ASTM E512-94(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E 512 – 94 (Reapproved 1999)
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 E 512; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) 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
desired limits. For some coatings, this degradation of properties occurs rapidly; others may take a long
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 E 275 Practice for Describing and Measuring Performance
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
1.1 This practice describes procedures for providing expo-
eters
sure of thermal control materials to a simulated space environ-
E 296 Practice for Ionization Gage Application to Space
ment comprising the major features of vacuum, electromag-
Simulators
netic radiation, charged particle radiation, and temperature
E 349 Terminology Relating to Space Simulation
control.
E 434 Test Method for Calorimetric Determination of
1.2 Broad recommendations relating to spectral reflectance
Hemispherical Emittance and the Ratio of Solar Absorp-
measurements are made.
tance to Hemispherical Emittance Using Solar Simulation
1.3 Test parameters and other information that should be
E 490 Solar Constant and Air Mass Zero Solar Spectral
reported as an aid in interpreting test results are delineated.
Irradiance Tables
1.4 This standard does not purport to address all of the
E 491 Practice for Solar Simulation for Thermal Balance
safety concerns, if any, associated with its use. It is the
Testing of Spacecraft
responsibility of the user of this standard to establish appro-
E 903 Test Method for Solar Absorptance, Reflectance, and
priate safety and health practices and determine the applica-
Transmittance of Materials Using Integrating Spheres
bility of regulatory limitations prior to use.
3. Terminology
2. Referenced Documents
3.1 Definitions:
2.1 ASTM Standards:
3.1.1 absorbed dose—the amount of energy transferred
from ionizing radiation to a unit mass of irradiated material.
This practice is under the jurisdiction of ASTM Committee E-21 on Space
Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.04 on Space Simulation and Thermal Radiation. Annual Book of ASTM Standards, Vol 03.06.
Current edition approved Feb. 15, 1994. Published April 1994. Originally Annual Book of ASTM Standards, Vol 15.03.
published as E 512 – 73. Last previous edition E 512 – 73 (1985). Annual Book of ASTM Standards, Vol 12.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 512
3.1.2 absorbed dose versus depth—the profile of absorbed 3.1.16 synergistic—relating to the cooperative action of two
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 (e)—the ratio of the thermal-
initially damaged material. Also referred to as annealing. radiant exitance (flux per unit area) of the radiator (specimen)
to that of a full radiator (blackbody) at the same temperature.
3.1.4 equivalent ultraviolet sun (EUVS)—the ratio of the
solar simulation source energy to a near ultraviolet sun for the
4. Summary of Practice
same wavelength region of 200 to 400 nm.
4.1 The most typical approach in performing this test is to
3.1.5 far ultraviolet (FUV)—the wavelength range from 10
measure the radiative properties of the specimen under consid-
to 200 nm. Also referred to as vacuum ultraviolet or extreme
eration, then to place the specimen in a vacuum chamber and
ultraviolet.
expose it to the desirable simulated space environments. The
3.1.6 far ultraviolet sun—the spectral and energy content of
specimen temperature is controlled during the period of expo-
the sun in the wavelength range from 10 to 200 nm. The
sure. The radiative property measurements are performed in
spectrum is characterized by a continuum spectrum to approxi-
situ without exposing the specimen to atmospheric pressure,
mately 160 nm and a line spectrum to 10 nm. The solar energy
after exposure and before measurement. Unless it has been
in the FUV fluctuates and for purposes of irradiation of thermal
established that the material under investigation is not affected
control coatings, the UV sun is defined as 0.1 W/m for the
by postexposure measurements, the in situ approach is the
wavelength range from 10 to 200 nm (see Tables E 490) at 1
preferred method. Usually only the radiative property of solar
AU (astronomical unit) (1.495 988 2 3 10 m) (1).
absorptance, a , is of interest, and the net result of the test is a
3.1.7 in situ—within the vacuum environment. It may be s
measurement of change in solar absorptance, Da . For detailed
used to describe measurements performed during irradiation as s
discussions of methods of determining radiative properties, see
well as those performed before and after irradiation.
Test Method E 903 and Refs. (2), (3), and (4).
3.1.8 integral flux—the total number of particles impinged
4.2 The most effective method is to combine the radiation
on a unit area surface for the duration of a test, determined by
components of the space environments and investigate the
integrating the incident particle’s flux over time. Also referred
synergistic effects on radiative properties of the thermal control
to as fluence.
materials.
3.1.9 irradiance at a point on a surface—the quotient of the
radiant flux incident on an element of the surface containing
5. Specimen Analysis
the point, by the area of that element. Symbol: E , E;
e
1 2
5.1 A method characterizing the behavior of thermal control
E 5 df /dA; Unit: watt per square metre, W/m . (See Ter-
e e
materials during space environment exposure is through spec-
minology E 349.)
tral reflectance measurements. The two parameters of engineer-
3.1.10 near ultraviolet—the wavelength range from 200 to
ing importance are total solar absorptance (a ) and total
s
400 nm.
hemispherical emittance (e ). Solar absorptance is generally
h
3.1.11 near ultraviolet sun—for test purposes only, the solar
determined from spectral reflectance measured under condi-
irradiance, at normal incidence, on a surface in free space at a
tions of near normal irradiation and hemispherical viewing
distance of 1 AU from the sun in the wavelength band from 200
over the wavelength range from 0.25 to 2.5 μm. For these
to 400 nm. Using the standard solar-spectral irradiance, the
2 measurements, an integrating sphere with associated spectro-
value is 8.73 % of the solar constant or 118 W/m (see
photometer is commonly used. For reflectance measurements
Terminology E 349). This definition does not imply that any
beyond 2.5 μm, a blackbody cavity or parabolic reflectometer
spectral distribution of energy in this wavelength band is
is frequently used.
satisfactory for testing materials.
5.2 Postexposure Measurements:
3.1.12 particle flux density—the number of charged par-
5.2.1 Although in situ measurements are necessary, many
ticles incident on a surface per unit area per unit time.
measurements must be performed after removal of the speci-
3.1.13 reciprocity—a term implying that effect of radiation
men from the test chamber. The accuracy of such measure-
is only a function of absorbed dose and is independent of dose
ments should be verified by in situ measurements because of
rate.
possible bleaching.
3.1.14 solar absorptance (a )—the fraction of total solar
s
5.2.2 Postexposure measurements of properties should be
irradiation that is absorbed by a surface. Use the recommended
accomplished as soon as possible after the exposure. Where
spectral-solar irradiance data contained in Tables E 490.
delays allow the possibility of bleaching, it is necessary to
3.1.15 solar constant—the solar irradiance, at normal inci-
minimize atmospheric effects by maintaining the specimens in
dence, on a surface in free space at the earth’s mean distance
the dark and in vacuum until measured. In the event that
from the sum of 1 AU. The value is 1353 6 21 W/m (see
evacuation is impractical, it is desirable that the specimens be
Tables E 490).
maintained under a positive pressure of dry argon. Note that
bleaching by diffusion of oxygen or nitrogen into the system
has been observed to occur in the dark, although more slowly,
than in the light.
The boldface numbers in parentheses refer to the list of references at the end of
this test method. 5.3 In Situ Analysis:
E 512
5.3.1 Calorimetric measurements of thermal-radiative prop- SIMULATION SYSTEM
erties have received some attention in connection with in situ
6. Vacuum System
studies of thermal-radiative property changes. A calorimetric
determination gives a direct measure of a /e and therefore 6.1 General Description—The vacuum system shall consist
s
indicates the in situ changes in thermal-radiative properties. If of the specimen test chamber, all other components of the
edoes not change, then the change in a /e shows the change in simulation system that are joined to the chamber without
s
a . If the electromagnetic radiation source provides a good vacuum isolation during specimen exposure, and the transition
s
match to the air-mass zero solar-spectral irradiance, then a will sections by which these components are joined to the chamber.
be equal to a . The limiting factors in calorimetric a /e The vacuum system must perform the following functions:
s s
determinations are the deviation of the spectral irradiance 6.1.1 It must provide for a reduction of pressure of atmo-
produced by the simulated solar source from that of the solar spheric gases in the test chamber to a level in which none of the
irradiance and the accuracy of the irradiance measurement (see constituents can react with the specimen material to affect the
Test Method E 434). validity of the tests. This provision implies a pressure no
−6
5.3.2 In situ measurements allow the determination of the greater than 1 3 10 torr (133 μPa) at the specimen position.
reflectance or absorptance in a vacuum environment. The 6.1.2 It must provide that the specimen area be maintained
environment maintained for in situ measurements should have as free as possible from contaminant gases and vapors. These
no effect on the property being measured. The annealing of the gases and vapors may originate anywhere in the system
specimen after irradiation may occur sufficiently fast to make including from the test specimens themselves.
the posttest measurements misleading. In situ reflectance 6.1.3 It must promptly trap or remove any volatiles out-
measurements allow the investigator to plot a curve of the gassed from the test specimens.
change in thermal radiative properties as a function of the 6.1.4 It must provide for accurate pressure measurements in
exposure or absorbed dose. Posttest measurements limit the the chamber. (See Practice E 296.)
data to one point at the total dose. 6.2 Test Chamber:
5.4 Physical Property Analysis: 6.2.1 Construction—The specimen test chamber should be
5.4.1 The complete evaluation of thermal control coatings constructed of materials suitable for use in ultra-high vacuum.
does not depend only on thermal-radiative property measure- Metals, glasses, and ceramics are used. Tables E 490 contain
ments; coatings must have the adhesion and stability required information on materials for vacuum applications. Austenitic-
for retention on a specified substrate. One method used to stainless steels, such as Type 304, are frequently used for
evaluate the ability of the coating to remain firmly attached to vacuum-chamber construction.
the substrate in space is through thermal cycling of the 6.2.1.1 Welding and brazing should be performed in accor-
specimens either during or after radiation exposure in a dance with good high-vacuum practice and the temperature
vacuum. requirements of the chamber. Materials to be joined must be
5.4.2 The loss of mass of thermal control coatings can be properly cleaned so that sound, leaktight, nonporous joints can
measured, to provide an indication of the amount of decom- be made. Inert gas arc welding (TIG), using helium or argon,
position products leaving the coating during exposure. This and electron beam welding have been used. Brazing materials
may be important in the study of the curing, outgassing, and and cleaning techniques are discussed in Refs (5) and (6).
contamination potential of thermal control coatings. Welds should be on the vacuum side to eliminate the possibility
5.4.3 Vacuum gas analysis (mass spectroscopy or residual of trapping gas in cracks and crevices, thus creating a virtual
gas analysis, RGA) can be used to assess the type and leak. Parts must be absolutely clean before welding. An oil film
concentration of decomposition products. can cause gas to evolve and result in a porous, leaky weld.
5.5 Surface Analysis of Specimens—X-ray photoelectron 6.2.1.2 Dimensions of the test chamber should be suffi-
specotroscopy (XPS), auger electron spectroscopy, and
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