Assurance of COTS Fiber Optic Cable Assemblies for Space Flight Melanie N. Ott Swales Aerospace / Goddard Space Flight Center Component Technologies and Radiation Effects , 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 Jack e t Strength Members Coating Glass Fiber Buffer Hermetic Seal Core Cladding Core Cladding

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

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

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 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 axisZ 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 °C

Characterization of the MTP Ribbon Cable Assembly Pre thermal testingPost thermal testing Evidence of pistoning causing cracking on optical fiber endface, found during post thermal examination

Conclusions Generic testing for shrinkage: l Preconditioning procedure should be specific to cable configuration. l One cable may not meet all needs. l Spectran Flight Guide & W.L. Gore FON 1008, least shrinkage. l Shrinkage of all cables less than.1% at 60 cycles. l 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: dB & -.16 dB -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 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