Investigation of the THOR anthropomorphic test device for predicting occupant injuries during

23 Pages·2014·4.5 MB·English

by  Shean Phelps

TECHNOLOGYREPORT
published:17March2014
BIOENGINEERING AND BIOTECHNOLOGY doi:10.3389/fbioe.2014.00004
Investigation of theTHOR anthropomorphic test device for

predicting occupant injuries during spacecraft launch

aborts and landing

JeffreyT.Somers1,NathanielNewby1,CharlesLawrence2,RichardDeWeese3,DavidMoorcroft3 and
SheanPhelps4,5*

1ScienceTechnologyandEngineeringGroup,Wyle,Houston,TX,USA

2GlennResearchCenter,NationalAeronauticsandSpaceAdministration,Cleveland,OH,USA

3CivilAerospaceMedicalInstitute,FederalAviationAdministration,OklahomaCity,OK,USA
4GeorgiaTechResearchInstitute,Atlanta,GA,USA
5GeorgiaInstituteofTechnology,Atlanta,GA,USA

Editedby: The objective of this study was to investigate new methods for predicting injury from
TarunGoswami,WrightState expectedspaceflightdynamicloadsbyleveragingabroaderrangeofavailableinformation
University,USA
ininjurybiomechanics.Althoughallspacecraftdesignswereconsidered,theprimaryfocus
Reviewedby:
wastheNationalAeronauticsandSpaceAdministrationOrioncapsule,astheauthorshave
HenriqueDeAmorimAlmeida,
PolytechnicInstituteofLeiria,Portugal the most knowledge and experience related to this design.The team defined a list of
AmyTeresaNeidhard-Doll,Wright criticalinjuriesandselectedtheTHORanthropomorphictestdeviceasthebasisfornew

StateResearchInstitute,USA standardsandrequirements.Inaddition,theteamdown-selectedthelistofavailableinjury

*Correspondence: metrics to the following: head injury criteria 15, kinematic brain rotational injury criteria,

SheanPhelps,HealthSystems,
GeorgiaTechResearchInstitute,260 neckaxialtensionandcompressionforce,maximumchestdeflection,lateralshoulderforce
14thStreetNW,Suite455,Atlanta, and displacement, acetabular lateral force, thoracic spine axial compression force, ankle
GA30332,USA moments,andaveragedistalforearmspeedlimits.Theteamfeltthatthesemetricscapture
e-mail:[email protected] alloftheinjuriesthatmightbeexpectedbyaseatedcrewmemberduringvehicleaborts
and landings. Using previously determined injury risk levels for nominal and off-nominal
landings, appropriate injury assessment reference values (IARVs) were defined for each
metric.Musculoskeletaldeconditioningduetoexposuretoreducedgravityovertimecan
affectinjuryriskduringlanding;thereforeadeconditioningfactorwasappliedtoallIARVs.
Althoughthereareappropriateinjurydataforeachanatomicalregionofinterest,additional
researchisneededforseveralmetricstoimprovetheconfidencescore.

Keywords:injurycriteria,spaceflight,dynamicloads,anthropometrictestdevice,testdeviceforhumanoccupant

restraint,injuryassessmentreferencevalues

INTRODUCTION develop a standardized test methodology (i.e., ATD, seat, suit,
PURPOSE acceleration profiles, etc.) for inclusion in National Aeronautics
The objective of this work was to: (1) identify a list of criti- andSpaceAdministration(NASA)Standard3001,andallrelated
cal spaceflight injuries from dynamic loading that need to be programrequirements(NationalAeronauticsandSpaceAdmin-
protectedagainsttoenablemissionsuccess,(2)identifyananthro- istration,2011). The information included is based on available
pomorphic test device (ATD) to be used to predict the thresh- data at the time of the report and upon opinions from experts
old at which human injuries will occur, and (3) develop a at NASA, the National Highway Traffic Safety Administration
table of ATD thresholds known as injury assessment reference (NHTSA),and the FederalAviationAdministration (FAA). The
values (IARVs) for each critical injury. The eventual goal is to teamconsideredoccupantprotection(OP)needsduringdynamic

Abbreviations:AIS,abbreviatedinjuryscale;ATD,anthropomorphictestdevice;
BDRC, Brinkley dynamic response criterion; BrIC, brain rotational injury cri- Center;KSC,KennedySpaceCenter;LEO,lowearthorbit;LM,LockheedMartin;
teria; CAMI, Civil Aeromedical Research Institute; CG, center of gravity; CM, LOC,lossofconsciousness;MPCV,multi-purposecrewvehicle;mTBI,mildtrau-
command (crew) module; CSDM, cumulative strain damage measure; DAR, maticbraininjury;NASA,NationalAeronauticsandSpaceAdministration;NBDL,

definition of acceptable risk; EAFB, Edwards Air Force Base; EVA, extravehic- Naval Biodynamics Laboratory; NESC, NASA Engineering and Safety Center;

ular activity; FAA, Federal Aviation Administration; FE, finite element; FEM, NHTSA,NationalHighwayTrafficSafetyAdministration;OP,occupantprotec-
finite element modeling; FTSS, First Technology Safety Systems; GRC, Glenn tion;PMHS,post-mortemhumansurrogates;SID,side-impactdummy;SLS,space
Research Center; HIC, head injury criteria; HRP, Human Research Program; launchsystem;SRB,solidrocketboosters;TBI,traumaticbraininjury;TBD,to
HSIR, human-systems integration requirements; IARVs, injury assessment bedetermined;THOR,testdeviceforhumanoccupantrestraintmodificationkit;
reference values; IRL, Indy Racing League (aka: INDYCAR™); ISS, interna- USAARL,United StatesArmyAeromedical Research Laboratory; USSR,United

tionalspacestation;JARI,JapanAutomobileResearchInstitute;JSC,JohnsonSpace SovietSocialistRepublic;WSTF,WhiteSandsTestFacility.

www.frontiersin.org March2014|Volume2|Article4|1
Somersetal. THORATDIARVsforspaceflight
phasesofspaceflight,whichincludeabort(padabortandascent
abort)aswellasre-entryandlanding.Althoughvariousspacecraft
designswereconsidered,theprimaryfocuswastheNASAOrion
capsule,astheauthorshavethemostknowledgeandexperience
relatedtothisdesign.

SPACEFLIGHTDESIGNCONSIDERATIONS
Vehicledesigns
Reachingspacerequiresanextremeamountofkineticenergy,and
effective systems to dissipate this energy on the return to Earth.
Whilemostofthisenergyiscontrolled,dissipated,orabsorbedby
thevehicle,someamountofkineticenergymaybetransmittedto
theoccupantsaboardthespacecraft.Thisenergy,ifnotproperly
managed,maycauseinjurytothecrewmembers.Vehicledesignis
animportantconsiderationformanagingthisenergy,particularly
duringlaunchabortsandlanding.

Launchandabortsystems. Currently,chemicalrocketsareused
to launch humans into space. These systems typically accelerate
the crew vehicle to orbital velocities >6,900m/s (15,430mph)
FIGURE1|Nominalcapsulelandingorientationwithrespecttowater
to attain low earth orbit (LEO) within 10min of launch. These (landlandingsimilar).
sustainedaccelerationsaredesignedtobewellwithinhumantol-
erance. Because of the amount of energy stored in the launch
vehicle(eitherliquidorsolidpropellant),therearefailuremodes positionedreclined90°fromverticalontheirback,contactingthe
thatnecessitatethedesignofabortsystems. impact surface feet first, resulting in a combined +X (eyeballs
Mosthumanspaceflightvehiclesdesignedtodatehaveincluded in)and+Z (eyeballsdown)primarylandingload(seeFigure1),
launchphaseabortcapabilities.FortheMercuryandApollopro- althoughlandingdynamicsareheavilydependentonthespecific
grams in the U.S. – as well as the Soyuz program in Russia – a designandfailuremodes.
launch escape system was included in the spacecraft design to TheMercury,Apollo,multi-purposecrewedvehicle(MPCV),
allow quick separation of the crew module away from the main andSpaceXDragonaredesignedtolandprimarilyintheocean,
vehicleincaseofacatastrophicfailureofthelaunchsystem. but can also land on land in contingency cases. The Vostok,
For the Russian Vostok and Buran programs, as well as the Voskhod, Soyuz, and Boeing CCT-100 are all designed for pri-
U.S.Geminiprogram,ejectionseatswereincludedinthespace- mary landing on land, with contingency landing capability in
craftdesigntoallowcrewmemberstoescapeseparatelyfromthe water.Capsulesmayincludeadditionalenergymanagementfea-
entirelaunchvehicle,althoughtheycouldonlybeoperateddur- tures such as retrorockets, airbags, energy-absorbing structures,
ingaveryshortperiodofthelaunchprofile.Noabortcapabilities and/orstrokingseats.
existedoutsideofthisperioduntilsufficientaltitudewasreached
toallowforanormalseparationanddescent.TheU.S.SpaceTrans- Liftingbodydesign. Aliftingbodydesignimprovesuponthecap-
portation System Program (the formal name for NASA’s“Space suledesignbyaddingliftingsurfacestoincreasemaneuverability
Shuttle” program) included four primary elements: an orbiter andcross-rangeperformance.SierraNevada’sDreamChaserisan
spacecraft (Space Shuttle), two solid rocket boosters (SRB), an exampleof aliftingbodydesign,andisbasedonNASA’sHL-20
externaltankhousingfuelandoxidizer,andthethreeSpaceShut- prototype(NationalAeronauticsandSpaceAdministration,2013;
tle main engines. The Space Shuttle included ejection seats that SierraNevadaCorporation,2013).FromanOPstandpoint,alift-
were disabled after the first four flights and eventually removed ingbodyrepresentsalessviolentlandingenvironment,asitdoes
(Jenkins,1999). notrelysolelyonparachutestodissipatelandingvelocity.Evenin
All future NASA vehicles are required to have a crew escape off-nominallandingconditions,thisdesignfeatureisexpectedto
system(NationalAeronauticsandSpaceAdministration,2012a). reducethepotentialforinjury.
Becausecrewescapesystemsmustquicklyseparatethecrewaway
fromthelaunchvehicle,thecrewmaybeexposedtohighdynamic Landingloadsandvectors
loads.Theseloadswillvarydependingonvehicledesign,phaseof Becauserelativelylittleisknownaboutlandingloadmagnitudes
flight,andothervehicleperformancecharacteristics. and direction vectors for future commercial vehicles (SpaceX
Dragon, Boeing CCT-100, and Sierra Nevada Dream Chaser),
Capsule landing systems. The capsule design was the original knowledge of the MPCV design was used as a logical basis for
designchosenforhumanspaceflightprimarilybecauseitismass this work. This is likely the bounding case for all of the com-
efficient and simple. To date, this design has been used for all mercialvehiclesforseveralreasons.First,theMPCVislargerand
humanspaceflightprograms,withtheexceptionoftheU.S.Space heavierthanitscommercialcounterparts,whichshouldresultin
Shuttle.Capsulevehiclestypicallylandwiththecrewinaseated larger landing loads than the commercial vehicles. Second, the
FrontiersinBioengineeringandBiotechnology|Biomechanics March2014|Volume2|Article4|2
Somersetal. THORATDIARVsforspaceflight
MPCV was evaluated for its performance during land landings. Although Orion used a slightly different method of defin-
Although the landings were severe, they were not significantly ing nominal and off-nominal,based on the probabilities of off-
worse than some off-nominal water landing scenarios. In addi- nominallandingsandtheassociatedlevelsofriskforeach,thetotal
tion,the MPCV was not designed for a primarily land landing, landingcasesthatare≤µ+1.5σthresholdareanapproximation
sovehiclesthataredesignedprimarilyforlandlanding(likethe oftheOrionrisklevelfornominal,andthelandingcasesbetween
CCT-100) would likely have a softer land landing. Finally, for µ+1.5σandµ+2.5σaresimilartotherisklevelforoff-nominal.
the lifting body designs, the MPCV water impact will be more Allcasesaboveµ+2.5σlandingcasewouldbecontingencyand
severethanoff-nominallandingsencounteredduringahorizontal not considered for design purposes (0.6% of cases). Using this
landing. definition,an off-nominal event will occur approximately every
For the MPCV,the landing loads are primarily +X (eyeballs 4yearsandacontingencyeventevery40years,oreffectivelynever
in)and+Z (eyeballsdown).Thisisasimilarorientationtothe (assumingfourlaunchesperyear).
ApolloCM(seeFigure1).The+X componentisprimarilydue
toverticalvelocityof thevehicleandisdependentonparachute Crewdeconditioning
performance.Inthecaseofatwo-parachutelanding,thevertical Severalphysiologicchangesoccurinresponsetomicrogravity.The
velocity will be higher, resulting in a higher +X load. The +Z twomainchangesconcerningimpacttolerancearebonemineral
componentisdrivenbytwofactors.First,thehorizontalwindand densitylossandmusculartissueatrophy.
wave speed affects the horizontal velocity. At high wind speeds Duringprolongedspaceflight,skeletaldensitychangesprimar-
the+Z loadismuchhigher.Second,thevehicleisdesignedwith ilyinthelowerextremitiesandspine(Langetal.,2004)consistent
a set hang angle,tilting the entire capsule so that only the edge with Wolff’s law (Wolff, 1986). Studies conducted using dual
ofvehiclecontactsthewaterfirst.Evenwithnohorizontalwind, energy X-ray absorptiometry (DXA) have shown bone mineral
thishanganglewillimparta+Z axisloadbasedonthevertical densitydecreasesonaverageof1–1.6%inthespine,femoralneck,
velocity. In addition,wave slope during water landings and ter- trochanter,and pelvis,with an average loss of 1.7% in the tibia
rainslopeduringlandlandingscontributetotheeffectiveimpact after only 1month in microgravity (LeBlanc et al., 1998; Vico
angle. et al.,2000). Because skeletal deconditioning is time dependent,
Althoughthesevectorsareprimarytothelandingload,theload anymethodforaccommodatingthelosseswillbemissionlength
isalsodependentonthevehiclemaintainingthecorrectorienta- specific.
tion,so that the crew are oriented correctly at landing (i.e.,feet Changesinmusclemassandstrengthalsooccur,andaredepen-
first).Anonboardcontrolsystemisneededtomaintainthisori- dentontheexerciseregimeemployedduringspaceflight.During
entation.Withoutacontrolsystem,thevehiclecanrotatebefore Skylabmissions,legvolumedecreasedby7–10%(Thorntonand
impact, imparting loads in other directions. The landing loads Rummel,1977)andupto19%increwmembersaboardtheMir
may be quite complex,necessitating consideration of all vehicle spacestation(Stein,1999;LeBlancetal.,2000).Themuscleloss
dynamics. experienced by crewmembers is also selective; muscle fiber size
in the vastus lateralis decreased after 5–11days in flight at dif-

Landingmodes ferentrates.Edgertonetal.(1995)andZhouetal.(1995)found

Each spaceflight vehicle design has a unique launch, abort, re- decreases of 16% in Type I,23% in Type IIa,and 36% in Type

entry, and landing environment. Each vehicle is optimized for IIbfibers.Intermsofmusclestrengthduring6monthmissions,

itsparticular“nominal”caselanding,orthelandingthathasthe astronautsexperiencedmusclestrengthlossupto24%attheknee

highestprobabilityofoccurring.Todeterminethislandingmode, andupto22%intheankle(Gopalakrishnanetal.,2010).

detailed analyses of the vehicle systems and environmental fac- Itiscurrentlyunclearhowthesechangesaffecthumanphysiol-

tors are conducted. These analyses identify the distribution of ogyandimpacttoleranceinthesettingofspaceflightandlanding

all possible landings related to the normal and tangential veloc- following long duration mission profiles. However, it is fairly

ities. Assuming a normal distribution of all landing probabili- evident that greater OP measures will be needed for decondi-

ties,thresholdsfornominalandoff-nominalcanbedefined(see tioned crewmembers. Currently, these effects are accounted for

Table1).Itshouldbenotedthatforcapsule-basedvehicles,even byapplyinglowerdynamicloadlimits,whicharebasedonNASA’s

nominallandingdynamicsaremorelikeanautomobileaccident, IntegratedMedicalModel(Lewandowskietal.,2008).TheInte-

thannormalautomotiveaccelerations. gratedMedicalModelofbonelossisderivedfrombonemineral

Table1|Comparisonofpossiblenominalandoff-nominaldistributionthresholds.

Threshold Percentageof Percentageofcases Exp.freq. Approx.occurrenceforonelandingoutside Approx.designlevels
landingcases outsideofrange outsideofrange ofrange(assumingfourflightsperyear) forOrion

≤µ+1σ 84.1 15.9 1in6 Every18months
≤µ+1.5σ 93.3 6.7 1in15 Every4years Nominal
≤µ+2σ 97.7 2.3 1in44 Every11years
≤µ+2.5σ 99.4 0.6 1in161 Every40years Off-nominal
≤µ+3σ 99.9 0.14 1in769 Every200years
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Somersetal. THORATDIARVsforspaceflight
density changes, not on actual measured and scientifically vali- this phase of flight. Additionally, the launch, launch abort, and
datedhumanimpacttoleranceintheseconditions.Thisapproach landingenvironmentsforNASAareextremeinnaturecompared
maybeacceptableforshortstaysontheinternationalspacesta- withwhatisnominallyexperiencedduringautomobiledrivingor
tion(ISS),butmaynotapplytoorprotectagainstthedeleterious civilian/militaryflight.Thedifferencesbetweenautomotive,mil-
physiological effects of longer-duration missions to near-Earth itary,andNASAoperationalenvironmentsmakeitimportantto
objects,themoon,and/orMars,sincethereislittleknownabout considertheoverallacceptableprobabilityofinjury,giventhatoccu-
spaceflight deconditioning beyond 6months to 1year. In addi- pantsinaspacevehiclewillincurimpactconditionseverytime
tion,inflightcountermeasuresarebeingdevelopedtocounteract thevehiclereturnstoEarth.
thesephysiologicalchanges,sointhefuture,loweringtheresponse
Suitconsiderations
limitsmaynotbenecessary.
OneoftheuniqueaspectsoftheNASAenvironmentisthepres-

sureorspacesuit.Thissuitprotectsthecrewfromthevacuumof
Injuryriskposture
spacebyprovidinga pressurizedenvironmentaroundthebody,
TogaininsightintowhatNASA’sinjuryriskpostureshouldbe,it
abreathableatmosphere,thermalprotection,andmicrometeorite
ishelpfultoreviewotherindustriesandtheirrespectiveriskpos-
protection(whenoutsidethevehicle).Inadditiontothesebasic
tures derived from their contextual operational scenarios based
functions,otherconsiderationsinsuitdesignincludemobility,fit
uponscientificevidencegatheredtherein.
onawiderangeofcrewmembers,andcontingencyextravehicular
Fortheautomotiveindustry,specificallypassengercars,most
activity (EVA). With all of these demands on the suit, the final
injurylimitsarebasedona5–50%riskof anabbreviatedinjury
scale(AIS)3+injury,whichdelineatestheoccurrenceofasevere design is often not optimized for OP. There are several consid-
erations for the occupant during abort and landings that relate
injury(AssociationfortheAdvancementofAutomotiveMedicine,
to suit design. First,the suit,unlike most clothing,may contain
2005).Althoughthisseemslikeanobjectionableriskposture,there
rigid elements. Depending on the placement of these elements,
aretwomainreasonsthatthispostureisacceptablefortheauto-
point-loads or blunt trauma may occur resulting in crew injury
motiveindustry.First,theselimitsarebasedonstandardizedtests
(McFarlandandDub,2010).Therefore,theplacementanddesign
that represent a worst case scenario, and not a“representative”
ofthesecomponentsarecriticaltoprotectingthecrew(Danelson
collision. Second, the overall probability of a person being in a
etal.,2011).Second,head-mountedmasscanposeaseriousthreat
crashanytimeheorshegetsintoavehicleisveryremote(1in
tocrewmembersiftheadditionalmassiscarriedbytheneck(Rad-
120,000) for passenger vehicle usage (National Highway Traffic
fordetal.,2011).Finally,becausethesuitisapressuregarment,
SafetyAdministration,2007,2009). Therefore,after considering
thereisachanceoflandingwiththesuitinflated.Inthiscase,the
theseverityofthecollisionandtheprobabilityofactuallyhaving
vehiclerestraintsystemisnolongerrestrainingthecrewmember,
acollision,thetotalriskofinjurytoautomobiledriversisverylow.
butisinsteadrestrainingthesuit.Insidethesuit,thecrewmember
For military aircraft, the situation is similar, although more
maybefreetomove,increasingthepossibilityofinjury.Inall,the
inherentriskisinvolved.Militaryaircraft(bothfixedandrotary
suitpresentsauniquechallengethatmustbeaddressedtoprevent
wing)aredesignedtoallowforahigherriskposturethanwhatis
crewinjury.
desiredandacceptableforspacecraftoccupantsassignedtoNASA.
Again,thesehigherlevelsof riskareconsideredacceptablegiven Genderandanthropometrics
thattheoverallriskofinjuryper“sortie”(definedasonedeploy- UnlikepreviousNASAcapsuledesigns,futureNASAvehiclesmust
mentordispatch–launchwithsubsequentlanding–ofamilitary becapableof accommodatingmenandwomeninawiderange
aircraftonamission)is1in670(orless),eventhoughthisissig- ofanthropometrics.CurrentNASAvehiclerequirementsstipulate
nificantlyhigherthantheriskseenintheoperationofpassenger a vehicle must accommodate a 1st percentile female to a 99th
cars(Mapes,2006). percentile male. Protecting for such a wide range of sizes is a
ForNASA,thesituationisverydifferent.Withpassengervehi- challenge. Most OP data are based either on young,male,mili-
cles,millionsofmilesaredriveneachyearwitharelativelylowrisk tarysubjects,oronelderlymalepost-mortemhumansurrogates
ofcollisionorinjury.Forthemostpart,passengervehicleriskis (PMHS).Asof2011,theastronautcorpsmedianageis47.1years
constantduringtheentiretripor“sortie.”Similarly,formilitary for males (range 35–56) and 43.3years for females (range 32–
aircraft,thousands of flight hours are logged with relatively low 52), with males accounting for 76% of the corps. In terms of
risksofinjury,andlikepassengervehicles,thereissignificantrisk anthropometry,statureis177.3±4.9cm(4th–95thpercentile)for
during the entire mission although this risk is a direct result of male crewmembers, and 168.9±4.3cm (25th–97th percentile)
differentvariablecauses(enemyfire,mechanicalfailures,weather, for female crewmembers. For weight, male crewmembers are
piloterrors,humanfactors,etc.).However,unlikepassengervehi- 79.3±6.9kg (6th–75th percentile), and 63.2±8.9kg (4th–65th
cles,militaryaircrewsaresubjecttoahigherriskofinjuryduring percentile) (as shown in Table2). Because of the wide range of
takeoff and landing. This risk is closer to NASA’s environment demographics, accurately determining injury risk for the entire
where risk of injury due to dynamic loads is concentrated dur- rangewithintheastronautcorpsisdifficult,andtheresultswill
inglaunchandlandingphasesofoperationswhenflightproduces containacertainamountofuncertainty.
the highest loads on the vehicle. Unlike passenger vehicles and
military aircraft, there is very low risk of injury due to impact CURRENTNASASTANDARDS
onceastableorbithasbeenreached,dueprimarilytothefactthat Currently, NASA standards for transient accelerations (≤0.5s)
thereareverysmallloadsappliedtothevehiclestructureduring are based primarily on the Brinkley dynamic response criterion
FrontiersinBioengineeringandBiotechnology|Biomechanics March2014|Volume2|Article4|4
Somersetal. THORATDIARVsforspaceflight
Table2|NASAastronautcorps,gender,andanthropometric • Phase 5 – injury risk functions and NASA standards develop-
distribution(asof2011). ment.

Gender Medianage Percentage Stature Weight OnlyPhase1oftheforwardplanisdiscussedinthisreport.

(range) ofcorps (percentile) (percentile)

LITERATUREREVIEWANDSTANDARDSFRAMEWORK
Male 47.1(35–56) 76 177.3±4.9cm 79.3±6.9kg DEVELOPMENT

(4th–95th) (6th–75th) Basedontheresultsof theexpertpanelsummit,workbeganto
Female 43.3(32–52) 24 168.9±4.3cm 63.2±8.9kg determinealistof criticalinjuriesthatneedtobemitigated,the

(25th–97th) (4th–95th) bestATDforpredictingbiodynamicresponses,andIARVneeded

tomitigatetheinjuryrisk.Basedoncurrentliterature,aframe-

work was developed for completing these tasks and identifying
(BDRC)(NationalAeronauticsandSpaceAdministration,2011).
areasinneedofadditionalresearch.
The BDRC is a simple,lumped-parameter,and single degree of
freedom model that estimates the whole body response due to CRITICALINJURYDEFINITION
appliedacceleration,andiscomputationallyefficientandrequires Theexpertpanelidentifiedtheneedforaconciselistof“critical”
verylittleintermsofvalidationtesting. injuriesthatNASAwouldneedtomitigate.Entriescouldbebased
However, the BDRC has limitations (Somers et al., 2013). It onlikelihood(basedonpreviousspaceflightexperience)orthose
onlypredictsrangesof injuryriskandcannotprovideinforma- thatcouldcausethecrewtobeincapableofperformingpostflight
tion as to the severity or anatomical location of an injury. Only tasks. The list is not all-inclusive,but is intended to protect the
the+Z axisinjuryriskiswellvalidated(withoperationalejection crew from injuries that if successful,would also allow a level of
seatdata);the±X,±Y,and−Z injuryrisklevelsarestatistically protectionfrommoresevereinjuries.Forexample,ifNASAwere
limited (Brinkley,1985). In addition,these data do not account toprotectagainstribfracturesandlungcontusions,theassump-
for the interactions between crewmembers, suit, and seat. The tionisthatotherinternalorganswouldbeprotectedtothesame
seat and helmet used in the human testing and development of levelaswell.
the BDRC are very different from what is actually planned for ThelistofinjurieswasusedtoformthebasisoftheATDselec-
MPCV. Previously performed tests did not typically include a tion.TheATDneededtobecapableofgeneratingaresponsethat
suit,sosuitinteractionsarenotaccountedforintheinjuryrisk isrelevanttothetypesof injuriesNASAwishestomitigate.The
prediction. injurylistcombinedwiththeselectedATDwouldultimatelydrive
Given the limitations of the current NASA Standards, the theselectionoftheinjurymetricsandIARV.
humanresearchprogram(HRP)andtheNASAEngineeringand Before establishing a critical injury list, several assumptions
SafetyCenter(NESC)beganstudyingalternativesforinclusionin weremadebasedontheexistingNASAstandardsasfollows:
thestandard.Thisstandardupdateworkisprimarilyfocusedon
theOrionvehicle. • Afive-point(orbetter)racingharnesswouldbeused.
• Transient accelerations (<0.5s) would not exceed a moderate
EXPERTPANELSUMMIT injuryrisklevels.
AfterworkingwiththeOriondesignexclusively,theOPteamheld • Sustained (>5s) linear accelerations, rotational accelerations,
anexpertsummitinHoustoninJune2010.Thegoalofthesum- rotationalvelocities,andaccelerationrateofchangewouldnot
mit was to develop an OP plan that would not only further the exceed levels specified in the standard (NASA Standard 3001)
Orioneffort,butalsoadapttothecommercialcrewvehicles. (NationalAeronauticsandSpaceAdministration,2011).
Experts from the U.S. Army, U.S. Navy, U.S. Air Force, • Transientrotationalaccelerationswouldnotexceedlevelsspeci-
FAA, NHTSA, Indy racing league (IRL) (INDYCAR™), univer- fiedinthestandard(NASAStandard3001)(NationalAeronau-
sity researchers fromVirginia Tech,Wake Forest University and ticsandSpaceAdministration,2011).
Wayne State University, and automotive biomechanics experts • Minimalornobodymovement(basedontheBrinkleyAmpli-
attendedthesummit.NASApersonnelfromseveralareasinclud- ficationRule).
ing the Human Health and Performance Directorate (HRP, the • Thevehiclewouldmaintainanoccupantsurvivablevolume.
Biomedical Research and Environmental Sciences Division,and • Requirements would be met as for any other vehicle such as
theSpaceandClinicalOperationsDivision),theAstronautOffice, sharpedges,pinchpoints,etc.
theSafetyandMissionAssuranceDirectorate,andtheNESCalso
participated. Some assumptions were developed that were thought to be
Groupconsensuswasreachedontheforwardplanconsisting generalenoughtoencompassmostfutureNASAvehicles,yetcon-
ofthefollowingelements: strained enough to allow a useful set of injuries to be defined.
Theseare:
• Phase1–literaturereviewandstandardsframework.
• Phase 2 – ATD testing and finite element model (FEM) • Crewmembers may be in a pressurized suit,an unpressurized
assessment. suit,orunsuited.
• Phase3–humanexposuredatamining. • Thecrewwouldberecoveredwithin24h(thisisbasedonanaly-
• Phase4–humantestingandcorrelationtoATDresponse. ses conducted during NASA’s Constellation Program showing
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Somersetal. THORATDIARVsforspaceflight
that most locations worldwide can be reached within this interest and concern for returning crewmembers, as spaceflight
timeframe). deconditioningcanaffecthipstrength.Hiploadswereaddedto
• Thecrewmustbeprotectedtotheextentthatallpost-landing the matrix (see Table3) after the initial discussion with experts
egresstaskscanbecompleted. basedontheriskoffemoralheadfractureduetolateralloads.
• Crewmembertasksrequiredtoegressthevehiclepost-landing
areassumedtobesimilarinhumanperformancetoOrion(i.e., INJURYMETRICANDANTHROPOMORPHICTESTDEVICESELECTION
similar physical abilities needed, but not necessarily the same Following the expert panel recommendations,a team was orga-
tasks). nized to determine the best ATD (and associated metrics) for
• Dynamicloadsexperiencedbythecrewwouldbelessthanor validating against the critical injury list. The team (consisting
equaltothecurrentpredictionsfortheOrionvehicle(withinthe of researchersfromNHTSA,FAA,andNASA)beganevaluating
sameorderofmagnitudeofthecurrentOrionassumedloads). whichATDmetricswerethebestchoicesgiventhelistofcritical
• Design of the vehicle would prevent inadvertent contact with injuries and NASA’s dynamic environment. The team examined
vehicleinteriorexcludingtheseatandsuit(i.e.,seatcanstroke eachanatomicalregionandidentifiedavailableinjurymetricsthat
into other structures, knees can’t contact control panel, and couldaddresseachcriticalinjury.Eachmetricidentifiedwasasso-
stoweditemswillnotbefree). ciatedwithanATDthatprovidesthatmeasurementcapability(see
• Only considering injuries induced by dynamic loads (i.e.,not Table3).
consideringinhalationdangers,fire,etc.). BecauseIARVsarerelatedtotheparticularATDemployed,the
teamconsideredalloftheapplicableATDsavailableincludingthe

Based on these assumptions, the team identified the critical Hybrid-III, the WorldSID, and the test device for human occu-

injuries in several regions including the head,face,chest,upper pantrestraint(THOR).Duringdiscussionsoftheinjurycriteria,

extremities,lowerextremities,andthespine.Forthehead,concus- the team reviewed the benefits and drawbacks of each ATD as

sionwithandwithoutthelossofconsciousness,skullfracture,and shown in Table 4. The final consensus was to use the 50th per-

traumaticbraininjurywereallidentifiedbythepanelascritical centileTHORATDastheprimaryATDfortestingandanalysis.

injuries.Fortheface,eyeandearinjuries,andfacialfractureswere Although it is only currently available in one size and the cur-

allidentified.Lungcontusions,ribfractures,hemo-,pneumo-,and rentFEMisstillpreliminary,theteamchosetheTHORbecause

hemopneumothoraxwereclassifiedascriticalchestinjuries.For of its biofidelity and multi-axis performance. To overcome the

upperandlowerextremities,jointinjury(includingshoulderdis- limitations of the THOR, IARVs will eventually be chosen that

location)andskeletalfracturewerecategorizedascriticalaswell. incorporate the increased risk of gender differences and various

Finally, for the spine (cervical, thoracic, and lumbar), brachial anthropometries.Inaddition,lateraltestscomparingthe50thper-

plexusinjury,cordcontusion,vertebralfracture,herniateddisks, centileWorldSID and the 50th percentile THOR are planned to

anddiskrupturewerealladdedtothelist. determineif theTHORisapragmaticchoiceforlateraltesting.

After working with the expert panel, and in the process of AlthoughtheTHORwasnotdesignedforside-impactconditions,

testing, the team determined that hip loads are of particular the IRL has conducted side-impact testing using the THOR. If

Table3|Matrixshowingtheinjurymetricchosenandtherelationshipwiththecriticalinjuries.

y y
ur ur
Headinjury Facialtrauma Cervicalspinetrauma Blunttrauma Lungcontusion Ribfracture Hemopneumothorax Upperextremityjointinj Upperextremityfracture Femoralheadfracture Thoracicspinetrauma Lumberspinetrauma Lowerextremityjointinj Lowerextremityfracture

HIC15 T/H
BrIC T/H
Neckaxialtension T/H
Neckaxialcompression T/H
Maxchestdeflection T T T
Lateralshoulderforce(deflection) T/W T/W T/W T/W T/W
Acetabularlateralload T/W
Thoracicspineaxialcompression T/H T/H
Anklemoments T
Contactlimits/restrains(designconstraint) X X X X X X

H,Hybrid-III;T,THOR;W,WorldSID;X,designconstraint.
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Somersetal. THORATDIARVsforspaceflight
Table4|BenefitsandlimitationsofeachATD.

Hybrid-III THOR WorldSID

Benefit Limitation Benefit Limitation Benefit Limitation

Injurycriteria Injurycriteria Notrepresentativeof Improvedneck Severalinjurycriteria Improvedshoulder Severalinjury
readily humanresponses biofidelity stillindevelopment biofidelityover criteriastillin
available Simulatedneckmuscle EuroSID development
tension
Injurycriterianot Improvedchest Improvedchest
developedforlow geometryandresponse biofidelityover
injuryrisk Betterfrequency EuroSID
response
Betterresponseatlow
dynamics

FEmodel FEmodel Notwellvalidatedin FEmodelispreliminary NoFEmodel
status commercially otherloading anddoesnotreflect available
available directions currentdesign

Anthropometry 5th,50th, 5tha,50th Onlyone 5tha,50th Onlyone
95th anthropometricsize anthropometric
currentlyavailable sizeavailable

Directionality Validatedin Requiresmodification Validatedinfrontal Unknownresponsesin Validatedin NotsuitedforX
frontal forZ axisb impacts Y andZ axesc side-impacts axis
impacts NotsuitedforY axis ClosestATDto
multidirectional

Availability Readily Limitedavailability Limited
available availability

aFifthpercentileTHORandWorldSIDcurrentlyindevelopment.WillnotbeavailableforNASAuseforseveralyears.

bZaxistestingwiththeHybrid-IIIrequiresmodification(“Aerospace”model).

cUsedbytheIndyracingleague(IRL)inside-impacttests.Furthertestingrequired.

possible,the team would prefer to use the THOR in all axes to Table5|Injuryclassificationmappingandacceptablerisklevels.
simplifyanalysisandtesting;however,furtherevaluationsof the

THOR and WorldSID in lateral loading conditions will be nec- Injuryclass Acceptablerisklevel

essary to validate this approach. In the event that the THOR acrossallmissions

is found to be inadequate in predicting injuries due to lateral
Nominal(%) Off-nominal(%)
loads,theteamwouldrecommendusingtheWorldSIDforsuch

cases. ClassI(AIS1+) 5 19
ClassII(AIS2+) 1 4
INJURYASSESSMENTREFERENCEVALUESASDETERMINEDFROMA ClassIII(AIS3+) 0.3 1
LITERATUREREVIEW ClassIV(AIS4+) 0.03 0.1
Having selected the ATD and injury metrics, work focused on
the IARV associated with each metric. Since most available lit-
eratureclassifiesinjuriesaccordingtotheAIS,theteamdecided IARVforheadinjurycriteria
tomaptheAISleveldirectlytoeachinjuryclassification(Associ- Theheadinjurycriteria(HIC)arethestandardheadinjurypre-
ationfortheAdvancementof AutomotiveMedicine,2005).The dictorintheautomotiveindustry.Equation1isusedtocalculate
teamusednominalandoff-nominalrisklevelsfromthedefinition theHIC(PrasadandMertz,1985).
ofacceptablerisk(DAR)todeterminetheappropriateIARVsfor Headinjurycriteriaformula:
eachmetricasshowninTable5(Somersetal.,2014).Inaddition,
fitoartievaechesItAimRaVt,eaocfotnhfiedceonncfiedsecnocreeiinsitnhceluIAdeRdV.sTrheipsosrctoerdeaisnadqisuoaln- HIC = max (cid:32)(t −t )(cid:20)(cid:90) t2a(t)dt 1 (cid:21)2.5(cid:33) (1)
ascaleof0–5(noconfidence–fullconfidence,respectively). 15 0≤t2−t1≤0.015 2 1 t1 t2−t1
www.frontiersin.org March2014|Volume2|Article4|7
Somersetal. THORATDIARVsforspaceflight
Recentstudiesofmildtraumaticbraininjury(mTBI)infoot- ATDused,soisapplicabletotheTHOR.TheBrICiscalculated
ball players can be very useful for determining the appropriate usingEq.4.
thresholdforheadinjury.SinceAIS1and2injuriestothebrain BrICformula:
areofprimaryconcern,theHICinjuryriskfunctionsfromFunk
(cid:115)
Vetiragl.in(2ia0T0e7c)hwdilaltbaereupsoedrte(Edqb.y2F).uTnhkeisne2d0a1ta2wbeecraeucsheotsheenHoIvCervtahle- BrIC= (cid:18)ωωx (cid:19)2+(cid:18)ωωy (cid:19)2+(cid:18)ωωz (cid:19)2 (4)
xC yC zC
uesfromthe2007studyaremoreconservative(Funketal.,2012).
BecauseconcussioninjuryriskdeterminedfromNASCARhead where,ω is the maximum angular head velocity in the i plane,
injury modeling resulted in much higher allowable HIC values ω istheiangularheadvelocitycriticalvaluefortheiplane.
(Somersetal.,2011),theFunkHIC15curvewillbeusedtobe iCThe critical values are 66.3,53.8,and 41.5rad/s for the X,Y,
conservativeuntiltheNASCARresultscanbeverifiedwithaddi- andZ axes.Equation6detailshowtodetermineIARVsforBrIC.
tional datasets. In addition,the THORATD is assumed to have Figure3showstheresultantinjuryriskcurves.
similar head kinematics as the Hybrid-III ATD. That allows for BrICinjuryriskmodel:
theuseofidenticalHIClimitsforbothATDs.Figure2showsthe
resultantHIC15injuryriskfunction. (cid:16) (cid:17)2.84
Headinjurycriteriainjuryriskmodel: p(AIS≥n|BrIC)=1−e− BλrInC (5)

(cid:16) (cid:17)α
p(cid:0)inj|AIS≥1(cid:1)=1−e− HβIC (2) BrICIARVdetermination:

(cid:113)
HeadinjurycriteriaIARVmodel: IARV(100p%|AIS≥n)=λn· 2.84−log(cid:0)1−p(cid:1) (6)

IARV(cid:0)100p%|AIS≥1(cid:1)=β−(cid:113)αIn(cid:0)1−p(cid:1) (3) where,nisthespecifiedAISlevel,λnisthescaleparameterforthe
specifiedAISlevel.

UsingEq.6withtheassociatedscaleandshapeparameterval-
where,αisthecutpointforthespecifiedAISlevel,βistheregres-
ues,alongwiththeDARprobabilities,theIARVsinTable6can
sioncoefficient.UsingEq.3withα=4.34andβ=671,alongwith
bederived.Tosatisfythedesiredprobabilitiesofinjuryassociated
the DAR probabilities, the IARVs for nominal and off-nominal
withallfourAISlevels,theminimumBrICfornominalandoff-
are340and470,respectively(Table6).Basedontheavailablelit-
nominal conditions was selected. For nominal and off-nominal
eratureanditsapplicabilitytotheenvironmentexpectedduring
conditions,aBrICof 0.04and0.07,respectively,arerequiredso
spaceflight,theconfidenceintheseIARVsisratedata4onascale
thatallfourAISlevelsaresatisfied.Althoughthesevaluesaremost
from0to5,with5beingthemostconfident.
conservative,theBrICwasdevelopedforAIS≥4injurylevelsand

thenscaledtootherAISlevels.Basedontheuncertaintyassoci-

IARVforkinematicrotationalbraininjurycriteria
ated with the extrapolation of the BrIC for low injury risk, the

To further mitigate the risk of mTBI, an injury metric related
confidenceintheseIARVsisratedata2.

to angular head dynamics was selected. Takhounts et al. (2013)

reportsthecalculationmethodforderivingbrainrotationalinjury
IARVforneckaxialtension

criteria(BrIC).TherevisedBrICcanbeappliedregardlessofthe
TheTHORneckisdesignedtomimicthehumanneckresponse

bymeetingbiofidelitygoalsbasedonperformancecorridorsfrom

Mertzetal.(1997),NavalBiodynamicsLaboratory(NBDL),and

JapanAutomotiveResearchInstitute(JARI)humanvolunteertests

(Whiteetal.,1996).Althoughthegoalwastoproduceaneckthat

isbiofidelicinallloadingconditions,theaxialstiffnessisgreater

thandesired(Dibbetal.,2006).However,theaxialperformance

oftheneckinloadingthroughthecenterofgravity(CG)canbe

relatedtothecomputationmodelof PMHS.Thisisexpectedto

betheprimaryloadingexpectedinNASAlandingsduetoinertial

loads on the head. The computational model used was a vali-

datedfiniteelement(FE)modelofthehumanneck.Notethatthe

THORModKitATDwasrevisedtobehavesimilartotheTHOR-

NT without muscle cables case, which correlates well with the

computationalmodel.Usingthisrelationship,atransferfunction

betweentheTHORModKitandthecomputationalmodelcanbe

determined(Eq.9).

THORaxialtensionrelationshiptoappliedforce:

FIGURE2|Headinjurycriteria15injuryriskfunction(Funketal.,2007).
FzTHOR =0.8228·Fapplied (7)
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Somersetal. THORATDIARVsforspaceflight
Table6|TableofproposedTHORinjuryassessmentreferencevalues(IARV).

Conditioned Deconditioned IARVconfidencelevel(0–5)

Nominal Off-nominal Nominal Off-nominal

HIC15 340 470 340 470 4
BrIC 0.04 0.07 0.04 0.07 2
Neckaxialtensionforce(N) 880 1,000 760a 860a 4
Neckaxialcompressionforce(N) 580 1,100 500a 950a 3
Maxchestdeflection(mm) 25 32 25 32 2
Lateralshoulderforce(N) 2,700 3,300 2,700 3,300 4
Acetabularresultantforce(N) 1,600 2,900 1,200b 2,200b 3
Thoracicspineaxialcompressionforce(N) 5,800 6,500 5,000a 5,600a 3
Ankledorsiflexionmoment(Nm) 18 31 14b 23b 3
Ankleinversion/eversionmoment(Nm) 17 22 13b 17b 3
Averagedistalforearmspeed(m/s) 8.1 10 8.1 10 3

aSpinaldeconditioningfactorof0.86applied.
bLowerextremitydeconditioningfactorof0.75applied.

FIGURE3|BrainrotationalinjurycriteriaTHORinjuryriskfunctions

(Saundersetal.,2012). FIGURE4|Neckaxialtensionforceriskfunctionsdevelopedfrom

Philippensetal.(2011).

PMHSaxialtensionrelationshiptoappliedforce:
Necktensioninjuryrisk:
F =0.5983·F (8)
zPMHS applied p(AIS≥n|Fz)=1−Φ(cn−Fz ·β) (10)

THORaxialtensionrelationshiptoPMHS:
Necktensioninjuryriskmodel:

FzTHOR =1.38·FPMHS (9) IARV(cid:0)AIS≥n|p(cid:1)= cn−Φ−1(cid:0)1−p(cid:1) (11)
β
AstudyreportedbyPhilippensetal.(2011)wasperformedto
determinetheaxialtensionforceinjuryriskfunctionassociated where,nisthespecifiedAISlevel,ΦisthestandardGaussiandis-
withPMHSinjuries.Usinganorderedprobitanalysisonthemax- tribution,CnisthecutpointforthespecifiedAISlevel,c1=6.30,
imumreportedAIS(anatomicalandclinical),theriskfunctions c2=8.56,c3=9.28,c4=10.19,andβistheregressioncoefficient
showninEqs10and11,andFigure4weredeveloped. (0.0053).
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Somersetal. THORATDIARVsforspaceflight
UsingEqs9and11alongwiththeDARprobabilities,theIARVs as a starting point,the results of another Pintar et al. (1990a,b,
inTable6canbederived.TheAIS≥1IARVs(880and1,000N 1998a)studywereinvestigated,whichwasbasedondatacollected
fornominalandoff-nominalconditions,respectively)arelowest, previously.Equation12givesthe50%injuryriskfunctionbased
andareselectedtobeconservative. onmultiplefactorsincludingloadingrate,age,andgender.Com-
National Highway Traffic Safety Administration is proposing bining the logistic regression equation with Eq. 12 gives Eq. 13.
anIARVof2,520Nforneckaxialtensionforautomotiveuseand Thisequationcanthenberewrittentodetermineinjuryriskbased
relatestoa22%riskofanAIS≥3injury(Dibbetal.,2006).Based onaneckaxialcompressionforce(Eq.14).
on the assumptions made and the comparison to the NHTSA Neckcompressionfracturetolerancemodel:
IARVs,theconfidenceintheseIARVsisratedata4.
Fz =β0+β1·A+β2·LR+β3·G+β4·A·LR (12)
IARVforneckaxialcompression

Neckcompressionisofparticularconcernduringspacecraftland- where,β0istheconstantcoefficientwithavalueof934.2,β1isthe
ing, because there can be a significant +Z acceleration causing agecoefficientwithavalueof8.9,β2istheloadingratecoefficient
neck compression from the inertial effects of the head. In addi- with a value of 11.0,β3 is the gender coefficient with a value of
tion,anyhead-mountedmass,suchasaconformalhelmet,could 665.0,andβ4istheageandloadingratecoefficientwithavalueof
increasetheloadontheneck. −0.134.
Aswithnecktension,theassumptionwasmadethattheTHOR Neckcompressioninjuryrisk:
neckisbiofidelic,andthuscadavericinjuryriskfunctionscanbe

directlyapplied.Althoughthismaynotbethecase,itisassumed 1
p(AIS≥2|F )= (13)
thatthemechanicalneckoftheTHORwouldbestifferthanthe z 1+eβ5(β0+β1·A+β2·LR+β3·G+β4·A·LR−Fz)
human (similar to the trend seen in neck tension). Pintar et al.

(1998a) conducted an experiment consisting of nine male and Neckcompressioninjuryriskmodel:

four female cervical PMHS spines to developed neck compres-

sion injury risk functions for axial compression. The mean age IARV(cid:0)AIS≥2|p(cid:1)=β +β ·A+β ·LR
0 1 2
of the subjects was 59years old (range of 39–82). These data (cid:16) (cid:17)
log 1 −1
werecollectedduringhyperflexion,whichisthecauseof48–70% +β ·G+β ·A·LR+ p (14)
of neck injuries (Allen et al., 1982; Yoganadan et al., 1989). As 3 4 β
5
this represents the most likely mechanism for injury and is the

mostconservativeforneckcompression,thesedatawillbeusedto where,F isthepeakneckaxialcompression(N),pistheproba-
Z
developneckcompressionIARVs. bilityofneckinjury,β arethemodelcoefficients,Aisthesubject
n
Pintar et al. (1998b) report an injury risk function based on age(years),LRistheloadingrate(m/s),Gis0forfemales,and1

cervicalcompressionforce(Figure5A).Usingthisriskfunction formales.

FIGURE5|Neckaxialcompressionforceinjuryriskfunction.(A)OriginalPintarriskfunction(Pintaretal.,1998a)withconfidencelimits(dashedlines)and

(B)expandedriskfunctionsformaleandfemaleastronauts.Solidlinerepresentsmeanastronautage(47.1and43.3formalesandfemales,respectively),
dashedlinesrepresenttheyoungestandoldestastronauts(male:35and56;female:32and54).Notethatforcetolerancedeclineswithage.

FrontiersinBioengineeringandBiotechnology|Biomechanics March2014|Volume2|Article4|10