220 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 22, NUMBER 3 (2001) I Systems Engineering of Air and Missile Defenses Jerry A. Krill n the Air Defense Systems Department, systems engineering is a way of thinking. More than a “process,” the systems perspective drives our approach to solving emerging air and missile defense problems as the threat becomes more advanced and the tactical environ- ment more complex. This perspective and the requisite tools have evolved with the increas- ing complexity of those systems. In this article I describe the systems approach to the devel- opment of missile defenses and cite recent examples illustrating the associated activities. THE SYSTEMS ENGINEERING PERSPECTIVE The scientific method, with its methodical and logi- cal order, has been widely used for centuries. As scien- tifically developed and engineered devices have evolved into complex systems with interacting elements, a sys- tems engineering approach has arisen that is analogous to, and a derivative of, the scientific method. A dia- gram of the scientific and systems engineering thought sequences is shown in Fig. 1. 1 The systems perspective has been recognized and articulated primarily in the latter half of the 20th century, with its greatest impetus from World War II. Because the Air Defense Systems Department (ADSD) carries forward the APL legacy of the development of the proximity fuze from that era through evolution to modern guided missile defense, the Laboratory’s systems engineering perspective has evolved with the emerging national recognition of this discipline. In fact, the ADSD mission statement is steeped in the context of systems-level thinking to solve complex problems. Before describing how systems engineering is applied to air and missile defense, I first briefly describe what constitutes a good system and the corresponding sys- tems engineering perspective and development meth- odology. A system is considered to be “interrelated components functioning together toward a common objective.” 1 The practice of systems engineering is “an interdisciplinary approach toward methodical realiza- tion of a successful system.” Finally, a successful system is one that meets the users’ needs; interfaces with, and complements, the operation of related systems; func- tions over the range of exposed environmental and operational conditions; and can be adapted to future needs, environments, and interfacing systems. 1 Systems engineering is a discipline necessary to pro- duce a successful system. The logical sequence of generic systems engineering steps is shown along with the scien- tific method in Fig. 1; this is a way of thinking through any phase or level of detail during the development. The system development cycle uses this methodology, from system conception to answering a need through system realization. Why is a methodical, interdisciplin- ary approach needed? A caricature of a missile design as
Thescientificmethod,withitsmethodicalandlogi-calorder,hasbeenwidelyusedforcenturies.Asscien-tificallydevelopedandengineereddeviceshaveevolvedintocomplexsystemswithinteractingelements,asys-temsengineeringapproachhasarisenthatisanalogousto, and a derivative of, the scientific method. A dia-gramofthescientificandsystemsengineeringthoughtsequencesisshowninFig.1.1Thesystemsperspectivehas been recognized and articulated primarily in thelatterhalfofthe20thcentury,withitsgreatestimpetusfromWorldWarII.BecausetheAirDefenseSystemsDepartment (ADSD) carries forward the APL legacyofthedevelopmentoftheproximityfuzefromthaterathrough evolution to modern guided missile defense,the Laboratory’s systems engineering perspective hasevolvedwiththeemergingnationalrecognitionofthisdiscipline. In fact, the ADSD mission statement issteepedinthecontextofsystems-levelthinkingtosolvecomplexproblems.
Beforedescribinghowsystemsengineeringisappliedto air and missile defense, I first briefly describe what
constitutes a good system and the corresponding sys-tems engineering perspective and development meth-odology. A system is considered to be “interrelatedcomponents functioning together toward a commonobjective.”1Thepracticeofsystemsengineeringis“aninterdisciplinary approach toward methodical realiza-tionofasuccessfulsystem.”Finally,asuccessfulsystemisonethatmeetstheusers’needs;interfaceswith,andcomplements, the operation of related systems; func-tions over the range of exposed environmental andoperational conditions; and can be adapted to futureneeds,environments,andinterfacingsystems.1
Systemsengineeringisadisciplinenecessarytopro-duceasuccessfulsystem.Thelogicalsequenceofgenericsystemsengineeringstepsisshownalongwiththescien-tificmethodinFig.1;thisisawayofthinkingthroughany phase or level of detail during the development.Thesystemdevelopmentcycleusesthismethodology,from system conception to answering a need throughsystemrealization.Whyisamethodical,interdisciplin-aryapproachneeded?Acaricatureofamissiledesignas
viewedbyvariousspecialists1illustratestheneedforamultidisciplinaryapproach(Fig.2).Clearly,eachexperthasauniqueperspectiveaboutthesystemandtherela-tiveimportanceofhisorherspecialcontributionand,therefore, about decisions concerning the priority ofallocations.Systemsengineeringmustbringthisexper-tise together to develop a balanced system where thecomponents and technologies are appropriately allo-catedandcostand riskarecontained.WithinADSDresidespecialists insuchfieldsascontroltheory,aero-dynamics, communications, software engineering, andmicrowave and optics theory. There are also combatsystemsengineerswhoprovideanalysisandengineeringcontributions to blend these disciplines. Many times,specialistschoosetoevolvetheircareerstowardatotalsystemsperspective.Also,manyspecialistshavedevel-opedakeensystemsperspective,themselves,fromlongexperience.Thesespecialtiesareincludedinanumberof articles in this issue, but they are viewed for theircontributionstotheirrespectivetotalsystems.
Why is an air/missile defense system consideredcomplex? Figure 3 depicts air defense elements in abattle force. Each element can be considered as aninterfacedsubsysteminaforce-wideairdefense“super-system.”Yeteachelementis,itself,asystem.Figure3illustrates both perspectives. The components of thecombatantsinteractinacomplexmanner.Forexam-ple, the Cooperative Engagement Capability (CEC)sensor network allows the computers controlling theradars of different ships and aircraft to interact tomaintain tracking of targets. The Aegis ship’s weap-onscontrolcomputermayusetheradarreturndataofthe target from another Aegis ship to develop Stan-dardMissile(SM)midcourseguidancecommands.Thecommandsareuplinkedviathelaunchingship’sAegisSPY-1radartoareceiver inthemissile foruse in itsguidancecomputer.Thus,thereal-timeinteractionofcomponentsamongelementsofabattleforcetosup-portamissileinterceptrequirestheentireforcetobetreatedasasystem.Thecomplexityintermsofcompo-nents,functionalintricacy,technologyblend,andper-formancestringencytoachievedefenseagainstavari-etyofthreatsmakesnetworkedairandmissiledefenseamongthemostcomplexsystemsintheworld.Arti-clesinthisissuefurtherillustratethispoint.
How does systems engineering relate to programmanagement? Systems engineers and program manag-ersarepartnersintheleadershipofsystemdevelopmentteams.WithintheNavy’sprogramofficesandprogrammissionoffices,programmanagersandsystemsengineersprovide programmatic and technical expertise for the
Figure 1. Scientific (a) and systems engineering (b) approaches. The scientific method of hypothesis posing and testing is analo-gous to the systems engineering method of system element syn-thesis and validation.
Figure 2. Specialists’ whimsical perspectives of a missile system. Each specialty might have a different viewpoint about a system centered on unique expertise and technology. A systems engi-neer must perform from a balanced perspective, giving appropri-ate attention to each specialty, often in conflict with one another for resources and requirements satisfaction.
Increasingly, chief, systems, and lead engineers arebeingformallydesignated,primarilyfromthetechnicalgroups, tocomplement theprogramandprojectman-agers in leadership of systems engineering tasks. Thechief/leadsystemsengineersandprogram/projectman-agers work in partnership, in addition to leading theengineeringteam,toensurethatdevelopmentisorderlyand timely and that sufficient resources are provided.As team co-leads, their functions must overlap some-whatsothateachrecognizesandtendstotheneedsandresourcesoftheotherwhiletheyperformtheirprimaryroles.Asteampartners,forexample,thesystemsengi-neer may develop the technical performance require-mentsandspecificationsandleadsystemmodelingand
criticalexperimentstovalidatetherequirements.Theprogram manager provides the programmatic contextfor these requirements in thekeyprogramdocumentsand articulates the underlying programmatic requiredresourcesandscheduletoachievethem,includingthefunding, equipment, and facilities for modeling andexperimentvalidations.Someoverlapintheirrolescanoccur.Forinstance,theprogrammanagermayhaveaneffectonthetechnicalrequirementsbecauseofashortscheduleor fundingconstraints.Thesystemsengineercanhaveaneffectonfundingandschedulingbyarticu-latingandprovidingevidenceofkeytechnicalrisksthatmustfirstberesolvedbyprototypingorexperiments.
Figure 4 illustrates the system development cycleusing the Navy Theater Wide (NTW) Tactical Bal-listicMissileDefenseSystemasanexample.APLwasrecentlydesignatedtheTechnicalDirectionAgentforthissystem,i.e.,APLhasbeengiventheresponsibility
Figure 3. A networked missile defense system is actually a system of systems, with several major systems interfaced as subsystems of a larger force-level system. Shown are an SM, an Aegis ship combat system that guides the SM to its target, an E-2C airborne early warning system that first detects the target and reports via tactical links and the Cooperative Engagement Capability, and amphibious assault ships with the elements of the Ship Self-Defense System in Mark I and Mark II versions featuring integrated NATO Sea Sparrow and Rolling Airframe Missile engagements.
oftechnicaloversightforthesuccessofthesystemandits upgrade evolution. NTW is developed as a systemeven though it ispartof themoreencompassing shipcombat system and battle force defense network. Partofthemissiledefensesystemsengineeringchallengeistodevelopsuchelementswhileensuringtheshipandforce-levelsystemperspectives.
Iwillbrieflydiscussthephasesofsystemsengineer-ingfromFig.4asameansofintroducingtheremain-ing sectionsof this article.Webeginwith theneed.Often one or more concepts are explored to deter-minehow to articulate theneed.Although themis-sionneedisnotspecifictothedesignapproach,itmaybenecessary toconvey theneed for suchconceptualelements as communication or sensing. Operationalrequirementsareintroducedinthecontextofrequiredfunctions, criticalparameters, andeffectivenessmea-sures. This generally requires system-level modelingandexplorationoftheconceptinmoredetail,aswellas critical experiments, componentdevelopments,ordata collections to define and validate the require-ments. Conceptual alternatives are assessed to selectthepreferredapproach,andthesystemrequirements,tracedtotheoperationalrequirements,aredevelopedastheprimarybasisforthesystemdesign.
Figure 4. A system development cycle for NTW Tactical Ballistic Missile Defense. The cycle shows systems engineering progression from top-level requirements through concept formulation and assessments; risk reduction activities; development, including design trade-offs, modeling, and fabrication; system element validation and integration; the series of testing leading to a full-scale missile intercept test; and, finally, Fleet introduction, life-cycle support, and upgrade.
Thesystemconceptandconceptofoperationsformthebasis,alongwithmodelingandsimulationandriskreductionactivities,forpartitioningandallocatingthesystemfunctionsandperformancetosuccessivelygreaterlevels of detail. Iteration and feedback are critical tothismethodologybecauseatsomelevelofdetailafunc-tion may prove infeasible as defined, thus requiring amodificationathigherlevelstoreallocaterequirementsandfunctionality.Modelingandsimulationcanbeper-formedatthevariouslevelsofdetailrequiredtoverifythe viability of performance allocations (timing andaccuracybudgetsandgainmargins)forradarsandmis-sileguidanceinvariousphysicalenvironments;evenanentirebattleforceairdefensenetworkcanbemodeled.Later in this article, I discuss other uses and forms ofsimulationsandmodels.
ADSD develops and applies models at all levels,many of which have become the Navy standard fortheirvalidatedaccuracy.Prototypingofportionsofthesystemisgenerallyneededtovalidatethattherequiredperformancecanbeachievedortovalidateportionsofthemoredetailedrequirementsthathavebeenderivedfrom the primary ones. When the partitioning hasreached the component level (and has passed a seriesofdesignreviews),thecomponentscanbeengineered,
fabricated,and tested.Thenthebottom-upprocessofsuccessively integrating and testing components com-mencesinreverseorderfromthetop-downrequirementspartitioning process. The fabricated components areintegratedandtestedagainstpredictedperformanceatthecorrespondingrequirementsallocationlevel,build-ingintosubsystemsand,finally,thetotalsystem.Like-wise,testingbeginsatcomponentintegrationandbuildstoward full system-level testingby the intendedusers,i.e.,theFleetoperators,toevaluateachievementoftheoperational requirements in the representative envi-ronments. Systems engineering includes system main-tenance and support, as well as planned capabilityupgradesandmodernizationthroughoutthelifeofthesystem;theseaspectsarereceivinggreaterattentionastotalsystemlifecostisgivenincreasingemphasis.
ADSD has been involved in all phases of systemsdevelopment.Thephasesarenextdescribedingreaterdetail,andvariousexamplesareprovided.
ARTICULATING THE NEED AND DEFINING REQUIREMENTS
A mission need is defined through a continuousassessmentofcurrentandproposedcapabilitiesagainstanevolvingthreat.Itisthebasisforestablishinganewoperational capability, improving an existing capabil-ity,orexploitinganopportunity.Amissionneedstate-ment isverybroadandnot system specific.1ForDoDsystems,thismissionneedisdocumentedinaMissionNeeds Statement.2 As part of that document, a con-vincingcasemustbemadethattheneedcanfeasiblybemetbyexistingordemonstrabletechnology.
After the need is identified, critical operationalrequirements must be developed. These generally areinsomecontextoftheexpectedtechnicalapproaches’fundamentalpropertiessothatmeaningfulcriticalfunc-tionsandperformanceparameterscanbedefined.Forexample,itwouldlikelybeunderstood(basedonmodel-ing,experimentation,orleveragingofexistingsystems)whetheranewsystemmayrequireanewsensororcom-munications element. As a result, a radar or commu-nicationrangemaybecomeakeyperformanceparam-eterinanOperationalRequirementsDocument.2Thismay be nearly coincident with an analysis of alterna-tives(AoA)3fromwhichaninitiallargersetofconceptcandidates is reduced toa small setofpreferredcases.Critical experiments and prototype tests may also berequiredtovalidatetherequirementsandthefeasibil-ity of the concepts. Operational requirements, there-fore, are based on alternatives assessments, feasibilityexperiments,andothermeansofconceptexploration.Theyincludethreshold(minimumrequired)andobjec-tive(desiredupperbound)keyperformanceparametervalues and performance and effectiveness measures.Bothtechnicalandoperational(user)requirementsare
provided.Itisimportantthatthesethresholdandobjec-tive values be measurable by analysis or tests. ADSDhas played a key role in providing technical supportfor a number of major system Operational Require-mentsDocuments,includingthoseforCEC,SM,AreaAirDefenseCommand,NTWTacticalBallisticMissileDefense,andtheShipSelf-DefenseSystem(SSDS).
DEVELOPING SYSTEM CONCEPTS AND ASSESSING ALTERNATIVES
The previous section indicated the importance ofsystemconceptsandalternativesassessmentsasabasisfor defining needs and requirements. In this section Ifurtherdefinewhataconceptconsistsofandhowitisassessed.Aconcept isgenerallyknownasasetof thefollowingdescriptiveitems:
Withthislevelofcompleteness,alternativeconceptscanbeevaluatedagainsteachother in thecontextofa Design Reference Mission (DRM), which describesthe threat, geopolitical, and natural operational envi-ronmentsinwhichthesystemisexpectedtoperform.4The concepts are defined in sufficient detail for top-level performance modeling to reflect expected tech-nical capabilities and cost factors. These are thencompared according to weighted criteria to identifypotential“best”candidates.
Figure 5 is an example of model development andAoAconceptsfortheNTWdefensemissile,theSM-3.Theinitialassessmentconcludedthatamissilederivedfrom prior SM-2 components with prototype kinetickilltechnologyandwithsubstantialinterceptrangeforinlandprotectionwasthebestapproach,havingscoredthehighestfortheratingcriteria.Itwasassumed,onthebasisofcriticalstudiesandexperiments,thatanevolvedversionof theAegisCombatSystemwouldguide theSM-3.FurtherdefinitionoftheNTWSystemfromtheAoAresultsusedmoredetailedmodelsandtheDRMscenarios to evaluate such critical features as missileboostvelocity,theabilityoftheAegisSPY-1Bphasedarray radar to discriminate warheads from debris, andcountermeasuresversusmodificationoptions. Figure6illustratesthefeaturesoftheNTWDRM.ThisDRM,developedbyAPL’sJointWarfareAnalysisDepartment(JWAD) in partnership with ADSD, is necessarily ofsufficientdetailtoallowcomprehensivemodelingand
activities as well as from resultsofmaturingtechnologyandsystemstudies.Figure7isanearlyillustra-tionoftheSMconceptofstandard-ization featuring common compo-nents inmissilesusedintheAegisandtheTerrier/Tartarweaponsys-temsofthe1970s.Suchstandardiza-tionprovidedamajorlife-cyclecostsaving and performance similarityacross the Fleet. It formed a basisfor system functional requirementsandperformancerequirementallo-cations to subsystems, risk assess-ments,andtrade-offstudies,asdis-cussed later. With the retirementofTerrierandTartarships,leavingAegis as the only area defensesystem, standardization evolved tothe use of modularity in blockupgrades tomeetadvancing threatcapabilities.
Inthepastdecade,withAegisastheonlyU.S.weaponsystemusingSM-2, standardization has been aprimary means of containing costandriskinblockupgradestomoreadvanced versions or even as thebasisforintroducinganewmission
capability.Intheformercase,ahighdegreeofcommon-alityexistsamongthelatestblockupgrades—III,IIIA,IIIB,andIV—allowingrelativelyrapidandcost-effec-tivemeanstoaddressadvancingthreats.Morerecently,commonalityoftheSMserieshasexpeditedthedevel-opment of new Navy missions with the SM-2 BlockIVA for Area Tactical Ballistic Missile Defense andtheSM-3forTheaterTacticalBallisticMissileDefense.StandardcomponentsevenallowtimelydevelopmentofalandattackversionknownasSM-4.
PERFORMING CRITICAL RISK REDUCTION ACTIVITIES
Becausenewsystems,ormajorsystemupgrades,rep-resentanewcapability,therearealwaysunknownsintheimplementationoftheconcepts.Asetofactivitiesis required for riskreductiontoresolvetheunknownsbydeterminingfeasibility,identifyingnewphenomena,developingormaturingnewtypesofcomponentsandtechnologies,andlearningaboutnewoperatingparam-eterregimes.Thepurposeofriskreduction,then,istoresolvesuchissuesinadvance.Suchactivitiesincludethefollowing:
• Collecting data on critical phenomena not fullyunderstood
Figure 6. The NTW System will be capable of intercepting longer-range, theater-class, tactical ballistic missiles. To ensure that the analyses and trade-off studies from the devel-opment team (from multiple laboratory and industrial organizations) would be consistent, a DRM was developed. Shown is an example operational situation with Joint missile defenses arrayed against tactical ballistic missiles fired from multiple directions and at dif-ferent times. A variety of conditions are defined that serve as a basis for modeling system element performance versus design allocation alternatives. (BMC4I = battle management command, control, communications, computers, and intelligence.)
Threatcharacterization
Threattactics
Physicalenvironment
BMC4I
Threat BallisticMissile trajectories
BlueForce
locations
Joint campaigncontext
Figure 5. APL played a key role in an assessment of alternative NTW missile conceptual configurations. Of the alternatives shown, the SM LEAP derivative with a kinetic kill capability was deter-mined to be the best approach in terms of cost, risk, capability, and schedule. This alternative was the basis for SM-3.
• Determining alternative work-around technologiesor elements should the risk items fail or becomedelayed
• Performing appropriate development tests/criticalexperimentstoverifyfeasibilityandperformanceinexpectedenvironments
AcriticalriskitemforSM-2BlockIVAwasaninfra-red window for the seeker terminal homing detector/imager.Thewindowhadtomaintainsufficienttranspar-ency, low distortion, and detector protection in severeflightheating,vibration,andaccelerationenvironments.Asetofmaterialswastheoreticallyidentifiedandexper-imentally tested,and sapphirewas selected.Uponcrit-ical prototype fabrication and wind tunnel testing, anumberofseeminglyrandomfailuresoccurred.Amoredetailedtheoreticalmodelrevealedthattheorientationofthe sapphire crystal lattice was important; while oneorientationmetrequirements,othersdidnot.Thiseffort
Numerous examples can be cited for CEC as well,including fade margin tests and prototype transmitterandantennacomponentsfortheCECdatadistributionfunctionandradardatacollectionsforplaybackintopro-totypealgorithmsforthecompositetrackingfunction.
In 1996 an advanced concept technology demon-stration (ACTD) was conducted in Hawaii in whichAPLwasthelaboratoryco-leadwiththeMassachusettsInstituteofTechnology/LincolnLaboratory.Thedem-onstrationfeaturedtheuseofCECtoenableanAegiscruisertofireamodifiedSM-2BlockIIIAtoengageatargetbeyondtheship’shorizonforthefirsttimeusinganelevatedterminalhomingtargetillumination(onamountain to represent a potential future aircraft illu-minationcapability).Themissileengagementterminalhoming was in a range, approach angle, and altituderegime not previously considered in missile design.Theoretical modeling indicated the need for a morefrequency-selective illumination reference receiver
Figure 7. An early SM concept illustration. In the late 1960s and early 1970s evaluations of technologies, costs, and performance require-ments led to a system concept definition of standardized area defense missiles.
An example is the APL Defended Area Model(ADAM) widely used in the NTW Tactical BallisticMissile Defense Program to explore combinations ofradar rangeandSM-3configurationsagainst avarietyof targets. Figure 8 illustrates the model elements ofADAMandexamplesofitsoutput,indicatingtheareawithinwhicha shipcouldoperateanddefenda loca-tionfromathreatdirection.Themodel’sADAMcom-ponents are a federation of APL and Navy models,and ADAM’s development and use are a collabora-tionbetweentheADSDandAPL’sStrategicSystemsDepartment.Anew,moredetailed,andcomprehensivesimulationcalledARTEMIS isbeingdevelopedas an
Figure 8. The ADAM allows a wide variety of tactical ballistic missile defense concepts to be evaluated. It includes linked models of sensors, the intercepting missile, command and control features, and kinetic kill vehicle (KKV) homing. Workbench post-processing tools provide visual analysis products (yellow). The blue boxes identify ADAM and associated APL and DoD community models. The clear boxes indicate input and intermediate data. (6-DOF = 6-degree-of-freedom, EOB = enemy order of battle, KW = kinetic warhead, TBM = tactical ballistic missile, Tgo = time to go, TOF = time-of-flight, WCS = Weapons Control System.)
modificationtothemissile.However,toreducetheriskof failure in this new over-the-horizon regime, a “cap-tivecarry”criticalexperimentwasperformed.Thiscap-tivecarryexperimentpriortotheMountainTopACTD(describedlater)consistedofamissileseekerattachedtothewingofaLearjettoflyportionsofthemissiletrajec-toryandverifymidcourseguidancehandofftoterminalhomingandseekerlockontothetarget.ThissuccessfulriskreductioncriticalexperimentisdescribedinRef.5.
USING MODELING AND SIMULATIONModeling and simulation are key to all phases of
the systemsdevelopmentcycle. Ingeneral,amodel isa simplified representation of a system or system ele-mentorfeature.Examplesofmodelsareequations,scalemodelsandmockups,andlogicflows;someofthesecanbe implemented into computerprograms.Simulationsgenerallyconsistoflinkedcollectionsofmodelsinthecontextofatimesequence.
Figure 9. Key elements of a virtual demonstration in the APL Warfare Analysis Laboratory. Shown are the conceptual elements of the OCMD concept featuring (a) a CEC “forward pass” cooperative engagement with advanced E-2C detection and tracking of a target, an Aegis ship-launched advanced SM guided from an airborne fire control suite via CEC and Aegis weapon control, terminally illuminated from the fire control aircraft; (b) a depiction of the high-fidelity models from multiple organizations incorporated to simulate the conceptual system; and (c) an illustration of simulated cruise missile attacks against South Korea for engagement analysis.
integration of validated detailed models of the entireSMkillchainfromtargetdetectionthroughintercept.Modelsvalidatedbytestresultscanalsoserveasvirtualtest vehicles for regions of the performance envelopewhere actual tests cannot be safely or cost-effectivelyconducted.
Modelsandsimulationscanbeusedtopredictper-formanceandconducttrade-offstudies.Trade-offstud-iesinvestigatetechnicalapproachestomeetingrequire-mentsateachlevelofdesigndetail.Modelingcannotbea substitute for real-world testing,asmodels reflectonly a simplified version of the system and its opera-tion and do not fully represent the actual system initsoperationalenvironment.Theremustbeabalancebetween modeling and simulation (since one cannottestforeverycondition)andtesting(sincerealisticvali-dationisrequiredandexpected).
Figure 9 is an illustration of a collection of modelslinked into a simulation of Overland Cruise MissileDefense (OCMD). One concept of CEC is a form ofcooperative engagement known as “forward pass” inwhich a ship-launched missile flies beyond the ship’shorizon to intercept a target tracked by an airborneradar and guided by data from the airborne radar. A
(a)
(c)
(b)
successfulACTDofforwardpassoccurredin1996,5usingprototypeandshipelementsonamountaininHawaiitorepresentpotentiallightweightairbornesensorsandfirecontrolelements.ThesuccessoftheACTD,knownasMountainTop(referredtoearlier),ledtofurtherinter-est indefiningtheadvancedelementsof suchasystemfordefenseofAlliedassets far inland.Thesystemcon-ceptconsistedofairbornedetection,trackingsufficientlyaccuratetosupportmissileguidance,andmodifiedver-sions of SM, CEC, and Aegis to enable a forward-passhandover of missile guidance from the ship to the air-craft.Avirtualfollow-ontestwasperformedinJWAD’sWarfareAnalysisLaboratory6usingthesimulationofthesystemnetwork, as shown inFig.9c, in thecontextofaDRM-likescenariooverSouthKorea.Theresultscon-firmedandilluminatedrequirementsandcorrespondingperformancefortheOCMDcapabilitythatcouldbefur-therdeveloped.Theyalsoenabledidentificationofsuchissuesasdeterminingtheappropriatelocationsoftheair-borneradarandshipaswellasthetimingofmissileinter-ceptstominimizeterrainblockage.
PROTOTYPING WITH INDUSTRIAL DESIGN AND MANUFACTURING AGENTS
ADSD’s role in systemdevelopmentgenerallygoesthroughatransitiontooneofsupporttoanindustrialagent in the detailed design, fabrication, and integra-tion phases. This support is often in the form of pro-totyping to determine the feasibility or to reduce the
risk of a critical component or unproven technology.For such prototyping ADSD generally provides tech-nical guidance to suppliers of the new technology orcomponents.PrototypinghasbeenakeyservicetotheNavy in risk management, feasibility demonstration,andmaturingnewtechnology.
ADSDalsosupportsthesystemdevelopmentphaseofdesignandfabricationbyourinvolvementindetaileddesign reviews and software walk-throughs. A designrequiresdefinitionofallaspectsofasystemorprototypeofsystemelementsdowntothecomponentlevel.Suffi-cientdocumentationandengineeringguidancemustbeavailabletofabricatesuchcomponentssothattheycanbeinterconnectedduringintegrationinafullyconsis-tentandmatchedmanner.ADSDhelpstoensurethatcontractors’designsmeetthesestandards.
An example of prototyping and component designistheCECDataDistributionSysteminthelate1980sinwhichanewtransmitterwasrequiredatafrequencyand waveform regime that did not exist in available(late1980s)components.Inpartnershipwiththeprimecontractor,E-Systems,St.Petersburg(nowRaytheon),ADSDdevelopedaprototypetransmittersubsystemwithspecialcontrolfeaturesandqualifiedatransmittertubevendorunderacompetitiveeffort.E-Systems’participa-tionduringtheAPL-ledprototyping,inturn,ledtotheirsuccessfully developing, in a short time, an improvedengineeringandmanufacturingmodelofthetransmitterthat fully met requirements. Somewhat later, APL ledthedevelopmentofsolid-statetransmit/receivemodulesforanairbornetransmitter/antennaconfiguration.
USING STIMULATORS FOR SYSTEM INTEGRATION
Just as a design involves decomposition of require-ments into allocated elements in a top-down fashion,assemblyandintegrationgenerallyinvolveabottom-upapproach to successively more complex build-up andtestofcomponentsintosubsystemsand,finally,thetotalsystem.1 When certain system elements are not readyfor integration, testing canproceedbyusing so-called“stimulators”intheirplace,whichreplicatetheinputsand outputs of themissing elements.Twoof thebestknownsuchstimulators,orelement-in-the-loopconfig-urations,aretheADSD-developedwraparoundsimula-tion programs (WASPs) for CEC and SSDS and theSMGuidanceSystemEvaluationLaboratory(GSEL).
TheWASPapproachwasoriginallydevelopedfortheTerrier/Tartar airdefense systemsas ameans toensurethat subsystemsbeingdeveloped separatelybydifferentorganizationswouldbetestedearlyviaWASPinterfacesto reduce the risk that the subsystems would not cor-rectly interface. The approach was recognized as nec-essary for CEC integration testing because the CECsubsystems are developed by different teams, and the
TheGSEL(Fig.10)allowsthemostcriticalelementofthemissile,theguidancesystem(includingtheseekersubsystems), to be tested in a simulated environmentthatincludesthethreattargetandtheguidanceinterfacetothecombatsystem.Thisguidancesystem-in-the-looptesthasprovencritical to successfulmissile integrationaswellastoreconstructionofunexpectedresultsoffull-scalemissilefiringtestsforanalysis.
Forexample,theGSELwasrecentlyinstrumentalinthesuccessofacriticalSM-3test.Confirmationofthetest objectives and configuration was followed by thediscoveryofasoftwareflawthatcouldhaveresultedintest failure. The GSEL allows an unprecedented leveloftestpreparationthoroughnesswhencoupledwiththevalidatedAPLmodelsandtheexpertiseofthestaff.
PERFORMING TEST AND EVALUATION ACTIVITIES
ADSD has been intensely involved in all forms oftest andevaluation(T&E), including scientificexper-iments, critical subsystem experiments, prototype ele-ment tests, Fleet data collections and exercises, inte-gration tests, test facility operations, flight tests, andfull-scalebattleforcetechnicalandoperationalevalua-tions.Thelegacyisacontinuousthreadextendingfromtheproximityfuzeeraandhasbeenmuchofthebasisforvaluablehands-onexperienceandunderstandingofFleetoperationsbytheADSDstaff.Thedesignoftestapproaches and the embedding of data collection andmeasurementpointsinasystemstartatthebeginningofthedevelopmentcycle,andtestexecutioncanspantheentirecycle,includingcriticalriskreductionexper-iments.T&Ebecomepredominant as an independentactivity (from the developers) toward the end of theintegration testing and throughout the formal system-leveltests.
• Protectingamajorsysteminvestmentbytestingearlyandprovidingtestpointsforextractionofmeasure-ment data that can be examined from the earlieststagesofintegration
• Gaining confidence and reducing risk of failure bycriticalprototypeanddatacollectiontests
Figure 10. The interior of the GSEL in Building 1. The seeker section of an SM round is mounted and integrated in an anechoic chamber so that the seeker receives simulated guidance commands from computers and specialized interface instruments and its sensor observes simulated microwave or infrared target signatures in the chamber. This hardware-in-the-loop approach has long been a key element in successful SM block upgrade developments.
cycleillustratedinFig.4.Thetestassetsrepresentingthethreat and operational environment must be specifiedto simulate the threat andenvironmentdefined in theoperationalrequirements.Thescenariosmustbeconsis-tent with the DRM in representing the expected useroperation and must provide for relevant performanceand effectiveness measures. The spectrum of test sce-narios must cover the required operational parametersand conditions. The design of scenarios, including testrangesafetyconstraints,generallyrequiresdetailedmod-elingandsimulationtoensurethattheexpectedresultsarevalidandthatthesafetymarginsaresufficient.Theassumptions and inputs to these models can provideinsightsintoinstrumentationandtestcontrolsaswellastheirlimitations.
Major testsmustbe thoroughlyorganizedandcon-trolled.EarlyinsystemdevelopmentsADSDoftenpar-ticipates inmanyof themain test roles, except thoseofgovernmentoversight.Testsuccessrequiresrigorandthoroughness. In theMountainTopACTDdescribedearlier,sinceanover-the-horizonengagementhadneverbeenattempted,anextensivedatacollectionandpre-testexperimentserieswasconductedoneveryelementofthesystem.Asmentioned,eventhemodifiedmissileseekerwasflownagainstthedronetarget,mountedonaLearjet,toensurethatsea-surfacereflectionshadbeenproperlymodeledandaccommodated in thedesignoftheSMrearreferencereceiver.Virtuallyeverymeansoftestingofeveryelementhadbeenexercisedandmod-eled,other than running the test itself.Theveryfirst
RF/IR flight environment IR target generator
RF guidance section RF/IR guidance section IR seeker
Thesystemdevelopmentcycleandassociatedactivi-ties described earlier are applicable at several stages inthelifeofasystem.Atypicalsystemdevelopmentpro-gramgoesthroughseveralphases.Duringtheconceptualphase,prototypingof someormostofa systemmayberequired to demonstrate feasibility and potential. ThatwasthecaseforCECasanewtypeofsystemforwhichtherewerenoprecedents.ThesystemdevelopmentcyclewasexercisedfortheCECprototype,albeitwithtailor-ingandabbreviationofsomeoftheactivities.
The next phase is generally the development of aversion of the system that, as a goal, meets the pre-scribedenvironmentalrequirementsandisdesignedtofacilitatemanufacturinginaproductionline.Thisver-sionoftenhassomelimitinfunctionality,forexample,toconstraincostsonlow-riskfeaturesatthisstageortodemonstratepartialcapabilitybeforeamorecompleteandsophisticatedversionofthecapabilityisattempted.Thisengineeringandmanufacturingdevelopmentpro-totype ismore extensively testedagainstboth techni-cal and operational requirements. In many programsit is determined that certain capabilities and perfor-mancearenotneededduringinitialoperationandthatanumberofpreplannedimprovementsshouldbeincor-poratedasabaselineupgradeprogram.Otherreasonsforabaselineupgradewouldbetoextendtheservicelifeofasystembyintroducingnewcharacteristicstokeeppacewithanevolvingthreat.Forexample,Aegishasunder-gonesixbaselineintroductionssinceitsInitialOpera-tional Capability in 1983, and SM-2 is introducing aBlock IV. Often the capabilities of later baselines arefaradvancedovertheinitialversion.Ineachbaselineupgrade, a portion of the basic development cycle isexercised.
ADSD has been involved in determining requiredcapabilitiesforbaselineupgradesofmostNavyairandmissile defense systems. SSDS is entering its secondblock,andCEC isenteringBaseline2.For somepro-grams,suchasSM,majorchangesintechnology,perfor-mance,andsystemfunctionsmaybemade,withlesserchangesforadaptationtospecificcombatsystems.Suchchangesareidentifiedbylettersaftertheblocknumbers,e.g.,IIIAandIIIB.ForsystemssuchasCEC,upgradestosoftwarealgorithmsorsubsystemcostreductions,suchasarrayredesigns,aregenerallyfeatured.
Technology refresh is a significant activity forsystemevolution.Forexample,commercialoff-the-shelf(COTS) processor cards are used in CEC. These are
replacedwithnewerversionsas thoseversionsreplaceolderformsonthecommercialmarket.APLhasplayedakeyroleindesigningthesystemtoreadilyaccommo-datenewCOTSproducts.Atransparent software ser-vice layer between the applications modules and theCOTS processor network was developed to facilitateCOTSrefresh.
InAPL’searlierversionsofCECandSSDSwepio-neered theuseofCOTS.We found that, in return forsupportingthecommercialvendorsintheirbetatestinganddebuggingofnewproductswhilewebenchmarkedthe capabilities of candidate products in parallel, thecommercial companies were willing to add features totheirproductsthatwouldbenefittheNavysystems(eventhoughtheNavyisasmallclientcomparedtothecom-mercialmarket).Thus,our involvement influencedthecommercialproduct.Morerecently,wehavepioneeredthe introduction of commercial, solid-state, microwavemoduletechnologyintotheCECphasedarrayantennasasacost-reductionmeasure.Wehavealsobegunacollab-orativeeffortwithRaytheonandtheNationalSecurityAgencytodevelopanti-tamperprotectionoftheCOTSprocessor and COTS-based software for CEC. APL isprototypingmodifiedCOTSprocessor components andprotectivesoftwareandsoftwareloadfeatures.ThesewillserveasadesignbasisforthenextRaytheonproductionversion.Theseactivitieshave,overtheyears, reliedonthetechnologyandmanufacturingbaseofAPL’sTechni-calServicesDepartment.
ADSD, with JWAD, has performed life-cycle costandreliabilityanalysesatthebeginningofnewsystemefforts or baseline upgrades. These are used not onlyas part of AoA concept selection but also to specifyreliability and life-cycle costs and, in some cases, todeterminedesignapproachesforrapidrepairorbackupchannels to maintain operations during battle. Theseanalyses are also sometimes the basis for determiningthenumberofsparesrequired.
FUTURE SYSTEMS ENGINEERING CHALLENGES
TheNavyhasestablishedauthoritativesystemsengi-neering activities to ensure proper system integrationof a battle force and all the missions of that force, ofwhichairandmissiledefenseisonlyone.Theprincipalagencies at present include NAVSEA SEA-053 andthe Office of the Assistant Secretary of the Navy forResearch, Development, and Acquisition Chief Engi-neer. We have determined that the fundamental sys-tems engineeringperspective, approach, and activitiesareeffectiveandevenmorenecessaryasairandmissiledefensesystemsbecomemoresophisticated.Webelieve,however,thatnewtoolsarerequiredtomakethesystems
Figure 11. Computer illustration of the new System Concept Development Laboratory featuring (a) an electronic library, (b) a “war room,” (c) a visualization laboratory, (d) a force modeling laboratory (with JWAD), and (e) a test participation facility. The laboratory com-plex is interconnected with other APL laboratories and, via satellite links, to Navy Fleet elements. It is also designed to interface with the merging distributed engineering plant networking being developed within the DoD.
engineeringpracticesmoreeffectiveforlarge-scalesystems.Thetrendisthat greater force automation canlead to greater interaction amongthecomputersandlinksofcombat-ants, and interoperability becomesat once more important and moredifficult to attain and maintain.ADSDhadanticipatedthisneedinthedesignofthenewBuilding26,whichhousestheSystemConceptDevelopmentLaboratory.
Thefollowingnewtoolsarebeingdeveloped for the described activ-ities and the features that enablethemintheSystemConceptDevel-opmentLaboratory(Fig.11):
• Automatedvisualizationoflarge-scale system diagrams for anentirebattleforcewithdatabaselinkages to associated require-ments, specifications, models,program offices, design agents,andsystemequipmentandcom-puterprograms
• The ability of this visualizationtoidentifyinconsistencies,gaps,andshortfalls
• Development of WASPs forremote,networkedtestingatthedevelopmentsitesandforlinkageto systems at different combatsystemsitestotestelements forcompatibilityandinteroperabil-ityattheearlieststagesofdevel-opmentandintegration
• Collaborative specification,de-sign, test, and simulation andexperimentationviaautomated,networkedlaboratories,facilities,andtestsites
CONCLUSIONWe see that the systems engi-
neering perspective and practicesare key to the past and futuresuccess and accomplishments ofADSD.Trendscallforanincreased
needforrigor,methodicalsteps,anenvironmentinwhichcriticalques-tions are welcomed, and a process that is open to inspection. Newtoolsarerequiredtoensurethatthegrowingnumbersofparametersandconditions can be considered and tracked. With the reduction in thenumberofexperiencedengineeringstaffinmilitaryindustriesandservices,the growth of system complexity, and a diminishing tolerance forfailure, the long-standing systems engineering tradition and culture ofADSDwillbeincreasinglyimportantinnext-generationairandmissiledefensesystems.
JERRYA.KRILLreceivedaPh.D. inelectricalengineering fromtheUniversityof Maryland in 1978. He joined APL in 1973 and is a member of the PrincipalProfessionalStaff.Hewas recentlyappointedHeadof thePowerProjectionSys-temsDepartment.Since1983hehasbeenaninstructorofphysicsandsystemsengi-neeringfortheJHUPart-TimeGraduatePrograms.Dr.Krillhaspublishednumer-ousarticlesinguidedwavetechnologyandelectromagneticscatteringandholdsanumberofU.S.patents.Duringthe1970sand1980sheledseveralsystemsengi-neeringeffortsandcriticalexperimentsassociatedwiththeAegisandBattleGroupAAW Coordination programs. He is one of the founders of the CEC concept,havingdevelopedandanalyzedmanyofitsrequirementssince1974.HeservedasLeadSystemEngineerforCECfrom1987through1996,includingthe1996Moun-tainTopACTD.HeispresentlyservingastheAPLpointofcontactfortheASN/RDAChiefEngineerTechnicalAdvisoryGroupandwasthetechnicalleadfortheConceptFormulationWorkingGroupfortheBMDO/NavyMissileDefenseCon-ceptDevelopmentStudy.Hise-mailaddressisjerry.krill@jhuapl.edu.
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