ASTM E2089-00
(Practice)Standard Practices for Ground Laboratory Atomic Oxygen Interaction Evaluation of Materials for Space Applications
Standard Practices for Ground Laboratory Atomic Oxygen Interaction Evaluation of Materials for Space Applications
SCOPE
1.1 The intent of these practices is to define atomic oxygen exposure procedures that are intended to minimize variability in results within any specific atomic oxygen exposure facility as well as contribute to the understanding of the differences in the response of materials when tested in different facilities.
1.2 These practices are not intended to specify any particular type of atomic oxygen exposure facility but simply specify procedures that can be applied to a wide variety of facilities.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.3 The values stated in SI units are to be regarded as the standard.
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Designation:E2089–00
Standard Practices for
Ground Laboratory Atomic Oxygen Interaction Evaluation of
Materials for Space Applications
This standard is issued under the fixed designation E2089; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
A = exposed area of the witness sample, cm
1.1 The intent of these practices is to define atomic oxygen
k
A = exposed area of the test sample, cm
exposure procedures that are intended to minimize variability s
E = in-space erosion yield of the witness material,
k
in results within any specific atomic oxygen exposure facility
cm /atom
as well as contribute to the understanding of the differences in
E = erosion yield of the test material, cm /atom
s
the response of materials when tested in different facilities.
f = effective flux, atoms/cm /s
k
1.2 These practices are not intended to specify any particu-
F = effective fluence, total atoms/cm
k
lar type of atomic oxygen exposure facility but simply specify
DM = mass loss of the witness coupon, g
k
procedures that can be applied to a wide variety of facilities.
1.3 This standard does not purport to address all of the
3. Significance and Use
safety concerns, if any, associated with its use. It is the
3.1 These practices enable the following information to be
responsibility of the user of this standard to establish appro-
available:
priate safety and health practices and determine the applica-
3.1.1 Material atomic oxygen erosion characteristics.
bility of regulatory limitations prior to use.
3.1.2 An atomic oxygen erosion comparison of four well-
1.4 The values stated in SI units are to be regarded as the
characterized polymers.
standard.
3.2 The resulting data are useful to:
3.2.1 Compare the atomic oxygen durability of spacecraft
2. Terminology
materials exposed to the low Earth orbital environment.
2.1 Definitions:
3.2.2 Comparetheatomicoxygenerosionbehaviorbetween
2.1.1 atomic oxygen erosion yield—the volume of a mate-
various ground laboratory facilities.
rial that is eroded by atomic oxygen per incident oxygen atom
3.2.3 Comparetheatomicoxygenerosionbehaviorbetween
reported in cm /atom.
ground laboratory facilities and in-space exposure.
2.1.2 atomic oxygen fluence—the arrival of atomic oxygen
3.2.4 Screen materials being considered for low Earth
to a surface reported in atoms/cm
orbital spacecraft application. However, caution should be
2.1.3 atomic oxygen flux—the arrival rate of atomic oxygen
exercised in attempting to predict in-space behavior based on
−2 −1
to a surface reported in atoms·cm ·s .
ground laboratory testing because of differences in exposure
2.1.4 effective atomic oxygen fluence—the total arrival of
environment and synergistic effects.
atomic oxygen to a surface reported in atoms/cm , which
would cause the observed amount of erosion if the sample was
4. Test Specimen
exposed in low Earth orbit.
4.1 In addition to the material to be evaluated for atomic
2.1.5 effective atomic oxygen flux—thearrivalrateofatomic
oxygen interaction, the following four standard witness mate-
−2 −1
oxygen to a surface reported in atoms·cm ·s , which would
rials should be exposed in the same facility using the same
cause the observed amount of erosion if the sample was
operating conditions and duration exposure within a factor of
exposed in low Earth orbit.
3, as the test material: Kaptont polyimide H or HN, TFE-
2.1.6 witness materials or samples—materials or samples
fluorocarbon fluorinated ethylene propylene (FEP), low-
used to measure the effective atomic oxygen flux or fluence.
density polyethylene (PE), and pyrolytic graphite (PG). The
2.2 Symbols: −2 −1
atomic oxygen effective flux (in atoms·cm ·s ) and effective
fluence (in atoms/cm ) for polyimide Kapton H or HN should
1 be reported along with the mass or thickness loss relative to
These practices are under the jurisdiction ofASTM Committee E–21 on Space
polyimide Kapton H or HN for the test material, TFE-
Simulation and Applications of Space Technology and are the direct responsibility
of Subcommittee E21.04 on Space Simulation Test Methods.
fluorocarbon FEP, PE, and PG. For atomic oxygen interaction
Current edition approved May 10, 2000. Published June 2000.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2089
21 2
testing at effective fluences beyond 2 3 10 atoms/cm , standardwitnesscouponsinthisconfigurationbeforeanyother
polyimide Kapton H should be used and not Kapton HN testing to determine the effects of the masking on the atomic
becauseKaptonHNcontainsatomicoxygenresistantinorganic
oxygen flux.
particles which begin to protect the underlying polyimide thus
5.3.2 Cladding—Samples which are coated with protective
resulting in incorrect fluence prediction.
coatings on one side can be clad together by means of
4.2 It is not necessary to test the four standard witness
adhesivestoallowtheprotectivecoatingtobeexposedonboth
samples for each material exposure if previous data exists at
sides of the sample. The use of thin polyester adhesives (or
the same exposure conditions and if the fluence for the test
other non-silicone adhesive) is recommended to perform such
sampleiswithinafactorof3ofthestandardwitnessexposure.
cladding. The use of silicone adhesives should be avoided
When possible, the recommended standard witness polymer
because of potential silicone contamination of the sample.
materials should be 0.05 mm thick and of a diameter greater
Although cladding allows samples to be tested with the
than 5 mm. It is recommended that the pyrolytic graphite
protectivecoatingsonbothfaces,edgeexposureofthesamples
witness sample be 2 mm thick and of a diameter greater than
and their adhesive does occur and should be accounted for in
5 mm. High-fluence tests, which may erode through the full
calculating erosion characteristics of the desired surfaces.
thickness of the standard polymer witness, can use the recom-
5.4 Dehydration and Outgassing (for Samples Undergoing
mended thickness sample materials by stacking several layers
Weight Measurement)—Because most nonmetals and nonce-
of the polymer on top of each other.
ramic materials contain significant fractional quantities of
5. Procedure
water or other volatiles, or both, it is recommended that these
types of materials be vacuum-dehydrated before weighing to
5.1 Sample Preparation:
eliminate errors in weight because of moisture loss. Dehydrate
5.1.1 Cleaning:
samples of a thickness less than or equal to 0.127 mm (5 mils)
5.1.1.1 The samples to be evaluated for atomic oxygen
in a vacuum of a pressure less than 200 millitorr for a duration
interactions should be chemically representative of materials
of 48 h before sample weighing to ensure that the samples
that would be used in space.Thus, the surface chemistry of the
retain negligible absorbed water. Dehydrate and weigh thicker
samples should not be altered by exposure to chemicals or
samples periodically until weight loss indicates that no further
cleaningsolutionswhichwouldnotberepresentativelyusedon
water is being lost. Dehydrate multiple samples in the same
the functional materials to be used in space.
5.1.1.2 Wiping samples or washing them may significantly vacuum chamber provided they do not cross-contaminate each
other,andthattheyarenotofsufficientquantitysoastoinhibit
alter surface chemistry and atomic oxygen protection charac-
teristics of materials, and is therefore not recommended. uniform dehydration of all the samples.
However, if the typical use in space will require preflight
5.5 Weighing—Because hydration occurs quickly after re-
solventcleaning,thenperformsuchcleaningtosimulateactual
moval of samples from vacuum, weighing the samples should
surface conditions expected.
occurwithinfiveminutesofremovalfromvacuumdehydration
5.2 Handling—The atomic oxygen durability of materials
chambers. Reduction of uncertainty associated with moisture
withprotectivecoatingsmaybesignificantlyalteredasaresult
uptakecanbeminimizedbyweighingthesamplesatmeasured
of mechanical damage associated with handling. In addition,
intervals following removal from vacuum and back extrapo-
unprotected materials can become contaminated by handling,
lating to the mass at time of removal from vacuum. Weigh
resulting in anomalous consequences of atomic oxygen expo-
samples using a balance whose sensitivity is capable of
sure. It is recommended that samples be handled such as to
measuring the mass loss of the atomic oxygen fluence witness
minimize abrasion, contamination and flexure. The use of soft
samples. For 2.54-cm-diameter by 0.127-mm-thick Kapton H
fluoropolymer tweezers is recommended for handling poly-
polyimide fluence witness samples, a balance sensitivity 1 mg
meric films with protective coatings. For samples too heavy to 19 2
is acceptable for effective fluences of at least 10 atoms/cm .
be safely held with tweezers, use clean vinyl, latex, or other
Weigh the samples at room temperature (20 to 25°C). If the
gloves which will not allow finger oils to soak through and
temperature is outside this range, measure and record at the
which are lint-free to carefully handle the samples.
time of weighing.
5.3 Exposure Area Control:
5.6 Effective Fluence Prediction:
5.3.1 Masking—Frequently it is desirable to limit the expo-
5.6.1 Fluence Witness Samples:
sureofatomicoxygentoonesideofamaterialoralimitedarea
5.6.1.1 Ifthetestsampleisamaterialthatdoesnothaveany
on one side of the material. This can be done by wrapping
protective coating, then use polyimide Kapton H or HN
metalfoil(suchasaluminumfoil)aroundthesample,covering
samples to determine the effective atomic oxygen fluence. If
anareawithasacrificialpolymer(suchasKapton),orbyusing
the test sample has an atomic oxygen protective coating, then
glass to cover areas not to be exposed. It is recommended that
theprotectivecoveringbeinintimatecontactwiththematerial test an unprotected sample of the substrate material as well.
The unprotected sample can also be used to determine the
to prevent partial exposure of the masked areas. When using
metal foil within the RF or microwave excitation region of an effective atomic oxygen fluence provided that in-space erosion
yield data is available. If such in-space data is not available,
atomic oxygen source, it is likely that electromagnetic interac-
tions could take place between the metal and the plasma that then use a sample of polyimide Kapton H or HN should be
used for determination of effective atomic oxygen fluence
couldcauseanomalousatomicoxygenfluxesorshieldingfrom
−24 3
charged species, or both. It is important to expose the four assuming an in-space erosion yield of 3.0 3 10 cm /atom.
E2089
5.6.1.2 It is recommended that where physically possible, protected samples, it is important to weigh both samples as
the atomic oxygen fluence witness material be exposed to close as possible to the same time interval after removal from
vacuum.
atomic oxygen simultaneously with the test samples to enable
calculation of the effective atomic oxygen fluence. If chamber 5.6.4.2 Thickness Loss—Witness coupon material loss can
also be measured using various surface profiling techniques if
geometry prevents this, expose a fluence witness coupon just
the exposure area is too small for accurate weight measure-
prior to or immediately after the test sample. If high-fluence
ments to be taken. Profiling can be accomplished by stylus
exposureisnecessary,quiteoftenpolymericsheetsaretoothin
profiling,scanningatomicforcemicroscopy,orotherrecession
to survive long exposures. Therefore, thick coupons of poly-
measurement techniques. Take care when exposing samples to
imide or graphite are suggested to be used for high-fluence
atomic oxygen which will be subsequently used for profiling
weight or thickness loss measurements. The atomic oxygen
measurements that a portion of the original surface is kept
erosionyieldofpyrolyticgraphiterelativetopolyimideKapton
intact and that a clear step exists between the original surface
H or HN is different in some ground laboratory facilities than
and the atomic oxygen exposed portion. This requires that a
in space. Therefore, it is necessary to convert the mass loss or
thin (<0.2 mm thick) removable mask be used that is in
thicknesslossofthepyrolyticgraphitetotheequivalentlossof
intimate contact with the surface during the atomic oxygen
polyimide Kapton H. This can be accomplished by simulta-
exposure.
neous or sequential exposure of pyrolytic graphite and the
Kapton,andwillenabletheeffectivefluencetobecalculatedin
6. Calculation
terms of Kapton effective fluence, which is the accepted
6.1 Atomic Oxygen Kapton Effective Fluence Determina-
standard.
tion:
5.6.1.3 It is recommended that, periodically, samples of
6.1.1 Measurementofabsolutefluenceingroundlaboratory
Kapton H or HN, TFE-fluorocarbon FEP, polyethylene, and
facilities is typically difficult to perform. In addition, such
pyrolytic graphite be exposed to atomic oxygen in the test
measurements do not reliably predict in-space durability be-
chamber to verify operational consistency and to allow com-
cause of differences in erosion yields in the ground laboratory
parisons to be made between this test facility, space, and other
facilitycomparedtoin-space.Thereislikelytobeasubstantial
ground-basedsystems.Reportthisdataalongwithanytestdata
dependence of erosion yield upon energy of the oxygen atoms,
so that test results can be compared more easily.
which is also material-dependent.
5.6.2 Test, Standard Witness, and Fluence Witness Sample
6.1.2 To assist in the prediction of in-space performance
Position and Orientation—Facilities typically experience
based on ground laboratory atomic oxygen testing, it is
some spatial flux variation depending on how the atomic
desirable,tomeasureaneffectivefluenceforthematerialbeing
oxygen is formed. Minimization of errors in effective atomic
tested using a comparison of mass or thickness loss.
oxygen fluence will be achieved if witness samples are placed
6.1.3 Ifin-spaceatomicoxygenerosiondataisnotavailable
ascloseaspossibletothesamelocationasthetestsample,and
for the material being tested, then an effective fluence can be
thattheexposedsurfacesofthetestsampleandwitnesssample
reported based on witness sample erosion of a material of
areidenticalinsizeandorientation.Theuseofwitnesssamples known in-space erosion yield (such as polyimide Kapton H).
ofthesamesize,position,andorientationasthetestsamplesis
The witness sample material used must b
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