ASTM E512-94(2004)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information.
Designation:E512–94 (Reapproved 2004)
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 priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This practice describes procedures for providing expo-
sure of thermal control materials to a simulated space environ-
2. Referenced Documents
ment comprising the major features of vacuum, electromag-
2.1 ASTM Standards:
netic radiation, charged particle radiation, and temperature
E275 Practice for Describing and Measuring Performance
control.
of Ultraviolet and Visible Spectrophotometers
1.2 Broad recommendations relating to spectral reflectance
E296 Practice for Ionization Gage Application to Space
measurements are made.
Simulators
1.3 Test parameters and other information that should be
E349 Terminology Relating to Space Simulation
reported as an aid in interpreting test results are delineated.
E434 TestMethodforCalorimetricDeterminationofHemi-
1.4 This standard does not purport to address all of the
spherical Emittance and the Ratio of SolarAbsorptance to
safety concerns, if any, associated with its use. It is the
Hemispherical Emittance Using Solar Simulation
responsibility of the user of this standard to establish appro-
E490 Standard Solar Constant and Zero Air Mass Solar
Spectral Irradiance Tables
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 Sept. 1, 2004. Published September 2004. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1973. Last previous edition approved in 1999 as E512–94 (1999). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E0512-94R04. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E512–94 (2004)
E491 Practice for Solar Simulation for Thermal Balance 3.1.13 reciprocity—a term implying that effect of radiation
Testing of Spacecraft is only a function of absorbed dose and is independent of dose
E903 Test Method for Solar Absorptance, Reflectance, and rate.
Transmittance of Materials Using Integrating Spheres 3.1.14 solar absorptance (a )—the fraction of total solar
s
irradiationthatisabsorbedbyasurface.Usetherecommended
3. Terminology
spectral-solar irradiance data contained in Tables E490.
3.1.15 solar constant—the solar irradiance, at normal inci-
3.1 Definitions:
dence, on a surface in free space at the earth’s mean distance
3.1.1 absorbed dose—the amount of energy transferred
from the sum of 1 AU. The value is 1353 6 21 W/m (see
from ionizing radiation to a unit mass of irradiated material.
Tables E490).
3.1.2 absorbed dose versus depth—the profile of absorbed
3.1.16 synergistic—relatingtothecooperativeactionoftwo
energy versus depth into material.
or more independent causal agents such that their combined
3.1.3 bleaching—the decrease in absorption of materials
effect is different than the sum of the effect caused by the
following irradiation because of a reversal of the damage
individual agents.
processes. This results in a reflectance greater than that of the
3.1.17 thermal emittance (´)—the ratio of the thermal-
initially damaged material. Also referred to as annealing.
radiant exitance (flux per unit area) of the radiator (specimen)
3.1.4 equivalent ultraviolet sun (EUVS)—the ratio of the
to that of a full radiator (blackbody) at the same temperature.
solar simulation source energy to a near ultraviolet sun for the
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.
measuretheradiativepropertiesofthespecimenunderconsid-
3.1.6 far ultraviolet sun—thespectralandenergycontentof
eration, then to place the specimen in a vacuum chamber and
the sun in the wavelength range from 10 to 200 nm. The
expose it to the desirable simulated space environments. The
spectrumischaracterizedbyacontinuumspectrumtoapproxi-
specimen temperature is controlled during the period of expo-
mately 160 nm and a line spectrum to 10 nm.The solar energy
sure. The radiative property measurements are performed in
intheFUVfluctuatesandforpurposesofirradiationofthermal
situ without exposing the specimen to atmospheric pressure,
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 4
AU (astronomical unit) (1.4959882 310 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, a , is of interest, and the net result of the test is a
s
well as those performed before and after irradiation.
measurementofchangeinsolarabsorptance, Da .Fordetailed
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
1 2
E =df /dA; Unit: watt per square metre, W/m . (See Termi-
e e
5. Specimen Analysis
nology 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-
3.1.11 near ultraviolet sun—fortestpurposesonly,thesolar
ing importance are total solar absorptance (a ) and total
s
irradiance, at normal incidence, on a surface in free space at a
hemispherical emittance (´ ). Solar absorptance is generally
h
distanceof1AUfromthesuninthewavelengthbandfrom200
determined from spectral reflectance measured under condi-
to 400 nm. Using the standard solar-spectral irradiance, the
tions of near normal irradiation and hemispherical viewing
value is 8.73% of the solar constant or 118 W/m (see
over the wavelength range from 0.25 to 2.5 µm. For these
Terminology E349). This definition does not imply that any
measurements, an integrating sphere with associated spectro-
spectral distribution of energy in this wavelength band is
photometer is commonly used. For reflectance measurements
satisfactory for testing materials.
beyond 2.5 µm, a blackbody cavity or parabolic reflectometer
3.1.12 particle flux density—the number of charged par-
is frequently used.
ticles incident on a surface per unit area per unit time.
5.2 Postexposure Measurements:
5.2.1 Although in situ measurements are necessary, many
measurements must be performed after removal of the speci-
Withdrawn. The last approved version of this historical standard is referenced
men from the test chamber. The accuracy of such measure-
on www.astm.org.
ments should be verified by in situ measurements because of
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this practice. possible bleaching.
E512–94 (2004)
5.2.2 Postexposure measurements of properties should be 5.6 Auxiliary Methods of Specimen Analysis—Severalother
accomplished as soon as possible after the exposure. Where techniques for specimen characterization and analysis are
delays allow the possibility of bleaching, it is necessary to availabletotheinvestigator.Asarule,theseareusuallyusedin
minimize atmospheric effects by maintaining the specimens in studies of damage mechanisms rather than engineering tests.
the dark and in vacuum until measured. In the event that They are included in Table 1 to give a more complete account
evacuation is impractical, it is desirable that the specimens be ofmethodsforanalysisofthermalcontrolsurfacesdamagedby
maintained under a positive pressure of dry argon. Note that electromagnetic or particle irradiation, or both.
bleaching by diffusion of oxygen or nitrogen into the system
SIMULATION SYSTEM
has been observed to occur in the dark, although more slowly,
than in the light.
6. Vacuum System
5.3 In Situ Analysis:
6.1 General Description—The vacuum system shall consist
5.3.1 Calorimetric measurements of thermal-radiative prop-
of the specimen test chamber, all other components of the
erties have received some attention in connection with in situ
simulation system that are joined to the chamber without
studies of thermal-radiative property changes. A calorimetric
vacuum isolation during specimen exposure, and the transition
determination gives a direct measure of a /´ and therefore
s
sectionsbywhichthesecomponentsarejoinedtothechamber.
indicates the in situ changes in thermal-radiative properties. If
The vacuum system must perform the following functions:
edoes not change, then the change in a /´ shows the change in
s
6.1.1 It must provide for a reduction of pressure of atmo-
a . If the electromagnetic radiation source provides a good
s
sphericgasesinthetestchambertoalevelinwhichnoneofthe
matchtotheair-masszerosolar-spectralirradiance,then awill
constituents can react with the specimen material to affect the
be equal to a . The limiting factors in calorimetric a /´
s s
validity of the tests. This provision implies a pressure no
determinations are the deviation of the spectral irradiance
−6
greater than 1 310 torr (133 µPa) at the specimen position.
produced by the simulated solar source from that of the solar
6.1.2 It must provide that the specimen area be maintained
irradianceandtheaccuracyoftheirradiancemeasurement(see
as free as possible from contaminant gases and vapors. These
Test Method E434).
gases and vapors may originate anywhere in the system
5.3.2 In situ measurements allow the determination of the
including from the test specimens themselves.
reflectance or absorptance in a vacuum environment. The
6.1.3 It must promptly trap or remove any volatiles out-
environment maintained for in situ measurements should have
gassed from the test specimens.
noeffectonthepropertybeingmeasured.Theannealingofthe
6.1.4 Itmustprovideforaccuratepressuremeasurementsin
specimen after irradiation may occur sufficiently fast to make
the chamber. (See Practice E296.)
the posttest measurements misleading. In situ reflectance
6.2 Test Chamber:
measurements allow the investigator to plot a curve of the
6.2.1 Construction—The specimen test chamber should be
change in thermal radiative properties as a function of the
constructed of materials suitable for use in ultra-high vacuum.
exposure or absorbed dose. Posttest measurements limit the
Metals, glasses, and ceramics are used. Tables E490 contain
data to one point at the total dose.
information on materials for vacuum applications. Austenitic-
5.4 Physical Property Analysis:
stainless steels, such as Type 304, are frequently used for
5.4.1 The complete evaluation of thermal control coatings
vacuum-chamber construction.
does not depend only on thermal-radiative property measure-
6.2.1.1 Welding and brazing should be performed in accor-
ments; coatings must have the adhesion and stability required
dance with good high-vacuum practice and the temperature
for retention on a specified substrate. One method used to
requirements of the chamber. Materials to be joined must be
evaluate the ability of the coating to remain firmly attached to
properly cleaned so that sound, leaktight, nonporous joints can
the substrate in space is through thermal cycling of the
be made. Inert gas arc welding (TIG), using helium or argon,
specimens either during or after radiation exposure in a
and electron beam welding have been used. Brazing materials
vacuum.
and cleaning techniques are discussed in Refs (5) and (6).
5.4.2 The loss of mass of thermal control coatings can be
Weldsshouldbeonthevacuumsidetoeliminatethepossibility
measured, to provide an indication of the amount of decom-
of trapping gas in cracks and crevices, thus creating a virtual
position products leaving the coating during exposure. This
leak.Partsmustbeabsolutelycleanbeforewelding.Anoilfilm
may be important in the study of the curing, outgassing, and
can cause gas to evolve and result in a porous, l
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