ASTM E2311-04(2021)
(Practice)Standard Practice for QCM Measurement of Spacecraft Molecular Contamination in Space
Standard Practice for QCM Measurement of Spacecraft Molecular Contamination in Space
SIGNIFICANCE AND USE
5.1 Spacecraft have consistently had the problem of contamination of thermal control surfaces from line-of-sight warm surfaces on the vehicle, outgassing of materials and subsequent condensation on critical surfaces, such as solar arrays, moving mechanical assemblies, cryogenic insulation schemes, and electrical contacts, control jet effects, and other forms of expelling molecules in a vapor stream. To this has been added the need to protect optical components, either at ambient or cryogenic temperatures, from the minutest deposition of contaminants because of their absorptance, reflectance or scattering characteristics. Much progress has been accomplished in this area, such as the careful testing of each material for outgassing characteristics before the material is used on the spacecraft (following Test Methods E595 and E1559), but measurement and control of critical surfaces during spaceflight still can aid in the determination of location and behavior of outgassing materials.
SCOPE
1.1 This practice provides guidance for making decisions concerning the use of a quartz crystal microbalance (QCM) and a thermoelectrically cooled quartz crystal microbalance (TQCM) in space where contamination problems on spacecraft are likely to exist. Careful adherence to this document should ensure adequate measurement of condensation of molecular constituents that are commonly termed “contamination” on spacecraft surfaces.
1.2 A corollary purpose is to provide choices among the flight-qualified QCMs now existing to meet specific needs.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2311 − 04 (Reapproved 2021)
Standard Practice for
QCM Measurement of Spacecraft Molecular Contamination
in Space
This standard is issued under the fixed designation E2311; 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.
1. Scope E1559Test Method for Contamination Outgassing Charac-
teristics of Spacecraft Materials
1.1 This practice provides guidance for making decisions
2.2 U.S. Federal Standards:
concerningtheuseofaquartzcrystalmicrobalance(QCM)and
MIL-STD-883Standard Test Method, Microcircuits
a thermoelectrically cooled quartz crystal microbalance
MIL-S-45743 Soldering, Manual Type, High Reliability
(TQCM)inspacewherecontaminationproblemsonspacecraft
Electrical and Electronic Equipment
are likely to exist. Careful adherence to this document should
FED-STD-209EAirborne Particulate Cleanliness Classes in
ensure adequate measurement of condensation of molecular
Cleanrooms and Clean Zones
constituents that are commonly termed “contamination” on
spacecraft surfaces.
NOTE 1—Although FED-STD-209E has been cancelled, it still may be
used and designations in FED-STD-209E may be used in addition to the
1.2 A corollary purpose is to provide choices among the
ISO designations.
flight-qualified QCMs now existing to meet specific needs.
2.3 ISO Standards:
1.3 The values stated in SI units are to be regarded as the
ISO 14644-1 Cleanrooms and Associated Controlled
standard. The values given in parentheses are for information
Environments—Part 1: Classification of Air Cleanliness
only.
ISO 14644-2 Cleanrooms and Associated Controlled
1.4 This standard does not purport to address all of the
Environments—Part 2: Specifications for Testing and
safety concerns, if any, associated with its use. It is the
Monitoring to Prove Continued Compliance with ISO
responsibility of the user of this standard to establish appro-
14644-1
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3. Terminology
1.5 This international standard was developed in accor-
3.1 Definitions:
dance with internationally recognized principles on standard-
3.1.1 absorptance, α,n—ratio of the absorbed radiant or
ization established in the Decision on Principles for the
luminous flux to the incident flux.
Development of International Standards, Guides and Recom-
3.1.2 activity coeffıcient of crystal, Q, n—energy stored
mendations issued by the World Trade Organization Technical
during a cycle divided by energy lost during a cycle, or the
Barriers to Trade (TBT) Committee.
quality factor of a crystal.
2. Referenced Documents 3.1.3 crystallographic cut,Φ,n—rotationanglebetweenthe
optical axis and the plane of the crystal at which the quartz is
2.1 ASTM Standards:
cut;typically35°18'ATcutforambienttemperatureuseor39°
E595Test Method for Total Mass Loss and Collected Vola-
40' cut for cryogenic temperature use.
tile Condensable Materials from Outgassing in a Vacuum
3.1.4 collected volatile condensable materials, (CVCM),
Environment
n—tested per Test Method E595.
3.1.5 equivalent monomolecular layer, (EML), n—single
-8
This practice is under the jurisdiction of ASTM Committee E21 on Space layer of molecules, each3×10 cm in diameter, placed with
Simulation andApplications of SpaceTechnology and is the direct responsibility of
centers on a square pattern. This results in an EML of
Subcommittee E21.05 on Contamination. 15 2
approximately1×10 molecules/cm .
Current edition approved April 1, 2021. Published May 2021. Originally
approved in 2004. Last previous edition approved in 2016 as E2311–04(2016).
DOI: 10.1520/E2311-04R21.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2311 − 04 (2021)
3.1.6 field of view, (FOV), n—the line of sight from the 3.2.1 density of quartz—at T = 25°C, ρ = 2.6485 g/cm
q
5 3
surface of the QCM that is directly exposed to mass flux. (1);at T=77K, ρ = 2.664 g/cm (2).
q
3.1.7 irradiance at a point on a surface, n—E , E(E = 3.2.2 mass sensitivity—AT or rotated cut crystal (3).
e e
-2
dI /dA),(wattpersquaremetre,Wm ),ratiooftheradiantflux
e
4. Summary of Practice
incident on an element of the surface containing the point, to
the area of that element. 4.1 Measurement of molecular contamination on spacecraft
can be performed in a variety of ways. The specific methods
3.1.8 mass sensitivity, S, n—relationship between the fre-
depend upon such factors as knowing its contamination source
quency shift and the arriving or departing mass on the sensing
andtheapproximatelevelofoutgassing,theabilityorinability
crystal of a QCM. As defined by theory:
to place a sensor in the immediate area of concern, the
∆m/A 5 ~ρ c/2f ! ∆f (1)
q
variation of the solar thermal radiation striking the sensor, the
powerdissipationoftheQCMandhowitaffectscertaincritical
where:
spacecraft cooling requirements, cost to the program, and the
∆m = mass change, g,
schedule.Therefore,itisnotdesirableorpossibletoincludeall
A = area on which the deposit occurs, cm ,
QCMtestinginonetestmethod.Theengineersmustdetermine
f = fundamental frequency of the QCM, Hz,
and provide the detailed monitoring procedure that will satisfy
ρ = density of quartz, g/cm , and
q
their particular requirements and be fully aware of the effects
c = shear wave velocity of quartz, cm/s.
of any necessary deviations from the ideal.
3.1.9 molecular contamination, n—molecules that remain
on a surface with sufficiently long residence times to affect the
5. Significance and Use
surface properties to a sensible degree.
5.1 Spacecraft have consistently had the problem of con-
3.1.10 optical polish, n—the topology of the quartz crystal
taminationofthermalcontrolsurfacesfromline-of-sightwarm
surface as it affects its light reflective properties, for example,
surfacesonthevehicle,outgassingofmaterialsandsubsequent
specular (sometimes called “clear polish”) or diffuse polish.
condensation on critical surfaces, such as solar arrays, moving
3.1.11 optical solar reflector, (OSR), n—a term used to
mechanical assemblies, cryogenic insulation schemes, and
designate thermal control surfaces on a spacecraft incorporat-
electrical contacts, control jet effects, and other forms of
ing second surface mirrors.
expelling molecules in a vapor stream. To this has been added
the need to protect optical components, either at ambient or
3.1.12 quartz crystal microbalance (QCM), n—a piezoelec-
cryogenic temperatures, from the minutest deposition of con-
tric quartz crystal that is driven by an external electronic
taminants because of their absorptance, reflectance or scatter-
oscillator whose frequency is determined by the total crystal
ing characteristics. Much progress has been accomplished in
thickness plus the mass deposited on the crystal surface.
this area, such as the careful testing of each material for
3.1.13 reflectance, ρ,n—ratio of the reflected radiant or
outgassing characteristics before the material is used on the
luminous flux to the incident flux.
spacecraft (following Test Methods E595 and E1559), but
3.1.14 surface of interest, n—any immediate surface on
measurementandcontrolofcriticalsurfacesduringspaceflight
which contamination can be formed.
still can aid in the determination of location and behavior of
3.1.15 super-polish, n—polish of a quartz crystal that pro- outgassing materials.
duces less than 10Å root mean square (rms) roughness on the
6. General Considerations
surface.
6.1 A QCM sensor is used to measure the molecular
3.1.16 QCM thermogravimetric analysis, (QTGA),
contamination of critical surfaces on spacecraft at one or more
n—raising the temperature of the QCM deposition surface
temperatures for an extended period of time. A piezoelectric
causes contaminants to evaporate, changing the QCM fre-
crystalisexposednexttoa“surfaceofinterest”orintheplane
quencyasafunctionoftimeandthemassloss.Relevantvapor
where molecular flux is expected. It is then cooled to the
pressurescanbecalculatedforvariousspeciesandcanbeused
temperature at which the crystal should condense whatever
to identify the molecular species.
molecular contaminant exists at that temperature (according to
3.1.17 total mass loss, (TML), n—when tested per Test
the vapor-pressure characteristics of that constituent). By
Method E595.
measuring the frequency-shift of the crystal and knowing the
3.1.18 thermoelectric quartz crystal microbalance,
mass sensitivity (frequency to mass-added factor for that
(TQCM), n—The temperature of the crystal is controlled with
crystal), the mass accumulated can be determined. Sunlight
a thermoelectric element so that the rate of deposition and the
striking the solar panels may cause outgassing that intercepts
species that condense onto the QCM can be related to the
temperature.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
3.2 Constants: this practice.
E2311 − 04 (2021)
the surface of interest. The probable source and extent of Fig. 3. Some actual deposition rate conditions on a spacecraft
-12 -2 -1
contamination can be determined from known components of have been observed to be 1.2 × 10 gcm s for a sunlit
-13 -2 -1
the spacecraft and probable sources. vent-viewing OSR (4),2×10 gcm s for a mature large
-14
satellite (4), and a projected Space Station budget of1×10
6.2 PotentialcontaminationproblemareasareshowninFig.
-2 -1
gcm s (daily average) (5).
1.
6.2.1 The performance of thermal control surfaces is de-
7. Defining Molecular Contamination
graded as a result of the accumulation of contaminants, which
7.1 The process termed outgassing is a combination of
may increase the surfaces’ solar absorptance;
events (Fig. 4) including the solid state diffusion of molecules
6.2.2 Optics may be degraded by increasing “light” scatter-
to the surface, followed by desorption into the high-vacuum
ing or reflectance loss;
environment of space.When those molecules reach a sensitive
6.2.3 Electronic modules with high rates of outgassing
surface, either by line-of-sight or indirect (non-line-of-sight)
components may have voltage arc-over;
transport and deposit, the deposit is termed “molecular con-
6.2.4 Internal to the spacecraft there may be outgassing
tamination.” At low altitudes atmospheric molecules some-
sources which will degrade (for instance, mass spectrometer
times play a role in these processes by scattering or deflecting
causing signal overload conditions);
molecular contamination.
6.2.5 Windows and optical elements may be degraded by
adsorption of a contaminant film leading to a loss of
7.2 The definition of equivalent monomolecular layer
transmittance,reflectance,oranincreaseinscatteredlight;and
(EML)ofwateronasurface(Fig.5)isbasedontheconceptof
-8
6.2.6 Solar arrays are adversely affected by the absorptance
a uniform single layer of molecules, each3×10 cm in
of contaminants.
diameter, placed with centers on a square pattern. This results
inanEMLbeingdefinedasapproximately1×10 molecules/
6.3 Some of the sources of contamination and mechanisms
cm . However, molecular deposits are not always formed as
for transporting them are shown in Fig. 2. Pre-launch, vacuum
uniform films.
test-induced contamination remains a problem as well as
launch-induced contaminants. High-angle plume impingement
7.3 Given, for instance, water with a gram molecular mass
from spacecraft orientation thrusters, as well as multi-layer
of 18 g/mole andAvogadro’s number of6×10 molecules/g
-8 -8 2
insulation surrounding cryogenic surfaces, are also sources of
mole, this results in3×10 g/EML or3×10 g/cm .
contamination. Frequently, the largest long-term sources are
warm,relativelythick,non-metallicmaterialsofthespacecraft 8. QCM Theory
construction. High vapor pressure (low molecular mass) mol-
8.1 Crystal Frequency:
eculesmayphotopolymerizeonsurfacestobecomelowvapor
8.1.1 A piezoelectric quartz crystal (Fig. 6) is externally
pressure (high molecular mass) stable contaminants. Vapor
driven by an electronic oscillator attached to two metal plates
pressure-controlled self-contamination needs to be in the
(usually deposited by vacuum evaporation) placed on both
design engineer’s mind; however, some parameters are still
sides of the quartz blank. This imposes a time dependent
uncertain,thatis,backscatteringofoutgassedmoleculesdueto
electric field across the plate, which causes the crystal to
atmospheric gas collisions, influence of free oxygen and
oscillateatafrequencydeterminedbythetotalthicknessofthe
charged particles as they impact the spacecraft surface.
crystal plus any mass on these electrodes. The oscillation
6.4 Sometypicalspacecraftoutgassingratesandtheexperi- appears as a Gaussian distribution of displacement, peaking at
mental determination of the resolution of QCMs are shown in the center and vanishing at the electrode edge. The frequency
FIG. 1 Examples of Spacecraft Component Degradation Due to Contamination
E2311 − 04 (2021)
FIG. 2 Sources of Contamination and Transport Mechanisms
FIG. 3 Typical Outgassing Rates
of the surface motion decreases as a layer of contaminant is Thequartzplateelectrodemayhaveadifferentdiameteronthe
formed (mass addition), according to the degree to which each topmost surface than on the bottom because the α/ε value for
element is being displaced by the oscillation. The arriving or aluminum, which is commonly used as an electrode material,
departing molecules (mass flux) are deposited or desorbed forirradiationfromthesunislowerthanforquartz.Electrodes
randomly. Therefore, integrating the distribution of surface of gold, platinum, and other metals are also often used.
displacementsprovidesuswithavalidsensitivity(massfluxto Aluminum is commonly chosen because of it’s low absorp-
change in frequency) for the quartz plate. Experimental con- tance coeff
...
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