ISS Fiber Investigation Teleconference 12/23/99

1. ISS Fiber InvestigationTeleconference 12/23/99 C. T. Mueller J. G. Coffer N. Presser G. Stupian December 22, 1999 THE AEROSPACE CORPORATION

2. Outline • SEM photographs of Bubble #1 • SEM photographs of Bubble #2 • Observations • Scenarios • Recommendation for Lab Cable

3. Bubble #1 Optical Inspection • Shape: classic rocket engine with wings at fiber center SEM • Debris on polyimide surface • 1 micron diameter spheres • thin slivers (crystalline in shape) • 1 micron diameter hole in polyimide • clogged with 1 micron spheres • may have filled in since formation • pinhole character • Sinkhole shape is absent

4. SEM close-up of Polyimide Coating Outside Bubble #1 • Enclosed are SEM photographs of the "pinhole" opening in the polyimide coating on "Bubble #1." Clearly the hole is quite small and has filled in (at least partially) with the small 1 micron spheres or droplets after the reaction has taken place. With the exception of the debris of spherical balls or droplets and slivers (which may be crystalline material), the polyimide surface appears to be intact. This latter observation does not support a violent ESD-type attack, but suggests the existence of a pinhole or puncture to the polyimide/carbon layers. Again, at this point we cannot say that all bubbles in the glass fiber and/or polyimide coatings outside them look alike so I would be hesitant to jump to any conclusions.

5. Bubble #1

6. Bubble #1

7. Bubble #1

8. Bubble #1

9. Bubble #2 Optical Inspection • Shape: football with long, narrow chimney SEM • Debris on polyimide surface • 1 micron “Hershey’s kisses” and sea of “extruded worm-like” columns • rectangular crystalline shapes • No pinholes in polyimide • Sinkhole shape above chimney location “football” To fiber edge “chimney”

10. Bubble #2 Optical

11. Bubble #2 SEM

12. Location of “Sinkhole” w.r.t. Debris flow

13. Bubble #2 above exit chimney

14. Bubble #2 Surface

15. Bubble #2 Surface

16. Bubble #2 Crystalline Debris

17. Root Cause Tree Start here

18. Observations -1 • Bubble features and external debris provide clues about the reaction that took place • Bubble inside glass • ridges indicate a slow reaction and/or selective etching process • shape of bubble with narrow neck or chimney and enlarge base at fiber center suggests a selective etching process • Ge-rich areas etch faster than pure silica regions (“football shape”) • Debris on top of polyimide • remaining exit hole in polyimide layer is small (~1 micron) • similar to droplet size of debris • clogged with droplets • hole sometimes closed, but appears to have been small (~1 micron) • sinkhole shape remains

19. Observations -2 • Debris on polyimide (cont.) • appears to have been extruded from the small hole in the polyimide • no evidence of burns or cracks at polyimide surface • large ESD event unlikely • location correlates with bubble • Unjacketed fiber (that was re-spooled) • optical photographs show some features

20. Unjacketed Fiber • Sample of unjacketed fiber was received from BiccGeneral for inspection • re-spooled, but not run through extrusion process • This sample was the one that was run through the respooler while Jeannette Plante and I probed for ESD fields. While this fiber has only seen the respooling process once, and may not have been in absolutely perfect condition prior to respooling process at BiccGeneral, tracking down the characteristics of the defects in the polyimide layer is important. • HeNe test does not show an evidence of bubbles in the glass • Optical inspection under the microscope reveals some problem areas in the polyimide coating • polyimide in one area appears to be delaminated in a bubble-like fashion • no physical break in the surface • polyimide in another area appears to be “flattened” • SEM inspection should reveal any damage to the polyimide surface

21. Possible Scenarios • ESD induced breach in polyimide/carbon coating followed by HF etching of glass • Delamination in polyimide is transformed into an opening by extrusion process allowing HF to attack the glass through cracks in the carbon layer • Delamination in polyimide creates a reservoir for HF etchant • pinholes in carbon layer allow HF to attack glass

22. Recommended Plan of Action for Lab Two-part Plan • Verify no bubbles in glass of installed fiber • Qualify mechanical strength of same-vintage fiber Rationale • Verifying the absence of bubbles in the glass fiber proves that the fiber is defect-free and most probably does not contain the precursors to their formation (i.e HF) • Ensuring adequate mechanical strength can be used to verify the 15 year life and can also prove that the precursors to bubble formation, such as ESD-induced damage are not present. • ESD-induced damage appears to reduce the strength of the fiber by introducing flaws in the surface of the glass

23. Plan Part I. Verify no bubbles in glass of installed fiber • He-Ne illumination for those cable that are visible • Optical Time Domain Reflectometry (OTDR) for all hidden cables • short pulsewidth 1 nS • short wavelength 850 nm • ability to eliminate end reflection

24. Plan Part II. Qualify mechanical strength of same-vintage fiber • Use gauge lengths and number of samples commensurate with amount of cable installed • Dynamic (tensile) and Static fatigue (tensile or bend) tests • Break strength and distribution • Weibull modules and N-parameter per ISA procedures • Lifetime calculation based on test data and conditions of fiber use