# Presentation: 408867

## 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@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

- Core

- Cladding

- Core

- Cladding

## 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.

- 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.

## 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

## Generic Environmental Parameter Testing

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

## Optical Testing for Shrinkage From Thermal Cycling

- Generic Environmental Parameter Testing

## Summary of Test Results and Cable Parameters from Generic Shrinkage Testing

## FODB COTS Application: Twelve Channel FO Cable Assembly12 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

- 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

- Y axis

- Z axis

## Thermal Cycling Test Results: Cable Set 3

- Post thermal
- optical power
- average =  -.13 dB
- Stand. Dev. .70 dB

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

- Loss -.16 dB @
- -20°C

## 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

## 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 < .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 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.