A brown stain of varying thickness was present on most of the exterior surface of the retrieved Long Duration Exposure Facility (LDEF). Tape lifts of Earth-end LDEF surfaces taken in Feb. 1990 showed that the surface particle cleanliness immediately after retrieval was very good, but faint footprints of the tape strips on the tested surfaces indicated a very faint film was removed by the tape. Solvent wipes of these surfaces showed that the stain was not amenable to standard organic solvent removal. Infrared spectra of optical windows from tray E5 and scrapings indicate that the film is primarily of organic composition, but is not similar to the oil that seeped from tray C12. Very dark and heavy deposits of the stain are present at openings and vents to the interior of the LDEF. Heavy brown and blue-green deposits are present in the interior of LDEF where sunlight penetrated through cracks and vent openings. Photographs of the deintegrated LDEF graphically show the stain distribution. The exterior of the LDEF had significant areas painted with a white polyurethane paint for thermal control, and almost all of the interior was painted with a black polyurethane paint for thermal control. The brown staining of the LDEF is consistent with long-term outgassing of hydrocarbons from these paints followed by rapid solar-ultraviolet-induced polymerization of the outgassed hydrocarbons when the outgassed molecules stuck to surfaces exposed to sunlight

Harvey, Gale A.

English

NASA Technical Reports Server

ORGANICCONTAMINATIONOFLDEF
Gale A. Harvey
NASA Langley Research Center
Hampton, VA 23665-5225
Phone: 804-864-6742, Fax: 804-864-7790
N92-23290
SUMMARY
A brown stain of varying thickness was present on most of the exterior surface of the retrieved
LDEF. Tape lifts of Earth-end LDEF surfaces taken in February 1990 showed that the surface particle
cleanliness immediately after retrieval was very good, but faint footprints of the tape strips on the
tested surfaces indicated a very faint film was removed by the tape. Solvent wipes of these surfaces
showed that the stain was not amenable to standard organic solvent removal. Infrared spectra of
optical windows from tray E5 and scrapings indicate that the film is primarily of organic composition,
but is not similar to the oil that seeped from tray C12. Very dark and heavy deposits of the stain are
present at openings and vents to the interior of LDEF. Heavy brown and blue-green deposits are
present in the interior of LDEF where sunlight penetrated through cracks and vent openings.
Photographs of the deintegrated LDEF graphically show the stain distribution.
The exterior of LDEF had significant areas painted with a white polyurethane paint for thermal
control, and almost all of the interior was painted with a black polyurethane paint for thermal control.
The brown staining of LDEF is consistent with long-term outgassing of hydrocarbons from these
paints followed by rapid solar-ultraviolet-induced polymerization of the outgassed hydrocarbons when
the outgassed molecules stuck to surfaces exposed to sunlight.
INTRODUCTION
The Langley Research Center developed and manages the Halogen Occultation Experiment
(HALOE, ref. 1) to measure stratospheric ozone chemistry on a global basis. The HALOE instrument
is a mid-infrared optical instrument which is sensitive to organic film on optical surfaces because the
two spectral bandpasses for measurement of HCL and CH4 include the 3.41a hydrocarbon absorption
band (ref. 2). The HALOE contamination control program makes extensive use of high-resolution-in-
transmission Fourier Transform Infrared (FTIR) spectroscopy of the 3.4t.t band to monitor HALOE
organic cleanliness (ref. 3). The HALOE measurement-of-organic-film techniques have been applied
to the retrieved LDEF.
TAPE LIFT DATA
Taking of tape lifts is an established procedure for measuring surface particle cleanliness. Particle
cleanliness is related to MIL-STD-1246B (ref. 4) which gives the particle cleanliness level, CL, which
is a standard method of specifying particle cleanliness. Specific descriptions of particles and their size
distributions are used to evaluate sources of particle contamination and to evaluate cleaning procedures.
PRECEDING P,_GE BLANK NOT FILMED
179
https://ntrs.nasa.gov/search.jsp?R=19920014047 2020-03-17T11:47:51+00:00Z
Theprocedureconsistsof preparingtape-liftkits, takingtapelifts of atestsurface,andreadingthetape
lift stripsin acleanenvironment.
Sixteentapelifts of removedLDEFFlighthardwareandsurfacesin theSAEF2 cleanroomwere
takenonFebruary14,1990. ThecleanlinesslevelsareplottedinFigure1. Theparticlecleanliness
levelof theretrievedLDEF endpanelsasseenin Figure1wasbetterthan300,which is quiteclean.
However,observersof thetapelift operationnoticedfaint "footprints"of thecontactareaof thetape
stripswerevisibleon thetestedLDEF surfacesindicatingafaint film wasremovedbythetape.
Subsequenttapelifts indicatedthesurfacecleanlinessrapidlydeterioratedwithdeintegrationactivities.
SOLVENTWIPEDATA
Extractedcleanroomwipes(ref. 5)wereusedextensivelyin thecleanlinesscertificationof
thermal-vacuumchambersusedfor testingtheHALOE instrument.Theprocedureis to wet thetest
surfacewith acleaningsolvent(ie spectroscopicgradeisopropylalcohol)whichwill allow transferof
someof theorganicfilm (typicallyabout75percent)to anextractedcleanroomwipe. Thewipeis air
driedat thefield site,bagged,andtransportedto ananalyticallab. Thecleanroomwipeis soakedin a
highpurity transfersolventatthelab,andtheorganiccontaminationis thenextractedandtransferredto
anIR windowfor weighingandFTIR spectroscopy.Thesurfaceconcentrationfactorfrom wipeto IR
windowis 1,000.The3.4gspectrumof anisopropylalcoholwipeof 1squarefoot of anLDEF
Earthendthermalcontrolpanelis presentinFigure2 alongwith thespectrumof acontrolwipe. The
LDEF EarthendthermalcontrolpanelwipehadabouttwicetheNVR asthecontrolwipe. Thatis,the
thermalcontrolpanelhadabout0.06mg/ft2of organicfilm thatwoulddissolvein isopropylalcohol.
ABSORPTIONSPECTRAOFE5OPTICALWINDOWS
ExperimentS0050-1containedseveralinfraredtransmittingwindows.Theseopticalwindows
werein a 1/6compartmentof trayE5 whichwascoveredwitha50percentransmitting/50percent
blockingsunscreen.Theinsidesurfaceof thesunscreenwaspaintedwith ChemglazZ306blackpaint
for thermalcontrol.
A 3.4gspectrumof theCaF2windowflown onLDEF is presentedasFigure3. SimilarCaF2
windowsareusedextensivelyin theHALOEcontaminationcontrolprogram(ref. 6)andalargedata
baseof organicfilms onCaF2windowsexistsatLaRC. The3.41.tabsorptionon theLDEF windowis
about7 percent.
An estimateof theorganicfilm masspersquarefootcanbeobtainedbyratioingtheNVRmass
with 7 percentabsorptiononan IR window/weighingpanof smallarea(0.08in2) to 1squarefoot of
area.Numerousmeasurementsof organicfilm show0.1mgof organicresidueona
0.08in2of CaF2correspondsto 7 percentabsorptionat 3.4g. Thus,acalculatedmass/ft2of organic
film on theLDEF windowis:
180
144in2 x 0.1mg = 180mg/ft 2
1 ft-7 0.8 in 2
This is a lot of organic film. One mg/ft2 or less of organic film is the standard cleanliness level "A"
typically required of contamination sensitive flight hardware.
The visual discoloration of this film can be seen in a photograph of a film-bracket-covered area and
uncovered area in tray E5, shown in Figure 4.
ABSORP'i'ION SPECTRA OF SEEPAGE FROM TRAY C12
Tray C12 of LDEF was observed to be leaking fluid several days after LDEF was moved to
SAEF 2 for deintegration. This tray had heavy deposits at the edges of the tray cover, ranging from
yellow-brown stains to a black layer of deposited material. The interior contained runs of fluid along
the walls and a wet band about 6 cm wide by 60 cm long on the bottom of the tray against one end.
Fluid from one of the runs was contact transferred to a clean CaF2 window. The 3.41a spectra of this
fluid is presented as Figure 5. The great strength of the methel stretch at 2860 cm- 1 and 2960 cm- 1
shows that the hydrocarbon composition of this fluid is much different than the hydrocarbon
composition of the contamination of Tray E5.
EXTERIOR PHOTOGRAPHS
Visual inspection of the deintegrated LDEF in April of 1990 clearly revealed several characteristics
of the organic stain on LDEF. Figures 6 and 7 show the stain on the trailing edge (row 3) of LDEF.
Figures 8 and 9 show a much fainter stain on the leading edge (ram direction=row 9) of LDEF. But
Figures 10, 11, 12, and 13 show the heaviest deposits on end plates surface near vents from the
interior. At these locations the deposits were so heavy they were curling off the rough milled surfaces
of the end plates. It is concluded that the stain at one time was greatest on all leading edges, but that
the direct ram surfaces were effectively cleaned by atomic oxygen during the later months in orbit.
Figure 14 shows light NVR on the trailing edge of an end plate.
INTERIOR PHOTOGRAPHS
Brown stains were present on unpainted diagonal braces behind cracks between two sections of
micrometeoroid panels (Figure 15). Brown stains were also present on unpainted end braces. Dark
blue and blue-green deposits were present on interior surfaces facing the ram direction where sunlight
was incident through cracks or vent holes. Figure 16 and 16a show the undeposited shadow of a
fastener surrounded by a blue-green deposit. A blue deposit is shown in Figure 17 with a rail clip and
its shadow. The deposit behind a 3/4" x 3/4" tray comer vent hole is shown in Figure 18. These
deposits could be scraped off to uncover the black thermal-control paint underneath.
These photographs demonstrate that the organic stain was polymerized by sunlight and that the
heaviest deposits were on the ram side.
181
OUTGASSINGMEASUREMENTSOFTHE THERMAL CONTROLPAINTS
Threeindependentmeasurementsof outgassingof theblackthermalcontrolpaint(Z306)usedon
LDEF weremadeatLaRCfollowingtheretrievalof LDEF. Exposuresin avacuumovengave
0.1percentmasslossafter1weekat24° C;
1.4percentmasslossafter 1weekat60° C;
and23.0percentmasslossafter 16hoursat 177° C.
The 16hoursat 177° C wouldcorrespondto 6 yearsatambient(25° C) temperature if the 10 ° C rise in
temperature produces a doubling of outgassing rule applied.
High resolution FTIR spectra (Figures 19 and 20) of Z306 heated in an evacuated gas cell show
considerable CO2 and CO, and some CH4 and H20 outgassing during the first few hours at
approximately 120 ° C. Heavier hydrocarbon absorption is also present at 2960 cm" 1 (CH3 stretch) in
Figure 21. The mass loss during heating was 2.8 percent. A brown film coated the gas cell walls after
heating of the 16 mg paint sample. Also shown in Figure 20 is a spectrum of scraped film from an
LDEF end plate. The 3.41.t spectrum of the end plate scraping is almost identical to the gas cell film,
but very unlike the spectrum from Tray E5 (Figure 3) and Tray C12 (Figure 5). The LDEF end plate
scraping has 2 gm/ft 2 of mass per unit area.
Time-sequence FTIR spectra were obtained of outgassing of the white Chemglaz paint (A276) in
an evacuated gas cell heated to 115°C. Spectra were obtained after 5, 10, 25, 40, 65, and 155 minutes
of heating. Spectra of the unheated cell were also obtained 1 and 2 days later. These spectra are
presented in figures 21-24. The 3.4 m absorption is the same as that of Chemglaz Z306. This
absorption is the strongest feature in the 5 minute spectrum, but is surpassed in strength by CO2 after
25 minutes of heating at 115°C. The mass loss after 155 minutes at 115°C was 2.7 percent.
Atomic mass spectra (figure 25) of outgassing at room temperature from a 5 month cured sample
of Chemglaz Z306 was obtained with a residual gas analyser. A mass fragment of 113 amu is the
most abundant paint outgassing heavy-mass-fragment. Additional mass-spectral data are reported in
references 6 and 7.
CONCLUSIONS
The major conclusions drawn from studies of LDEF relating to organic film contamination are:
° The primary source of the ubiquitous brown stain was outgassing of the black thermal control
paint (Chemglaz Z306). The stain is a different hydrocarbon composition at the vent openings
than on tray surfaces.
2. The paint outgassing and redeposition was temperature driven and retention on surfaces was
strongly affected by solar ultraviolet induced polymerization of outgassed molecules.
3. Atomic oxygen severely eroded the stain on the leading edge (row 9) late in the mission.
182
REFERENCES
°
2.
,
,
°
,
7.
UARS Project Data Book, General Electric Astrospace Division, April 1987.
Harvey, G. A., J. L. Raper, and R. N. Messier, "Microcontamination of IR Spacecraft Optics,"
in Proceedings of Microcontamination Conference and Exposition, Anaheim, CA, pp. 237-259,
October 1989.
Harvey, G. A. and J. L. Raper, "Halogen Occultation Experiment (HALOE) Optical Witness-
Plate Program," NASA TM 4081, February 1989.
Military Standard Product Cleanliness Levels and Contamination Control Program, MIL-STD-
1246A, August 18, 1967, Department of Defense, Washington, DC 20301.
Harvey, G. A., J. L. Raper, and D. C. Zellers, "Measuring Low-Level Nonvolatile Residue
Contamination on Wipes, Swabs, and Gloves," Microcontamination, 8(11): 43-46, 69, 1990.
Colony, J. A., "Mass Spectrometry of Aerospace Materials," NASA TN D-8261, June 1976.
Glassford, A. P. M. and J. W. Garrett, "Characterization of Contamination Generation
Characteristics of Satellite Materials, WRDC-TR-4114," WRDC/MLBT, WPAFB, Ohio,
November 1989.
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ORIGINAL PAGE
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188
Figure 9. NVR on Space-end Row 9.
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Figure 13. NVR on Space-end plate (ram direction).
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Figure 16. Earth-end interior fastener.
Figure 16a. NVR around interior fastener.
192
ORIGrNAL PAGE
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Figure 17. Blue NVR at cable clamp.
Figure 18. NVR behind tray-corner hole.
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196
SPACE ENVIRONMENTS
IONIZING RADIATION
197



Organic contamination of LDEF

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