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Managing Electrical Connections Systems and Wire Integrity on Legacy Aerospace Vehicles

Presented by:Presented by:Luci Crittenden, ATSRAC MemberLuci Crittenden, ATSRAC MemberNASA Langley Research CenterNASA Langley Research Center

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Managing Electrical Connections Systems and Wire Integrity on Legacy Aerospace Vehicles

Steven SullivanSteven SullivanKennedy Space CenterKennedy Space Center

NASANASAand and

George SlenskiGeorge SlenskiMaterials DirectorateMaterials Directorate

Air Force Research LaboratoryAir Force Research Laboratory

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Outline

! Introduction

! Aging Wiring Issues

! Shuttle Wiring Failure

! Shuttle Wiring Inspections

! Conclusions

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Aging WiringWiring is just one part of the electrical Interconnection system

– Wiring, connectors, relays, circuit breakers, powerdistribution panels, and generators makeup the system

Aging wiring can be understood as degraded performancedue to accumulated damage from long-term exposure.

– Damage is from chemical, thermal, electrical, andmechanical stresses

– Stresses are often induced by the operationalenvironment and installation and maintenance practices

– Wiring failures often appear as broken conductors anddamaged insulation which can disrupt electrical signalsand/or lead to arcing.

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Wiring System FailuresWiring System Failures

In-Flight Electrical FireIn-Flight Electrical Fire InitiationInitiation

Site Site

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Chafed Wire Failure

Phase A

Phase B

Phase C

Failure Initiated by DegradedBearings and Wire Chafing

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Wiring Failure MechanismsWiring Failure Mechanisms

ElectricalElectrical MechanicalMechanical

ChemicalChemicalThermalThermal

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Arc Tracking Wire Failures

Field FailureField Failure

Dry Arc TrackingDry Arc Tracking

PolyimidePolyimide Insulation Insulation(Mil-W-81381)(Mil-W-81381)

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Aging Aircraft Wiring Systems

Wiring Failure Data for a Typical Fighter–46% Broken Wires–30 % Insulation Chafing Damage–14% Outer Layer Chafing–10% Failure in Contractor Connector

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Function

interconnections 43%

electronics 23%

electromechanical 34%

System

instruments 26%

power systems 45%

avionics 9%

total electrical failure-system

unknown 1%

fuel systems 8%

flight control 11%

Age Groups of Mishap Aircraft

0

10

20

30

40

50

60

70

2 to 5 6 to 10 11 to 15 16 to 20 21 to 25 26 to 30 31 to 35 36 to 53

AF Mishap Data For Electronic RelatedFailures

(1989-99)

Data provided by the AF Safety Agency

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AF Mishap Data Related to ElectronicFailures (1989-99)

Components Contributing to AF Mishaps

conductors 29%

light 0%

generator 18%

batteries 1%

capacitors 1%

circuit breakers 2%

avionics 7%

electric panel 8%

fuel probe 1%

relays 7%

motors 2%

resistors 1%

switch 3%

transformers 6%

connectors 14%

Data provided by the AF Safety Agency

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PROCESS ENGINEERING

OV102 Launch STS-93

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PROCESS ENGINEERING

OV102 Electrical Short- Midbody

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OV102 Electrical ShortPROCESS ENGINEERING

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PROCESS ENGINEERING

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Closeup of Burred ScrewPROCESS ENGINEERING

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Electron Microscope Picture of FaultPROCESS ENGINEERING

No evidence of vibrationinduced damage

(3 Independent Labs andAFRL Mal Lab)

Damage was caused bysignificant impact to cable

Oxide growth revealed thatdamaged wire had flownseveral times

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What To Inspect?? “A learning process”

Orbiter Wire Inspection Decision Logic

Inspect &Repair

Cleared For FlightPerform Inspection

of Areas DuringOMM to Confirm

Validity ofAssumptions

Redefine InspectionCriteria &Corrective

Action

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HighTrafficArea?

ModWork

?

YES

NO

PRACAHistory?

Redun’Together or

Crit 1/1?

Vulnerable?

NO

InspectionRisk/BenefitAcceptable

?

YES

YES

YES

YES

YES

New RootCause

Identified?

NO

NO

YES

Document Rationale

PROCESS ENGINEERING

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Analysis of W

iring Dam

age History

PRA

CA

SUM

MA

RY (FW

D/M

ID/A

FT)

0

100

200

300

400

500

600

700

Thrust Str (Side Wall/LH2/LO2 Umb/Floor)

Avionics Bay (FWD)

Avionics Bay (AFT)

Below Wire Tray (MID)

VESS

Flight Deck

APU Area

ECLSS

1307 Bulkhead

Mid Deck

Wire Tray

Body Flap

FRCS

SILL/MPM

WING/ELEVON

LNDG GR

Lwr Heat Shield

576 Bulkhead

Mission Station/Pld

ODS/AIRLOCK

Vert Stab

On-Orbit Station

Location

Wire Damage (# of wire)

Series1

Areas Inspected

PRO

CESS EN

GIN

EERIN

G

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PROCESS ENGINEERING

Wire Harness Inspection

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PROCESS ENGINEERING

Wire Harness Inspection

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Orbiter Midbody Wire Harness InspectionPROCESS ENGINEERING

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PROCESS ENGINEERING

Wire Harness Inspection

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PROCESS ENGINEERING

1500 VDC DWV Testing

HOW GOOD IS A DWV TEST (HIPOT)????

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Types of DamagePROCESS ENGINEERING

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Convoluted TubingPROCESS ENGINEERING

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PROCESS ENGINEERING

Glass Cockpit Modifications – MEDS

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PROCESS ENGINEERING

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When you think you have seen everything??PROCESS ENGINEERING

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Wire Harness Separation ModificationPROCESS ENGINEERING

View inside a “closedwire tray”

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Orbiter/ External Tank Electrical Monoball ProductionBreak

PROCESS ENGINEERING

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PROCESS ENGINEERING

“Inspect & Protect” Awareness Campaign

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PROCESS ENGINEERING

Repetitive Dielectric Withstanding Voltage (DWV) Study(Planned)

• Effects of Repetitive DWV

Larry Ludwig – NASA KSC Mal Lab (321)-867-7049

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Solid Rocket Booster Cabling

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Wire Damage MappingPROCESS ENGINEERING

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Wire Damage Mapping - MidbodyPROCESS ENGINEERING

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Transmitter/

Receiver(3 ea)

Xo = 941.6Yo = -86.4Zo = 347.8

PlasticPick-up

Location Aid

Display

Wire Damage Mapping – x y z coordinate locator(Study Phase)

PROCESS ENGINEERING

*Note: Latest concept does not use transmitters

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PROCESS ENGINEERING

LASER 3-D ScanningStudy Phase

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PROCESS ENGINEERING

LASER 3-D Scanning Study Phase

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Standing Wave Reflectometry

PROCESS ENGINEERING

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Summary:

•Scheduled wire inspections at major modification (Performed by twoindependent inspectors NASA quality and USA quality)

•Inspector and technician training and certification on wire damage assessment

•“Hands on Trainer” developed and class

•Wiring specifications tightened and clarified for assessing cable damage

•Maintenance requirements added that when cable clamps removed technicianand quality will fan wire harness out for inspection

•Platforms and area protection on work platforms

•Convoluted tubing installed in “high traffic” areas (>150lbs per orbiter)

•Aging polyamide wire study with Boeing and Lectromec (800 page report)

•Orbiter wire separation study to assess any areas that there may have been aviolation of critical circuits routed together

SummaryPROCESS ENGINEERING