a comparison of tactical ballistic missile defense ... · a comparison of tactical ballistic...

272 JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME23,NUMBERS2and3(2002)

S. MOSKOWITZ, R. J. GASSLER, and B. L. PAULHAMUS

D

AComparisonofTacticalBallisticMissileDefenseEngagementCoordinationSchemes

Simon Moskowitz, Rebecca J. Gassler, and Bart L. Paulhamus

ealingwithlargeballisticmissileraidswillrequireanunprecedentedlevelofsyn-ergybetweendissimilarairdefenseunitsbecauseanyindividualunitwilllikelybeover-whelmed.Shooterselectionschemescurrentlyinuseincludeunbiddedfirstlaunchanduniquedefendedassetassignment.Thesemethodsonlyattemptdeconflictiontoavoida“freefire”situation.Pastanalysishasshownthataschemeexiststhatyieldsmuchbetterresults than these unit-centric schemes. That scheme fits into the distributed engage-mentdecisionparadigmofpreferredshooterselection.ThisarticleusestheAPLCoor-dinatedEngagementSimulation(ACES)tocontrasttheperformanceoftheaforemen-tionedschemesinarealisticsimulationenvironment.Thedistributionsofraidoutcomesforeachschemeundertwoconfigurations,idealandachievable,arecompared.Operatingconditionsareexaminedthroughselectingreal-worldoptionsandmodelingunderlyingprobabilitydistributions,whereapplicable.

INTRODUCTIONWhentacticalballisticmissiles(TBMs)areusedin

thefuture,theywilllikelycomeinamassiveraidandbemoreadvancedthaninthepast.Dealingwithsucha raid will require an unprecedented level of synergybetweendissimilar airdefenseunitsbecauseany indi-vidualunitwilllikelybeoverwhelmed.Continuedunit-centric and service-independent doctrine and warfareimpede achievement of this goal. Shooter selectionschemescurrentlyinuseincludeunbiddedfirstlaunchanduniquedefendedassetassignment.Thesemethodsonly attempt deconfliction to avoid a “free fire” situ-ation. Inaddition tominimizing thenumberofunin-tentionaloverengagements,whichtheseschemesstrivefor,themoreimportantaspirationofminimizingleakers

(i.e.,TBMsthatpenetratedefenses)mustbeaddressed.Minimizing leakersmeansminimizing free riders (i.e.,unengagedthreats)andmaximizingdepthoffire(i.e.,numberofsalvosseparatedbykillassessmentperiods),as well as selecting the engagements that have thegreatestchanceofsuccess.Forareatacticalballisticmis-sile defense (TBMD) systems, reengagement after killassessmentisseldompossible.

Past analysis has shown that a scheme exists thatyields much better results than the unit-centricschemes.Thatschemefitsintothedistributedengage-ment decision (DED) paradigm of preferred shooterselection. In this scheme, individual units estimatetheir own effectiveness and schedule their own shots,

JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME23,NUMBERS2and3(2002) 273

COMPARISON OF TBMD ENGAGEMENT COORDINATION SCHEMES

theinformationisdistributed,andthenallunitsuseacommonalgorithmtoarriveatasynchronizedengage-ment assignment solution for the force. Units defertheirownshotsiftheyarenotpreferred.

This article contrasts results using the aforemen-tionedschemes(freefire,firstlaunch,uniquedefendedasset assignment, and DED) in a realistic simulationenvironment.Thedistributionsofraidoutcomes(e.g.,leakers,freeriders,overengagements)foreachschemeunder two configurations, ideal and achievable, arecompared.Operatingconditionsareexaminedthroughselecting real-world options and modeling underly-ing probability distributions, where applicable. Withthe creation of the APL Coordinated EngagementSimulation (ACES), generation of the air picture ismodeled at an adequate level of fidelity, includingmulti-objectthreatswithaspect-dependentradarcrosssection(RCS),“just-in-time”radarsearchsetup,launcheventcounting(i.e.,estimatinghowmanyTBMswerelaunched),clustering(i.e.,decidingwhichobjectsorigi-nated fromwhichTBM),primaryobject track(POT)selection(i.e.,whichobjectsshouldbechosentorep-resent each TBM), and correlation. CommunicationsoveranetworksimilartoLink16account for latencyviabandwidth,time,andcontent-constrainedtransmis-sion. Probability of kill depends on other actions andoutcomes during the raid, such as whether the lethalobjectisbeingtrackedbyaradar.

ACES ENGAGEMENT COORDINATION SCHEMES

The current version of ACES, version 0.9, imple-mentsfourdifferentengagementcoordinationschemes:free fire, simple sectored with unique defended assetassignment,firstlaunch,andDED.Thissectionbrieflyexplains the first three schemes and then presents adetaileddiscussionofthe lastscheme.InformationonengagementcoordinationschemetaxonomyandfutureschemestobeimplementedinACESisdiscussedinthearticlebyShaferetal.,thisissue.

Free FireThefreefireengagementschemeisthemostprimi-

tive of the four coordination schemes. Actually, thisschemeinvolvesnocoordination.Allofthedefendingunits act independently and are free to fire at what-evertheywant.Thisschemeisoftenusedtoillustratethe need for coordination because it usually performspoorly.Unitsoftenendupfiringatthefirstthreatstoappear. This results in the units expending all theirradar resources, thereby overengaging (i.e., launchingmoredefensivemissilesthantheforcefiringpolicycallsfor—onesalvoperthreat inthisarticle)a fewthreatswhilelaterthreatsbecomefreeriders(i.e.,threatsthatarenevershotat;theyreceivea“freeride”).Ingeneral,

themorethecoverageofeachunitoverlaps,theworsefreefirewillperform.

Simple SectoredSimplesectoredengagementschemesareunbidded,

static schemes that do not rely on any communica-tions.Inthemostfamiliarvariantofthesimplesectoredcategory (the one discussed in this article), all of thedefendedassetsaredividedamongtheunitsinaforcesothateachassetisassignedtoonlyoneunit.Theunitsonlyengagethreatsthatareaimedatoneoftheirowndefendedassets.Muchpreplanningisinvolvedsothatthedefendedassetsareassignedtothedifferentunitsinanintelligentmanner.

Oneadvantageofthisschemeisthatitisverysimpleto implement because it does not use any communi-cations.Anotheradvantage is that itusuallyproducesa very low number of overengagements because theengagement decision is well defined. The only timeanoverengagementoccursiswhenathreat’spredictedimpactareaoverlapstwoassetsdefendedbytwodiffer-entunitsorwhentwounitsdisagreeonthetarget’spre-dictedimpactarea.

However, the scheme’s main disadvantage occurswhenoneunit’sassetsreceivemostofthethreatsinaraid.Thisusuallycausestheunittobeoverwhelmedandunabletoengageallthethreats,resultinginfreeriders.At the same time, simple sectored does not permit aneighboringunittohelptheoverwhelmedunit,eveniftheneighboringunit’sassetsarenotbeingattackedandtheneighboringunitcanengagethreatsaimedtowardtheoverwhelmedunit’s assets.This leads to the forceunderutilizingitsresourceswhilelettingthreatsattacksomedefendedassetswithoutanyengagement.

First LaunchThe thirdengagementcoordination scheme imple-

mented by ACES is first launch. The rules of thisschemeallowtheunitsinaforcetoactindependentlywhile planning engagements. From a force commandand control (C2) perspective, units are not aware ofinorganic(i.e.,otherunits’)threat–weaponpairinguntilthey are notified of (defending) missile launch. How-ever, once a unit launches against a threat, it sendsoutanengagementmessagestatingthatithaslaunchedagainst that track. Upon receiving the message, allotherunitsthatwereplanninganengagementagainstthe same track defer. If, for some reason, there is aninterceptorfailure,thefiringunitwillsendoutanotherengagementmessagewiththe status“engagement ter-minated.”Thiswillallowotherunitstothenschedulean engagement against that track number again. Theschemeisunbiddedanddynamic,andreliesonasimplecommunications network. In a low-density (spatialand temporal) raid, it may be possible to implement



avariantof this schemewithoutanycommunicationsnetwork;unitswouldtrackotherfriendlyunits’missilelaunches and predict which threat they were headingtoward.

One main advantage of the first launch scheme isthatitattemptstominimizethenumberoffreeridersbyallowingeveryunitthatcanshootagainstathreattodosounlessanotherunithasalreadyengagedit.Whencom-paredagainst simple sectored, this schemedoes a goodjobatlettingunitshelpanoverwhelmedunit.Anotherbig advantage is that it is easy to implement; it doesnotrequirechangestothecommunicationsnetworkandonlyimpingesminimallyonunit-levelautonomy.

Infirst launch, theunits’uniquecapabilitiesversuscertainthreatsdonotaffectthechoiceofshooter.AllNavyareaTBMDunitshavenearlythesamepredictedinterceptpoint(onthetargettrajectory),regardlessoftheir location, because of the small endo-atmosphericinterceptwindow.Theunitfarthestawayfromthepre-dictedinterceptpointhasthelongestinterceptortimeofflight(TOF).Therefore,thefarthestunitisthefirstonetolaunch,ifitisnotalreadytoobusy.Thus,oftenaunitthatisuniquelycapableagainstacertainthreatwillhave launched against threats that other units couldhave engaged, and then that unit may not have any(radar) resources left toengagetheonesonly itcouldhavetaken,resultinginfreeriders.Thefarthestengage-mentsmayalsobetheengagementopportunitieswiththe least chance of success, increasing the number ofleakersinthescenario.

Another disadvantage is the scheme’s reliance onthe communications network. If the network is slow,the engagement messages may arrive too late for theotherunitstocanceltheirownengagements,resultingin overengagements. Overengagement can also occur,no matter how fast the communications network is,whenunitsarepositionedoncontoursofconstantTOF,causingtheirlaunchtimestobeidentical.Dualtrackswillinevitablyalsoleadtoanoverengagementbecausetheunitsthinktheyareengagingdifferentthreats.Also,incorrectly correlating tracks can result in one unitconfusingtheengagementmessageagainstaparticularthreat as an engagement message against a differentthreat,resultinginfreeriders.Ofcourse,theselasttwodisadvantagesapplytoalldynamicschemes.

Distributed Engagement DecisionACEScurrentlyimplementsaschemefromtheDED

category. It is the only bidded scheme that has beenimplementedinACES,version0.9.DEDschemesarealso dynamic and rely heavily on a communicationsnetwork. Because this is a very complex scheme thatmaybenewtomanyreaders,itwillbedescribedinmoredetailthanthethreepreviousschemes.

IntheDEDscheme,allunitsinaforceshareinforma-tionabouttheirpossibleengagementsandthentheforce

makes intelligent decisions about which units shouldengagewhichthreats.FromaforceC2perspective,earlyawarenessofthreat–weaponpairingsprovidesabasisforcommand reaction, as needed. The fundamental ideabehindtheschemeisasfollows:ifalltheunitsusethesame engagement information with the same engage-mentselectionalgorithm,alltheunitswillarriveatthesameengagementdecisions.

Like first launch, the DED scheme has the advan-tageoversimplesectoredofallowingneighboringunitsto help each other. However, the main advantage ofthisschemeisitsbiddedproperty.Unlikefirstlaunch,where the coordination takes place after the engage-menthasbeenmade,DEDmakesdecisionsbefore theactual engagements. This allows the scheme to makeintelligent decisions toward balancing and optimizingalloftheengagementsfortheforce.

ThemaindisadvantageofDEDisitsdependenceonacommunicationsnetwork.Thecommunicationsnet-workisevenmoreimportanttotheDEDschemethanthefirstlaunchschemebecausemuchmoreinformationisbeingshared.Anotherdisadvantageisitssusceptibil-itytoerrorscausedbymiscorrelation.

Thenext four sections givemoredetails about theDED scheme. First, a database is described for orga-nizing all of the possible engagement information fortheentireforce.Thentheselectionalgorithmfordecid-ingwhichoftheengagementsshouldbecarriedoutisexplained.Aspartofthisalgorithm,theshotelimina-tion tests and criteria are defined. Both thedatabaseandtheselectionalgorithmexistoneveryunit.

Data ManagementBecauseofthecomplexityoftheDEDscheme,data

management is very important. Information must beshared,stored,andprocesseduniformlyacrossallunits.Engagement information for theentire force is sharedviaengagementmessagesandstoredinaforceengage-mentschedule(FES)oneachunit.TheFEScontainseverypossibleengagementwithintheforce.TheentriesontheFESaredefinedbyathreat,unit,weapon,andshot number. The threat is the TBM track that isexpectedtoimpactadefendedasset,theunitistheunitthathastheshotagainstthethreat,theweaponistheunit’sweaponfortheshot,andtheshotnumberisthenumberof theshot inasalvo.Currently inACESallunitshaveonlyoneweapon,StandardMissile-2BlockIVA,andallengagementsaredualsalvos.Therefore,foreachunit,threatpairingcanonlyresultintwoentriesonitsFES(oneforeachshotinasalvo).

EachunitusestheFEStodecidewhichoneshouldshoot at which threats. To make that decision, theentriesontheFESareusedtobuildatemporaryhier-archicaldatabasewiththreelevels:group(thehighestlevel),threat,andpossibleshot.Withineachgrouparethreats that are spatially very close together. Within



each threat level are the possible shots against thatthreat.Figure1showsanexampleofthedatabasefromasimplescenario,whichcontainsthreethreats(A,B,andC)andthreeunits(1,2,and3).Alineconnect-ingaunittoathreatdenotesthattheunitisengage-ableagainstthatthreat.Inthisexample,unit1isonlyengageableagainstthreatA.Thedashedovalsrepresentthreatgroups.Inthefigure,threatsBandChavebeenassembled into group II. The database format showshowthisexample scenariowouldbeorganizedwithintheDEDdatabase.

Engagement Selection AlgorithmTheengagement selectionalgorithmhas twomain

parts.Thefirstpartbuildsthedatabaseandthesecondselectsapreferredshotforeachthreatinthedatabase.

Building the database.Thefollowingfivestepsbuildthedatabase:

1. Buildthethreatlevel.2. Addthepossibleshotstoeachthreat.3. Combinethreatsintogroups.4. Freezegroups.5. Orderthegroups.

Step 1 creates the threat level of the database bymakingeveryuniquethreatontheFESathreatinthedatabase.Step2addsthepossibleshotstoeachthreatinthedatabasebywalkingthroughtheFESandaddingeachshottoitscorrespondingthreat.Oncethethreatandshotlevelsofthedatabasearecreated,step3cre-ates the group level by collecting threats that have ageometric separationdistance less thanthegroupdis-tancethresholdintothesamegroup.Whenobjectsarecloselyspaced,theymaybecomecross-correlated(e.g.,whenthereare really twothreatsandtwounitsagreethattherearetwothreats,butoneunitlabelsthemAandBandtheotherunitlabelsthemBandA).Ifone

unitisdeclaredtohaveallthepre-ferredshotsforeverythreatwithinagroup, anoverengagementandafree rider can be avoided. If all ofthe threats within a group do nothaveatleastonepossibleshotfromthesameunit,thegroupisdivided.A threat can only belong to onegroup,andeverythreatisinagroup,evenifthereisonlyonethreatinagroup.

Aftertheentiredatabaseisbuilt,theinformationisorganizedbeforebeing processed by the preferredshot selection algorithm. Step 4freezes certain groups in the data-base.Agroupisfrozenwhenthereisnotenoughtimetoactonachangemade to the preferred shot of one

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Figure 1. Example illustrating DED database construction.

ofthethreatsinthegroup(i.e., it iswithinminimumcoordinationtimeofplannedtimetolaunch).Ifagroupis frozen, none of its threats’ preferred shots can bechanged.Therefore, thegroup is skipped intheselec-tionalgorithm.

Thefinalstepintheprocessordersthegroupsinthedatabaseaccordingtothefollowingcriteria:frozen,size,uniquelycapable,maximumthreatpriority,andmaxi-mumthreatnumber.Thedatabaseissortedbecausethepreferredshotselectionalgorithmisrunonthedatabaseso thathigherpriority isgivento themore importantthreats.

Running the preferred shot selection algorithm.Afterthe database is built and organized, the preferred shotselectionalgorithmisrun.Thegoalofthealgorithmistoremovethelessdesirablepossibleshotsfromeachthreatuntilonlyonepossibleshotremainsforeachthreat.Thatshot is then called the “preferred shot” for the threat.Theunitwiththepreferredshotagainstathreatisthepreferred shooter for that threat. In Aegis, the secondshotofthedualsalvoisnotscheduleduntilthefirstshotis in flight. Thus, in ACES, each (Aegis area TBMD)unitonlyhasonepossible scheduled shot against eachthreat,sofindingthepreferredshooterforathreatisthesameasfindingthepreferredshot.Inaddition,becausethesameunitmustengageeverythreatinagroup,find-ingthepreferredshooterforagroupisthesameasfind-ingthepreferredshotforeverythreatwithinthatgroup.Therefore,anotherwayofstatingthegoaloftheelimina-tiontestsistofindapreferredshooterforeachgroup.

Elimination TestsEliminationtestsareusedtofindapreferredshotfor

every threat in the scenario by sequentially removingpossible shots from each threat. This is accomplishedbysievingeachgroupthroughaseriesofeightcriteria.After each elimination test, if only one possible shot



remains for each threat in the group, sieving on thatgroupiscomplete.Manypossiblecriteriacouldbeusedin the elimination tests, and the order in which thetestsareperformedisjustasimportantastheteststhem-selves. The eight tests and the order in which theyare performed in ACES is just one possibility. AfterACESisabletomodelmorediversesystems,suchastheNavy Theater Wide system, and more scenarios havebeenexamined,otherDEDvariantswithdifferenttestsand/ordifferentorderingsof testswillbe investigated.This section explains, in order, the eight eliminationtestsusedinthisparticularDEDscheme.

1. Notification time testeliminatesthepossibleshotsthatdonotallowtheforceenoughtimetocoordinate.This is done by removing all shots that have a latesttime-to-launch that is less than the current timeplustheminimumcoordinationtime.Theminimumcoordi-nationtimeisanestimateoftheleastamountoftimenecessarytoguaranteethat—afteradecisionismadeononeunit—thereisenoughtimeforthesamedecisiontobemadeonallotherunits.

2. Maximum concurrent engagement test removespossible shots that cannot be carried out because theshot’s unit has already reached its hard engagementcapacity(i.e.,maximumnumberofengagementsthataunitcancarryoutatonetime).Todetermineifashotcausesitsshootertoexceeditshardengagementcapac-ity,theshot’snumberofsimultaneousdiscriminationsiscalculated.DiscriminationinthiscontextisexpendingadditionalradarresourcestogathermetricstodeterminewhichTBMobjecttointercept.Thenumberofsimul-taneous discriminations for a particular shot is foundby counting all of the unit’s discriminations (currentengagementsandpredictedengagementsofhigherprior-ity)thatoverlapthediscriminationtimeneededforthatshot.Thetesteliminatesashotfromathreatiftheshot’snumberofsimultaneousdiscriminationsisgreaterthantheunit’shardengagementcapacity.

3. Inventory sufficiency test eliminates possibleshots from a threat’s possible shot list if the shot’sshooterdoesnothaveenoughinventorytocarryouttheengagement.Tosupportoneofitsshotsbeingselectedas apreferred shot, aunitmusthaveenoughplannedinventory to engage all the threats within the group.Aunit’splannedinventoryistheamountofinventoryleftafteraccountingforallofitsotherpreferredshotsofhigherpriority.

4. Engagement loading test tries to balance thenumberofsimultaneousengagements foraunitacrossalltheunits intheforcetofacilitateengagementofafuturethreatthatmaybeengageablebyonlyaspecificunit.Thisisdonebycomparingthenumberofsimulta-neousdiscriminationscalculatedinthemaximumcon-currentengagementtesttotheunit’ssoftengagementcapacity.Thelatteristhemaximumnumberofengage-mentsatonetimethatcanbehandledbyaunitwithout

stress.Itmustbelargeenoughsothatothercriteriacanbeusedtomakepreferredshotdecisions.Theactualtestremovesashotiftheshootingunit’snumberofsimul-taneousdiscriminationsisgreaterthanthesoftengage-mentcapacityoftheunit.

For any threat in the group, if all the shots on thethreat’s possible shot list are removed by the engage-ment loading test, it means that all of the units thatcanengage the threatarealreadyunder stress.For thisreason,allthepossibleshotlistsforeverythreatinthegrouparerestoredtotheirpreteststatus.Afterall,engag-ingathreatunderstressisbetterthannotengagingit.

5. Reengagement testtriestomaximizethenumberof reengagement opportunities. It eliminates possibleshotsthatdonotallowforanotherinterceptopportu-nity.Ashotallowsa reengagementagainsta threat iftheshot’slatesttime-to-launchisgreaterthanorequaltothepredictedtimeof intercept,plusthekillassess-menttime,plustheminimumcoordinationtime.Thetest works by checking if any of the shots within thegroupallowforareengagement.Ifaunithasnoshotsthatallowforareengagement,allofthatunit’sshotsareremovedfromthethreat’spossibleshotlists.

Forany threat in thegroup, if all the shotson thethreat’spossibleshotlistareremovedbythereengage-menttest, itmeansthatnoneoftheunitshasareen-gagementopportunity.Therefore,allthepossibleshotlists foreverythreat inthegrouparerestoredtotheirpreteststatus.

6. Maximum inventory testattemptstobalancetheamountofavailableinventoryforeachunitacrosstheforce. The test removes a unit’s possible shot from athreatifanotherunitwithsignificantlymoreinventoryhas a possible shot (i.e., their inventory difference isgreaterthantheinventorytesttolerance).It usestheplanned inventoryassociatedwitheachshot fromtheinventorysufficiencytest.

7. Time-of-flight test breaks a tie in case a groupstillhasmorethanonepossiblepreferredshooter.Foreachgroup,aunit’sshotTOFsagainsteachthreatinthatgroupareaddedtogether.Theresult isthetotalTOFnecessaryifthatunitisselectedasthepreferredshooter.TheunitwiththeleastamountoftotalTOFisselectedasthepreferredshooteragainstthegroup,andforeachthreatinthegroup,allshotsonthethreat’spossibleshotlistnotbelongingtothepreferredshooterareremoved.

8. Unit number testisexecutedintherarecasethattwounitshaveshotswithexactlythesameamountoftotalTOFagainstall the threats inagroup.This testselects the unit with the lowest unit number as thepreferredshooter.Thenallshotsoneachthreat’spos-sible shot list not performed by the preferred shooterareremoved.Becausethisisthelastoftheeliminationtests,itmustleaveonlyoneshotoneachthreat’spos-sibleshotlist.SinceACESonlyhasoneweapontype



anddoesnotdividesalvos,examiningtheunitnumberisenoughtoensurethiscondition.However,whenACESexpandstousingmultipleweaponsanddividingsalvosamongunits,thistestwillalsoneedtobeexpanded.

Elimination Criteria ConstantsTable1liststhevaluesoftheeliminationcriteriaconstantsusedforthis

analysis.

thoughtthatthesethreatswouldbephysicallyengageable,butasshowninthefigure,thisisnotalwaystruebecauseofdifferencesinmodeling.

Communications NetworkNavyNetwork021Awasused1

asthebasisfordevelopingareason-able Link 16 network (Fig. 3) forthisscenario.ItisassumedthattheCooperativeEngagementCapabil-ity(CEC)ofthiseraisstilllimitedtoanti-airwarfare,althoughfutureanalysiswithACESwillincludeaspacetrackpicturebasedonCEC-likesensorfusion.Thedashedlinesin Fig. 3 indicate network par-ticipation groups (NPGs) relayedby an E-2C Hawkeye or E-3AAirborne Warning and ControlSystem. Although not shown onthe maps, this network was sizedfor20oftheC2unitsand36ofthefighterspresentinthetheater.Onthe surveillance NPG, time slotswere allocated as follows: 18 forthe Theater High-Altitude AreaDefensebattery,30forthePatriotBattalion Information Coordina-tion Central, and 8 for each oftheotherC2units(includingAegisarea TBMD ships); this allowsall units at least one opportunityto transmit every 1.5 s. On theEngagement Coordination NPG,eachofthepotentialshooterswasgiven14timeslots,yieldingatrans-missionopportunityevery0.875s.

Table 1. Values of elimination criteria constants.

ValueusedConstantname Usage inthisanalysis

Minimumcoordinationtime Notificationtimetest 4.375s(ideal); 12.25s(achievable)Softengagementcapacity Engagementloadingtest 3Hardengagementcapacity Maximumconcurrent 5 engagementtestInventorytesttolerance Maximuminventorytest 3Groupdistancethreshold Grouping 1000m

Table 2. Impact locations of threats.

Assetno. Threatnos.

6 207 1,3–5,178 None12 13,14,1613 1215 1120 7,8,1922 None24 2,6,9,10,15,1825 None

ACES ANALYSIS

ScenarioThis scenario uses selected TBM launch and impact points from day

D+5 from the Northeast Asia scenario used in the Capstone and NavyTBMDCostandOperationalEffectivenessassessments.Threattrajectorieswere generatedusing theDefense IntelligenceAgency/Missile andSpaceIntelligenceCenter’ssix-degree-of-freedommodel,DICE.Fourunitsdefendagainst20threatslaunchedfromfivelaunchareas.FifteenofthethreatsareScudCsandfiveareNoDongs,whichhave reentryvehicles (RVs) thatseparatefromthespentboostershortlyafterburnout.Thereare29entrieson the defended asset list for this scenario, but only 10 of them can bedefendedfromalllaunchareasbyatleastoneoftheships.Sevenofthese10areneartheaimpointsandactualimpactpointsintheraid.

Table2showsthedefendedassetsused,aswellasthenumberofthreatsthatimpactateachone.However,thedefendedassetsizeswereincreasedtoencompasstheimpactpointsbecausetheaimpointswereatfacilitiesnotactuallycontainedwithintheassets.Forexample,afuelstoragetankonadockwastargetedandtheassigneddefendedassetwasthenavalbaseontheothersideofthedock.Impacttimeforthe20threatswasrandomlydistrib-utedover10sforeachMonteCarlorun.ThefourunitlocationswerebasedonthoseusedfortheaforementionedCostandOperationalEffectivenessassessments.

In this scenario, not every unit is in position to engage every threat;thisisrealisticandchallenging.Figure2showswhichunitsarephysicallyengageableagainsteachthreat. In fact,noneof the20threats isengage-ablebyallfourunits.Ninethreatsareengageablebythreeunits,sevenareengageablebytwounits,andfourareengageablebyonlyoneunit.ThereisnochanceforreengagementtooccurinthisscenariobecauseofthesizeoftheareaTBMDengagementvolumeandspeedofthethreats.

Theradarsetupisbasedonplannedpairsoflaunchareasanddefendedassets (see Modeling Fidelity and Assumptions). The yellow shading intheboxesinFig.2signifiesthat—forthegivenunit—theindicatedthreatwas from a planned launch area/defended asset pair. In planning, it was



Modeling Fidelity and Assumptions

ACESversion0.9wasusedasthemodelingenvironmenttoconductthestudydocumentedinthisarticle.ACESisbeingcreatedtopro-videamodelingandsimulationframeworkforthedevelopmentandanalysisofadvanceddis-tributed weapons coordination concepts. Assuch, it helps analyze the performance andinteractionsofmultipleweaponandsensorsys-temswhentheyaredeployedasanintegratedtheaterairandmissiledefenseforcefacingthefullspectrumoftheaterairandmissilethreats.ACESfunctionalityaccuratelyrepresentsunit-level engagement decision, control, and exe-cutionprocessesinarelativelycomplexenvi-ronment(i.e.,multi-sensor,multi-weapon,andmulti-target). Weapon and sensor controlfunctions, functional flow, and informationexchange are being modeled with sufficientfidelityto facilitatetheevaluationofalterna-tiveconceptsforautomatedengagementcoor-dinationandtheassessmentofforce-andunit-leveleffectivenessandefficiencyinperformingmultiple simultaneous theater air and missiledefensemissions.

ACESversion0.9islimitedtoAegisareaTBMD;otherTBMDunittypesandwarfareareas will be implemented in the future.Engagement coordination performance wascomparedundertwosetsofconditions:

• Ideal: an abstract set without problemscaused by limited search setup and re-sources,trackinaccuracy,correlationerrors,

Figure 2. Planned pairs for (a) free fire, first launch, and DED and (b) simple sectored.

Figure 3. Modified Link 16 network (RTT = round-trip timing, PPLI = precise participant location and ID).

lack of communication band-width, or imperfect interceptorperformance

• Achievable:amorerealisticsetincluding these disturbances tothe air picture and nonunitaryprobabilityofkill

Unlike in anti-air warfare,TBMD hemispherical search cov-erage is not possible with currentradarresourcesbecauseoftheneedto detect targets at much greaterdistances.Fortheidealset,thisreal-itywasignoredandahemisphereofmaximumwaveformwasused.ForAegisBaseline6Phase3,thesolu-tionimplementedwasconstructionof search sectors with the goal ofdetectingTBMsonlyearlyenoughto complete a minimum reactiontime engagement for intercept at

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theplannedaltitude.TheAPL-developedArrayRadarGuaranteed Useful Search tool was used to generatesuch types of search sectors (waveform, slant rangelimits,andslantrangeratelimitsasfunctionsofbeamposition,alongwith the search frametime) foruse inthe achievable set. Each ship was assigned an Aegisresourceplanningandassessment(RP&A)extendedairdefensemission(goalof95%probabilityoftrackinitia-tionat least20 sbefore the specialauto-TBMDreac-tiontimefortheplannedlaunch).TheRCSvaluesusedinplanningrepresenttheconstantmeanvalueforthelethal object used in a Swerling IV distribution (i.e.,what RP&A intends to use). However, for detectionand tracking, ACES uses a roll-averaged, frequency-averaged (over AN/SPY-1B[V]/D band), vertical-ver-tical polarized, aspect-dependent RCS for each TBMpieceasthemeaninaSwerlingIVdistributionbecausethisapproachisbelievedtobemoreaccurate.

InACES,oncethetargetisintrack,theaccuraciesof the measurement are based on the signal-to-noiseratioreturn.Agenericapproachisusedtomanipulatetheserawaccuraciestoapproximatetheeffectsoffilter-ing.Thetrackmeasurementsarecreatedby randomlydrawingfromanormaldistributionusingthecalculatedstandarddeviationsoferrorandthetargetgroundtruthvaluesasthemeans.Localbiaserrorsarethenaddedtothemeasurements.Thesebiasesrepresentresidualerrorsinsensorregistrationandnavigation.Atthebeginningof the simulation run, position and orientation biaserrors are randomly drawn for each sensor, and thesebiasesareheldconstantthroughout.Whenreportingonatrack,thestandarddeviationoftheresidualnetworkbiasisaddedtothecovarianceofthetrackstate.Theradar measurement and track accuracies used for theachievablesetwerecommensuratewiththosefromtheAN/SPY-1B(V)/DradarpresentonAegisareaTBMDships.Residualbias standarddeviations representativeofCECoperationswereusedbecauseoperationalnum-bersforLink16werenotavailable.TheLink16require-mentis8.7mradand150minrange,2andtheAegisownship sensor installation and navigation misalign-mentrequirementissignificantlybetterthantheLink16 requirement, but not as good as that achieved byCEC.ItisknownthatAegisshipsachievemuchbettersensor registrationthantheLink16requirement,anditwasassumedthat sensor registration shouldprovidesomebenefitoverownshipmisalignment.Fortheidealset,allmeasurementsandtrackswereassumedtohavenopositionorvelocityerrors,andcorrelationofremotetracks to local tracks was perfect. More details ofthe ACES detection, track, and correlation modelingmethodologyareavailableinthearticlebyBatesetal.,thisissue.

For the nonideal set of runs, two messages wereallowed per time slot. For the ideal set, this limitwasremoved.ACESexchangesdata intheJ3.6space

trackmessageandtheJ3.0referencepointmessage(tocommunicateimpactpoint)ontheSurveillanceNPG.ACESalsoexchangesdatainanenhancedengagementstatus message (including J10.2I and J10.2C2 engage-mentstatuswords);thisisnecessaryfortheDEDschemeto function. Further details on how communicationsnetworksoperateinACESareavailableinthearticlebyMcDonaldetal.,thisissue.

ACEScurrentlyperformsgroundtruthclustering;anRVisselectedasthePOTandclusteredwithitsspentbooster if they are both in track. Future versions ofACESwillperformclusteringandlinkingonthelocaltrackpicturebasedonlogicconsistentwithAegisBase-line6Phase3.

ACESthreatassessment,engageability,andschedul-ingareperformedon local tracks inamannerconsis-tentwithAegisBaseline6Phase3,althoughschedulingrequiredchangespreviouslymentioned(i.e., theaddi-tionofthe“deferred”engagementstatusanduseofthepreferredshooterindicator)toaccommodatetheDEDscheme.FutureversionsofACESwillalsoallowthesefunctions to be performed on remote tracks. ThreatassessmentprojectsthetrackstateofthePOTandformsa3-impactpointerrorellipse.ThePOTisgiventhepriority of the highest-priority defended asset, whichhasanyareawithin theellipse.EngageabilityprojectsthePOT(againignoringdrag)throughtheappropriateirregularhexagonindownrangevs.altitudespaceasafunctionofcrossrangeandspecificenergy.

Thenumberof simultaneous targetdiscriminationsallowedtobescheduledbyaplatformisfive;thisisthenumberchosenforpastanalysisandconstructionofthescenario,andrepresentedthebestestimateofcapabilityatthetime.Thethresholdandobjectiverequirementsforthenumberofsimultaneousdiscriminationsarecon-tainedintheNavalTBMDOperationalRequirementsDocument.Thepriorities for choosingwhich engage-mentstoschedule,inorder,areasfollows:(1)iftheunitisthepreferredshooteronthistrack,(2)higherthreatpriority, and (3) earlier latest time to launch. Thesefunctions, as well as force engagement selection (i.e.,decidingonpreferredshots),areperformedperiodicallyeverysecond.

ACESengagementoutcomehas severalprobabilis-tictests:launcherfailures,missileprelaunchreliability,missile in-flightreliability,uplink/downlinkreliability,handover/designation,andlethality.Thesetestsdonotdependongeometry(butdodependonwhethertheRVisintrack).GeometricdependenceisplannedforfutureversionsofACES.

ResultsBecause this scenario is saturated (i.e., number of

simultaneousdiscriminationsnumberofshootersdepth of fire per shooter = number of threats), eachoverengagementwillleadtoafreerider,exceptincases



where not all discriminations overlap. Each unit canonlyperformfivesimultaneousdiscriminations.Incer-tain raid timings, units may be able to engage sixthreatsbecauseoneinterceptoccursbeforethenextdis-criminationmustbegin.Inthefreerider,overengage-ment,andleakerfiguresshownthroughoutthetext,theorangehorizontallinesindicatetheactualresultsofthe100MonteCarloruns;thelightyellowportionsrepre-senta95%confidenceinterval.Intheidealcase,theleaker and free rider charts are the same because theeffectiveprobabilityofkillofthemissileequals1.

IdealFree fire.Infreefire,therearealmostalwaysfouror

fivefreeriders,asseeninFig.4.Thiscanbeexplainedbythewaytheunitsdeterminewhichthreatstoengage.Becausetheunitsintheidealcasehavedetectedeachthreat with plenty of time to engage it, they have afairlycompletepictureoftheraid.Whenaunitsched-ulesintercepts,itprioritizesthethreatsbythreatprior-ity and thenby the earliest latest time to launch.Bylookingatthethreatlevelsandwhichunitcanengagewhichthreat, itcanbedeterminedthatonlytwooutofsixthreatstoasset24(seeTable2)willbeengaged.Thismeansthateachrunisguaranteedatleastfourfreeriders. It is also true that two units will each engagefour out of five threats to asset 7. Depending on thelatesttimestolaunchforeachunit,thiscouldleadtoone free rider and will guarantee three or four over-engagements.Figure5showsthatincaseswhereaunitcanengagesixthreats,thereisalmostalwaysanotheroverengagement.

Simple sectored.Becauseofthewaytheassetswereassigned in the simple sectored case and the way theraid actually occurs, several units have more threatsagainsttheirassetsthantheycanpossiblydefend.Thissituation leads toahighernumberof free riders thanwithfreefire.Also,oneunithasnoneofitsdefendedassetsthreatenedandthereforedoesnotcontributetothedefense.Table3showsthenumberofthreatsthateachunitmustdefendagainst.

Unit 1 will be able to engage all of its threats. Inmostcases,unit2willmisstwoofitsthreatsandunit3willmissfour.Thisaccountsforthelargepercentageofcaseswithsixfreeriders.Forasmallerpercentageofthetimethereareonlyfivefreeridersbecauseunit2or3wasabletoengagesixthreats,asshowninthetable.

As seen inFig.5, thereareneveranyoverengage-mentsinthesimplesectoredcase.Becausethisengage-mentschemehasstaticdefendedassetassignmentsandtheunitshaveperfectknowledgeofthetrackstatesintheidealruns,theywillneverconfusetheimpactpointofa threat.Thismeansthataunitwillneverbelievethatathreatistargetingitsdefendedassetifitisnot.Therefore, the units will only engage threats to theirdefendedassets.

Figure 4. Free riders (ideal).

Figure 5. Unintentional overengagements (ideal).

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First launch.AsshowninFig.4,firstlaunchper-forms better than both free fire and simple sectored.Likefreefire,thisschemeallowsallunitstopotentiallyengageallthreatsthatarephysicallyengageableandinlocaltrack.Unlikefreefire,anengagementstatusmes-sageissentonceaunithaslaunchedtopreventotherunitsfromengagingthesamethreat.Thisdramaticallycuts down the number of overengagements betweenfreefireandfirstlaunch.Theonlytimeanoverengage-ment can occur in the ideal case is when two unitsmust launch at nearly the same time. This does notallow time for an engagement status message to bereceived before launcher assignment/missile commit.Byhavingfeweroverengagements,theunitsareavail-abletofireatwhatmayhavebecomefreeridersinthefreefirecase.Thisdoesnotmeanthatthereareneverfree riders. In this scenario, units 1 and 4 may eachbeleftwithlessthanfivethreatsthattheycanengagebecause units 2 and 3 fired first. This leaves severalthreatsthatunits1and4cannotengage,whileunits2and3areoccupied.

Distributed engagement decision. Figures 4 and 5show that under the ideal configuration, the DEDscheme outperforms all the others. Overengagementsseldomoccurred,leavingeachunitfreetocarryoutitsmaximum number of simultaneous engagements. Thethree times overengagements happened were when adualtrackresultedfromaunitthatneverlocallytrackedthespentboosterofoneoftheNoDongs;itsRVtrackcould not inherit the remote track number from theboosterasdidtheotherunits.Occasionally,freeriderscanstilloccurbecauseofthesequentialnatureofthecurrentDEDalgorithm.Thisschemehadmanyoftheadvantages of first launch with the added advantagethatdecisionsweremadewellbeforeanyoftheengage-mentstookplace.Intheidealsituation,allthetargetsaredetectedatleast40sbeforethefirstplannedlaunchtime. Pairing of units to targets before launch solvedthe communications latency problem present in firstlaunch.

AchievableAsexpected,mostof the resultsunder theachiev-

ableconfigurationareworse(agreaternumberof freeridersandoverengagements)thanthoseobtainedunderthe idealconfiguration.Mostof thediscrepanciescanbeattributed to the inferiorairpicturecreated in theachievable configuration. The achievable air picturehadfewerthreatsdetected,andthosethatweredetectedwere seen later. Multiple tracks (multiple track num-bers assigned to the same object) and miscorrelations(multiple objects assigned to the same track number)furtherdegradedtheinformationavailable.

Free fire. The results of the achievable case arealmostthesameastheidealcase.However,someoftheachievablerunshadonlythreefreeriders.Thereason

forthisislikelythatfewerthreatsweredetectedbytheunits,whichthenchangedtheorderinwhichtheinter-ceptswerescheduled.Thiswouldmeanthatifahigher-prioritythreatwasnotdetected,alower-prioritythreatthatwasneverengagedintheidealcaseisnowengaged.Figure6showsforeachplannedpair(asseeninFig.2a)inallrunstheamountoftimebetweendetectionandanidealplannedtimetolaunch.Thosedetectedlaterthanplannedmaynotyieldadequatetimetoplanandexe-cuteanintercept.Thereare708threats(outofapos-sible4500)thatarenotdetectedatallbytheplannedunit. The RP&A methodology failed to meet its goal(95% probability of track initialization at least 20 sbefore the special auto-TBMD reaction time for theplannedlaunch)becausetheRCSvaluesusedbyRP&Aaretoohighinthiscase.Thegoalismetlessoftenwiththenominalmission(atthespecialauto-TBMDreac-tiontime); thus, theextendedmissionwaschosenforthisarticle.

Simple sectored.Figures7and8showthatthesimplesectoredresultsfromtheachievableconfigurationwerenearly the sameas the resultsobtained fromthe idealconfiguration(Figs.4and5).Thedefendedassetswereassigned so that the track errors did not create anyconfusionas towhichunit’sdefendedassetwasbeingtargeted by a threat. Therefore, no overengagementsoccurred. For the reason previously explained in theideal simple sectored case, there will typically be fiveorsixfreeriders.Inotherinstances,becauseofstatisti-calvariation,thenumberoffreeridersdecreasedtofourbecauseunits2and3eachhadsixshots.

First launch.Asexpected,theresultsinFigs.7and8 show that first launch performed worse under theachievableconditionsthanundertheidealconditions.Unlike free fire or simple sectored, the overengage-ment results are considerably different than the ideal

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configurationresults.Thiscanbeexplainedbythefactthatfirst launchreliesonacommonairpictureandacommunicationsnetwork,whereasfreefireandsimplesectored do not. In the achievable runs, errors in thetrackpictureledtomultipletracknumbersforthesameobject.Becausetheforcetreatsthatobjectasmorethanone different threat, overengagements usually result.This is a product of the bad air picture and not theengagement coordination scheme. In the first launchresults,96%ofoverengagementsarecausedbymultipletracknumbersforthesameobject.Theremainderofthe

Figure 7. Free riders (achievable).

overengagements can be attributed to engagementstatus messages arriving too late (nearly simultaneouslaunches).Thenumberof free riders didnot increasesignificantlybecausetheunitsthatoverengagedthreatshadnotalwaysreachedtheirmaximumcapacityintheidealcase.

Distributed engagement decision. Similar to firstlaunch, the results in Figs. 7 and 8 show that theDEDoutcomesbecameconsiderablyworseundertheachievableconditions.Justlikefirstlaunch,thedegra-dationcanbecontributedtotheuncleanairpicture.IntheDEDresults,88%oftheoverengagementsarecausedbymultipletracknumbers.Figure9showsthevariability over Monte Carlo runs of the number ofunique remote tracknumbers at theearliestplannedlaunch time for DED (other schemes are similar).Theorangeportionofthebarsindicatesboosterswithremotetracknumbers;usuallyatleastoneboosterwasreported(becausesomeonewasnottrackingthecor-respondingRV),butnotalways.Thegoalwastoreportone track for each of the 20 events; this never hap-pened. Often there were fewer unique remote tracknumbers than the number of objects (25), but theaveragewas28(or1.3unique remote tracknumbersperobjectwitharemotetracknumber).Theseextraremote track numbers are the result of a failure tocorrelate either initially or because recorrelation isnotallowedafterdecorrelation.Miscorrelations(morethanoneobjectwiththesameremotetracknumber)aremorerare,asseeninFig.10.

The air picture also varies significantly with time.ForMonteCarlorun24,Fig.11showsthenumberofobjectsintrackbyatleastoneunit(cyan),thenumberofmiscorrelations(yellow),andthenumberofuniqueremote track numbers (magenta). In this run, severaldecorrelationsoccurafterthefirstlaunchat407sandbefore the first intercept at 469 s, which can clearlycause problems. After successful intercepts occur, the

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local tracks on these objects degrade before they aredropped,leadingtofurtherdecorrelations.

As previously mentioned, not all of the planneddetections always occurred. This reduces the solutionspace (i.e., eligible number of engageable threat/unitpairs) for the algorithm. Launches can occur beforedetectionofallobjects,asseeninFig.12.Itisimpos-sibletoguaranteeacorrectsolutionifdecisionsmustbemadebeforecompleteinformationavailability.

More launches occur in DED than in first launchbecauseunits1and4nearlyalwayshadfivetargetstoengage.Morelaunchescausemoremissilefailures(dudsandfailureofuplinkordownlink).Eachmissilefailurecauses an engagement status message with the statusset to“engagement terminated” tobe sent.Once thisoccurs,thealgorithmdecidesagainwhichunithasthebest shot on that particular track. Currently in themodel, this is being counted as an overengagementbecausetwounitsengagedthesametrack.Inthefuture,theseoverengagementswillbecountedseparatelyfromtheunintentionaloverengagements.InDED,theotherunits aremore likely than infirst launch tobe avail-abletoshootbecauseoftheload-levelingaspectsofthealgorithm.

Finally, for all schemes, thenumberof leakerswillusually exceed the number of free riders in the realworldbecausemissilesarenotinfallible.Figure13showsthenumberofleakersfortheachievablecaseforallfourschemes.Only in1 runoutof the400didno leakersmakeitthrough;itwasforDED.

CONCLUSIONSThe results reveal two important truths. Under

idealconditions,aDEDschemeperformssignificantly

Figure 11. Run 24 air picture (DED, achievable). The dashed lines represent the first scheduled launch time and the first sched-uled intercept time.

better (and nearly perfectly in this scenario) thanotherschemes.However,realisticshortcomingsintheinformationavailable to theunitsblur thedifferencesbetweenDEDandfirstlaunch.

Theresultsofbothsetupconfigurations(i.e.,idealandachievable)canbeused to showageneralcom-parisonofthefourengagementcoordinationschemesimplementedinACES.Usingfreeridersasthemetrictocompareperformance,simplesectoredprovedtobethe least effective in this particular scenario, closelyfollowedbyfreefire.Thetwodynamicschemesweresignificantly better, with the DED scheme modeledoutperformingfirstlaunch.

The achievable air picture formed in this scenarioleaves much to be desired. None of the schemes was

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Figure 13. Leakers (achievable).

abletoovercomenumerousinstancesofmultipletracks(averaging1.3uniqueremotetracksperobjectwitharemotetracknumber),severalmiscorrelations,andtoomany targets going undetected by units that plannedtoseethem.Theeffectsofcommunicationlatencyandchangingplannedlaunchtimesseemedtohavelessofaneffectthanairpicturequality.

FUTURE WORKTherearefivemainareasforfurtherresearch.

1. Investigateexcursions in theachievableconditions(primarily radar setupandcorrelation/decorrelationrules)todeterminewhatcanbechangedintherealworldtoimproveperformance.

2. Analyzeotherscenarios(i.e.,differenttheaters,raids,and unit locations) to ensure that the conclusionshereextendtothemaswell.

3. Examine other engagement coordination schemesthat exist, including those being considered foruse.

4. Includemoredefensivesystems(e.g.,NavyTheaterWide, Patriot, and Theater High-Altitude AreaDefense)thatwillbepresentinfutureconflicts.

5. Allow other warfare areas (i.e., Anti-Air WarfareandOverlandCruiseMissileDefense)tocompeteinrealtimefordefensiveresources.

REFERENCES 1JNL 198 Quick Reference Guide,NTSCI(1Nov1998). 2Link-16 Operational Specification OS-516.2, Change 2, 3, Published

undertheDirectionofCNO(N62)bytheNavyCenterforTacticalSystemsInteroperability(Mar2000).

ACKNOWLEDGMENTS:TheauthorswouldliketoespeciallythanktheOfficeofNavalResearchandtheNavyTheaterWideProgramOffice for fundingtheresearchdiscussedinthisarticle.Theauthorsalsowanttothanktheothermem-bers of the ACES development team (S. R. Allen, C. W. Bates, M. J. Burke,J.F.EnglerSr.,J.M.Henly,B.LHolub,E.M.McDonald,andK.E.Shafer)fortheircontinuingcontributionstothemodelingandanalysiseffortsdiscussedhere.Forfurtherinformation,pleasecontactR.A.Phillippi,APLProgramManagerforJointMissileDefenseProjects.

THE AUTHORS

SIMONMOSKOWITZearnedaB.S.inaerospaceengineeringfromtheUniver-sityofVirginiain1993andanM.S.insystemsengineeringfromtheUniversityofArizonain1994.HeisaSeniorProfessionalStaffmemberoftheAirDefenseSys-temsEngineeringGroup.HejoinedAPLin1994.TheaterAirandMissileDefenseradar searchandengagementcoordinationalgorithmdevelopmentandmodelingcomprisehiscurrentprimaryfocus.HisexpertiseincludesTBMDthreatcharacter-ization,conceptofoperations/scenariodevelopment,effectivenessanalysis,visual-ization,requirementsdevelopment,andspecificationreview.Hise-mailaddressissimon.moskowitz@jhuapl.edu.

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REBECCAJ.GASSLERgraduated fromVirginiaTechwithaB.S. inaerospaceengineering.She is currentlypursuinganM.S. in information systemsand tech-nologyfromTheJohnsHopkinsUniversity.ShejoinedtheAirDefenseSystemsEngineeringGroupinADSDinJune2000andhasdedicatedmostofhertimetoworkingonACES.Ms.Gassler’sprofessionalinterestsconcernmodeling,simula-tion,andanalysisofcurrentandfuturetheater-andcampaign-leveloperations.Here-mailaddressisrebecca.gassler@jhuapl.edu.

BARTL.PAULHAMUSisamemberofAPL’sAssociateProfessionalStaffintheAirDefenseSystemsDepartment.HereceivedB.S.andM.S.degreesincomputerscienceandengineeringfromPennStateUniversityin1998and2000,respectively.HejoinedAPLin2000andiscurrentlyworkingondevelopingmodelingandsimu-lationsoftwarefortheAirDefenseSystemsEngineeringGroup.Hise-mailaddressisbart.paulhamus@jhuapl.edu.

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