Electron Spectroscopy for Chemical Analysis (ESCA) survey measurements completed on the tray wall sections cut from LDEF tray locations C6-2, A4-9, and E10-8 are reported

Pippin, Gary

English

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NASA-CR-ZO521Z
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Comparison of Spacecraft Contamination Models with
Well-Defined Flight Experiment
NAS8-40581
Progress Report for May 15, 1997 to August 15, 1997
Prepared by:/_/L_ i_,
Gary Pippin
Approved by: :
y_lvester G. Hill
https://ntrs.nasa.gov/search.jsp?R=19980003847 2020-06-16T00:35:40+00:00Z
1. During this reporting period, ESCA survey measurements were completed on the tray
wall sections cut from LDEF tray locations C6-2, A4-9, and El0-8. This concludes the
ESCA survey activities on this contract, pending any additional requests by the contract
monitor. All results to date from these three surfaces are included in figures 1-3. A first
set of depth profiles has been carried out at locations on El0-8. Figures 5 through 13
show the auger sputtering profiles from the locations identified in figure 4. Profiles taken
at locations C-1 through -5, and C-8, show thin layers which appear to be essentially
silicon dioxide. The ratio of silicon to oxygen is approximately 1 to 2. The carbon
profile shows a little surface carbon, as expected from exposure to the atmosphere post-
flight, and then extremely low carbon levels in the silicon dioxide layer. At the depths
where the silicon intensity begins to decrease, the aluminum peak begins to increase.
This indicates the top of the aluminum oxide(anodized) coating. The profile for location
C-6, which is quite close to the discolored region, shows a much thicker silicon dioxide
layer( almost 1500 angstroms) but otherwise is similar to the previously discussed peaks.
The depth profiles from locations C-7 and B-1 are quite complex. The silicon and carbon
profiles show periodically varying intensities. The best initial estimate is that these
profiles represent very thick deposits from both the silicone based adhesive and
hydrocarbon based outgassing sources, such as the polyurethane based paint from the
interior of the tray, covered by a silicon dioxide layer. Because the sputtering system is
calibrated for SiO2, the sputter rate becomes more difficult to interpret as the carbon
content of the material increases. This means the depths shown on the profiles are not
very accurate after the first several thousand angstroms of sputtering.
To begin to interpret these profiles it should be kept in mind that the mission time
essentially goes from right to left. The first material deposited is the material with the
very high carbon content. The periodicity in the intensity levels may be a function of
seasonal variation of the sun orientation with respect to the surface, but this is just a guess
at present. The oxygen flux rate was much greater toward the end of the LDEF flight
relative to the first 3-4 years, so much of the surface oxidation could have occurred over
the last few months of the flight. In summary, the contamination deposits directly across
from the vents are complex mixtures of materials and the mechanisms by which they may
have been changed, once deposited on the surface, are not yet clear. The next surface to
be depth profiled will be from tray C6, which saw less than 1% of the atomic oxygen
exposure received by tray El0. Tray C6 did see about 60% of the solar exposure level
received by tray El0.
Figures 14 and 15 show peak energies and peak shapes for silicon ESCA peaks at
different sputtering depths. The peak positions have not yet been corrected for possible
charging effects. The position of the Carbon peak has also been measured at each of the
nominal depths, but this data is not yet available. The areas under the peaks reflect the
relative amounts of silicon at the different depths. Figure 15 shows the peaks normalized
to identical areas in order to show the relative shapes of the peaks. The peaks at a
nominal depth of 101.5 nm suggest at least two very different materials mixed at this
level.
Scanningelectronmicroscopeimagesof fracturespecimensfrom trayEl0-9 showa
flexible elastomericcontaminantlayercoveringtheanodizedaluminumlayeron thetray
lip. This is essentiallymaterialdepositedfrom thesiliconegasketpost-flight. The
contaminantlayeralongthetray wall hasaverybrittle structure,suggestinganoxidized
materialfrom theon-orbitexposures.Thesequenceof photosin figure 16showsaview
of a discoloredareafrom anareanearpositionE10-9(asurfaceattheEarthendof thetray
facing space)andlocationsfrom whichfracturesamplesweretaken. Theremaining
photosshowviewsof thesurfaceat selectedlocationsandedge-onviewsto showthe
structureof thecontaminantlayerson topof theanodizedaluminum.
Resultsof work-to-dateon thiscontractwerereportedat aSpacecraft
Coatings/ContaminationworkshopJuly9-10,1997. This workshopwassponsoredbythe
ContaminationWorking Groupof theSpaceEnvironments& EffectsProgram.
2. At this time,thereareno technicalissuesimpedingtheprogressof therequired
contracttasks.
3. During thelastphaseof this contract,depthprofiling will becompleted,themodel
calculationswill becarriedout,resultsfor all work on thiscontractwill besummarizedin
presentationsgivenat MSFC,andthefinal reportwill bewritten. Resultswill be
packagedfor inclusionon theSpaceEnvironments& EffectsProgramwebpage.
4. Costsarein line with thepercentageof completionof tasks.Theexpendedbudgetis
81%of thetotal andtheprojectis approximately81%complete.Approximately 15%of
theoverallbudgetis identifiedfor thesubcontractorson thiscontract.
List of Figures
Figure 1.
Figure2.
Figure3.
Figure4.
Figure5.
DiagramshowingPercentSiliconon thetray surfaceC6-2atthemeasured
locationsfor all individualESCAmeasurements.
DiagramshowingPercentSilicononthetray surfaceE10-8atthe
measuredlocationsfor all individualESCAmeasurements.
DiagramshowingPercentSiliconon thetray surfaceA4-9 atthemeasured
locationsfor all individualESCAmeasurements.
Locationsof augerdepthprofilesobtainedto-datefrom traylocation
El0-8.
DepthProfileshowingSilicon,Carbon,Aluminum, andOxygenelemental
%'s at location"C-1" from tray surfaceE10-8.
Figure6.
Figure7.
Figure8.
Figure9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
DepthProfile showingSilicon, Carbon,Aluminum,andOxygenelemental
%'s at location"C-2" from tray surfaceEl0-8.
DepthProfile showingSilicon,Carbon Aluminum,andOxygenelemental
%'s at location"C-3" from tray surfaceEl0-8.
DepthProfileshowingSilicon,Carbon Aluminum,andOxygenelemental
%'s at location"C-4" from tray surfaceEl0-8.
DepthProfileshowingSilicon,Carbon Aluminum,andOxygenelemental
%'s at location"C-5" from tray surfaceE10-8.
DepthProfileshowingSilicon,CarbonAluminum, andOxygenelemental
%'s at location"C-6" from tray surfaceEl0-8.
DepthProfile showingSilicon,Carbon Aluminum, and Oxygen elemental
%'s at location "C-7" from tray surface El0-8.
Depth Profile showing Silicon, Carbon Aluminum, and Oxygen elemental
%'s at location "C-8" from tray surface El0-8.
Depth Profile showing Silicon, Carbon, Aluminum, and Oxygen elemental
%'s at location "B-1" from tray surface E 10-8.
Silicon 2p peaks at selected sputtering depths, showing relative peak areas.
Silicon 2p peaks from figure 14, with areas normalized, to show peak
shapes more clearly.
Sequence of photos showing surface morphology for different locations
near vent location El0-9. Photos show both results of on-orbit deposition
and post-flight contact with tray cover gaskets.
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near vent location El0-9. Photos show both results of on-orbit deposition
and post-flight contact with tray cover gaskets.
(This figure is four pages of photos and Scanning Electron Microscope
images of tray surfaces and deposited contamination)
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Comparison of Spacecraft Contamination Models with Well-Defined Flight Experiment

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