ASTM E512-94(2010)
(Practice)Standard Practice for Combined, Simulated Space Environment Testing of Thermal Control Materials with Electromagnetic and Particulate Radiation
Standard Practice for Combined, Simulated Space Environment Testing of Thermal Control Materials with Electromagnetic and Particulate Radiation
ABSTRACT
This practice describes the standard procedures for providing exposure of thermal control materials to a simulated space environment comprising of the major features of vacuum, electromagnetic radiation, charged particle radiation, and temperature control. Broad recommendations relating to spectral reflectance measurements, as well as test parameters and other information that should be reported as an aid in interpreting test results are delineated. Specifications are provided for the vacuum system, solar simulator, charged particle sources, safety precautions, and data interpretation.
SCOPE
1.1 This practice describes procedures for providing exposure of thermal control materials to a simulated space environment comprising the major features of vacuum, electromagnetic radiation, charged particle radiation, and temperature control.
1.2 Broad recommendations relating to spectral reflectance measurements are made.
1.3 Test parameters and other information that should be reported as an aid in interpreting test results are delineated.
1.4 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.
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Designation: E512 − 94(Reapproved 2010)
Standard Practice for
Combined, Simulated Space Environment Testing of
Thermal Control Materials with Electromagnetic and
Particulate Radiation
This standard is issued under the fixed designation E512; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Spacecraft thermal control coatings may be affected by exposure to the space environment to the
extent that their radiative properties change and the coatings no longer control temperatures within
desiredlimits.Forsomecoatings,thisdegradationofpropertiesoccursrapidly;othersmaytakealong
time to degrade. For the latter materials, accelerated testing is required to permit approximate
determination of their properties for extended flights. The complexity of the degradation phenomena
and the inability to characterize materials in terms of purity and atomic or molecular defects make
laboratory exposures necessary.
It is recognized that there are various techniques of investigation that can be used in space
environment testing. These range in complexity from exposure to ultraviolet radiation in the
wavelength range from 50 to 400 nm, with properties measured before and after testing, to combined
environmental testing using both particle and electromagnetic radiation and in situ measurements of
radiative properties. Although flight testing of thermal control coatings is preferred, ground-based
simulations, which use reliable test methods, are necessary for materials development. These various
approaches to testing must be considered with respect to the design requirements, mission space
environment, and cost.
1. Scope 2. Referenced Documents
1.1 This practice describes procedures for providing expo- 2.1 ASTM Standards:
sure of thermal control materials to a simulated space environ- E275PracticeforDescribingandMeasuringPerformanceof
ment comprising the major features of vacuum, electromag- Ultraviolet and Visible Spectrophotometers
netic radiation, charged particle radiation, and temperature E296Practice for Ionization Gage Application to Space
control. Simulators
E349Terminology Relating to Space Simulation
1.2 Broad recommendations relating to spectral reflectance
E434Test Method for Calorimetric Determination of Hemi-
measurements are made.
sphericalEmittanceandtheRatioofSolarAbsorptanceto
1.3 Test parameters and other information that should be
Hemispherical Emittance Using Solar Simulation
reported as an aid in interpreting test results are delineated.
E490Standard Solar Constant and Zero Air Mass Solar
1.4 This standard does not purport to address all of the
Spectral Irradiance Tables
safety concerns, if any, associated with its use. It is the E491Practice for Solar Simulation for Thermal Balance
responsibility of the user of this standard to establish appro-
Testing of Spacecraft
priate safety and health practices and determine the applica- E903Test Method for Solar Absorptance, Reflectance, and
bility of regulatory limitations prior to use.
Transmittance of Materials Using Integrating Spheres
3. Terminology
3.1 Definitions:
This practice is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of SpaceTechnology and is the direct responsibility of
Subcommittee E21.04 on Space Simulation Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2010. Published May 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1973. Last previous edition approved in 2004 as E512–94 (2004). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E0512-94R10. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E512 − 94 (2010)
3.1.1 absorbed dose—the amount of energy transferred 3.1.15 solar constant—the solar irradiance, at normal
from ionizing radiation to a unit mass of irradiated material. incidence, on a surface in free space at the earth’s mean
distance from the sum of 1 AU. The value is 1353 6 21
3.1.2 absorbed dose versus depth—the profile of absorbed
W/m (see Tables E490).
energy versus depth into material.
3.1.16 synergistic—relatingtothecooperativeactionoftwo
3.1.3 bleaching—the decrease in absorption of materials
or more independent causal agents such that their combined
following irradiation because of a reversal of the damage
effect is different than the sum of the effect caused by the
processes. This results in a reflectance greater than that of the
individual agents.
initially damaged material. Also referred to as annealing.
3.1.17 thermal emittance (ε)—the ratio of the thermal-
3.1.4 equivalent ultraviolet sun (EUVS)—the ratio of the
radiant exitance (flux per unit area) of the radiator (specimen)
solar simulation source energy to a near ultraviolet sun for the
to that of a full radiator (blackbody) at the same temperature.
same wavelength region of 200 to 400 nm.
3.1.5 far ultraviolet (FUV)—the wavelength range from 10
4. Summary of Practice
to 200 nm. Also referred to as vacuum ultraviolet or extreme
4.1 The most typical approach in performing this test is to
ultraviolet.
measure the radiative properties of the specimen under
3.1.6 far ultraviolet sun—the spectral and energy content of
consideration,thentoplacethespecimeninavacuumchamber
the sun in the wavelength range from 10 to 200 nm. The
and expose it to the desirable simulated space environments.
spectrumischaracterizedbyacontinuumspectrumtoapproxi-
The specimen temperature is controlled during the period of
mately 160 nm and a line spectrum to 10 nm.The solar energy
exposure. The radiative property measurements are performed
intheFUVfluctuatesandforpurposesofirradiationofthermal
insituwithoutexposingthespecimentoatmosphericpressure,
control coatings, the UV sun is defined as 0.1 W/m for the
after exposure and before measurement. Unless it has been
wavelength range from 10 to 200 nm (see Tables E490)at1
established that the material under investigation is not affected
11 3
AU (astronomical unit) (1.4959882×10 m) (1).
by postexposure measurements, the in situ approach is the
3.1.7 in situ—within the vacuum environment. It may be
preferred method. Usually only the radiative property of solar
usedtodescribemeasurementsperformedduringirradiationas
absorptance, α , is of interest, and the net result of the test is a
s
well as those performed before and after irradiation.
measurement of change in solar absorptance, ∆α . For detailed
s
3.1.8 integral flux—the total number of particles impinged discussionsofmethodsofdeterminingradiativeproperties,see
on a unit area surface for the duration of a test, determined by Test Method E903 and Refs. (2), (3), and (4).
integrating the incident particle’s flux over time.Also referred
4.2 The most effective method is to combine the radiation
to as fluence.
components of the space environments and investigate the
3.1.9 irradiance at a point on a surface—thequotientofthe
synergisticeffectsonradiativepropertiesofthethermalcontrol
radiant flux incident on an element of the surface containing
materials.
the point, by the area of that element. Symbol: E , E; E
e e
=dφ /dA; Unit: watt per square metre, W/m . (See Terminol-
5. Specimen Analysis
e
ogy E349.)
5.1 Amethodcharacterizingthebehaviorofthermalcontrol
3.1.10 near ultraviolet—the wavelength range from 200 to
materials during space environment exposure is through spec-
400 nm.
tralreflectancemeasurements.Thetwoparametersofengineer-
ing importance are total solar absorptance (α ) and total
3.1.11 near ultraviolet sun—fortestpurposesonly,thesolar
s
hemispherical emittance (ε ). Solar absorptance is generally
irradiance, at normal incidence, on a surface in free space at a
h
determined from spectral reflectance measured under condi-
distanceof1AUfromthesuninthewavelengthbandfrom200
tions of near normal irradiation and hemispherical viewing
to 400 nm. Using the standard solar-spectral irradiance, the
over the wavelength range from 0.25 to 2.5 µm. For these
value is 8.73% of the solar constant or 118 W/m (see
measurements, an integrating sphere with associated spectro-
Terminology E349). This definition does not imply that any
photometer is commonly used. For reflectance measurements
spectral distribution of energy in this wavelength band is
beyond 2.5 µm, a blackbody cavity or parabolic reflectometer
satisfactory for testing materials.
is frequently used.
3.1.12 particlefluxdensity—thenumberofchargedparticles
5.2 Postexposure Measurements:
incident on a surface per unit area per unit time.
5.2.1 Although in situ measurements are necessary, many
3.1.13 reciprocity—a term implying that effect of radiation
measurements must be performed after removal of the speci-
is only a function of absorbed dose and is independent of dose
men from the test chamber. The accuracy of such measure-
rate.
ments should be verified by in situ measurements because of
3.1.14 solar absorptance (α )—the fraction of total solar
s
possible bleaching.
irradiationthatisabsorbedbyasurface.Usetherecommended
5.2.2 Postexposure measurements of properties should be
spectral-solar irradiance data contained in Tables E490.
accomplished as soon as possible after the exposure. Where
delays allow the possibility of bleaching, it is necessary to
minimize atmospheric effects by maintaining the specimens in
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this practice. the dark and in vacuum until measured. In the event that
E512 − 94 (2010)
evacuation is impractical, it is desirable that the specimens be They are included in Table 1 to give a more complete account
maintained under a positive pressure of dry argon. Note that ofmethodsforanalysisofthermalcontrolsurfacesdamagedby
bleaching by diffusion of oxygen or nitrogen into the system electromagnetic or particle irradiation, or both.
has been observed to occur in the dark, although more slowly,
SIMULATION SYSTEM
than in the light.
5.3 In Situ Analysis:
6. Vacuum System
5.3.1 Calorimetric measurements of thermal-radiative prop-
6.1 General Description—The vacuum system shall consist
erties have received some attention in connection with in situ
of the specimen test chamber, all other components of the
studies of thermal-radiative property changes. A calorimetric
simulation system that are joined to the chamber without
determination gives a direct measure of α /ε and therefore
s
vacuum isolation during specimen exposure, and the transition
indicates the in situ changes in thermal-radiative properties. If
sectionsbywhichthesecomponentsarejoinedtothechamber.
edoes not change, then the change in α /ε shows the change in
s
The vacuum system must perform the following functions:
α . If the electromagnetic radiation source provides a good
s
6.1.1 It must provide for a reduction of pressure of atmo-
matchtotheair-masszerosolar-spectralirradiance,then awill
sphericgasesinthetestchambertoalevelinwhichnoneofthe
be equal to α . The limiting factors in calorimetric α /ε
s s
constituents can react with the specimen material to affect the
determinations are the deviation of the spectral irradiance
validity of the tests. This provision implies a pressure no
produced by the simulated solar source from that of the solar
−6
greater than 1×10 torr (133 µPa) at the specimen position.
irradianceandtheaccuracyoftheirradiancemeasurement(see
6.1.2 It must provide that the specimen area be maintained
Test Method E434).
as free as possible from contaminant gases and vapors. These
5.3.2 In situ measurements allow the determination of the
gases and vapors may originate anywhere in the system
reflectance or absorptance in a vacuum environment. The
including from the test specimens themselves.
environment maintained for in situ measurements should have
6.1.3 It must promptly trap or remove any volatiles out-
noeffectonthepropertybeingmeasured.Theannealingofthe
gassed from the test specimens.
specimen after irradiation may occur sufficiently fast to make
6.1.4 Itmustprovideforaccuratepressuremeasurementsin
the posttest measurements misleading. In situ reflectance
the chamber. (See Practice E296.)
measurements allow the investigator to plot a curve of the
change in thermal radiative properties as a function of the
6.2 Test Chamber:
exposure or absorbed dose. Posttest measurements limit the
6.2.1 Construction—The specimen test chamber should be
data to one point at the total dose.
constructed of materials suitable for use in ultra-high vacuum.
Metals, glasses, and ceramics are used. Tables E490 contain
5.4 Physical Property Analysis:
information on materials for vacuum applications. Austenitic-
5.4.1 The complete evaluation of thermal control coatings
stainless steels, such as Type 304, are frequently used for
does not depend only on thermal-radiative property measure-
vacuum-chamber construction.
ments; coatings must have the adhesion and stability required
6.2.1.1 Welding and brazing should be performed in accor-
for retention on a specified substrate. One method used to
dance with good high-vacuum practice and the temperature
evaluate the ability of the coating to remain firmly attached to
requirements of the chamber. Materials to be joined must be
the substrate in space is through thermal cycling of the
properly cleaned so that sound, leaktight, nonporous joints can
specimens either during or after radiation exposure in a
be made. Inert gas arc welding (TIG), using helium or argon,
vacuum.
and electron beam welding have been used. Brazing materials
5.4.2 The loss of mass of thermal control coatings can be
and cleaning techniques are discussed in Refs (5) and (6).
measured, to provide an indication of the amount of decom-
Weldsshouldbeonthevacuumsidetoeliminatethepossibility
position products leaving the coating during exposure. This
of trapping gas in cracks and crevices, thus creating a virtual
may be important in the study of the curing, outgassing, and
leak.Partsmustbeabsolutelycleanbeforewelding.Anoilfilm
contamination potential of thermal control coatings.
can cause gas to evolve and result in a porous, leaky weld.
5.4.3 Vacuum gas analysis (mass spectroscopy or residual
6.2.1.2 Dimensions of the test chamber should be suffi-
gas analysis, RGA) can be used to assess the type and
cientlylargeinrelationtothoseofthespecimenholder,sothat
concentration of decomposition products.
contaminants outgassed from any
...
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