WF/PC-I SOFA Inspection

WF/PC-I: Molecular Contamination Analysis

• Chemical Analysis Methods.
• Pre-Launch Molecular Contamination Summary.
• Post-Flight Solvent Wipe Analysis Results.
• Optical Microscopy of CCD's #5 and #6.
• Future/Ongoing Work.

WF/PC-I SOFA Inspection

• Pre-disassembly electrical testing of SOFA performed by Schaeffer Magnetics Inc. showed no change in electrical parameters and no change in motor torques from original values.
• During disassembly of SOFA the following was noted:
  • Some filters showed evidence of delamination (see filter report by John Trauger).
  • Air gaps between rotors and staters all in specification.
  • No visible evidence of contamination seen on any mechanical parts or filters.
  • All bearings free running (note: bearing disassembly/inspection not performed as yet - will occur after January 1995).
  • No evidence of wear seen on any mechanical parts.
• To date Schaeffer Magnetics personnel have seen nothing that would preclude a recommendation to refly as is.

Chemical Analysis Methods

• Optical and Electron Microscopy
• Fourier Tansform Infrared (FTIR) Spectroscopy
  • Chemical Functional Groups, Quantitative Analysis.
  • Diffuse Reflectance (DRIFT) for trace analysis of solvent wipe samples.
  • FTIR Microscope for identification of non-metallic particles.
• Gas Chromatography/Mass Spectroscopy (GC/MS)
  • GC separation and MS chemical analysis.
  • Individual chemical components identified.
• X-Ray Photoelectron Spectroscopy (XPS)
  • Chemical Functional Group and Elemental Analysis.
  • Thin Film Analysis (sub-monolayer sensitivity).
• Size Exclusion Chromatography (HPLC/SEC)
  • Polymer Analysis: Modecular Weight Distribution.
• Atomic Force Microscopy (AFM)
  • Very high resolution 3-D surface imaging.
  • Thin organic films can be interactively imaged and manipulated to determine film thickness.

WF/PC-I Prelaunch Molecular Contamination

• Major Components:
  1. Esters (Aliphatic/Aromatic). This is a broad class of materials. The most common source is plasticizers (phthalate esters).
  2. Silicone (polydimethysilozane). Many possible sources. A major component of RTV silicone rubbers. Vacuum pump oils.
  3. Hydrocarbon Oils. Common contamination that has many sources (lubricants, outgassing components of polyolefin materials). Typically have a broad distribution of molecular weights.
• Minor Components:
  
  
  1. Amines are typically from Epoxy and Polyurethane curing agents.
  2. Organic Acid Salts. Typically from RTV accelerators and possibly from ethanol residue.
• Contamination Levels:
  • Molecular Contamination was generally less than ~1 microgram per square centimeter (1 µg/cm squared=~1 mg/ft squared=~10 nanometer film). Vent Tube 0.15 µg/cm squared or 1.5 nm film.

Post-Flight Molecular Contamination Analysis

• Analytical Method:
  • FTIR infrared spectroscopy, Diffuse Reflectance (DRIFT). Solvent (Freon/IPA) rinse using porous Teflon^® wipes.
• Quantitative/Semi-quantitative.
  • Sensitivity (nanograms, monolayer films) depends on sample area.
• Areas Tested
  • Vent Tube 0.82 µg/cm squared (0.15 before launch) ~20% Ester, trace amine, ~80% silicone.
  • Blanket (Light Pipe) 0.041 µg/cm squared (0.65 before launch) ~10% Ester, 80% silicone
  • Side Panel 0.077 µg/cm squared ~15% Ester, ~85% Silicone.
• Conclusions:
  • Post-flight surfaces are generally cleaner.
  • The ester (and amine) based components tend to be the most volatile.

• CCD (#5, #6) Window Surface Particles
  • Flatfield Images.
  • Haze on CCD #5.

• Optical Microscopy: CCD (#5,#6) Window surfaces.
  • Particles imaged on both CCD's.
  • Au particles, translucent particles and fibers.
  • Structured haze seen on #5.
• CCD Gold Cover and Thermal Shields (Near CCD window).
• XPS: The adjacent Au surface next to the CCD window has C-O and C=O functional groups present. CCD #5 has more residue and additional trace C-N functionality. No Si found (less than 0.1 monolayer).
• FTIR: The infrared spectra of rinses from the CCD thermal shield and baffles show silicone, ester and amines. The level is ~0.35 ug/cm squared for both #5 and #6.
• AFM: Shows the film thickness to be ~5.0 nanometers on the #6 CCD Au surface.
• Conclusion:
  • The material on the Au surfaces near the CCD windows is mainly ester and a lesser amount (on #5) of N-C material (i.e. possible amine). This is consistent with the previous wipes analysis showing that the ester components are volatile.

• Precisely correlate flatfield images to particles on the CCD windows.
• Complete FTIR, XPS and AFM on CCD surfaces.
• Analyze the residue on the CCD window by GC/MS and Size Exclusion Chromatography for component identification.

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