Development and Evaluation of Sensor Concepts for Ageless Aerospace Vehicles

25 Pages·2002·0.1 MB·English

NASA/CR-2002-211772
Development and Evaluation of Sensor
Concepts for Ageless Aerospace Vehicles
Threats and Measurands
DavidAbbott,Shaun Cunningham,Graham Daniels,BrionyDoyle,John Dunlop,Dean
Economou,TonyFarmer,DavidFarrant,CathyFoley, Bruce Fox,MarkHedley,Jan Herrmann,
Colin Jacka,Geoff James,MarkJohnson,BarryMartin,Geoff Poulton,Don Price,Torsten Reda,
Grahame Rosolen,AndrewScott,PhilipValencia,Damon Ward,John Winter,andAlan Young
CommonwealthScientific Industrial ResearchOrganisation
Telecommunications andIndustrial Physics
Lindfield,NewSouthWales,Australia
July 2002
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NASA/CR-2002-211772
Development and Evaluation of Sensor
Concepts for Ageless Aerospace Vehicles
Threats and Measurands
DavidAbbott,Shaun Cunningham,Graham Daniels,BrionyDoyle,John Dunlop,Dean
Economou,TonyFarmer,DavidFarrant,CathyFoley, Bruce Fox,MarkHedley,Jan Herrmann,
Colin Jacka,Geoff James,MarkJohnson,BarryMartin,Geoff Poulton,Don Price,Torsten Reda,
Grahame Rosolen,AndrewScott,PhilipValencia,Damon Ward,John Winter,andAlan Young
CommonwealthScientific Industrial ResearchOrganisation
Telecommunications andIndustrial Physics
Lindfield,NewSouthWales,Australia
NationalAeronauticsand
SpaceAdministration
LangleyResearchCenter PreparedforLangleyResearchCenter
Hampton,Virginia23681-2199 underPurchaseOrderL-15123
July 2002
Availablefrom:
NASACenterforAeroSpaceInformation(CASI) NationalTechnicalInformationService(NTIS)
7121StandardDrive 5285PortRoyalRoad
Hanover,MD21076-1320 Springfield,VA22161-2171
[phone] [phone]
1. Introduction
1.1 Project Aims
NASA’s goal ofageless aerospacevehicles requires thedevelopment ofvehicles that are
capableofstructural self-assessment andrepair.Thesefunctions canbedividedbetween
thosecarriedout bydistributedsensors andintelligent processingandcommunicationon
theskinorwithinthestructure,andthosethat couldbemoreeffectivelyprovidedby
autonomous roboticNDEagents whichcouldbedeployedtomonitordamageorintegrity
ofthevehiclestructure.
Critical tothesuccess oftheAgeless Vehicleprogram arethedevelopment ofappropriate
technologies fornon-destructiveevaluationofstructures,andthedevelopment of
strategies andtechnologies forprocessingNDEdata,storageandcommunicationofNDE
information,andanalysis ofNDEdatawithcapabilityforintelligent decision-making.
Theaim ofthis project is to develop and criticallyexamineconcepts forintegrated smart
sensingandcommunicationsystems that couldform thedistributedsensingfunctionofa
smart vehicle.Suchanintegratedsystem mayincludecomponents deployedforstructural
monitoringon an NDEagent.
1.2 Purpose,ScopeandOutlineof This Report
Thepurposeofthis report is topresent alist ofthetypes ofthreats towhichanaerospace
vehicleis subject,andwhichit must becapableofsurvivingifit is tobeconsidered
ageless.General strategies fordetectingeithertheapproachingrealizationofthese
threats,and/ortheireffects arealsolisted,as arethequantities that must bemeasuredfor
implementationofthestrategies.Requiredmeasurement rates andresponsetimes forthe
various threats arealsoconsidered,andtheimplications ofthis forthetypeofsensorand
thenatureoftheresponsearediscussed.Thus,this report sets thesceneforthemain
workoftheproject: it establishes inbroadterms therequirements that must besatisfied
bytheintegratedsensingsystem.
Therearetworeasons forthepreparationofthis report at this stageoftheproject,
approximatelytwomonths intoasix-monthworkperiod.Thefirst is toinitiateadialogue
withpersonnel from theNASANondestructiveEvaluationSciences Branch(NESB)
aimedat ensuringthat thesignificant performancerequirements ofasensingsystem have
beencaptured,andthat theproposedfuturedirections oftheworkareconsistent with
NESBexpectations.Wewelcomecomments from NESBpersonnel concerningany
aspects ofthis report.
Thesecondreasonwas toensureall members oftheCTIP team,whichis drawnfrom a
varietyofdisciplines andbackgrounds,hadanopportunitytothinkabout,discuss and
contributetothedevelopment ofthesystem requirements.Most team members have
contributedindepthtothediscussions that haveledtothis report,andconsequentlyhave
developedasoundappreciationofmanyoftheimportant issues involved.
Whileit is expectedthat inthelongerterm CTIP will contributesignificantlytothe
development ofappropriatesensors forageless systems andofmeasurement principles
andtechniques forsolvingoutstandingrelevant NDEissues,themainthrust ofthe
present project is todevelopconcepts forthewholeintegratedsystem: forsensing,data
processing,storage,communicationanddecision-making.Therefore,it has beenassumed
that it is not necessaryat this stagetoworkwithinascenariothat contains all conceivable
threats forall classes offutureoperational conditions,as longas it contains asampleof
possiblethreats that is representativeinterms ofthetypeandseverityofpotential
damage,thetimetakenfordamagetooccuroraccumulate,opportunities forprior
detectionandavoidance,thenatureandtimescaleofappropriateresponses,etc.Inshort,
thescenariomust berepresentativeinterms ofrequirements onthefunctionalityofthe
system.
This report is limitedinscopetoalisting ofthethreats,bothfrom theexternal
environment andfrom withinthevehicleandits structure,andstrategies fordetecting
damagethat mayresult from thesethreats.It does not discuss measurement techniques or
technologies inanydepth,eventhoughsomeofthemoreinterestingdiscussions within
theteam haverevolvedaroundmeasurement techniques.This is partlybecausesensing
andmeasurement techniques will beinfluencedtosomeextent bycommunications and
decision-makingrequirements,andpartlybecausethechoiceandavailabilityofsensing
technologies will changewithtime.Theseissues will bedealt withlaterintheproject.
Thestructureofthis report is as follows.A numberofissues havebeenraisedduringthe
courseofourdiscussions.Someofthesearepertinent tothelist ofthreats,andwill
discussedinthenext section,followedbythethreats andsensingstrategies.Following
this alist ofrequiredmeasurement rates andresponsetimes is presented.Theotherissues
mentionedabovearethenaddressed.Thesearemostlynot resolved,but areraisedas
issues fordiscussionandresolutionat alatertime.Finally,thereis abriefoutlineofhow
weplantoproceedwiththis project intheimmediatefuture.
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2. Preliminary Issues
Issues whichimpingedirectlyontheidentificationofthreats andsensingrequirements
foranageless vehicleare:
• thenatureofthreats tobeconsidered;
• thenatureandpurposeofthevehicle;
• vehiclestructureandthecapabilities ofmaterials.
2.1 TheNatureof theThreats tobeConsidered
Athreat is consideredtobeanyevent,situationorcharacteristicthat canresult indamage
tothevehicleorcanproduceanimpairment ofits function. Threats will bereferredtoas
external iftheyresult directlyfrom theexternal environment inwhichthevehicleis
operating(e.g.weatherconditions intheatmosphere,cosmicradiation),orinternal ifthey
aregeneratedwithinthevehicle,orindirectlyduetotheexternal environment (e.g.
material fatigue,pressureleaks,electronicsystem failure).
It was decidedthat malicious threats wouldnot beconsideredexplicitly,partlybecauseof
theenormous varietyofways inwhichmalicious damagecould beinflictedonavehicle,
andbymeans inthefuturethat weprobablycannot imaginenow.However,theeffects of
manyforms ofmalicious damagewill besimilartothoseofaccidental orunavoidable
damage.
Thepossibilitywas consideredthat weshould concentrateonthreats that leadto“ageing”
ofavehicle,i.e.thosethat producerelativelyslowprogressivedegradationofthe
materials andstructure.Certainlythis damageis amongthemost difficult todetect at an
earlystage(at least bycurrent methods inexistingmaterials)andneeds tobeacentral
part ofthestrategy,but theultimateobjectiveis todevelopasensingsystem foravehicle
that must havelong-term survivability.This means it must beabletorecoverfrom the
wholerangeoffast andslowdamageprocesses (andbecapableofavoidingpotentially
catastrophicincidents).
2.2 TheNatureandPurposeof theVehicle
Therearethreesignificantlydifferent environments inwhichfutureaerospacevehicles
arelikelytoberequiredtooperate.Thesemaybesummarizedas follows.
A. Aspacevehicle,whichwouldoperateonlyinspace,andneverintheearth’s
atmosphere.It woulddock,andcouldbeservicedifnecessary,at aspacestation.
It wouldnot besubject totherigours ofatmospherictravel (turbulence,drag,heat
generation,etc.)but flights wouldbelong,leadingtoastrongrequirement for
structural reliabilityandlongevity.Suchavehiclemaystill needtobecapableof
negotiatinganatmosphere,andperhaps oneofundeterminedpressureand
composition,e.g.at adestinationplanet.External threats (radiation,particles,
micro-meteoroids etc.)maybesignificant.
B. A“shuttle”-typevehicle,whichcommutes betweenearthandspace(e.g.toa
spacestation,themoon,…).It must becapableofhandlinghigh-speed
atmospherictravel,andlargeaccelerations,includingtheheat ofre-entry.Flights
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will probablybeshorterthanforthespacevehicle.Humaninterventioninthe
maintenanceprocess,ifrequired,couldbeavailableonearth orat aspacestation.
C. Anatmosphericvehicle(aircraft),whichmayhaveperformancerequirements
comparabletothoseofpresent aircraft.Requirements couldrangefrom short low-
level trips (inter-and/orintra-city)tolongerhaul (inter-continental)flights.It can
probablybeassumedthat thelatterwouldbefast andhigh,leadingtosimilar
requirements totheshuttlevehicle(B).
Ingeneral it is onlythethreats posedbytheexternal environment that aredifferent for
thedifferent vehicletypes.However,theseverity,frequencyandrelativeimportanceof
internal threats maybedifferent,as aretheopportunities forandmeans ofrepair.These
will makeclearlyimportant differences inpractice.Threats toall ofthesetypes of
vehicles havebeenconsidered.
2.3 VehicleStructureandCapabilities of Materials
Thegroupheldalongandinterestingspeculativediscussionabout thenatureofvehicles
andthesorts ofmaterials andstructural principles from whichtheymight beconstructed
at sometimeinourdistant imaginations.Whilethis discussiondidnot result ina
consensus beingreached(whichinretrospect was bothinevitableanddesirable),it
stimulatedlong-term thinking,andanumberofuseful points emerged.
Twospecificmodels ofmaterials andstructures wereconsidered,basedonproposals
presentedbytwogroupmembers,TorstenRedaandMarkJohnson.Onewas an
explicitlybiological model,basedoncontinuous regenerationofcells ofthestructure
from genericmaterial that is capableofassumingtherequiredcharacteristics ofanypart
ofthestructureaccordingtotheinformationcontainedinthecell’s nucleus (DNA-like)
andthechemical environment inwhichthecell finds itself.Theotherwas amore
engineering-orientedmodel,but ofasimilarlyself-regeneratingstructure.Inthis casethe
structurewas composedofidentically-shapedmodules,capableofself-assemblyintoa
varietyofstructural shapes,andwitheachonecarryingout aspecificfunctionrelatedto
thesensingandrepairofdamage.
Thesemodels ledtoconsiderations oftherequirements ofasensingsystem that are
(relatively)independent ofthecapabilities andproperties ofthematerials.
Whetherornot theultimateaerospacevehicleis,inwholeorinpart,aself-assembling,
self-regeneratingstructure,it is highlylikelythat it will containmaterials that havesome
capabilityforself-healing.Suchmaterials arealreadyunderdevelopment: composites
that containmicro-globules ofresinandhardenerdispersedwithintheirmicrostructure
havebeenreported,eventhoughinthis casetheself-repairmechanism is relatively
unsophisticatedandnon-repeatable.Weneedtoconsidertheimplications ofthis fora
sensing,communicationandsupervisorysystem.
Self-repairofamaterial orstructurerequires that,at somelevel,thematerial orstructure
must “know”it has beendamaged.Thefollowingarepossiblescenarios fordamage
detectionandrepair.
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1. Thedamagecouldberepairedas part ofacontinuous regenerationprocess.This
might beappropriateforslowlyaccumulatingdamage,suchas mayoccurdueto
fatigue,wear,corrosionorradiation.Inthis casetheregenerationcannot be
simplereplacement: it must bebasedoninformationabout theundamaged
material.
2. Thedamageis detectedandrepaired“automatically”bythematerial orits local
environment (i.e.without referencetootherparts ofthestructure),not bya
continuous process but “ondemand”inresponsetothedetectionofdamage.If
this is tobecarried out repeatedly,as required,thenbothinformation(possibly
storedlocally)andasupplyofreplacement material ondemandarerequired.
3. Thedamageis detected,locallyorremotely,andtherepairprocess is initiated
(andpossiblycontrolled)byanotherpart ofthestructure.
Thesethreescenarios requireratherdifferent balances tobestruckbetweensensed
informationthat is usedlocallytoinitiateandcontrol repair/healing/regeneration,and
that whichis communicatedtootherregions ofthestructure.
Whilescenario1maynot actuallyrequiretheactivedetectionoftheparticularforms of
slowlyaccumulatingdamage,such“automatic”repairwouldimplythat thesystem
continuouslyregenerates at aratethat does not dependontherateofdamage
accumulation,yet it regenerates sufficientlyquicklythat damageis repairedbeforeit can
accumulatebeyondsomecritical level.Theefficiencyofsuchcontinuous regeneration
wouldneedtobeexamined: whilematerials mayberecyclable,theprocess would
consumeenergy.Inanycase,it is likelythat asupervisorysystem wouldwant toknowif
this sort ofdamagewas occurring,andits rateofprogression.
Scenario2,whichallows forlocal repair/regeneration,but “ondemand”inresponseto
thedetectionofdamage,requires someform ofcommunicationtoanotherpart ofthe
structure,at least forthesupplyofreplacement material.
It thereforeseems likelythat,whatever thecapabilities of thematerials for self-repair or
regeneration,therewill bearequirement for knowledgeof theoccurrenceandnatureof
damagetobecommunicatedtosomeregionor regions of thestructureremotefromthe
damagesite.
Anothersignificant issuerelatingtomaterial capabilities is that ofinformation.Anyself-
repairingorregeneratingmaterial requires information,energyandasourceofnew
material (nourishment).
• Forbiological systems,theinformationis storedlocallyinthecell nuclei.Thus
eachcell ofthesystem contains ahugeamount ofinformation,muchofwhich
maynot berelevant at that specificlocation.Theprovisionofnourishment for
regeneration,andtheremoval ofwasteproducts,arecarriedout differently
accordingtothetypeandcomplexityofthesystem.Thecentral supervisory
system (central nervous system,brain)inhigheranimals mayplayarolein
damagerepair(andcertainlyinimplementingstrategies fordamage
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minimization),but insimplersystems theinformationrequiredforrepairand
regenerationappears tobemaintainedentirelylocally.
• Forthecurrent generationofself-healingcomposites,the“information”content
andtheabilitytorepairthematerial arebothverylimited.Onlyonephaseofthe
composite(theepoxymatrix)canberepaired,andtherequiredinformationis,
presumably,containedinthedistributionandcontent oftheadhesiveglobules,
andthus is entirelylocal.
• Ingeneral,onewouldimaginethat theinformationrequiredtorepairamaterial or
structurewouldbemost efficientlymaintainedinsomecombinationoflocal and
distributed(orcentralised)storage.
As afinal (self-evident)comment,it is worth notingthat biological models ofself-repair
aresomewhat imperfect:
• Thereis averyobvious process ofageing,ultimatelyduetoaloss orcorruptionof
local informationforregeneration.
• Evenintheabsenceofageing,over-useinjuries (insomecases analogous to
fatigueinengineeringmaterials),stress fractures,wear(e.g.at joints),etc.occur
that arenot adequatelyrepairedwithout external intervention.
• Biological systems aresuccessful statisticallyratherthanindividually.Theaim
hereis todesignvehicles withas closeto100%survivabilityas possible.
• Relianceonlocal informationstoragemayintroduceanewthreat –errors leading
toself-destructivebehaviour,suchas cancerinbiological systems.Ontheother
hand,theexistenceofacentral brainandnervous system inhigheranimals
represents aregionofhighvulnerabilityofthesystem.
Thus,biological models canprovideveryuseful andinterestingideas forageless
vehicles,but theirlimitations must berecognized.
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