Assurance of COTS Assurance of COTS Fiber Optic Cable Assemblies Fiber Optic Cable Assemblies

for Space Flightfor Space FlightMelanie N. Ott

Swales Aerospace / Goddard Space Flight Center

Component Technologies and Radiation Effects

301-286-0127, melanie.ott@gsfc.nasa.gov

http://misspiggy.gsfc.nasa.gov/tva

Commercialization of Military and Space Electronics, February 10, 1999

Outline

• Background

• Definitions

• Lessons Learned

• Characterization of Systems

• Testing and Failure Modes

• Tests and Analysis for COTS Usage

• Results of Thermal Testing of COTS Cables

• FODB COTS Application

• Characterization Results

• Conclusions

Background• Goals of Advanced Interconnect Program

– Cable assembly using Commercial-Off-the-Shelf Technology (COTS).

– Wide variety of products with parameters for usage in different space environments.

– NASA wide use.

– Multimode and singlemode applications.

• FODB (Fiber Optic Data Bus) for EO-1 – COTS Parts: smaller, less weight, less expensive, state of the art.

– High data rate communications for science data transmissions.

– For use on future missions (re-useable technology).

– Enhancing only when necessary to withstand harsher environments.

Optical Fiber Cable Definitions

JacketStrength Members

Coating

Glass FiberBuffer

Hermetic Seal

Core

Cladding

Core

Cladding

Lessons LearnedLessons Learned• Shrinkage of Fluoropolymers: Teflon & Tefzel (TFE,

ETFE, PFA, FEP) - causes optical losses.

• Hygroscopic Behavior of Kevlar.• Strippability of Polyimide Coating.• Processing Control of Acrylate Material (affect on stripping).

• Outgassing of Acrylate Fiber Coating.• Contacting Fiber Connection : Pull-Proof.• Dimensional Compatibilities.• Hermetic Coating Fabrication.

Characterization of Systems(for available COTS FO assemblies)

• Parameters for environmental use based on characterization studies.

• Knowledge of the failure mechanisms associated with most products.

• Testing to bring out known failure mechanisms.• Specify environment for system, post testing.• Recommendations on how to bring product to the

next harsher environment.• Some generic testing for a wide variety of missions.

Failure Modes, Testing, Solutions• Material Changes Attenuation (Hydrogen Diffusion into Glass over

time)

• Thermal Cycling (aging)– Hermetic coatings, polyimide coatings, or shorter duration

mission.

• Cold Temp Attenuation (microbends, transient effect)

• Thermal Cycling (dwell at low temp)– Low CTE buffer, strength members, loose tube buffers,

temperature regulation.

• Materials Shrinkage Attenuation, Fiber Exposure• Thermal Cycling (aging)

– Extrusion process, smaller diam cable, material choice, temp regulation.

Failure Modes, Testing, Solutions

• Cracking of fiber and crack propagation• Thermal Cycling (aging)

• Vibration (survival)

• Bend Radius Analysis

– Chemical stripping, Temp regulation, shorter duration mission, pull proof connectors, material compability, low CTE buffer, epoxy.

• Radiation Induced Effects• Total Ionizing Dose Testing (attenuation)

– shielding, tefzel jacket, hermetic coating, avoid low temps, polyimide coating.

• Electron testing (scintillation, SEE)

– system changes

Testing and Analysis for COTS FO Cable Assembly Usage

• Outgassing of Materials

• Compatibility of Materials(CTE, bend radius)

• Thermal Characteristics(aging and cycling)

• Vibration Characteristics

• Radiation Effects

Testing: Cable Component Shrinkage from Temperature Cycling

-30 to 140 degrees C, 1 degree C/min, 5 min dwell at extremes

Cable Component Shrinkage vs. Thermal Cycle

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

6 12 18 24 31 38 46 52 60

Thermal Cycle

% R

elat

ive

Sh

rin

kag

e

Spectran

Brand Rex

W.L. Gore

Generic Environmental Parameter Testing

Optical Testing for Shrinkage From Thermal Cycling

Optical Power Output After Thermal Cycling of Northern Lights Hytrel Cable and W.L. Gore FON 1008

0

2

4

6

8

10

12

0 7 14 22 28 36

Thermal Cycle

Ou

tpu

t P

ow

er

(mic

row

att

s)

Northern Lights

W.L. Gore

W. L. Gore

Generic Environmental Parameter Testing

Summary of Test Results and Cable Parameters from Generic Shrinkage Testing

Manufacturer W.L. Gore Spectran BrandRex

NorthernLights

Microcable

NorthernLights

MicrocableW. L. Gore

Part Number 8388Prototype 1

Flightguide OC 1008 1-HY-MC-62CFD

1-HY-MC-10C

FON 1008

Total samples tested 4 6 4 3 3 2Length of samples ~ 3 m ~ 3 m ~ 3 m ~ 3, 4 m ~ 3 m 100 m

Measurement Length Length Length Length, Optical Length OpticalJacket Material Fluoropolymer Tefzel Tefzel Hytrel Hytrel FluoropolymerOuter Diameter 2.5 mm 1.8 mm 2.75 mm .9 mm .9 mm 1.16 mmTotal Number of

cycles60 60 60 36 36 36

Ave Total %shrinkage

3 1.58 2.43 1.14 2.25

Total attenuation (28 cycles)

-- -- -- -- -- .25 dB/100m

Total Attenuation(36)

-- -- -- 3.6 dB/4 m -- .084 dB/100m

FODB COTS Application: Twelve Channel FO Cable Assembly12 channel cable assembly: MTP connector (US Conec) and (W.L. Gore) 12 channel

ribbon cable, 33 times lighter and 20 times less expensive than old 38999 type connectors. Terminations by W.L. Gore and USConec.

The COTS analysis and testing concerns are:

• Outgassing of Materials (analysis & ASTM E595 testing)

» Boot change necessary for enhanced version: from Kraton, TML 15.53%, CVCM 10.04% to silicone elastomer: TML .02%, CVCM .09%. Kynar jacket used instead of PVC.

• Vibration (analysis and testing)

» Use larger core fiber (100/140 instead of 62.5/125 micron)

» New ferrules• Radiation (analysis only)

» No changes, EO-1 Radiation Environment Analysis based on worst case dose rate: 15 Krads, 4E-2 rads/sec, 12 ft length, -15°C, 1300 nm, power loss < .13 dB for 100/140/250 graded index fiber.

• Thermal (analysis and testing)

» No changes

MTP Ribbon Cable Assembly Characterization

• Random vibration testing: active monitoring of one channel and post measurements of all 12 channels. (14.1 grms, 1 minute/axis)

• Thermal testing: – 30 cycles, -20 °C to +85 °C, 1 °C /min.

– 42 cycles, -20 °C to +85 °C, 3 °C /min up, 2 °C /min down.

• Random vibration testing 2: active monitoring of one channel and post measurements of all 12 channels. (20 grms, 3 minutes/axis)

MTP Random Vibration Test One: Cable set 3, Channel 9

0 10 20 30 40 50 608.56

8.58

8.6

8.62

8.64

8.66Random Vibration Test 1, Cable Set 3, Channel 9, Z Axis Test

Optical P

ow

er

(mic

row

att

s)

Time (sec)0 10 20 30 40 50 60

8.55

8.6

8.65

8.7

8.75

8.8

8.85

8.9

8.95Random Vibration Test 1, Cable Set 3, Channel 9, Y Axis Test

Optical P

ow

er

(mic

row

att

s)

Time (sec)

0 10 20 30 40 50 60

8

8.1

8.2

8.3

8.4

Time (sec)

Optical P

ow

er

(mic

row

att

s)

Random Vibration Test 1, Cable Set 3, Channel 9, X Axis TestFull rangescale on Y and X axis tests.4 microwatts,and .5 microwattsrespectively.

Full range scale for Z axistest is .10microwatts

X axis

Y axisZ axis

Thermal Cycling Test Results: Cable Set 3

Post thermal optical poweraverage = -.13 dBStand. Dev. .70 dB

42 cycles-20°C to +85°C, 3 °C/min up2 °C/min down

Loss -.16 dB @-20°C

0 20 40 60 80 1006.5

7

7.5

Opt

ical

Pow

er (

mic

row

atts

)

Time (hours)0 20 40 60 80 100

-50

0

50

100

Tem

pera

ture

(C

elsi

us)

42 Cycle Thermal Cycling Test for Cable Set 3, Channel 9

Post Test Measurements Cable Set 2(dB)

Cable Set 3(dB)

Vibration Average Loss .056 -.008Vibration Standard Dev. .11 .43

Thermal Average Loss -.46 -.13Thermal Standard Dev. .52 .70

Vibration 2 Average Loss -.08 -.09Vibration 2 Standard Dev. .57 .81

Characterization of the MTP Ribbon Cable Assembly

Pre thermal testing Post thermal testing

Evidence of pistoning causing cracking on optical fiber endface, found during post thermal examination

ConclusionsGeneric testing for shrinkage: Preconditioning procedure should be specific to cable configuration. One cable may not meet all needs. Spectran Flight Guide & W.L. Gore FON 1008, least shrinkage. Shrinkage of all cables less than .1% at 60 cycles. Larger diameter cables have higher shrinkage.

MTP 12 Fiber Ribbon Cable Assembly

• Twelve channel MTP connector/ribbon cable assembly with 62.5/125 micron fiber, characterized for EO-1

environment.• Vibration test one (1 min/axis): transients < .25 dB, and post test loss nearly zero.• Thermal cycling: -.026 dB & -.16 dB (loss) @ -20 °C,

– post test average loss < -.50 dB.

• Vibration test two (twice levels of test one for 3 minutes/axis) transients < .25 dB, average loss < -.10 dB.• Sources of uncertainty: source stability, fan out cables, rates of degradation.• One fiber in 48 pistoned (cracked) as a result of testing.

Data on Generic Space Environmental Testing“Fiber Optic Cable Assemblies for Space Flight II: Thermal and Radiation Effects,” M. Ott,Session on Photonics for Space Environments VISan Diego, July 1998, SPIE Vol. 3440.

Data on FODB Application“Twelve Channel Fiber Optic Connector Assembly: from Commercial off the Shelf to Space Flight Use,” M.Ott and J. Bretthauer, Session on Photonics for Space Environments VI, San Diego, July 1998, SPIE Vol. 3440.