**Wiring Integrity Technology Assessment**

Prepared by:

Jim Blanche, Marshall Space Flight Center/Allied Aerospace

Mark Strickland, NASA/Marshall Space Flight Center

December 2004

**[Introduction]{.underline}**

As the National Vision for Space Exploration focuses on extended
missions to the Moon, Mars and beyond, and as the Shuttle fleet
continues to age, the importance of wiring integrity and the effects of
age on wiring takes on growing importance to NASA. The military and
aircraft industry have been working on aging aircraft wiring integrity
even before the TWA Flight 800 disaster in July of 1996. NASA's Kennedy
Space Center and Johnson Space Center have been involved because of the
Space Shuttle Orbiter, and Langley Research Center and Ames Research
Center because of their aeronautics involvement. "All wiring systems are
subject to aging during their normal service life. Aging results in the
progressive deterioration of physical properties and performance of
wiring systems with the passage of time. This process can be greatly
accelerated by frequent handling or maintenance actions on or near the
wiring systems." \[1\] Obviously wiring problems are a concern because
they can result in opens or shorts, premature failures of a system,
degradation of system function, or increased sensitivity to
electromagnetic fields. Any wiring problem has the potential of being a
safety concern for aircraft or spacecraft.

A wiring problem occurred during the STS-93 mission resulting in the
commissioning of the Space Shuttle Independent Assessment Team. One of
the recommendations by that team led to the creation of a wiring
integrity research (WIRe) pilot study by NASA's Ames Research Center.
During the study the team concluded that Shuttle Orbiter test methods
being used were effective in detecting and locating wiring opens and
shorts, but there was no reliable technology for detecting wiring
defects before they became faults. Current inspections techniques for
wiring defects were not totally effective and were labor intensive.
Techniques such as Time Domain Reflectometry (TDR) and Standing Wave
Reflectometry (SWR) are capable of detecting some wiring defects but
need improvement in sensitivity and automation for field use. All test
techniques increase the risk of collateral damage, require access to
test points at connectors, impact schedules, and necessitate functional
retest after reconnections are made.

In the study report issued in August, 2000, the team presented several
conclusions and recommendations \[2\].

1\. NASA should establish an integrated agency-wide program to address
advanced techniques for ensuring the integrity of electrical systems in
the Space Shuttle Program.

2\. NASA should pursue development of automated integrity testing
technologies.

a\. Develop Integrity Testing Technologies

b\. Develop Automated Signal Processing Techniques

3\. NASA should pursue development of an integrated test management
system for the Orbiter

4\. NASA should conduct an in-depth cost-benefit analysis on test
technologies and test management software development and application
strategies in order to optimize the return on investment.

Discussions had taken place between the Orbiter operators at KSC and JSC
and the research scientists at ARC and LaRC to bring together the
technical needs and the research areas. This led to a proposal to
establish a NASA Wiring Working Group. NASA Headquarters recommended
approval of this NWWG in October of 2002 .Its purpose was, ".. to
provide a forum for Agency wide cooperation to improve the effectiveness
of communication and coordination in the NASA community, promote
technical integration between NASA and other agencies, improve customer
interfaces, and optimize the use of resources. The Working Group will
provide an integrated strategy to advise Agency in areas of evaluation,
inspection, testing, training, wire repair technology and future wiring
development." \[3\].

The functions of the NWWG were to be to:

-   Provide for Agency wide focus and a forum for the integration of the
    wiring needs. The Working Group shall address the total Agency wide
    programs, including definitions and standard practices,
    documentation requirements, operating practices, and new technology
    initiatives.

-   Promote improvements in communication and cooperation throughout the
    NASA community by sponsoring meetings, workshops, and other
    technical interchanges. Facilitate rapid Agency wide information
    exchanges through the use of newsletters, electronic information,
    and directory. Encourage intercenter and intracenter cooperative
    programs coupled with external organizations and technical societies
    through Memoranda of Understanding.

-   Promote productivity and efficiency through sharing experiences,
    procedures, techniques, resources, and efforts directed towards
    technology implementation.

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-   Foster partnerships between Program Offices, Engineering, Safety,
    Quality Assurance, and the NASA Community.

-   Provide an Agency wide forum for the sharing of wiring technology
    including technology transfer within NASA and to other government
    agencies. Provide an interface with U.S. universities and industry,
    and the international wiring community.

-   Champion the belief that accurate and reliable measurements are
    fundamental to the advancement of NASA's scientific and engineering
    programs

The NWWG membership initially identified representatives from NASA HQ,
ARC, JPL, JSC, KSC and LaRC, with representatives from all Centers to be
identified.

In December, 2003, a presentation was made to the ST Wiring Group at
Kennedy Space Center recommending establishment of a NASA Wiring Working
Group. The proposed charter was as follows:

-   \"The NASA-Wide Wire Group is established as a Subcommittee under
    the Agency Engineering Management Council under the authority of
    NASA HQ Chief Engineer's Office.

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-   The NASA-Wide Wire Group is established to provide a forum for
    Agency wide cooperation to improve the effectiveness of
    communication and coordination in the NASA community, promote
    technical integration between NASA and other agencies, improve
    customer interfaces, develop or adopt NASA preferred Standards or
    specifications and optimize the use of resources.

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-   The Wire Group will provide an integrated strategy to provide
    direction (through the Chief Engineer) and assistance to the Agency
    in the areas of requirements, evaluation, inspection, testing,
    training, wire repair technology and future wiring development.\"

Apparently no NASA-wide Wiring Working Group has ever been officially
chartered; however, NASA is identified as an adjunct member of the Joint
Council on Aging Aircraft, and there are individuals at the NASA Centers
working wiring integrity either individually or loosely connected. The
8^th^ Joint NASA/FAA/DoD Conference on Aging Aircraft in early 2005 is
being hosted by NASA (Dr. Richard Young, LaRC).

To define the concern by the military about aging effects on wiring, the
Air Force Research Laboratory has compiled some significant statistics
on its effects. A study of Air Force aircraft accidents/mishaps over the
last ten years showed that 43% were related to the wiring
interconnection system. These include numerous types of connector
failures, wiring faults, and circuit breaker failures. The Navy spends
1.8 million man-hours per year troubleshooting and repairing aircraft
wiring systems. Approximately 1077 mission aborts and 147,674
non-mission-capable hours per year are lost due to wiring incidents.
In-flight fires related to wiring failures occur at the rate of
approximately two per month \[4\].

The wiring failure data for a typical fighter shows that 46% were broken
wires, 30 % were insulation chafing damage, 14% were outer layer
chafing, and 10% were failure in the connector \[5\].

On the Space Shuttle program, during the 2003 stand down, orbiters
Discovery, Atlantis and Endeavor had 5632 problem reports written on
wiring. Exposed conductors made up 1091 of these reports and damaged
conductors made up the other 4541 \[6\].

The research for wiring integrity has been across five broad technology
areas: failure characterization, diagnostics, new materials,
interconnection technologies, and maintenance tools. There is work going
on for identification of wiring system failure mechanisms and
degradation processes, and aging models for wiring systems. New field
diagnostic tools and high assurance repair technologies are being
developed. Smart connectors and wiring for identifying electrical faults
and health monitoring systems for wiring, motors and actuators are being
investigated. Work is being done on wiring systems that are tolerant to
their environment and to maintenance. Materials research is being
conducted for robust insulators and conductors.

**[Diagnostic Tools]{.underline}**

Several techniques now used or under development to detect wiring
problems involve reflectometry. Common to all these methods is the
sending of a signal (a pulse, sine wave, or the like) down the wire and
sensing the reflection that returns from the wire\'s end. They are most
useful for detecting so-called hard errors, such as short circuits, but
have not proven as useful for less obvious wire problems.

Time domain reflectometry (TDR) is customarily used when a wiring
problem is already suspected. A short, typically rectangular pulse is
sent down the cable, and the cable impedance, termination, and length
give a unique temporal signature to the reflected signal. A trained
technician then interprets the signature to determine the health of the
cable. Such signal interpretation is particularly necessary for aircraft
systems, where wires branch into complicated network structures and
connect to active avionics.

Standing-wave reflectometry (SWR) involves sending a sinusoidal waveform
down the wire. A reflected sinusoid is returned from the wire\'s end,
and the two signals add to a standing wave on the line. The peaks and
nulls of this standing wave give information on the length and
terminating load of the cable; a healthy line\'s wave pattern will be
distinct from that of a line with an open or short circuit. The edge
this method has over TDR is that the electronics are simpler and
therefore less expensive.

Like SWR, frequency domain reflectometry (FDR) uses sine waves. FDR,
though, directly measures the phase difference between the incident and
reflected waves; any faults in the line will generate resonances between
the two signals. This method is being developed for *in situ* wire
testing by researchers at Utah State University with support from
Management Sciences Inc., Albuquerque, N.M., and the Naval Air Systems
Command. The goal is to allow preflight testing of cables with the touch
of a button, and without the risk of damaging the cables by
disconnecting them \[7\].

Spread Spectrum Reflectometry (SSR) is an energized wire-monitoring
enabling technology which uses a transmitted signal that has been
modulated (and spread in spectrum) via a pseudo noise digital code
(sequence) and is subsequently reconstructed by cross-correlating the
received signal with the original modulation sequence. It monitors
energized wires for faults due to wire (conductor) impedance changes
between samples, and is capable of detecting both hard (opens and
shorts) and soft (intermittent opens and shorts) fault detection and the
location on energized wires.

Another approach being investigated is Broadband Impedance Monitoring.

Broadband impedance spectra are sensitive to the physical and chemical
state of the wire's insulation and metal and to the location of any
changes in the wire's chemical and physical state. As a result,
broadband impedance monitoring has the potential to be used for
diagnostic/prognostic of electrical wiring.

**[Repair Technologies]{.underline}**

Within the overall aircraft/spacecraft wiring integrity program the
subject of repair tools and repair training has a high priority. This is
of less concern to NASA than it is to military, commercial and general
aviation. The primary reason is that there are 20K aircraft in military
aviation, 10K aircraft in commercial aviation and 240+K aircraft in
general aviation, while there are only three Space Shuttles. While there
are obviously a multitude of people working the aircraft repair at
worldwide repair sites only a few people provide repair to STS wiring
and they are certified, work to a step-by-step procedure for each
repair, and are monitored by the quality organization through the repair
operation.

A study was conducted to determine if wiring repair technology used in
Commercial and General Aviation offered any advantages to the military
repair procedures presently used \[8\]. The study indicated that there
was no notable difference between military and commercial aviation
wiring maintenance and repair techniques. The diversity of general
aviation made it difficult to evaluate. There is a Special Federal
Aviation Regulation, SFAR 88, which requires new fuel systems/fuel
quantity indicating systems wire/bundle installations and those
resulting from modifications to be contained to protect them from old
wires. The approved containment material is reinforced Kevlar. The
military felt this standard needed to be investigated closer. They also
felt that the FAA AC 120-YY wiring systems training program might be of
benefit to their training efforts.

**[Identification of Failure Mechanisms and Degradation
Processes]{.underline}**

Wiring anomalies can be considered as coming from four general sources
\[9\]:

[Contamination]{.underline} which includes things that degrade wire
insulation over time with prolonged contact, such as metal shavings from
repair that work their way into a wire bundle, or exposure to fluids
with Ph levels that change the physical properties of the insulation,
such as washing solutions or hydraulic fluids.

[Physical abuse]{.underline} which includes all physical experiences
that can cause breaking of the conductor or breaching the insulation.
Examples of physical abuse are stepping on the wire bundle, improperly
restraining a wire bundle with a tie-down, or a dynamic environment that
causes wires to flex or rub against other objects. Repeated hands-on
physical inspection of a wire harness inside a box can be a form of
physical abuse.

[Aging]{.underline} refers to changes in the physical and chemical
properties of insulation and conductors with time. Changes in
flexibility, hardness, tensile strength, compressive strength, and
torsion strength can result in insulation cracking and even separation
from the conductor. These changes are slow compared to the other
mechanisms and the appearance of the resulting flaws can be subtle.

[Environmental]{.underline} effects that include temperature, humidity,
vacuum and solar exposure have an effect on wire insulation. Wire ages
at different rates under different environmental conditions.

**[Materials Research]{.underline}**

Work is being done to develop better and more robust wire and
insulation. Kennedy Space Center has been actively pursuing a project
for the development of a self-healing wire insulation. They issued a
2004 NASA small business innovative research (SBIR) solicitation for
self-heal repair technologies. An example of self-healing is the repair
of a wire insulation which uses the stress induced by a microfissure to
rupture microcapsules of repair materials within the insulation. A
monomer is released along with a catalyst. The monomer is polymerized by
the catalyst and the microfissure is filled. They are also exploring a
fusible polymer that uses a chemical heater to bond an insulation splice
to existing insulation, and two monomers that form a polymer that heals
an insulation crack.

Momentary short-circuit arcs between a defective polyimide insulated
wire and another conductor may thermally char (pyrolize) the insulating
material. The charred polyimide, being conductive, is capable of
sustaining the short-circuit arc. The sustained arc may propagate along
the wire through continuous pyrolization of the polyimide insulation
(arc tracking). If the arcing wire is part of a multiple wire bundle,
the polyimide insulation of other wires within the bundle may become
thermally charred and start to arc track (flash over). Therefore, arc
tracking may lead to complete failure of an entire wire bundle or
harness. Arc tracking tests conducted by the Electro-Physics Branch,
Power and On-Board Propulsion Technology Division at the NASA Glenn
Research Center have been performed to evaluate candidate wire
insulation\'s susceptibility to arc tracking. A unique test procedure
has been designed to aid in the selection of a candidate insulation type
least susceptible to arc tracking. Tests have conducted in the following
three environments:

Air at atmospheric pressure and 1 gravitational (g) force.

Vacuum (2.67E-3 Pa) and 1g.

Air at atmospheric pressure and microgravity (\< 0.04g).

**[Smart Connectors and Wiring]{.underline}**

Significant work is going on in the area of smart connectors and smart
wiring systems that can become an integral part of the aircraft or
spacecraft wiring to continuously monitor and locate wiring faults and
wiring defects. The University of Utah Center of Excellence for Smart
Sensors, with support from the National Science Foundation, has
developed a smart connector which is a computer sensor and electrodes
that combine to form an automated testing system that eventually will be
embedded inside aircraft wiring systems. They predict that handheld
testers for the system will be commercially available in 2005, with a
fully embedded version ready within a year or two after that. A
commercially viable smart connector will have to be light and
inexpensive since a commercial jet will contain 800 to 1500 of them.

Aegis Devices Inc. Smart Wire System is a non-destructive *in situ*
inspection technology for aircraft wire integrity \[10\]. The Smart Wire
System is directed at inspection of installed wire harnesses where
disconnection of wire harness for inspection is unnecessary. This system
can be used for a final test of a reconnected wire harness, for systems
where disconnection of wire harness would require additional testing, or
for real time monitoring of an operational system. The Smart Wire System
consists of uniquely identifiable electronic modules that monitor the
signals within aircraft wiring without the need for disconnection. The
Smart Wire System monitors and learns the wiring signal information,
summarizes the results, and provides secure access to store the raw and
processed signal data to a database. Use of the system enables
real-time, non-destructive inspection of wiring integrity. It may be
used for ground based diagnostic purposes or installed permanently in an
existing aircraft to monitor for faulty wiring. The database keeps track
of signal status and wiring history. The data can be used to schedule
maintenance and repair of wire harnesses and to provide users with the
ability to perform statistical analysis of aircraft wiring.

Management Sciences, Inc. has developed a smart wiring system that uses
a microelectronic module with integral software signal processing and
sensors for the determination of wiring signal and integrity. The module
can be housed inside a wiring integration unit or junction box added to
conventional wiring. For smart connectors the module is connected to
specially modified connectors in the vicinity of a bulkhead mounted
unit. Sensing signals are issued to inspect the wiring. Digitizers are
used to monitor signals. Digital signal processing is used to locate
short, open, or frayed conditions \[11\]. The U.S. Navy has awarded MSI
a contract for testing and production of their smart wiring systems. The
first phase will be to build pre-production units. After the Navy has
tested these units in a pre-flight simulator, the next phase will be
in-air testing. The final phase, providing the tests are successful,
will be for production.

Boeing Phantom Works has developed a programmable solid state circuit
breaker/switch with arc detection and damaged wire detection/locator
module. It is intended for continuous monitoring and employs spread
spectrum reflectometry.

**[Aging Models for Wiring]{.underline}**

There have been three tasks underway by the Wire Integrity Research
(WIRe) program out of NASA's Ames Research Center that address modeling.
A hybrid reflectometry effort to develop computer models of wire and
defect responses to TDR, FDR, and SWR to tune stimuli to distinguish
defects from wire features, to automate analysis, and to partner with
industry to produce wire defect prognostic/diagnostic testers. This
effort was scheduled to run from FY02 to FY05. A second task scheduled
from FY02 to mid-FY04 is to investigate the use of quantitative
assessment techniques for optimizing Orbiter wiring maintenance
procedures. The third task is to develop Shuttle Orbiter wire test
management software. Its goal is to provide computer assisted schedule
and prioritization of wire inspection and test, and to automate trend
analysis and corrective action disposition \[12\].

The FAA also commissioned a multi-year study in 2002 to develop aircraft
electrical wiring interconnect system (EWIS) risk assessment tools. The
ultimate goal is an easy to use software application to facilitate
compliance with federal aviation regulations. These tools are being
developed by Lectromec Design Co.\[13\].

**[Recommendations]{.underline}**

It is recommended that a NASA Wiring Working Group be formally
established. The group should have representatives from each of the
Field Centers and probably be chaired by Headquarters. Most Centers are
working various wire integrity tasks and are sometimes communicating
with each other, but it is an informal thing and may or may not happen.
A formal working group would meet on some scheduled basis and through
this medium the efforts would not be duplicated and there would be a
synergism among tasks. The functions should be as was recommended in
Reference \[3\]:

The functions of the NWWG should be to:

-   Provide for Agency wide focus and a forum for the integration of the
    wiring needs. The Working Group shall address the total Agency wide
    programs, including definitions and standard practices,
    documentation requirements, operating practices, and new technology
    initiatives.

-   Promote improvements in communication and cooperation throughout the
    NASA community by sponsoring meetings, workshops, and other
    technical interchanges. Facilitate rapid Agency wide information
    exchanges through the use of newsletters, electronic information,
    and directory. Encourage intercenter and intracenter cooperative
    programs coupled with external organizations and technical societies
    through Memoranda of Understanding.

-   Promote productivity and efficiency through sharing experiences,
    procedures, techniques, resources, and efforts directed towards
    technology implementation.

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-   Foster partnerships between Program Offices, Engineering, Safety,
    Quality Assurance, and the NASA Community.

-   Provide an Agency wide forum for the sharing of wiring technology
    including technology transfer within NASA and to other government
    agencies. Provide an interface with U.S. universities and industry,
    and the international wiring community.

-   Champion the belief that accurate and reliable measurements are
    fundamental to the advancement of NASA's scientific and engineering
    programs

Since two of the four identified failure mechanisms and degradation
processes for aircraft and spacecraft wiring are "people induced"
another recommendation is to develop more intensive training programs to
minimize the effects of contamination and physical abuse. Its goal would
be to develop an awareness program for areas where harnesses are being
worked on and inspected to assure the wiring is properly installed,
cleaned, vacuumed, physically protected and accessible using scaffolds
or other GSE fixtures. It should also be directed toward technicians and
operators who work in wiring areas but not on the wiring to make then
aware of the potential effects of careless or thoughtless actions on the
vehicle, mission and crew.

NASA should support the development of smart connectors and wires, and
lightweight robust non-arc tracking insulations.

Future space exploration vehicles are going to have to survive in
harsher combined environmental conditions than NASA has ever dealt
with.  It would be worthwhile to devote some effort on research to
determine if there a better medium than insulated copper to transmit
data, commands and power that would not be susceptible to handling,
aging and environment.

**[References:]{.underline}**

\[1\] Aircraft Wiring System Integrity Initiatives -- A Government and
Industry Partnership, Joseph Slenski and Joseph Kuzniar, U.S. Air Force
Research Laboratory, presented at the 6^th^ Joint FAA/DoD/NASA
Conference on Aging Aircraft, San Francisco, CA, September 16, 2002

\[2\] Ames Research Center, Wiring Integrity Research (WIRe) Pilot
Study, Design for Safety Initiative, Document Number A0SP-0001-XB1,
August 25, 2000

\[3\] Presentation by Douglas Whitehead, NASA HQ, Code M-3, NASA Wiring
Working Group, October, 2002

\[4\] Embedded Wiring Condition Assessment Research, John H. Barnes, Air
Force Research Lab, 2^nd^ Information Exchange/Workshop, AFRL Wiring
Integrity System Characterization and Evaluation Program, 4-5 March 2003

\[5\] Aircraft Wiring System Integrity Initiatives, George Slenski,
Materials Directorate, Air Force Research Laboratory, WPAFB. OH

\[6\] IntelliWire -- Revolutionary Solution to Wiring Problems, Malcolm
J. Phillips, Boeing NASA Systems, FSSO, KSC, 12/16/03

\[7\] Down to the Wire, Cynthia Furse & Randy Haupt, Utah State
University,

Cover Story, Spectrum, IEEE on-line, February 2001,

\[8\] An Overview of Commercial Wiring Repair Best Practices, Tom Brown,
Universal Technology Corp., presented at the 2^nd^ Information
Exchange/Workshop, AFRL Wiring Integrity System Characterization and
Evaluation Program, 4-5 March 2003

\[9\] US Air Force Aging Aircraft Wiring Implementation Plan, Randy Hall
and Mark Brown, presented at the 6^th^ Joint NASA/FFA/DoD Conference on
Aging Aircraft, September 16-19, 2002

\[10\] A Smart Wire System for Non-Destructive Inspection of Aircraft
Wiring Harnesses, Erik C. Carlson, Aegis Devices Inc., presented at the
6^th^ Joint FAA/DoD/NASA Conference on Aging Aircraft, San Francisco,
CA, September 16, 2002

\[11\] Sentient Systems for Enhanced Safety and Reduced Cost, Kenneth
Blemel, Management Sciences, Inc., 2004 Virtual Acquisitions Showcase

\[12\] Wire Integrity Research (WIRe), Jim Cockrell, Ames Research
Center, presented at the 2^nd^ Information Exchange/Workshop, AFRL
Wiring Integrity System Characterization and Evaluation Program, 4-5
March 2003

\[13\] Advanced Risk Assessment Methods for Aircraft Electrical Wiring
Interconnection Systems (EWIS), Press, Bruning, Wood and Steinman,
presented at the 6^th^ Joint FAA/DoD/NASA Conference on Aging Aircraft,
San Francisco, CA, September 16, 2002