponents, together with a destructinspection.