## ISS Fiber Optic Failure Investigation

###### Executive Summary

In September of 1999, Boeing engineers began investigating failures of
optical fiber being used on International Space Station flight hardware.
Catastrophic failures of the fiber were linked to a defect in the glass
fiber (see Figure 1, "Rocket Engine Defect"). Following several meetings
with Boeing and NASA engineers and managers, Boeing created and led an
investigation team which examined the suitability of the cable for use
in the US Lab, where it was already installed, and identified the root
cause of the failures. Information was gathered from: regular telecons
and other communications with the investigation team, investigative
trips to the cable distributor's plant, the cable manufacturing plant
and the fiber manufacturing plant (including a review of build records),
destructive and non-destructive testing, and expertise supplied by
scientists from Dupont, and Lucent Bell Laboratories. Several theories
were established early on which were not able to completely address the
destructive physical analysis and experiential evidence. Lucent
suggested hydrofluoric acid (HF) etching of the glass and successfully
duplicated the "rocket engine" defect. The information provided below
explains this phenomenon and the conditions which exist in the cable and
how it is used, which support it.

In parallel with the root cause investigation was the review of the
reliability of fiber optic cable of the same part number, which was
installed on the US Lab module. Information about experiences during
manufacture and installation of the flight harnesses, and the strength
of fiber from similar lots, were used to make decisions about how to go
forward with the manufacture of the US Lab and what level of orbit
maintenance is expected. Recommendations in that regard are provided
herein. Lessons learned during the investigation are tabulated in
Appendix 2.

###### Introduction

In mid-1999 Boeing engineers were finding multiple failures of 1999
vintage optical cable being used to fabricate harnesses for the US Lab
module for the International Space Station (ISS) and associated ground
support equipment (GFE). Not only were fiber breaks being detected
during handling but breaks would be found over time with no handling
(sitting on the shelf). This was believed to a much different experience
than was encountered during population of the US Lab module with 14,000
feet of 1996 vintage cable of the same part number. The Boeing materials
and processes engineers performed destructive physical analysis (DPA) on
the fiber at the break locations. Figure 1 shows one of the first images
resulting from the DPA. The cone and bulb shape of the defect earned it
the name "rocket engine". This description replaced the term "bubble"
which according to the fiber manufacturer, is associated with a topology
that is unique and not represented by Figure 1.

Efforts were immediately made by Boeing and GSFC personnel to
investigate optical inspection methods being used, to uniquely identify
the stock of cable involved, and to expand the number and types of DPA
images of the defect and the surrounding fiber and cable elements.

A summit was called by Boeing in October of 1999 and included engineers
and scientists from various Boeing organizations (KSC, Huntington Beach,
JSC), the NASA ISS parts control board, the NASA GSFC Component
Technologies and Radiation Effects Branch, the cable manufacturer (BICC
General), the fiber manufacturer (Spectran Specialty Optics, now Lucent
Specialty Fiber Technologies), and Aerospace Corporation who had been
commissioned as an independent technical reviewer of the problem
resolution. During the summit an overview was presented of: the failure
found, methods used to detect the failures, the manufacturing processes
and fault trees produced by Boeing. Theories about the root cause were
discussed and a plan was drafted both to accomplish a root cause
investigation and to determine the suitability of the cable, both that
installed and future orders, for long term space flight. Boeing retained
lead for the latter portion of the investigation and assigned NASA GSFC
the lead of the former portion. This was done with NASA GSFC's
concurrence and NASA JSC's concurrence and funding support. The
attendees of the summit became the core of the combined investigation
team.

![](media/image1.png)Figure 1. "Rocket Engine" Defect

The plan for both portions of the investigation included a review of the
processes used by the cable distributer (Sea Wire and Cable), the cabler
and the fiber manufacturer. A review of process data was performed to
identify signficant changes that may have contributed to the root cause.
Research and experiments were also performed in support of the root
cause investigation by several of the participating organizations. A
preliminary review of the current governing cable specification was
done. Strength testing was performed by Boeing in support of the cable
suitability investigation. Weekly telecons were held to review the
emerging information and to formulate upcoming activities. Experts from
Dupont and Lucent Bell Laboratories were invited to participate to
assist in analysis of the test results being collected and to guide
emerging hypotheses. Lucent Bell Laboratories conducted testing for the
investigation.

A web site was established for the team and all photographs and
documents being distributed throughout the team were posted there. A
password protection system was put in place to keep access down to the
team members and to protect manufacture proprietary information.

The presentation of the hypothesis by Lucent Bell Laboratories which
described the root cause as a result of an HF etch and their subsequent
duplication of the defect using HF, was a turning point in the
investigation. Activities following this focused on understanding the
circumstances, both chemically and environmentally, which would support
this etching mechanism in the fiber. By understanding the conditions
which would support HF etching of the glass fiber, the failure cause
defects could be identified. The team also started to consider the
manufacturability of cable without defects and methods which can be used
to screen out the defects.

In parallel with the research on the HF etching mechanism, Boeing wrote
a test plan and constructed the test equipment to conduct strength
testing of fiber from similar lots. The intention was to provide a
statistical parameter used to define the life of glass which is aging
due to stress corrosion cracking; the "n value". The lifetime would also
consider the stress and temperature conditions the fiber will experience
as installed in the US Lab.^footnote1^ Testing was performed and though
the data did not clearly provide a n-value, it did show that once the
"rocket engine" defects were screened out, the fiber had low break
strength due to moisture induced due to moisture induced corrosion,
causing stress concentration and cracking.. Discontinuity in the fiber
coating contributes both to the "rocket engine" etch pit and the low
strength associated with stress corrosion.

Footnote 1: A complete treatment of the "n-value" as it relates to glass
reliability can be found in xxxxxxxx.

(may want to move this up somewhere) A second summit was held by Boeing
in February 2000 to summarize the progress made by the team and to
formulate a plan for future use of the installed cable and purchase of
new cable. Five teams were established for the following action areas:
1: cable redesign, specification rewrite and cable qualification, 2:
Root cause wrap-up, 3: Maintenance plan for on-orbit repair inside the
module, 4: Maintenance plan for extra-vehicular on-orbit repair, and 5:
. This report is the final deliverable for Team 2.

This report provides detailed information about the following:

-   failure of optical cable used for the International Space Station

-   suitability of cable installed in the US Module for long term
    spaceflight use

-   lessons learned associated with the investigation of the root cause
    of the failure and the suitability assessment.

The members of Team 2 are listed in Attachment 1. A table summarizing
the lessons learned is given in Attachment 2. Background information
relating to the lessons learned (LL) are marked with the corresponding
number (example: \[LL1\] indicates background information pertaining to
the first item listed in the table in Appendix 2). Recommendations are
summarized at the end of the report and are annotated throughout.

##### 

##### Cable History

#### **The Specification**

The optical cable being used by Boeing on ISS is governed by the NASA
specification SSQ 21654, Cable, Single Fiber, Multimode, Space Quality,
General Specification for. The custodian is McDonnell Douglas Space
Systems Company in Huntington Beach. This organization is now owned and
operated by Boeing. The most recent version is Revision B, dated June
28, 1996. A change revision was made by Boeing, named SSCN 000904, which
affected most of the paragraphs. This change notice is not dated.

A cursory review by GSFC identified significant problems with the
specification and indicated that it does not accurately describe the
physical characteristics and performance of the cable that is being used
and does not adequately document the qualification requirements that the
part in use meets. The condition of the specification is not considered
to be a leading cause of the failure of the cable. It requires
correction before more cable is purchased however \[R1\]. A working
group, being led by John White of Boeing in Huntington Beach, has been
formed to redesign the cable and provide a specification for that new
part.

####### 

####### The Cable Design and The Performance Requirements Used

Two part numbers were defined: NFOC-2TFF-1GRP-1 and NFOC-2FFF-1GRP-1.
The former was for a PFA jacketed and PFA buffered design and the latter
was for an FEP jacketed and FEP buffered design. Table A-1 of SSQ 21654,
Rev B., SSCN 000904 summarizes the optical performance ratings and cable
component materials and dimensions. A PFA jacketed, FEP buffered design
is shown. John White provided Figure 1 shown below to describe the cable
being investigated. Figure 1 describes an FEP jacketed and FEP buffered
design. The corresponding part number is NFOC-2FFF-1GRP-1.

SEA provided information about orders delivered for both the
NFOC-2TFF-1GRP-1 and NFOC-2FFF-1GRP-1 cable. Table 2 shows the length of
NFOC-2TFF-1GRP-1 cable ordered by several users.

Table 1. Use of PFA Jacketed Cable

  ------------------- -------- -------------------------------- -----------
  Invoice Period      No. of   Customer Name                    Total
                      Orders                                    length
                                                                ordered
                                                                (ft)

  8/11/93             1        MTP Aircraft                     525

  3/6/95 & 8/14/95    2        Beoing Hunstville                45

  9/6/95              1        Spar Aerospace (CAE Electronics) 700

  9/18/95             1        McDAC (Boeing HB)                5000

  12/95               1        ITT Cannon                       4500

  3/30/95             1        Space Systems Loral (for Japan)  197

  4/20/95             1        Standard Wire and Cable          434
  ------------------- -------- -------------------------------- -----------

A history of the use of NFOC-2TFF-1GRP-1 cable on Space Station
equipment was researched however no hard data was recovered. Gary
Bickel, of Boeing, was involved with the manufacture of harnesses using
this former design and reported that the design was replaced by that
seen in Figure 2, called NFOC-2FFF-1GRP-1, because the PFA contributed
excessive jacket shrinking. NASA GSFC was aware of the jacket shrink
issue but had no knowledge of whether the PFA jacketed cable was ever
installed in the flight hardware. The Boeing team members do not have
documentation supporting or refuting its having been used in Node 1 or
in the US Lab. The material delivered to ITT Cannon is believed to have
been used in the development and qualification of the connectors used by
ISS.

Figure 2. Cable Design

+-----+---------------+----------------+---------------+--------------+
| F   | Item          | Dimension      | Material      | Construction |
| ind |               |                |               |              |
+-----+---------------+----------------+---------------+--------------+
| A   | Core          | 100[+]{        | Doped Silica  | Drawn        |
|     |               | .underline}2um |               |              |
| B   | Cladding      |                |               |              |
|     |               | 140[+]{        |               |              |
|     |               | .underline}2um |               |              |
+-----+---------------+----------------+---------------+--------------+
| C   | Hermetic      | 0.025-0.05 um  | Carbon Based  | Chemical     |
|     | Coating       |                | Hermetic      | Vapor        |
|     |               | Thickness      | Sealer        | Deposition   |
+-----+---------------+----------------+---------------+--------------+
| D   | Fiber Coating | 170[+]{        | Polyimide     | Coat with    |
|     | Buffer        | .underline}2um |               | Heat Cure    |
+-----+---------------+----------------+---------------+--------------+
| E   | Cable Buffer  | 380-760[+]{.   | FEP-Teflon    | Extruded     |
|     |               | underline}25um |               |              |
+-----+---------------+----------------+---------------+--------------+
| F   | Strength      | 1.6mm OD       | Teflon        | Braided      |
|     | Member        |                |               |              |
|     |               |                | Impregnated   |              |
|     |               |                |               |              |
|     |               |                | Fiberglas     |              |
+-----+---------------+----------------+---------------+--------------+
| G   | Cable Jacket  | 2.10[+]{.un    | FEP-Teflon    | Extruded     |
|     |               | derline}0.05mm |               |              |
|     |               |                |               |              |
|     |               | .25mm Thick    |               |              |
+-----+---------------+----------------+---------------+--------------+

###  G F E D A, B and C

### 

### 

Table 1. Optical Characteristics

+-----------------------+-----------------------+-----------------------+
| Characteristic        | From SSQ 21654,       | Used by Manufacturer  |
|                       |                       |                       |
|                       | SSCN 00904            |                       |
+-----------------------+-----------------------+-----------------------+
| Attenuation           | 4 dB/km @ 1290 ± 10   | TBD                   |
|                       | nm                    |                       |
+-----------------------+-----------------------+-----------------------+
| Numerical Aperture    | 0.30 ± 0.02 @ 1290 ±  | TBD                   |
|                       | 10 nm                 |                       |
+-----------------------+-----------------------+-----------------------+
| Bandwidth             | 200 MHz-km @ 1290 ±   | TBD                   |
|                       | 10 nm                 |                       |
+-----------------------+-----------------------+-----------------------+
| Proof Strength        | 200 kpsi minimum      | 140 kpsi              |
+-----------------------+-----------------------+-----------------------+
| Core Ovality          | 5%                    | TBD                   |
+-----------------------+-----------------------+-----------------------+
| Cladding Ovality      | 4%                    | TBD                   |
+-----------------------+-----------------------+-----------------------+
| Core/Cladding Offset  | 98% minimum           | TBD                   |
+-----------------------+-----------------------+-----------------------+
| Cable Weight          | 5.5 lbs/1000 ft.      | Not measured (?)      |
|                       | maximum               |                       |
+-----------------------+-----------------------+-----------------------+
| Color                 | Violet per            | Violet                |
|                       | Mil-Std-104           |                       |
+-----------------------+-----------------------+-----------------------+
| Temperature           | Operating:            | Not measured (?)      |
|                       | -100°C/+75°C          |                       |
|                       |                       |                       |
|                       | Storage: -100°C/+85°C |                       |
+-----------------------+-----------------------+-----------------------+

Table 2 shows the NFOC-2FFF-1GRP-1 cable delivered by the sole
distributor, Sea, Wire and Cable (SEA) to various customers. Their
shipping records reference the cabler's internal part number, OC-1614
and contain a sentence at the bottom indicating that the cable was
"manufactured to and acceptance tested in accordance with the SSQ 21654,
and CR SSQ 21654-008". A description of the OC-1614 product has been
requested of the cabler to show that it is of the same design as
specified in Figure 2, which is associated with the part number
NFOC-2FFF-1GRP-1 \[LL2\].

SEA only performed cable outer diameter (OD) at each end of the reel as
an acceptance measurement. For all other acceptance measurements, they
used BICC generated "Certified Test Data" sheets to document the
conformance of the cable to the specification requirements. Samples of
these documents were provided by SEA and one is included in Appendix A.
Ten of the 25 characteristics are reported in a go/no go fashion, ten
are referenced to a "Spectran" inspection and five are shown as a
measured characteristic ("Spectran" refers to the fiber manufacturer,
formally known as Spectran Specialty Optics Company and now called
Lucent Specialty Fiber Technologies or Lucent-SFT). Several other
identifying numbers are shown on the sheet including reel number, date,
customer order number, BICC part number, Date of Manufacture (DOM) and
length. The BICC part number used was OC-1614. A footnote at the bottom
of the sheet indicates that the material is made and tested in
accordance with SSQ 21654.

Though some confusion exists regarding the part number, it appears that
all of the requirements referenced on the test data sheet correspond to
those listed in Figure 1 above. During a review of the processes used at
BICC by the investigation team, the attenuation and cable layer
dimensions measurements done by BICC were found to be in accordance with
the specification requirements. A review of the processes used at
Spectran showed that the proof test was not extending 200 kpsi to the
fiber. All other measurements of the fiber diameters and optical
properties were found to meet the specification intent.

BICC ordered the fiber from Lucent-SFT in accordance with a build
specification numbered BFO4515. The Lucent-SFT build records show that
the optical measurements were being done in accordance with the Figure 2
above. An on-site review showed that the proof test was not been done to
the 200 kpsi level but closer to 140 kpsi.

The conclusion is that both the fiber manufacturer, Lucent-SFT, and the
cabler, BICC, were delivering product in accordance with the details
shown in Figure 2 above with the exception that the proof test was not
achieved to the full 200 kpsi level.

#### 

#### **Indicted Stock**

A review of all NFOC-2FFF-1GRP-1 cable delivered by SEA and BICC to
Boeing-Huntington Beach (Boeing-HB) and Boeing-Kennedy Space Center
(Boeing-KSC) was performed by examining shipment data supplied by SEA
and BICC. Several spreadsheets were provided by each. SEA provided
information about lengths ordered, by whom and DOM for the cable or date
of shipment. BICC's information gave cable reel numbers, order numbers,
DOM and some traceability to fiber lot. A great degree of inconsistency
exists regarding the use of the term "lot" and as a result, several
significant blocks of data do not exist \[R2\].

Table 2 shows the amount of NFOC-2FFF-1GRP-1cable delivered by SEA.

Table 2. NFOC-2FFF-1GRP-1 Cable Delivered by SEA Wire and Cable

  ------------------ -------- ----------------------- ----------- ---------
  Invoice Period     No. of   Customer Name           Total       No. of
                     Orders                           length      Reels
                                                      ordered     
                                                      (ft)        

  6/12/96 & 7/26/96  2        MCDAC Huntsville        5031        8

  6/26/96 to         14       ITT Cannon              7423        
  12/30/98                                                        

  7/17/96 to 4/1/99  14       Boeing Huntville        40,695      41

  7/19/96            2        CAE Electronics         500         

  7/24/96 to 5/7/99  27       Boeing Huntington Beach 109,346     

  7/25/96 to         10       Nakano Aviation         9453        
  11/25/98                                                        

  8/9/96             1        Amphenol                1200        

  9/5/96 & 5/1/97    2        Space Systems Loral     8990        

  11/15/96 & 2/17/97 2        Pacer                   600         

  3/26/97            1        NTK Aviation            1000        

  5/28/97 & 4/7/99   2        Electronic Conn         701         

  6/17/97            1        Standard Wire and Cable 100         

  7/18/97 to         7        OHB Systems             11,596      
  11/25/98                                                        

  10/6/97            2        Boeing Downey           1496        4

  1/23/98            1        TRW Components          168         

  7/13/98            1        Boeing Seattle          100         

  11/30/98 & 5/7/99  2        L/M Houston             600         

  11/30/98 to        5        Boeing KSC              9575        8
  8/17/99                                                         

  12/16/98 & 7/2/99  2        Prime Cable             800         

  1/20/99            1        Elymat Industries       89          

  6/25/99 & 7/12/99  2        Undefined               400         
  ------------------ -------- ----------------------- ----------- ---------

Preliminary findings and discussions identified several significant
periods in the production and use of the cable related to the number of
defects found and process changes made. At one time, it was believed
that cable made before one or more processes changes were put into
effect, did not contain the defect. This was supported by the lack of
evidence of a "rocket engine" defect in reels manufactured prior to
1997. Later work found a "rocket engine" defect in 1996 vintage cable
and also indicated that many more may have been present but were
effectively screened when cable broke and was discarded during harness
manufacture. This left the team with the conclusion that all
NFOC-2FFF-1GRP-1 cable was suspect.

###### Manufacturing Processes

The manufacturing processes used by SEA, BICC and Lucent-SFT were
discussed regularly during the investigation and reviews at each of the
respective plants (two for Lucent-SFT) in order to understand the
processes being used and their possible contribution to the creation of
the defect.

######## Distributor

John White of Boeing-HB led the review and examined build records for
six specific cable reels which XXXXXXX. Some records were found while
others were not. SEA did no more than measure OD, cut cable to length
(including a respooling process) and re-label the spools to the cable
they received from BICC \[LL3,4\]. All cable shipped to
Boeing-Huntsville (Boeing-HTVL) was respooled to plastic reels because
the cabler's wood reels were damaging the cable \[LL5\],\[R3\].

The respooling process is believed to expose the cable to significant
levels of electrostatic charging, which when discharged, can damage the
fiber coatings (See a more detailed treatment of the ESD issue below).
Measurements of the field signs and strengths during respooling at SEA
was not done during the process review.

The review showed that, other than the re-spooling process which may
damage the fiber coatings, no processes used by SEA could have created
the "rocket engine" defect.

**Cabler**

BICC generally delivered the cable to SEA within six days of its
manufacture. Deliveries to SEA were made 20 times between 12/95 and
4/99, mainly centered around the second half of 1996 (46 kft total),
11/21/97 (15 kft), 10/98 (39 kft), and 4/99 (43 kft). There appears to
have been no production between these four main periods.

A review of the shipment records compared to the reels in which "rocket
engine" defects were found did not clearly show an abrupt increase in
defective cable corresponding to large changes in either production
volume or cable length, though there are distinct periods of high
throughput and shipment of multiple short lengths. A review of some of
the corresponding purchase order information indicates that the short
lengths were not specified by the buyer.

The processes given the most attention during the review at the BICC
facility were the records keeping, fiber respooling, the extrusion and
the optical measurement processes. Later discussions focused on the
extrusion process because findings were revealing that the extrusion
conditions were very likely causing a generation of HF which acts as an
etchant when it contacts glass.

# Record Keeping

Records for six reels of cable were exhumed. Most of the materials
traceability was not recorded. A buffer run sheet, which specifies
manufacturing settings/conditions and specifications of the
corresponding product, is provided to the extruder operator however it
is very often not filled out properly. The record keeping has improved
over the period that the NFOC-2FFF-1GRP-1 has been made at BICC however
it is still not sufficient to show a complete traceability history.
There is no fiber traceability, for example, for most of the reels made
in 1996 -- the vintage used to populate the US Lab module.

# Storage and Factory Environment Control

The factory was kept to a range of X°C to °C and X to X relative
humidity. Fiber storage was controlled in a separate area with limited
access but not a clean room. The cable manufacturing location also
limited general walking traffic while it contained an extrusion line for
other products. All processes following re-spooling and fiber storage,
were performed in the same room.

# 

# Respooler

Correspondence records supplied by BICC showed that in January of 1997
McDonnell Douglas (Now Boeing-HB) notified them that the polyimide
coating on the fiber in the NFOC-2FFF-1GRP-1 cable, was dimensionally
out-of-specification. This was confirmed by Boeing-HB personnel who were
not able to terminate the fiber in the connector ferrules because its OD
was too big (following return of the product it was realized that the
wrong fiber part number was shipped). Between 3/97 and 10/97
arrangements were made to use a LaserMike laser based measurement device
installed on a fiber coating machine (used to add colored coatings for
identification purposes, often called a color-line) to screen the fiber
for out-of-spec OD. Use of this system as a screen was first used on
10/7/97 and became a permanent process for the NFOC-2FFF-1GRP-1 cable.
Adjustments were made in April of 1998 to resolve calibration issues.

The respooling process was considered a source of ESD which could be
damaging the fiber. The polyimide coating, at 15μm thick and has a
dielectric strength of 336 V.*(still need to work these details out)*
Field measurements were made using the BF04515 polyimide/carbon coated
fiber and are shown in Table 3 (the ambient relative humidity was 45%).
Extremes of -10,000 V/inch and +850 V/inch showed that there were ample
opportunities for charging and discharging in the fiber while it was
traveling around the machine.

Table 3. Electrostatic Field Measurements Taken Around "Color Line"

  ----------------- ------------ -------------- ----------- -------------- -----------
  Location          Identifier   Field During   Field       Field During   Field
                    on Figure 1  20 m/min       During 50   20 m/min       During 50
                                 operation      m/min       operation      m/min
                                 (V/inch)       operation   (V/inch)       operation
                                                (V/inch)                   (V/inch)

                                 3M 709                     42720          
                                 Measurements               Measurements   

  Let-out reel      1            +40            +25         -200           +640

  1^st^ pair of     2            +30            +110                       
  tension control                                                          
  wheels                                                                   

  Pre-ionizier      3            -2000          \> -10,000  +350           
  wheel                                                                    

  Post-ionizer      3a                                      -980           -900

  Entrance into     4            -140           -1150       -300           -3500
  wheel/belt                                                               
  section                                                                  

  Exit out of       5            -35            -65                        0
  wheel/belt                                                               
  section                                                                  

  Pre-OD detector   6a                                                     -500

  Post OD detector  6            -25            -45                        

  Take-up reel      7            +85            +50         +50            -300
  ----------------- ------------ -------------- ----------- -------------- -----------

# 

# Extruder

BICC demonstrated the operation of the extruder after the FEP pellets
were added and melted in the reservoir. The original shipping containers
were kept near the secondary containers, which showed the color of the
pellets and were marked with the name of the material. The conditions
for heating the pellets, the extrusion temperature, and the extrusion
rate were reported by the process engineer. No special precautions were
taken to avoid creating corrosive decompositon products from extruding
in air such as baking out the pellets and confining the extrusion
atmosphere to something other than air. (would like to reference "Guide
to the Safe Handling of Fluoropolymer Resins" here but can't find the
right para. Yet). The BICC process engineer reported that it took 16
minutes for the melted FEP to appear at the die head during extruder
start-up. The steady state flow rate was reported as 0.725 oz/minute.
Temperatures range between 288°C (exposure to air following extrusion)
and 404°C during the extrusion process. Immediately following extrusion,
the cable passes through two water baths, the first maintained at 24°C
and the second at 52°C.

Research into the chemical conditions resulting from this extrusion
approach and others, revealed that the manner in which the pellets are
preconditioned and the environment in which the FEP material is extruded
can contribute to the creation of the "rocket engine" defect. More about
the chemical issues related to extruded FEP is discussed in detail in
the section below titled [HF Generation]{.underline}. The same process,
with a different extrusion head, is used when applying the jacket as is
used for the buffer.

The extrusion line was reviewed with the field meters the results of
which are shown in Table 4. Again, the cable is exposed to large
potential differences, however the dielectric layer between the charging
material and the fiber is greatly increased and opportunities for
damaging the fiber coating are not as prevalent as in the color-line
situation.

Table 4. Electrostatic Field Measurements Taken Around the Extrusion
Line

  ------------------------------------------------------ ----------------
  Location                                               Field (V/inch)

  Let-out reel                                           -750

  Air space between quenching baths                      -150

  Exit of second quenching bath                          -10

  Length counter (wheel & belt)                          \*

  Rubber belts -- entry                                  -110

  Rubber belts -- exit                                   -45

  Tension wheels -- 1^st^                                +2000

  Tension wheels -- 2^nd^                                +2250

  Tension wheels -- 3^rd^                                +75

  Ground chain                                           -100

  Metal feeder wheel                                     +305

  Take up reel (in path of de-ionizing fan)              -1500
  ------------------------------------------------------ ----------------

> \* Did not capture numerical data but recollection is that it was near
> the

minimum/floor of 50V/inch.

During the investigation, there was a recollection by team members
regarding the use of silicone oil wiped on the coated fiber to reduce
the loose tube's ability to stick to the fiber. It was resolved that
this process was never used on NFOC-2FFF-1GRP-1 cable.

# Strength Members

The equipment and materials used for applying the braided strength
members to the buffered fiber were briefly reviewed and found to be
industry standard with no detail that seemed related to the fiber
failure. BICC reported that the only time that they rejected finished
NFOC-2FFF-1GRP-1 cable was when lumps were found under the jacket due to
the strength members (associated with the ending or beginning of a spool
of the strength member material). Lengths with this defect were cut out
and not delivered to SEA.

# Optical Measurements

Both a Tektronix TFP2 FiberMaster and a GNNettest CMA 4000 are used, at
1300 nm wavelength, for measuring attenuation. The equipment and set-up
was witnessed and nothing was found that would indicate incorrect
measurements were being recorded or that the method being used
contributed to the fiber defect.

# Conclusions

The respooling operation is a likely source of fiber coating damaging
ESD. The process used for extruding FEP provides conditions which may
damage an undercured polyimide and will provide significant amounts of
COF2 which is the precursor to the formation of HF when moisture is
present.

**Fiber**

Great attention was also paid to the details of the fiber production
processes in order to understand the root cause of the defects and if
any conditions were found isolating them to specific lots or periods of
production.

# Raw Materials Used to Make the Preform

Lucent-SFT makes their own glass preforms so the raw materials in this
case include the natural quartz cladding tube and gases. The gases are
monitored for quality on an incoming sample basis and are monitored
daily, in-line, for water content. The tank farm for most of these gases
(some come in transportable cylinders) was moved between 1996 and 1997.
There was no strong evidence indicating that the move of the tank farm
or the handling of the gases allowed contamination of the gases or
contamination of the preform manufacturing processes.

The pure fused silica substrate tubes are reviewed for defects and
records are kept allowing traceability between the raw material and the
finished preform. Many of the preform build records showed a great
degree of "flaws" in the tubes however this is normal in natural quartz.

# Preform Fabrication

The BF04515 fiber is drawn from preforms uniquely identified by a part
number containing the number 320. All "320" preforms are made on lathe
number "E" and so also carry the "E" in the preform part number. The
"320" preforms are also the originating material for several other
variations of fiber dissimilar to the BF04515 only in the glass and
coating tolerances. Lathe E is also used to fabricate several other
preforms whose recipes use all the same ingredients as used for the
"320" product or some subset thereof. Lathe E is located apart from the
main production area in an area reserved for R&D activity, is
air-conditioned and is humidity controlled. R&D operators are selected
from previously trained operators.

The build sheets include requirements for the gas mixture and process
recipe and spaces for recording observations and process variations.
Changes to the recipe (tweaks), which are accomplished manually by the
operator, become part of the recipe and a new revision identifier is
assigned and recorded on the build sheet. That recipe stands until
another change supercedes it. The dimensions of the finished preform and
defects or features such as bubbles and air lines seen in the preform
are also recorded. A refractive index profile is measured for each
preform in a separate laboratory. An example of one is shown in Figure
X. The "MESA" database is used to link the preform records with the
records for the finished fiber. This automated filing system was started
in the second half of 1996.

Figure X. Preform Index Profile

Spectran.jpg

Preform processing includes cleaning and etching the substrate tube and
the finished preform. Both a hydrofluoric acid bath and fire polish is
used. These methods along with the CVD method for growing the
core/cladding transitional layer and the core leave eliminate the
possibility that contamination was trapped between the core and
cladding, inside of the core or in the surface of the cladding layer of
the preform. The creation of a void inside of the preform due to an
inside contaminant could only take place during the major neck-down of
the preform during the fiber draw process. This would produce a defect
elongated by at least some significant fraction of the drawdown ratio
which is approximately 12,000:1 in the longitudinal direction. This
amount of elongation is quite the opposite of the shape of the radially
elongated, bulb shaped defect.

The total process time required to make a "320" preform is about 19 hrs.
A review of the preform records showed manufacture of 181 "320" preforms
between 11/94 and 8/98, the heaviest period of production of being
between July of '96 and April of '97. Of these 181, 17 were traceable to
NFOC-2FFF-1GRP-1 cable. Eight were associated with reels found with a
"rocket engine" defect. A gap in production existed between October of
'97 and June of '98, which corresponds to the move of the draw facility
to its current location on Darling Drive. All preforms used for the
Boeing fiber were produced prior to August of '98, and were held in
stock up to a year before they were drawn into fiber.

# Fiber Manufacture

A review of the fiber draw and cabling facility in Avon was performed.
Though the traceability between the cable and the fiber is not complete
for much of the pre-1997 cable, the records indicate that at least 81kft
of fiber in the NFOC-2FFF-1GRP-1 cable was drawn at the current facility
and 53kft was drawn at a facility which as since be decommissioned. The
fiber drawn for the NFOC-2FFF-1GRP-1 cable is called BFO4515 by
Lucent-SFT.

The current facility, at Darling Drive in Avon, CT, contains several
draw towers although all of the BFO4515 fiber was drawn on tower "C".
The draw room is humidity and temperature controlled, and limited to
traffic through a clean-room entrance (approved personnel only, smocks
required, etc.).

Several in-line diameter measurements are used. Proof testing is
performed in-line. Optical performance test equipment and microscope
inspection equipment are kept in the same area and is used for lot
inspections. An auxiliary glass lathe for fire polish is kept in the
same area as the draw tower.

The carbon and polyimide coating processes were reviewed during the
on-site visit and were discussed several times over the period of the
investigation. Table 5 lists the concerns investigated and the
corresponding findings.

Table 5. Coating Issues & Findings

  ----------------------------------- -----------------------------------
  Issue                               Finding

  Is there an opportunity for debris  Pressurized air is directed
  to fall into the coating cups from  horizontally at the fiber below the
  the carbon application station      reactor to prevent this.

  Could the temperature of the carbon The process actually requires
  application process be re-melting   cooling of the glass as it exits
  the glass or vaporizing             the draw iris.
  contamination in the glass          

  Is the polyimide undercured making  Yes, this is possible.
  it susceptible to remelting during  
  FEP extrusion?                      

  Can the in-line diameter sensors    The three axis laser micrometer has
  detect the depressions and bubbles  an accuracy of resolution of XXX
  in the polyimide which tend to be   and is able to capture 800 μm of
  associated with the "rocket engine" the fiber length per sample. The
  defects?                            polyimide sink holes are XXX in
                                      size.......

                                      

                                      

                                      

                                      

                                      

                                      

                                      

                                      
  ----------------------------------- -----------------------------------

The build records start by instructing the draw operator how to manually
set the tower settings which include draw speed, iris settings, gas
flows and cure temperatures. The draw furnace is operated in the
vicinity of 2150°C. The reactor for the carbon coating is placed
immediately below the draw furnace, which is at the top of the tower,
since the coating must be applied as the fiber cools down from 800°C at
the exit of the draw furnace. The polyimide coating is applied in four
steps by independent coating systems. The polyimide is delivered to the
coating applicator cups as a resin dissolved in a solvent. Coating die
size, incoming fiber size, draw speed, and material viscosity
(temperature controlled) determine the actual volume per unit length
deposited onto the fiber. The coating application dies are fabricated
from specialized materials in order to preserve the ultra high precision
required over multiple draws. The operator looks for bubbles in the
coating as an acceptance screen during draw and measures the coating
thickness after the fiber manufacture is finished.

A wheel capstan with idler belt creates the pull tension that draws the
fiber down to size in the furnace and through the polyimide coating
systems. The fiber is proof-tested online during the draw using a
3-plane mandrel system. The unit has a different section for each plane
of test. The first and last sections are at 90 angles to each other and
the third plane is at one of the two 45 degree orientations to the other
two. Note that this system is not symmetric in that there is one plane
in the fiber in which the effective proof level is as low as 141 kpsi.
If the sections were oriented at 60 degrees to each other the minimum
proof level would be 173 kpsi on three planes.

The take-up is a dancer-controlled unit that winds the fiber onto a 14"
diameter Styrofoam spool. It is respooled when non-conforming sections
need to be removed and when shorter lengths are ordered. This respooling
is considered to provide an opportunity for damaging the fiber with
electrical discharging.

The fiber is measured for loss and bandwidth at a test station within
the draw facility prior to final spooling. Bandwidth measurements are
made at three wavelengths, loss measurements are made at approximately 6
wavelengths including 1380 nm for the water peak. Numerical Aperture
(NA) is measured at an unspecified wavelength.

Geometry measurements include:

-   Core and Cladding diameter

-   Core and Cladding noncircularity

-   Clad/Core concentricity

-   Polyimide Coating diameter

-   Coating concentricity.

## Optical Detection of the Defect

Comparisons of several different measurement methods were accomplished
over the course of the investigation. Attenuation meters, optical fault
finders and optical time domain reflectometers (OTDR) were used as part
of the harness acceptance procedure and during failure analysis.
Attenuation measurements were made with a Model XXXX RIFOCS meter (1300
nm wavelength, XXX range) after harness assembly and during their
integration into the US Lab module at KSC. A limit of 0.5 dB (per
what???) was imposed though most links were reported to have measured
closer to 0.2dB/???. After installation, a system level acceptence was
imposed based on successful operation of the data bus. The operational
margin afforded by the receivers is believed to allow several dB of loss
in the harnesses so the absence of latent defects can not be established
using a system level test.

Optical fault finders (OFF), which launch around 0.1 W of red
(wavelength??) light into the fiber core, were also used to find breaks.
The FEP and Teflon strength members are transparent to this wavelength
and revealed a glowing spot where light was escaping from the fiber
through a break or other defect that reached into the core. Research has
shown that operators must be dark adapted (@ 20 minutes in a completely
darkened room) to effectively use OFF's. Experiments at GSFC showed that
several of the defects believed to be "rocket engine" defects, were not
found with an OFF until the screen was done following dark adaptation.
By using a green laser (???nm), visual sensitivity is raised by a factor
of XXX further improving the efficiency of the screening method.
Increasing the power of the laser used will also improve the screen.
Although a limit above which the laser power would damage good fiber of
this type was not demonstrated, a 30 mW laser was found to be
non-destructive.

Optical time domain reflectometers (OTDR) were also used to measure
attenuation and to locate breaks. Several different models were used
with varying sensitivity due to the type of signal launch each used.
Models used were the Tektronics TFP2 FiberMaster and the Opto
Electronics Inc. OFM20 and OFM130. The OFM130 was determined to the best
of the three because it has a zero meter dead zone and a 0.1sec pulse. (
verify specifications, 0.1 sec is 18600 mi) An experiment was done to
determine the ability to find defects associated with "bright" and "dim"
glows, using the OFM130. It was possible to find all of the defects with
prior knowledge of where to look for them and by increasing the
amplifier gain to close to its maximum level. It is believed that the
"dim" spots would not have been found with the OTDR only. All three OTDR
models have shown ghost pulses when used with concatenated harnesses. A
Broullian OTDR was determined not to be useful in this application.

###### DPA Results

DPA's were done when multiple defects were being found following periods
where no stress was induced on the cable (glows appearing after the
cable sat on the bench overnight). Most of the early DPA's were done on
fiber ends. When a glow was found in the cable, the affected section was
cut from the spool or harness and the fiber was removed from the cable.
Often, the fiber broke during this removal operation. When it didn't,
the fiber was bent until a complete break occurred. In either case, the
break always occurred at the defect site. The end face images were not
mirrors of each other indicating loss of material during the break. As
the investigation progressed intact fiber with defects were imaged.

Figure 1 above is one of the very first images of a rocket engine defect
made available by Boeing-HB. Subsequent DPA's found other important
features which ultimately led to the HF etching theory. These are shown
in Figures 3 through 8.

Figure 3. FOC-16.jpg: sink in the polyimide coating

Figure 4. Photo-2.jpg: Si balls in polyimide void

Figure 5. TedGpage8.jpg: population of Ge crystals in etch pit
(TedG.page2.jpg is also good)

Figure 6. TedG.page4.jpg: Ge and Si debris on outside of coating

Figure 7. 190845DefectBpg2.jpg: spire in etch pit which reaches Si rich
center of core

Figure 8. Reel190848DefectC.jpg: characteristic void in polyimide above
shall etch pit

These figures were all produced with a scanning electron microscope. EDX
was used to determine the composition of the glass to determine the
presence of contamination and to identify the composition of the spheres
and crystals found in Figures 3 and 4. Optical microscope images are
also available but are more difficult to interpret independently. The
use of index matching gel and backlighting during imaging was found to
greatly enhance the optical microscope images. After submersion of an
intact piece of fiber in index matching oil and having left the sample
overnight, the oil was found to have filled the "rocket engine" hole
under examination. This confirmed that the surface of the "rocket
engine" defect was exposed to ambient moisture.

Xray was used to see if defects on the surface of the coated fiber could
be detected. Figure 9 shows that X-ray can be used to look at the fiber
without removing the cable elements which is useful for inspecting for
fiber which may be too long for the jacketing (in cases where the jacket
and/or buffer has shrunken). Figure 10 shows that an intentional scratch
of XXXXX size can be seen with Xray.

Figure 9. Bell23.jpg: E.Banks' sample with a broken fiber whose ends
overlap.

Figure 10. Not sure which photo to use here.

###### 

###### Material Behaviors and Interactions

**Teflon decomposition and Polyimide Hydrolysis**

The Society of the Plastics Industry, Inc., has published three editions
of their Guide to the Safe Handling of Fluoropolymer Resins, the latest
being in 1998. The graph below in Figure 11 shows the decomposition of
FEP, among other fluoropolymers, over their generally accepted
processing or use temperatures. The decomposition product of FEP is
principally carbonyl difluoride, COF~2~, which is a gas. In the presence
of moisture, it hydrolizes into HF and CO~2~. The rate of decomposition
of FEP in air increases with temperature becoming quite significant at
400°C.

Testing was performed to confirm the evolution of reactive, fluorine
containing gases, such as HF or COF~2~ from the cable due to mechanical
agitation and exposure to an electric field. A length of cable was
hooked up to a mass spectrometer. After pumping out all the gasses for
between 16 and 72 hours, the cable was stressed in the two different
ways. Mechanically twisting the cable resulted in the formation of HF
that persisted for about five minutes. The spark from a tesla coil was
run over a length of the cable to induce ESD through the cable jacket.
This again produced HF, in larger quantities, lasting again about five
minutes. In the case of minimal air leakage into the cable, the further
the spark was from the mass spectrometer, the lower the mass flux rate
from the cable, and the longer the duration of the mass flow. This test
verified the existence of simple ways to produce HF in a cable. In a
paper by Baker and Kasprzak^REF^, FEP was shown to produce HF and/or HF
precursors such as COF~2~. The HF precursors in the presence of trace
residual water such as that absorbed by the polyimide, violently react
to form HF. A test for HF evolution in an ionizing radiation environment
is planned.

Polyimide has been shown to retain as much as 1.7% water by weight in a
fully cured state. Review of Lucent-SFT's product found that the
polyimide layer is not fully cured and so retains as much as 3.4% water
by wieght. This water is strongly held in the polymer matrix, and is
only slowly released. The rate of release of the water is sufficiently
slow that a significant fraction of the gases entering the mass
spectrometer after 48 hours is water. This water amount is significantly
greater than can be attributed to atmospheric air leakage. The polyimide
provides more than sufficient water for all of the reactions seen to
date, without the need for providing an alternative source for water.

^REF:^ B.B. Baker Jr., D.J. Kasprzak, Thermal degradation of commercial
fluoropolymers in air, Polymer Degradation and Stability, 1993.

See
[http://www.nist.gov/cstl/div836/836.03/papers/NistTNFigure1.html-decomposition](http://www.nist.gov/cstl/div836/836.03/papers/NistTNFigure1.html(-decomposition)
products of Fluoro...\...

**HF etching**

HF is known as a "weak" acid. It is not significantly ionized in water.
As such, it is not reactive with polyimide or most other organic
materials. However, due to the polarity and hydrogen bonding
characterstics of HF it has a tendency to absorb readily into and
coordinate with the polyimide. Analogous to polyimide's tendency to
retain water, HF is also retained by the polyimide. The polyimide acts
as a sink for the HF. When HF becomes part of an etching reaction, more
HF is delivered from the surrounding polyimide to the etching site in
order to maintain chemical equalibrium.

Hydrofluoric acid is a well known etchant of glass. The reactivity and
reaction product of hydrofluoric acid with glass was first published in
a scientific journal in 1771 by Scheele. The formation of germanium
tetrafluoride was published by C. Winkler in 1886. The formulas
describing the reaction in the Ge doped fiber is:

> 4 HF (g) + SiO~2~ (s) ↔ SiF~4~ (g) + 2 H~2~O (l)
>
> 4 HF (g) + GeO~2~ (s) ↔ GeF~4~ (g) + 2 H~2~O (l)

The oxides are solid and ordered in the original fiber structure.
Mechanisitcally, the reaction of hydrofluoric acid with a silica surface
(or in similar manner with a germania surface) first requires the
insertion of water into a silicon oxygen bond. This insertion hydrates
the silica, providing a readily exchangable group to react with the
hydrofluoric acid. This step of the reaction is controlled by the
activities of the hydronium ion and the silica surface. As the silica is
hydrated, the hydroxyl groups present on the silica are replaced with
fluoride groups in an extremely exothermic reaction. The rate of the
reaction is dependant upon the equilibration of a wide variety of
species both as the products and the reactants. Due to the complexity of
the reaction, there have been few or no definative studies of the
reaction of HF with silicaceous materials inspite of the great interest
and long time elapsed since the discovery of the reaction.

Silicon and Germanium fluorides are gases and take up almost 840 times
more volume than the oxides, possibly causing a pressure "eruption" of
gases out of the orifice. The gas phase nature of the reaction products
provides for rapid mass transport of the products from the reaction
sight. This minimizes the build up of reaction products that could
result in slowing of the reaction. The gas phase reactants will also
react in the reverse reaction at a significantly higher rate due to the
faster mass transfer rate. Additionally, the reaction creates heat in
the forward direction, adding to the force of the eruption. The ejected
material is SiO~2~ and GeO~2~ . The escaped fluoridegases, in the
presence of water will be in equilibrium with SiO~3~H~2~ , GeO~2~ and
HF; this is essentially the reverse the reaction proceeding from the
point of the protonation of the glass surface. This regenerates the HF
in a catalytic manner. There are some side reactions that may slightly
decrease the active HF concentration, however, the HF is recoverable for
reaction with the glass until the HF is physically removed from the
system. The SiO~2~ precipitates as a silica gel when the water around it
evaporates giving rise to spherical shapes surrounding the hole. The
spheres are silica in a hydration state, but not vitreous glass. The
same occurs for the GeO~2~ , except that it forms a shard-like
crystalline structure. The reaction conserves mass and energy.

The shape of the cup in the cladding area reflects the speed at which
the reaction occurs in the pure silica material and its increasing speed
in the Ge rich material. (refer to Fan model here). The spike in Figure
7 corresponds with a region of low Ge concentration (also see Figure X.
PIP).

Dr. David DiGiovanni of Lucent experimented with ??? graded index silica
fiber whose coating had been breached as a result of exposure to an
electric discharge (field strength???). The breach was approximately 20
microns in diameter. The sample was then exposed to 50 wt% HF for 15 to
20 minutes. HeNe light was transmitted through the fiber during the test
and when light began to leak out of the side, the test was stopped.
Figure 11 shows the resulting defect with the characteristic bulb
pattern and ringed structure seen in the Boeing photographs. The sample
was rinsed to drive off the highly corrosive HF and probably also was
the reason why no GeO~2~ crystals or SiO~2~ balls were seen.

Dr. DiGiovanni observed that the Ge-doped core etches considerably
faster than the cladding. If the etch time is too long, then the entire
core can be removed, leaving a silica tube with a pinhole in it. This
indicates that the amount of HF present at the defect is the limiting
factor in the degree of pitting.

Figure 11. Etch Pit Resulting from Experimentation

![](media/image3.jpeg){width="3.2944444444444443in"
height="2.498611111111111in"}

######### Carbon/Silicon carbide

The Lucent-SFT fiber used in the NFOC-2FFF-1GRP-1 cable, is coated with
a 25nm coating of carbonaceous material deposited pyrolytically as the
fiber exits the draw furnace. A mixture of hydrocarbon gases enters into
a chamber in the presence of a nitrogen purge. This then cracks the
hydrocarbons onto the surface of the fiber. What results is a base layer
of SiC with pyrolytic carbon on top of it.

An intact film of SiC provides a significant barrier to attack from
protonating and etching materials. However, Pyrolytic carbon is known to
absorb significant amounts of hydrogen fluoride and hydrofluoric acid.
Where pyrolytic carbon exists, a significantly higher concentration of
the acid will be available for etching purposes. pyrolytic carbon coated
substrates etch at a rate that is several orders of magnitude higher
than clean surfaces.

The reason for this discrepancy was determined using ESCA (electron
spectroscopy for chemical analysis). A fiber was depth profiled through
the polyimide coating and it was determined that a significant fraction
of the carbon on the surface was present on the fiber was in the form of
silicon carbide. The genesis of this silicon carbide is the solid phase
high temperature reaction of the pyrolytically deposited carbon with the
silca. This is also a classicly known reaction. The reaction is not
commonly known as processes have been designed since the makers of early
glass to exclude carbon from areas with molten glass. Also the reaction
is highly diffusion limited.

As mentioned above, the protonation or surface hydration of the
silicaceous material is required prior to the formation of the
silicontetrafluoride. The protonation or hydration of the surface is
almost entirely controlled by the activity of the hydronium ion at the
surface of the silica or glass. In the case of silicon carbide, the
hydration of the surface is no longer a simple surface protonation. This
surface requires the conversion of the surface to a silicon oxygen or
other reactive species prior to reaction with hydrofluoric acid. In
neither the case of only hydrofluoric acid nor a mixture of strong acid
such as nitric acid and hydrofluoric acid is the silicon carbide
reactive.

The silicon carbide and carbon behave as semiconductors. At high
temperatures and high voltages, the material will behave as a conductor.
In the case of ESD, the temperature of the spark is several thousand
Kelvins. This temperature regime is more than sufficient to atomize (in
the literal sense of separating molecules into atoms) the fiber surface
and the silicon carbide. The expected rapid temperature drop from the
spark event could be expected to create molecular carbon both from the
silicon carbide, as well as from the polyimide and the Teflon FEP. This
could act as a concentrating medium for water and HF. This would result
in the acceleration of the reactions at this location.

**Electro Static Discharge (ESD)**

ESD may be triggered by several factors. The handbook value of the
dielectric breakdown field strength of bulk polyimide is 560 volts per
mil. The thickness of the polyimide coating applied to the FlightGuide
fiber is 0.60 mil. Thus, the dielectric breakdown voltage of the coating
is (at least) 340 volts. However, it is well known that the dielectric
breakdown field strength of a thin film is larger than for a bulk
specimen; sometimes the value doubles. Thus, the dielectric breakdown
voltage is almost certainly greater than 340 volts, and may be closer to
700 volts or even higher. Because the polyimide is highly thinned at the
bubble sites, and the void tends to "focus" the ESD event, the breakdown
strength at the bubble site is probably a factor or two or three less
than in the 15 μm solid coating layer.

Experiments by GSFC have shown the breakdown strength along a path
between the top of the polyimide, through the coating, down along the
conductive carbon and out of the polyimide at another site, as roughly
1,500 volts. This suggests a breakdown voltage of roughly 750 volts per
layer. GSFC has demonstrated that 2,500 volts burns a hole through the
polyimide coating and also destroys the carbon coating, as shown in
Figure 12.

Figure 12. Experimentally Produced ESD Damage

Recent test results found by GSFC has demonstrated that high electric
fields can cause charge travel all the way through the cable layers, not
only increasing the rate of FEP decomposition but damaging the fiber
coating (Figure 13).

Figure 13. Cut.jpg: J. Canham's 2/24 tesla coil test

Boeing also performed an ESD test on the coated fiber and found that
significant damage could be caused with XXXXXV (Figure 14).

Figure 14. ESDTEST(190845).jpg: John White's experiment with the
appearance of an ESD damaged site

###### Strength Testing

######## Test philosophy

**Testing performed**

**Results**

###### Conclusions

**Summary of the Root Cause**

The discoveries documented above provide support for the theory that the
"rocket engine" defects are an artifact of HF etching. A source of HF
has been identified: through the decomposition of the FEP in the
presence of water. The water is ubiquitous in the cabling process both
in the atmosphere and laden in the polyimide.

Sources of damage to the carbon coating are not as definitive. Damage
from electrostatic discharge has been demonstrated however work remains
to be done to show that the sources of ESD in the manufacturing
processes were responsible for the damaged carbon coating or if the
original quality of the carbon coating left it with defects exposing
bare glass to HF attack.

###### 

###### Recommendations

Appendix A

Item 1. Example of BICC Certified Test Data Sheet

Item 2. BICCTripJP.doc (details of ESD measurements taken)