Thermal Margins For Flight Electronics Review And Assessment
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of TechnologyThermal Margins for Flight ElectronicsReview and AssessmentG. Siebes, C. Kingery, C. Farguson, M. White, M. Blakely, J. Nunes,A. Avila, K. Man, A. Hoffman, J. ForgraveJet Propulsion Laboratory, California Institute of Technology2012-08-161 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16 AgendaScope of the InvestigationJPL Thermal MarginsComparison of Thermal MarginsMargins by Domain– Qualification / Protoflight– Thermal Control System– Parts and Derating– Reliability Integrated Margin and Conservatism Observations and Assessment ConclusionsGeorg Siebes2 of 27
ScopeThe scope of this investigation is limited to Electronic assemblies (typically instruments orbus mounted) Hot operating conditionsTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes3 of 27
JPL Thermal MarginsTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of al Reliability Margin (AFT 20 C or 70 C,whichever is higher,per Design Principles)FA ThermalReliability Margin( 5 C per DesignPrinciples)Thermal Design Margin, 0Worst CaseHot / rat ureRangeAllowableFlightTemperatureRangeProtoflight /QualificationTemperatureRangeFA ThermalReliability Margin(-5 C per DesignPrinciples)Thermal Design Margin, 0Protoflight/QualificationThermal Reliability Margin (AFT - 15 C or –35 C,whichever is lower,per Design Principles)Design & AnalysisTestingGeorg Siebes4 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-1620C Qual/ProtoMargin(min 70C)AFThot5C FA MarginGSFC andTypical IndustryMarginThe AerospaceCorporation(1540) Margin10C Qual/ProtoMargin10C Qual/ProtoMargin5C FA Margin5C FA MarginFor a seriesof satellites(for one of)- protoqual- FAWorst CasePredictionAFTcoldComparing JPL Margins5C Uncertainty11C Uncertainty(for test correlatedmodels)Worst CasePredictionWorst CasePrediction5C Uncertainty11C Uncertainty(for test correlatedmodels)- FA5C FA Margin15C Qual/ProtoMargin(max -35C)5C FA Margin5C FA Margin10C Qual/ProtoMargin10C Qual/ProtoMargin- protoqualAFT Allowable Flight TemperatureGeorg Siebes5 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Qualhot20C Qual/ProtoMargin(min 70C)Comparing JPL Margins10C Qual/ProtoMargin10C Qual/ProtoMargin5C FA Margin5C FA Margin5C Uncertainty11C Uncertainty(for test correlatedmodels)Worst CasePredictionWorst CasePrediction5C FA Margin5C Uncertainty11C Uncertainty(for test correlatedmodels)15C Qual/ProtoMargin(max -35C)5C FA Margin5C FA Margin10C Qual/ProtoMargin10C Qual/ProtoMargin5C FA MarginWorst CasePredictionQualcoldGeorg Siebes6 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Comparing JPL Margins10C Qual/ProtoMargin20C Qual/ProtoMargin(min 70C)WChot5C FA Margin5C Uncertainty11C Uncertainty(for test correlatedmodels)Worst CasePredictionWorst CasePrediction5C FA Margin5C Uncertainty15C Qual/ProtoMargin(max -35C)5C FA Margin11C Uncertainty(for test correlatedmodels)5C FA MarginWorst CasePredictionWCcold10C Qual/ProtoMargin5C FA Margin10C Qual/ProtoMargin5C FA Margin10C Qual/ProtoMarginGeorg Siebes7 of 27
Qual/PF Margin RequirementBus electronics design temperature rangeBus electronics shall be designed to operate within specification over thetemperature range of -35 C to 70 C or AFT temperature limits extended by 15 C and 20 C, whichever is more severe.“line in the sand”TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes8 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Historic Background Historic background from early Ranger missions:– Upper limit of 50C based on max temperature of awhite painted surface at full sun exposure betweenearth and moon– Lower limit of 5C based on freezing temperature ofHydrazine– Anticipated planetary mission to Venus andpotential passage through earth’s shadow resultedin 25 margin -20C/75C, later changed to -20C/70CGeorg Siebes9 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Qualification The minimum electronics Qual/PF temperature limit of70 C promotes a robust and reliable hardware designthat will lead to successful missions. Designing to a 70 C Qual/PF temperature constrainsthermal rise from the assembly baseplate to theelectronic part junctions, resulting in lower in-flightjunction temperatures, than would otherwise resultfrom lower Qual/PF limits. It decouples the electronic assembly thermal designfrom flight system thermal design, allowing bothdisciplines to proceed with their designs in parallel withlittle chance for margin deterioration.Georg Siebes10 of 27
QualificationThermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology- Requirement as statedTFAWS 2012- AFT2012-08-16Georg Siebes11 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Thermal Control System The thermal control system is designed tomaintain the payload and the spacecraftsubsystems within their Allowable FlightTemperature [AFT] requirements– for all operating modes, in all thermal environmentsit may be exposed to, throughout the missionlifetime. JPL’s standard thermal engineering practiceprescribes worst case methodologies for design Uncertainty in absolute temperatures and,consequently, in margins is usually estimated bysensitivity analysesGeorg Siebes12 of 27
Qualification and Thermal ControlTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16- Requirement as stated- AFTΔT (design space)available to heat rejectionGeorg Siebes13 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Parts and Derating Derating prevents small changes in operatingcharacteristics from creating large increases in failurerates. Present derating policy is intended to reduce theoccurrence of stress related failures and help assure longterm reliability. JPL derating guidelines provide derating factors to beapplied as a percentage of maximum rated values forcritical device parameters The derating factor needed depends on the tolerance ofthe design to variation in operating parameters A key derating parameter for microcircuits and discretesemiconductors (diodes, transistors, optoelectronics) isjunction temperatureGeorg Siebes14 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Parts and Derating Historically, junction temperature (Tj) derating for siliconmicrocircuits in ceramic hermetic packages has been limitedto between 110 C and 115 C. The basis of this calculation can be described as follows:𝑀𝑇𝑇𝐹 𝑒MTTFEakT𝐸𝑎 𝑘𝑇 mean time to failure activation energy, a constant Boltzmann’s constant Temperature, [K] In order to achieve twice the lifetime, the junctiontemperature must be lowered such that the MTTF is twice thenominal values For a 125 C max rated Tj device, assuming an Ea 0.6 eV, thetypical 10-year MTTF can be extended by a safety margin oftwo by lowering the junction temperature by 15 C to 110 C.Georg Siebes15 of 27
Qualification, Thermal Controland PartsTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16- Typical Junction Limit- Requirement as stated- AFTΔT (design space)available to heat rejectionGeorg Siebes16 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Packaging Packaging designs are dominated by multilayercircuit board technology using mostly packaged andscreened electrical components. Thermal performance is dominated by heatconduction, with no convection and usually minorradiation transfer. The primary margin is in the protoflighttemperature used for analysis compared to theallowable flight temperature (AFT).– No other margin is intentionally added in the thermalanalysis process.– But there is likely to be some margin in the powerdissipations used for analysis.Georg Siebes17 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Qualification, Thermal Control,Parts and Packaging- Typical Junction Limit- Requirement as statedΔT (design space)available to packaging- AFTΔT (design space)available to heat rejectionGeorg Siebes18 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Reliability Temperature is one of many factors for key reliability designanalysis These temperatures are based upon Qual/Protoflighttemperatures at the thermal control surface (TCS). Electronic Parts Stress Analysis (EPSA)– Identifies highly stressed parts– Commonly, the EPSA is completed first using the assumption of a20 C rise from the thermal control surface (70 C ) to the part case Worst-Case Analysis (WCA)– Demonstrates margined performance under extreme conditions– Assumes a 10 C rise from the thermal control surface (70 C) to thepart case for the hot condition Temperature rise assumptions used in the EPSA and WCAmust be verified and reconciled with the Thermal Analysisonce the results are available.Georg Siebes19 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Qualification, Thermal Control,Parts, Packaging and Reliability- Typical Junction Limit- Requirement as statedΔT (design space)available to packaging- AFTΔT (design space)available to heat rejectionGeorg Siebes20 of 27
Integrated Margins The figure depicts an integrated picture of JPL’s margin. Thecomplexity of the approach becomes readily apparent.TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes21 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of TechnologyConservatism In addition to margins, domains apply conservatism. Tothe degree that actual flight temperatures are lower thanpredictions because of this conservatism, actual junctiontemperatures are lowered by the same amount. Thedegree of applied conservatism is experience-based andcan be fine-tuned if resources onReliabilityThermal SubsystemMarginDerating/Screeningworst case powerworst case material propertiesworst case operating conditionsworst case voltage/currentworst case powerworst case material propertiesworst case operating conditionsworst case environmentworst case attitude70 C heat sink boundaryAFT 20 C70 C heat sink boundaryworst case configuration2012-08-16Georg Siebes22 of 27
Thermal Margin AssessmentObservations Existing margin requirementsTFAWS 2012National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology The relevant margin elements are2012-08-16– Are applied in a one size fits all fashion– Are agnostic to mission class Over time, responsibility for elements of the overallthermal design has been segregated into differentdisciplines and organizations– Reliability (Line In The Sand, aka LITS)– Qualification (AFT 20 C)– Derating (of allowable junction temperatures)Georg Siebes23 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Assessment Segregation facilitates concurrent design butdoes not consider uncertainties, risk andmargin in a holistic way The introduction of a considerable number ofnew parts to the design, which were not in usewhen margin requirements were originallyestablished, complicates the situation. Higher packaging density and resulting heatconcentration make it increasingly difficult tokeep the chassis to junction temperature risewithin the currently required 40 C.Georg Siebes24 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Assessment Benefits of a JPL margin reduction– vendor hardware qualification will be in family– compatibility with the margin approach of theGoddard Space Flight Center (GSFC) is established– the inherent risk posture of different mission classesis acknowledged– the thermal “headroom” for parts packaging isincreased– the number of waivers will be reducedGeorg Siebes25 of 27
Assessment Downside of reduced qualification and reliabilitymargins– design or hardware heritage for future use is limited– inflight anomalies need to be met with lower margins– junction temperatures can potentially increaseTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes26 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Conclusions This study has reinforced that robust margins areinherently tied to JPL’s mission success. It also has become apparent that today’s diversityof missions will benefit from a more flexibleapproach to defining margin requirements thanthe currently practiced one size fits all approach. The complexity of determining the marginapproach over the spectrum of applicablescenarios has so far prevented our institution fromconverging on a specific set of recommendation. This work provides a point of departure for futurediscussion that is soundly based on pastexperience and a renewed understanding of theintent and merits of our margin.Georg Siebes27 of 27
Thank you for your attention.Any questions?TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes28 of 27
Backup ChartsAppendixTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes29 of 27
NASA NPR 8705.4TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16CharacterizationClass AClass BClass CClass DPriority (Criticality toAgency Strategic Plan) andAcceptable Risk LevelHigh priority, very low(minimized) riskHigh priority, low riskMedium priority, mediumriskLow priority, high riskNational significanceVery highHighMediumLow to mediumComplexityVery high to highHigh to mediumMedium to lowMedium to lowMission Lifetime (PrimaryBaseline MissionLong, 5yearsMedium, 2-5 yearsShort, 2 yearsShort 2 yearsCostLaunch ConstraintsHighCriticalHigh to mediumMediumMedium to lowFewLowFew to noneIn-Flight MaintenanceN/ANot feasible or difficultMaybe feasibleMay be feasible and plannedAlternative ResearchOpportunities or Re-flightOpportunitiesNo alternative or re-flightopportunitiesFew or no alternative or reflight opportunitiesSome or few alternative orre-flight opportunitiesSignificant alternative or reflight opportunitiesAchievement of MissionSuccess CriteriaAll practical measures aretaken to achieve minimumrisk to mission success. Thehighest assurance standardsare used.Stringent assurancestandards with only minorcompromises in applicationto maintain a low risk tomission success.Medium risk of notachieving mission successmay be acceptable. Reducedassurance standards arepermitted.Medium or significant risk ofnot achieving missionsuccess is permitted.Minimal assurancestandards are permitted.ExamplesHST, Cassini, JIMO, JWSTMER, MRO, Discoverypayloads, ISS Facility ClassPayloads, Attached ISSpayloadsESSP, Explorer Payloads,SPARTAN, GAS Can,MIDEX, ISS complex subrack technology demonstrators,payloadssimple ISS, express middeckand subrack payloads, SMEXGeorg Siebes30 of 27
TFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Class D(DOD-HDBK-343 (USAF))Minimum Acquisition Cost.Class D is defined as a higher-risk, minimum-costeffort. The characteristics for Class D usuallyinvolve some combination of the followingfeatures: medium to low national prestige, shortlife. Low complexity, small size, single stringdesigns, simple interfaces. hard failure modes, noflight spares, lowest cost, short schedule, and anoncritical launch schedule. Vehicle andexperiment retrievability or in-orbit maintenancemay or may not be possible.Georg Siebes31 of 27
Projects in the Context of RequirementsTFAWS 2012Thermal Margin AssessmentNational Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology2012-08-16Georg Siebes32 of 27
Bus electronics design temperature range . It decouples the electronic assembly thermal design from flight system thermal design, allowing both . Qualification, Thermal Control, Parts, Packaging and Reliability -08 16 Georg Siebes - AFT - Requirement as stated
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VaR Margins: Value at risk margins to cover potential losses for 99.9% of the days. c. Extreme Loss Margins: Margins to cover the expected loss in situations that lie outside the coverage of the VaR margins. d. Base Minimum Capital: Capital required for all risks other than market risk (for example, operational risk and client claims).
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