Assurance of COTS Fiber Optic Cable Assemblies for Space Flight

1
Assurance of COTS Fiber Optic Cable Assemblies
for Space Flight

• Melanie N. Ott
• Swales Aerospace / Goddard Space Flight Center
• Component Technologies and Radiation Effects
• 301-286-0127, melanie.ott_at_gsfc.nasa.gov
• http//misspiggy.gsfc.nasa.gov/tva

Commercialization of Military and Space
Electronics, February 10, 1999
2
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

3
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.

4
Optical Fiber Cable Definitions
Cladding
Core
Cladding
Core
5
Lessons 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.

6
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.

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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.

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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

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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

10
Testing Cable Component Shrinkage from
Temperature Cycling
-30 to 140 degrees C, 1 degree C/min, 5 min dwell
at extremes
Generic Environmental Parameter Testing
11
Optical Testing for Shrinkage From Thermal Cycling
Generic Environmental Parameter Testing
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Summary of Test Results and Cable Parameters from
Generic Shrinkage Testing
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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, -15C, 1300 nm, power
  loss lt .13 dB for 100/140/250 graded index fiber.
• Thermal (analysis and testing)
• No changes

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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)

15
MTP Random Vibration Test One Cable set 3,
Channel 9
Y axis
Z axis
Full range scale on Y and X axis tests .4
microwatts, and .5 microwatts respectively.
Full range scale for Z axis test is
.10 microwatts
X axis
16
Thermal Cycling Test Results Cable Set 3
42 cycles -20C to 85C, 3 C/min up 2 C/min
down
Post thermal optical power average -.13
dB Stand. Dev. .70 dB
Loss -.16 dB _at_ -20C
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Characterization of the MTP Ribbon Cable Assembly
Evidence of pistoning causing cracking on optical
fiber endface, found during post thermal
examination
Pre thermal testing
Post thermal testing
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Conclusions

• Generic 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 lt .25
  dB, and post test loss nearly zero.
• Thermal cycling -.026 dB -.16 dB (loss) _at_ -20
  C,
• post test average loss lt -.50 dB.
• Vibration test two (twice levels of test one for
  3 minutes/axis) transients lt .25 dB, average loss
  lt -.10 dB.
• Sources of uncertainty source stability, fan out
  cables, rates of degradation.
• One fiber in 48 pistoned (cracked) as a result of
  testing.

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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
VI San 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.