ASTM E1997-15(2021)

Standard Practice for the Selection of Spacecraft Materials

SIGNIFICANCE AND USE
3.1 This practice is a guideline for proper materials and process selection and application. The specific application of these guidelines must take into account contractual agreements, functional performance requirements for particular programs and missions, and the actual environments and exposures anticipated for each material and the equipment in which the materials are used. Guidelines are not replacements for careful and informed engineering judgment and evaluations and all possible performance and design constraints and requirements cannot be foreseen. This practice is limited to unmanned systems and unmanned or external portions of manned systems, such as the Space Station. Generally, it is applicable to systems in low earth orbit, synchronous orbit, and interplanetary missions. Although many of the suggestions and cautions are applicable to both unmanned and manned spacecraft, manned systems have additional constraints and requirements for crew safety which may not be addressed adequately in unmanned designs. Because of the added constraints and concerns for human-rated systems, these systems are not addressed in this practice.
SCOPE
1.1 The purpose of this practice is to aid engineers, designers, quality and reliability control engineers, materials specialists, and systems designers in the selection and control of materials and processes for spacecraft, external portion of manned systems, or man-tended systems. Spacecraft systems are very different from most other applications. Space environments are very different from terrestrial environments and can dramatically alter the performance and survivability of many materials. Reliability, long life, and inability to repair defective systems (or high cost and difficultly of repairs for manned applications) are characteristic of space applications. This practice also is intended to identify materials processes or applications that may result in degraded or unsatisfactory performance of systems, subsystems, or components. Examples of successful and unsuccessful materials selections and uses are given in the appendices.  
1.2 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

• Status: Published
• Publication Date: 31-Aug-2021
• ICS: 49.025.01 - Materials for aerospace construction in general
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.05 - Contamination

Relations

• Refers: ASTM E595-07 - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• Effective Date: 01-Dec-2007
• Refers: ASTM E595-06 - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• Effective Date: 01-Nov-2006
• Refers: ASTM G64-99(2005) - Standard Classification of Resistance to Stress-Corrosion Cracking of Heat-Treatable Aluminum Alloys
• Effective Date: 01-May-2005
• Refers: ASTM E595-93(2003)e1 - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• Effective Date: 01-Oct-2003
• Refers: ASTM E595-93(2003)e2 - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• Effective Date: 01-Oct-2003
• Refers: ASTM G64-99 - Standard Classification of Resistance to Stress-Corrosion Cracking of Heat-Treatable Aluminum Alloys
• Effective Date: 10-Aug-1999
• Refers: ASTM E595-93(1999) - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• Effective Date: 10-Apr-1999

Overview

ASTM E1997-15(2021), Standard Practice for the Selection of Spacecraft Materials, provides essential guidelines for engineers, materials specialists, systems designers, and quality control professionals involved in choosing and controlling materials for spacecraft and related systems. Developed by ASTM International, this standard focuses on unmanned systems and the external portions of manned or man-tended systems, including usage in low Earth orbit, synchronous orbit, and interplanetary missions.

Selecting appropriate materials for spacecraft is fundamentally different from terrestrial applications, due to the unique challenges presented by space environments. These include extreme temperatures, vacuum conditions, radiation exposure, the risk of micrometeoroid impacts, and the presence of atomic oxygen. The standard aims to increase reliability, ensure long operational lifetimes, and mitigate the high cost and difficulty of repairs in space.

Key Topics

• Environmental Impact on Materials: Outlines how different orbital regions-low Earth orbit, synchronous orbit, and interplanetary space-impose specific constraints such as temperature extremes, radiation, debris, and atomic oxygen, each of which affects material selection and lifespan.
• Materials to Avoid: Advises against using substances known to perform poorly or degrade in space, including:
  • Metals with high vapor pressure (e.g., mercury, cadmium, zinc)
  • Pure tin, due to whisker growth and potential for electrical shorts
  • Stress-corrosion-sensitive metals unless properly treated
  • Materials with high outgassing or volatile emissions
  • Compounds prone to particulate contamination or instability under thermal cycling
• Material Selection Process: Emphasizes that only careful, informed engineering judgment, supported by rigorous testing and documentation, is sufficient for spacecraft materials selection. The need to verify properties, control suppliers, and avoid reliance on simple data sheets is highlighted.
• Control Methods: Promotes the establishment of approved materials and process lists unique to each space mission, frequent testing of key properties, close oversight by experienced materials engineers, and integration of materials review in all design phases.
• Documentation and Traceability: Recommends materials lists and process specifications be strictly controlled, configuration-managed, and reviewed by qualified specialists to ensure only suitable, proven materials are used.

Applications

ASTM E1997-15(2021) is widely applicable in the aerospace industry, specifically for:

• Spacecraft Construction: Useful in selecting both structural and non-structural materials for satellites, probes, and external equipment on manned space stations.
• Subsystems and Components: Guides selection for critical subsystems such as thermal blankets, antennas, solar arrays, electrical connectors, and adhesives.
• Mission Planning: Aids in evaluating material durability and compatibility for projected mission environments, such as exposure to vacuum, radiation, or outgassing-sensitive payloads.
• Quality Assurance: Serves as a reference for the development of internal material control policies, supplier qualifications, and compliance verification strategies.
• R&D and Risk Mitigation: Essential for new design or experimentation, helping to avoid unsuccessful material choices and increase mission reliability.

Related Standards

ASTM E1997-15(2021) references and complements several important industry standards, including:

• ASTM E595 - Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum
• MIL-STD-889 - Dissimilar Materials
• MIL-HDBK-5 - Metallic Materials and Elements for Aerospace Vehicle Structures
• MIL-HDBK-17 - Properties of Composite Materials
• ESA PSS-07/QRM-0 - European Space Agency Guidelines for Space Materials Selection
• QQ-A-250 - Federal Specification for Aluminum and Aluminum Alloy Plate and Sheet

These standards collectively help ensure that spacecraft materials are selected based on robust, reliable criteria, improving the long-term success and safety of aerospace missions.

---

Keywords: spacecraft materials, selection guidelines, ASTM E1997, space environment, outgassing, vacuum, radiation, quality control, aerospace materials, materials testing, approved process lists, unmanned systems, low Earth orbit materials, synchronous orbit, interplanetary missions.

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: E1997 − 15 (Reapproved 2021)
Standard Practice for the
Selection of Spacecraft Materials
This standard is issued under the fixed designation E1997; 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 Sodium Chloride Environments
2.3 Military Standards:
1.1 The purpose of this practice is to aid engineers,
MIL-STD-889Dissimilar Materials
designers, quality and reliability control engineers, materials
MIL-HDBK-5Metallic Materials and Elements for Aero-
specialists, and systems designers in the selection and control
space Vehicle Structures
of materials and processes for spacecraft, external portion of
MIL-HDBK-17Properties of Composite Materials
manned systems, or man-tended systems. Spacecraft systems
2.4 European Space Agency (ESA) Standard:
areverydifferentfrommostotherapplications.Spaceenviron-
PSS-07/QRM-0Guidelines for Space Materials Selection
ments are very different from terrestrial environments and can
2.5 Federal Standard:
dramatically alter the performance and survivability of many
QQ-A-250 Aluminum and Aluminum Alloy Plate and
materials.Reliability,longlife,andinabilitytorepairdefective
Sheet, Federal Specification for
systems (or high cost and difficultly of repairs for manned
applications) are characteristic of space applications. This
3. Significance and Use
practice also is intended to identify materials processes or
applications that may result in degraded or unsatisfactory 3.1 This practice is a guideline for proper materials and
process selection and application. The specific application of
performance of systems, subsystems, or components. Ex-
amplesofsuccessfulandunsuccessfulmaterialsselectionsand these guidelines must take into account contractual
agreements, functional performance requirements for particu-
uses are given in the appendices.
lar programs and missions, and the actual environments and
1.2 This international standard was developed in accor-
exposures anticipated for each material and the equipment in
dance with internationally recognized principles on standard-
which the materials are used. Guidelines are not replacements
ization established in the Decision on Principles for the
forcarefulandinformedengineeringjudgmentandevaluations
Development of International Standards, Guides and Recom-
and all possible performance and design constraints and
mendations issued by the World Trade Organization Technical
requirements cannot be foreseen. This practice is limited to
Barriers to Trade (TBT) Committee.
unmanned systems and unmanned or external portions of
2. Referenced Documents
manned systems, such as the Space Station. Generally, it is
applicabletosystemsinlowearthorbit,synchronousorbit,and
2.1 ASTM Standards:
interplanetarymissions.Althoughmanyofthesuggestionsand
E595Test Method for Total Mass Loss and Collected Vola-
cautions are applicable to both unmanned and manned
tile Condensable Materials from Outgassing in a Vacuum
spacecraft, manned systems have additional constraints and
Environment
requirements for crew safety which may not be addressed
G64Classification of Resistance to Stress-Corrosion Crack-
adequately in unmanned designs. Because of the added con-
ing of Heat-Treatable Aluminum Alloys
straints and concerns for human-rated systems, these systems
2.2 Marshall Space Flight Center (MSFC) Standard:
are not addressed in this practice.
MSFC-STD-3029Guidelines to the Selection of Metallic
Materials for Stress Corrosion Cracking Resistance in
4. Design Constraints
4.1 Orbital Environment—Theactualenvironmentinwhich
This practice is under the jurisdiction of ASTM Committee E21 on Space
SimulationandApplicationsofSpaceTechnologyandisthedirectresponsibilityof
the equipment is expected to operate must be identified and
Subcommittee E21.05 on Contamination.
defined. The exposures and requirements for material perfor-
Current edition approved Sept. 1, 2021. Published October 2021. Originally
mance differ for various missions. Environment definition
approved in 1999. Last previous edition approved in 2015 as E1997–15. DOI:
10.1520/E1997-15R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contactASTM Customer Service at [e-mail]. ForAnnual Book ofASTM AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
Standards volume information, refer to the standard’s Document Summary page on 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
the ASTM website. www.access.gpo.gov.
Marshall Space Flight Center, AL 35812, or everyspec.com. European Space Agency, 8–10, Rue Mario-Nikis, 75738 Paris Cedex, France.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1997 − 15 (2021)
includes defining the range of temperature exposure, number which can cause shorts in electrical components or break off
and rate of thermal cycles, extent of vacuum exposure, solar and become conductive contaminants. Some other metals such
electromagnetic radiation particulate radiation, (trapped by the
ascadmiumandzinchavesimilarwhisker-growingproperties,
earth’s magnetosphere, solar wind, solar flares, and gamma
but not to the extent that tin has. Since they can also grow
rays) micrometeroids, launch loads and vibration, structural
whiskers, they should not be used.
loads, and so forth. Materials suitable for one orbit or mission
5.1.2 Stress-Corrosion Sensitive Metals—Metals, which are
environment may be unsuitable for others. The applications
stress-corrosion sensitive, should be avoided. Examples are
and requirements will define the suitability of the materials.
2024 T6 and 7075 T6 Aluminum, which can be used if heat
treated to conditions, such as 2024 T81 and 7075 T73, which
4.2 Low Earth Orbit (Up to 100 km)—Materials in this
region could be exposed to trapped Van Allen belt (ionizing) arenotstress-corrosionsensitive.Manybrassesandsomesteel
radiation,solarultravioletradiation,corrosiveattackbyatomic alloysalsoarestress-corrosionsensitive;however,evenalloys,
oxygen (A.O.), and more frequent and more extreme thermal
which are stress-corrosion sensitive can be used if loaded in
cycling and thermal shock as a result of frequent excursions
compression or if loaded to low sustained tensile stress levels,
into and out of the earth’s shadow. Orbital impacts may be a
typically no more than 25% of yield strength (see Classifica-
problem because of the large amount of debris in low orbits.
tion G64 and MSFC-SPEC-522).
Design life in orbit typically is on the order of 5 to 15 years.
5.1.3 Materials Forming Galvanic Couples—Material
Inclination of the orbit affects the service environment, that is,
combinations,whichformgalvaniccouplesgreaterthan0.5ev
polar orbits have a different flight profile than equatorial orbits
when exposed to a temperature and humidity controlled
and have different profiles for radiation exposure.
environment, such as during fabrication, testing, and storage,
4.3 Synchronous Orbit (35 900 km)—Materials in this re- should be prohibited under most circumstances. Providing
gionarenotexposedtosignificantatomicoxygenorveryhigh protection from electrolytes and maintaining them in a con-
energy trapped radiation but may have more exposure to
trolled environment, such as during fabrication and testing,
mediumenergyionizingelectronsandprotons,solarflares,and inhibits galvanic corrosion. Some alloys, such as magnesium,
relatively high levels of electromagnetic solar radiation
magnesium lithium alloys, and gold, form a galvanic couple
(ultraviolet, VUV photons, and X-rays). The number of ther-
with most common structural materials and must be protected
mal cycles is less and may be over a narrower temperature
adequately to prevent creating galvanic couples which cause
range than low earth orbit. Meteoroids also should be consid-
theanodicmetaltocorrode.Carboncompositesareincludedin
ered but are less likely to be significant compared to the
the materials, which must be evaluated for galvanic potential,
manmade debris found in low orbits. Design life in orbit
since carbon forms galvanic couples with metals. If there is no
typically is 5 to 15 years, with recent designs ranging from 10
electrolyte present, galvanic couples greater than 0.5 ev are
to 17 years.
permissible.Galvanicprotectioncanbeobtainedbypreventing
electrolytefromcontactingtheinterfaces,interposingadielec-
4.4 Interplanetary (Out-of-Earth Orbit)—In addition to the
tric material, or adding a material that is compatible with each
thermal extremes and environments of synchronous orbit, in
of the other materials separately.
the interplanetary environment, temperatures may be more
extreme, and micrometeoroids, solar wind, and cosmic rays 5.1.4 Materials With Thermal or Environmental
may be critical. Ability to survive and remain functional for Limitations—Materials that are weak or brittle at the expected
many years is important. Probes to the inner plants typically
service temperature or environment should be avoided. These
have design lifetimes of 5 to 10 years. Those to the outer materials included polymeric materials used at very low or
planets and beyond may have design lifetimes of 15 to 30
very high temperatures and some metals used at low tempera-
years.
tures. In this context, “low” can be from -40 to -120°C and
“high”canbefrom150to200°Cforpolymers.Somematerials
5. Materials to Avoid
are readily attacked by certain chemicals or solutions. For
example,aluminumalloysshouldnotbeusedinstronglybasic
5.1 Certain materials are known to be undesirable and
or acidic environments. Steels, particularly high carbon and
should be avoided no matter what the mission. Others are of
ferritic grades, are embrittled by halogens and hydrogen.
concern for certain missions or of more concern for some
Silicones are attacked by toluene. Titanium is attacked by
missions than others. In general, it is recommended that one
methanol.
avoid the materials described below:
5.1.5 Materials Diffıcult to Fabricate or Test—Materials
5.1.1 Metals with High Vapor Pressure in Vacuum and
that are difficult to fabricate, form, test, or inspect, or do not
Unusual Behaviors—Avoid the use of metals such as mercury,
have a history of consistency of properties or performance,
cadmium, and zinc, either as plating or monolithic metals. It is
shouldbeavoided.Somematerials,suchasceramicsandmost
important to exclude these metals both from the flight equip-
refractory metals, are relatively difficult to machine or form.
ment and vacuum chambers. If these metals are used in
Others are difficult to weld by conventional means. Some
vacuum and heated even moderately, they will vacuum metal-
cannot be formed easily. Certain applications such as elevated
lize both the cold walls of the chamber and any cold surfaces
on equipment in the chamber. Also, pure tin has the curious temperature service may require use of ceramics or refractory
metals.That should not reduce the need for careful review and
property of dendritic growth as a result of compressive
stresses, or thermal or electrical gradients, forming whiskers functional design of the equipment.All materials must be very
E1997 − 15 (2021)
carefully evaluated to assure successful, economic fabrication and reproducible performance. It is important to select mate-
and that the fabricated parts can be inspected easily for hidden rials that are well understood and have established histories of
defects. consistentandpredictablephysicalandmechanicalbehaviorin
space.Itisalsoimportantthatthematerialsbecapableofbeing
5.1.6 Materials That Have Excessive Outgassing—If the
processed in a controlled, repeatable manner so that perfor-
materials have high collected volatile condensable materials
mance is dependable and reproducible in accordance with
(CVCM)ortotalmassloss(TML)whenexposedat125°Cand
5.1.5.
tested, they generally are excluded from spacecraft applica-
5.1.11 Radiation Sensitivity—Materials that are sensitive to
tions. Normal acceptance limits for outgassing according to
radiation, or radiation and vacuum, require care in selection
TestMethodE595arenohigherthan1.0%TMLandnohigher
and application. Many glasses and optical coatings are dam-
than 0.10% CVCM. Some of these materials release conden-
aged by radiation. Some polymeric materials may be degraded
sates that react adversely with solar radiation or radiation and
by radiation or solar flares. The susceptibility to particulate
vacuum and may degrade sensitive surfaces. Others can
radiation damage sometimes is increased in vacuum when
contaminate surfaces or equipment such that functionality is
simultaneously exposed to ultraviolet radiation. It is important
impaired. High mass loss can indicate a loss or properties and
to consider radiation sensitivity and the orbital environment
functionalityinspace.Sometimes,amaterialwillhaveaccept-
when selecting materials.
able outgassing per normal requirements, but it may be in a
5.1.12 Materials Particulate Contamination—Emission of
particularly sensitive location, or the outgassing product may
particles or flaking can cause interference with optical or
have an adverse effect on specific sensitive equipment. These
thermal control surfaces or perhaps jam mechanisms. Thor-
conditions can require establishing lower levels for acceptable
ough cleaning of materials and assemblies is important to
outgassing or may require analysis of outgassed components
preventemissionofparticles.Conductiveparticlesareparticu-
and evaluation of the acceptability for the specific application.
larly undesirable and must be avoided. Surfaces should be
NOTE1—Thetestisdefinedasperformedat125°Cunlessclearlystated
examined and verified for elimination of particles before
otherwise; therefore, acceptability is limited to exposures below 125°C.
components are assembled.
The test temperature of 125°C was assumed to be significantly above the
5.1.13 Fluid Compatibility—If the material is likely to be
expectedoperatingtemperatureinservice.Ifexpectedoperatingtempera-
tures exceed 85 to 90°C the test temperature should be increased. It is exposed to propellant, coolants, in-process solvents, and so
suggested that the test temperature be at least 30°C higher than expected
forth, it is important to test and verify fluid compatibility with
maximum service temperature in order to provide material comparisons
the materials in advance. Always check and verify the com-
for TML and CVCM.
patibility of the materials with all fluids in which they may
NOTE 2—Metallic materials do not “outgas,” but some metals, such as
come into contact and with all of the fluids used, including
zinc and cadmium, do exhibit high vapor pressure at relatively low
(<150°C) temperatures in vacuum. (See 5.1.1.) cleaning agents, solvents, and test fluids.
5.1.14 Arc Tracking of Wires—Kapton® wire insulation is
5.1.7 Materials That Release Undesirable Components—
susceptible to arc tracking when used in power-carrying
For example, acetic acid is released when curing certain
applications.Any damage or abrasion to this type of wire may
silicones.Theacidcanattackandcorrodeelectricalwiringand
cause dielectric breakdown and arcing, even in vacuum. Wire
contacts and cause failures. In some applications, the alcohols
insulations, such as Teflon-polyimide-Teflon® , which are not
released when silicones cure may be harmful.
susceptible to arc tracking and have been qualified as such are
5.1.8 Unstable Polymeric Materials—Some polymeric ma-
availableandshouldbeconsideredasreplacementsforKapton
terials may revert or change character when exposed to other
wire insulation.
materials or to the space environment. For example, certain
5.1.15 Inadequately Controlled Materials—Any material
silicones in contact with amine-cured epoxy can become fluid;
that is purchased and controlled only by vendor data sheet or
some polymeric materials are degraded by radiation or atomic
material certification, or both, has questionable controls. This
oxygen (A.O.), or both. Polyamide may become brittle in
type of product control should be viewed with caution. Data
vacuum and lose mechanical strength. PTFE and FEPbecome
sheets are not assurances of performance and often are mis-
brittle when exposed to radiation in vacuum. Lubricants
leading. For example, a maximum use temperature of a
containing graphite may lose lubricity in vacuum. ETFE wire
polymermaybegivenas200°C,butatthattemperatureitmay
insulation may become brittle and crack if heated to high
have low dielectric strength, poor modulus of elasticity and
temperatures and flexed or strained. Sulfur, which may be
strength, excessive outgassing, or significant loss of other
present in some latex and rubber gloves, can prevent proper
properties. Relying on vendor certifications alone can result in
curing of the silicones.
acceptance of lots, which, in fact, fail some specific property.
5.1.9 Unstable Nonmetallic Materials in Particular
Suppliershavebeenknowntosendsubstandardlotsofmaterial
Environments—Most nonmetallic materials are attacked by
to customers without properly testing and verifying properties
A.O. found in low earth orbit. They must be protected from
andquality.Therehavebeencasesofvendorssupplyinglotsof
direct exposure toA.O. either by coating them with a resistant
materialsthatweretestedandrejectedbyonecustomertoother
material, such as metal or oxide, or by shadowing or covering
them from direct exposure to A.O.
6 ®
Kapton , DuPont de Nemours, E.I., & Co., Inc., Barley Mill Plaza, Bldg. 10,
5.1.10 Reproducible Properties Uncertain—Materials that
Wilmington, DE 19880–0010.
7 ®
do not have repeatable, reproducible physical or mechanical
Teflon , DuPont de Nemours, E.I., & Co., Inc., Barley Mill Plaza, Bldg. 10,
properties may not be adequately controlled to assure reliable Wilmington, DE 19880–0010.
E1997 − 15 (2021)
customers without noting the prior rejection and reason. protective coatings, or special precautions; and so forth. It is
Critical properties should be tested and verified frequently, useful to indicate examples of previous successful use of the
even every lot if necessary. Materials should be defined and materialinthesameorasimilarapplication,forexample,used
controlled by a specification and should not be accepted and on the XXXYYY program. The mass and surface area of
used based only upon vendor data sheets and certifications. polymeric materials may be given to help in evaluating
5.1.16 Mismatched Coeffıcient of Thermal Expansion— contamination potential. This list could begin as a list of
Assemblies or equipment may use materials with significantly allowed materials, and by the end of the program, should
different coefficients of thermal expansion (CTE). Severe reflect all materials actually used both internally and by
thermalstressesandevenbondormaterialrupturecanoccurif subcontractors. Restricted and waived materials should be
these assemblies are subjected to wide temperature excursions listedinseparatesectionstofacilitateidentifyinganymaterials
of if the polymeric material isothermally cycled through its that are not fully acceptable as normally used, but which
glass transition point. If a low expansion material, such as a require special treatment or are used despite failure to meet
ceramicsubstrate,isbondedtoahighexpansionmaterial,such normal requirements. The list should be configuration con-
as aluminum sheet, there can be a large strain induced in the trolled and issued in the same manner as a specification or
bond joints as a result of CTE mismatch. This type of joint drawing with required approval signatures.
oftenfailsduringthermalcycling.Anotherpotentialproblemis
6.3 Materials Review of Design—The responsible materials
fatigue stress on various types of joints (solder, thermal,
specialist should assist in internal reviews of designs and
electrical,lightdutystructural)asaresultofthermalcyclingof
applications of materials. This is particularly important for
an assembly composed of materials with greatly different
composites,thermalcontrolmaterials,adhesives,anymaterials
CTEs. Materials and designs must be selected to minimize
usedathighorlowtemperatures(belowabout−20°Corabove
incompatibility caused by CTE mismatch between the various
about80°C),orwhenanymaterialisusedinanewordifferent
elements in the joints.
application or environment.
5.1.17 Materials That May Cause Environmental Damage
6.4 Drawing Review—An effective method for assuring
at the Fabrication Facility—Somematerialscangeneratetoxic
adequate materials design review is to require materials spe-
products, or require processing with toxic or environmentally
cialists to review and sign all drawings and drawing revisions,
damaging chemicals such as TCE or PCB. These solvents are
except those with no materials or process impacts, such as
often used to clean components of spacecraft and launch
schematics or dimensional identification.
vehicles.Ifnotproperlyhandledandstoredtheycanpolutesoil
and groundwater at the facility in addition to presenting toxic
6.5 Design Reviews—Materials specialists should be active
hazards to personnel.
participantsindesignreviewswhenevermaterialsorprocesses
are topics of discussion. These reviews allow direct interac-
6. Methods of Controlling Materials
tionswithdesigners,programoffice,users,andsubcontractors.
It is an effective method for preventing selection of unaccept-
6.1 Selection of materials always should be done by mate-
rial specialists, preferably those with experience in space able or inappropriate materials.
applications and requirements. Aircraft, ships, and weapons
6.6 Materials Specifications—Materials specialists should
exist in different environments and have different require-
prepare and approve all materials and processes specifications.
ments. Engineers who are not materials specialists rarely are
This approach permits identification of important materials
aware of the properties, peculiarities, and problems inherent in
propertiesfortestandcontrolandprovidesinteractionbetween
materials; therefore, it is vital to appoint an experienced
designers, materials, specification control, and purchasing.
materials specialist to oversee spacecraft materials selection,
Identification of properties to test and verify property
specification, control, and approval.This overall responsibility
requirements, specification of test methods, and selection of
isexercisedbestwithanorganizedsystemofmaterialscontrol.
approved sources can be aided by materials participation.This
The materials specialist should work closely with the program
processalsoallowsselectionofprocessesmostappropriatefor
office, reliability, designers, and manufacturing to assure
the particular material and application.
properuseofmaterialsandprocesses.Thereshouldbeasingle
6.7 Approved Process Lists—Each program should have a
responsible materials engineer for particular programs, sup-
list of approved processes for use in specific applications. The
ported as necessary by additional materials and processes
process list must include the process number, the revision
engineers.
letter, and a description of the process. It is desirable to
6.2 Approved Materials List—Each program should have a
cross-reference the process to the materials used as shown on
list of approved materials for use in specific applications. All
the materials list.All materials specified in any process, which
materials must be listed, both those used by the prime
becomepartofthedeliverableequipment,mustbeincludedon
contractor and those used by all subcontractors and subtier
the materials list. The list should be configuration controlled
subcontractors. The list should include item numbers for each
and issued in the same manner as a specification or drawing
material; the name of the material, commercial name, manu-
with required approval signatures.
facturer or supplier of the material; usage information such as
heat treat condition, mix ratio, cure cycle, post-cure, or 6.8 Process Preparation—Materials and processes special-
bakeouts; governing specification or other documentation; ists should be involved in the preparation or revision of all
application or use; pertinent properties, such as outgassing, process specifications to assure that the materials used are
E1997 − 15 (2021)
properlyappliedandprocessedandthattheprocessesarevalid 7. Keywords
and that they are used correctly. All process modifications
7.1 applications; contamination; design; design review; ma-
identified during development or production must be docu-
terials applications; materials selection; preferred materials;
mented and recorded fully in the process history to ensure
problem materials; process list; processes; space applications;
repeatability. New processes, processes used with a new or
spacecraft materials; testing; unmanned spacecraft
unusualmaterial,andprocessesthatmayrepresentasignificant
risk to the hardware, if incorrectly applied, shall be tested and
qualified on a test article before use on flight hardware.
APPENDIXES
(Nonmandatory Information)
X1. SPECIFIC MATERIALS RECOMMENDATIONS—METALS
X1.1 Metals—Important considerations are strength, X1.2.1 Magnesium is never a better choice than aluminum
strength/density ratio, stiffness or modulus of elasticity, ther- when the design is stiffness limited. Composites, such as
mal conductivity, electrical conductivity, magnetic properties, ceramic-reinforced metals or metal-reinforced metals, can be
sensitivity to stress corrosion, fracture toughness, toxicity, designed and fabricated to have high specific stiffness.
fabricability, and sometimes cost and availability.
X1.2.2 Strength and strength/density ratio are key proper-
X1.1.1 General—Pure tin should be avoided. It can grow ties in selecting metals. This is particularly true for structural
applicationsorwhenhigheststrengthforagiventhinsectionor
whiskers, which may create shorts, or the whiskers may break
off and float around the equipment in orbit causing arcing, light mass is required.
shorts, or intermittent electrical upsets. Often, tin plate is
NOTE X1.1—As in the case of specific modulus, do not just consider
specified on terminals, wires, or solder lugs. Pure tin in these
high strength but also consider strength/density ratio for best structural
applications should be overcoated, reflowed, or alloyed with
efficiency.
othermaterialssuchasleadorantimonywhichinhibitwhisker
X1.2.3 Toxicity and safety are concerns for some metals.
growth.Aslittleas3to5%ofanalloyingelementcanprevent
Beryllium and heavy metals, such as lead and the trans-
whisker growth. Fusing or oxidizing the pure tin, for example
uranium elements, are toxic and must be handled with care.
in hot peanut oil, also prevents whisker growth. Cadmium and
Magnesium,lithium,andmagnesiumlithiumalloys,aswellas
zinc also can grow whiskers and should not be used.
lithium and some uranium alloys, can be ignited and produce
X1.1.2 Some metal combinations result in undesirable al-
fires, which are very difficult to extinguish. They must be
loys. For example, gold and aluminum form a brittle interme- selected, fabricated, and handled with care.
tallic known as purple plague, which causes failures in elec-
X1.2.4 Methods of joining must be considered. Some
tronic circuits. This alloy forms at elevated temperatures, so
metals, particularly refractory metals, such as tungsten, and
one means of avoiding the problem is to keep exposure
reactive metals, such as magnesium, are difficult to braze or
temperatures below 200°C. Porous plating, such as gold on
weld and are best used with mechanical joints. Ease, cost, and
silver, may result in lack of adherence and flaking.
reproducibility of joining or assembly should be considered.
X1.1.3 Mercury and aluminum form an amalgam that de-
X1.2.5 Fatigue behavior must be considered in applications
stroys the physical properties of aluminum. Mercury must be
in which frequent repetitive stresses occur. Sometimes heat
bannedorverytightlycontrolledinthepresenceofaluminum.
treating or other processing will make metals more susceptible
X1.1.4 Direct contact of bare metals usually is undesirable. to fatigue. When assessing fatigue behavior, it is important to
If both metals have cubic crystal lattices, they may cold weld
lookatvariousheattreatmentsorotherprocesses,suchasshot
in space. Metals in direct contact under load or moving over peeningwhichimprovefatiguestrengthandfatigueresistance.
each may cold weld. It is preferable to coat one or both metals
X1.3 Corrosion and Stability—Corrosionresistanceofmet-
orusemetalswithdifferentcrystallatticesincontactwitheach
als and the presence of combinations of metals that create
other if cold welding is possible as a result of the application.
galvanic couples must be considered. In addition to atmo-
X1.2 Mechanical and Physical Properties—Whenselecting spheric corrosion, it may be important to know or determine
metalsforstiffness,considerspecificstiffness,thatis,modulus the corrosion compatibility with specific fluids, such as
divided by density. Often magnesium is selected over alumi- propellants, solvents, heat transfer fluids, lubricants, and cut-
num because it has lower density. In fact, the specific stiffness ting fluids. Galvanic corrosion normally is not a concern if the
of aluminum and magnesium alloys are almost identical. The EMF between two materials is 0.25 ev or less for severe
disadvantages of fabricating and protecting magnesium from environments or 0.50-ev EMF or less for temperature- and
corrosion and galvanic corrosion often exceed any gain from humidity-controlled environments. Since most spacecraft
lower density. assembly, integration, and storage is done in environmentally
E1997 − 15 (2021)
controlled areas, it should be acceptable to use metals in direct X1.6 Control of Properties—Most metals are defined and
contact, which have up to 0.50-ev EMF between them. Use of controlled adequately by national society, military, or federal
MIL-STD-889 to select approved galvanic couples for space-
specifications, for example, QQ-A-250, Mil-HDBK-5, AMS
craftisinadvisable.Thispracticefailstogiveactualvaluesfor
and ASTM specifications, and so forth. These specification
galvanic couples and is intended for exposure to seawater and
controls do not release using organizations from testing and
industrial atmospheres, neither of which apply to spacecraft.A
verifying actual properties on specific lots of materials as
better reference is ESA PSS-07/QRM-0, which gives actual
required.
EMF and is related directly to spacecraft. It is possible to use
metals with unacceptable galvanic electropotential if they are
X1.7 Preferred Materials—The clear preference is to use
insulatedfromeachotherorsealedtoexcludeelectrolytes.For
materials that are well characterized, readily available, have
example, anodized aluminum in direct contact with silver is
reproducibleandreliableproperties,fabricatereadily,andhave
acceptable, but bare aluminum in direct contact with silver
a history of successful use in the intended applications.
forms an impermissible large galvanic couple.
X1.8 Materials To Be Avoided—Avoid the use of metals
X1.4 Environmental Concerns—These concerns can apply
with high vapor pressure at low temperature in vacuum, such
to the manufacturing, testing, and assembly facilities. Process-
as mercury, cadmium, and zinc, either as plating or monolithic
ing operations and materials may present environmental haz-
metals. Mercury must be banned or very tightly controlled in
ards which must be identified and mitigated. See 5.1.17.
the presence of aluminum. Pure tin and other metals that grow
X1.5 Outgassing —This property does not apply. whiskers should be avoided.
X2. SPECIFIC MATERIALS RECOMMENDATIONS—ADHESIVES
X2.1 General —Adhesives may be structural or nonstruc- mayhaveusefulstrengthsattemperaturesupto300°C.Amore
typical adhesive upper use temperature is 80 to 100°C. If the
tural. Structural adhesives must be selected for bond strength;
peel strength; and vacuum stability including outgassing expected use temperature is above about 80°C, the bond
strengths of adhesives should be verified either from vendor
behavior, thermal properties, glass transition point, cost,
availability, and consistency of performance. Selection of the test data or by actual test.
proper adhesive for particular applications requires an under- NOTE X2.1—Outgassing in accordance with Test Method E595,at
standard conditions, is performed at 125°C. If operating temperatures are
standing of the materials to be bonded; proper surface prepa-
expected to exceed 85 to 90°C, the material should be tested for
ration; the need and suitability of primers or coupling agents;
outgassing at least 30°C above the expected operating temperature.
andtheoperatingenvironmentincludingtemperature,radiation
exposure, loading, and compatibility with other materials.
X2.3 Mechanical and Physical Properties—Normally, sup-
Adhesive process control is as important as selection of the
pliers provide data sheets that list material properties of
adhesive itself. Structural bonds (>1000-pi design loads) re-
adhesives. This information is not directly transferable to
quire specific training to apply the adhesive, including surface
specifications and standards. In fact, the vendor data sheets
preparation and process controls for consistency and effective,
usually have a disclaimer that the properties are typical only
reliable strength.
and not to be used for specifications. Users are advised to
performtestsofpropertiesofinterestandtousethosevaluesto
X2.2 General Usage Precautions—Usage precautions must
generate specifications.
be observed to avoid undesirable or unacceptable results and
even system failures. The importance of thermal sensitivity
X2.4 Corrosion and Stability—Some adhesives are sensi-
must not be overlooked. For example, the elastomeric seals,
tive to contact with organic materials or certain metals. For
which failed and resulted in the loss of the Challenger, were
example, silicones can be degraded by contact with amines
operated at a temperature below their known limits. Epoxies
commonly used as a curing agent in epoxies. RTV silicones,
often have brittle points in the −20 to −60°C range. Epoxies
whichcurebyreactionwithmoisture,cannotbecuredfasterby
shouldnotbeusedindirectcontactwithceramicparts,suchas
heating them. Such heating reduces the humidity at the
ceramic-cased diodes when usage temperatures are low. A
adhesive and inhibits cure. If heated to too high a temperature
flexibleintermediatematerialmustbeappliedtopreventbrittle
during cure, the silicone may even be damaged and never cure
fracture of the ceramic. Silicones are normally flexible at
properly. It is inadvisable to use silicones, which require
temperatures as low as −110°C. Flexible silicones should be
moisture to cure properly, to bond large area sandwich bonds
used rather than epoxies to bond ceramics for low temperature becauseofthelongtimesformoisturediffusiontothecenterof
applications directly (see 5.1.14). Urethanes tend to become
the joint. Moisture can inhibit cure of some epoxies but is
brittle at temperatures of approximately −20 to −40°C and essential to the cure of some silicones. Carbon dioxide may
should be used with great care or avoided at lower tempera-
react with and impair function of some curing agents.
tures. High temperatures result in significant loss in bond Adhesives,suchascyanoacrylites,cureintheabsenceofair.It
strength for adhesives. Few adhesives retain useful bond or may not be possible to assure exclusion of air during curing or
peel strength at temperatures above 60°C. Some polyimides to inspect and verify proper cure afterwards.
E1997 − 15 (2021)
X2.5 Environmental Concerns—Environmental effects on Materials have been tested at temperatures as high as 400°C,
adhesives must be considered as must compatibility of the but this high a test temperature is unusual.
manufacturing process and expected operating conditions.
X2.7 Controls on Properties—It is a general requirement
Exposure to atomic oxygen may degrade or attack adhesives.
that all materials used on spacecraft be identified fully and
Some adhesives lose mechanical and physical properties when
uniquely. This is not possible for almost all military or federal
exposed to radiation, especially in vacuum. Epoxies are more
specification products. Any adhesive must be tested and
likely to be darkened by radiation than silicones. Solar cell
qualified for the specific application of use. This normally
cover glasses are bonded with silicones that are not damaged
requires hardness and mechanical strength testing and evalua-
by solar radiation. If the application is inside the spacecraft
tion.
envelope, such as in electronic boxes, adhesives and other
organicmaterialsareconsideredtobeprotectedfromradiation
X2.8 Preferred Materials—The clear preference is to use
andatomicoxygenandwillexhibitnormalbehavior.Improper
materials that are well characterized, readily available, have
curing processes must be avoided to prevent uncured or partly
reproducibleandreliableproperties,arefabricatedreadily,and
cured coatings or bonds.
have a history of successful use in the intended applications.
X2.6 Outgassing —Adhesives are common sources of or-
ganic contamination in space applications as a result of X2.9 Materials To Be Avoided—Adhesives to be avoided
outgassing and deposition on flight surfaces. Before approving includeanythatarenotintendedfororqualifiedforspaceuse.
any adhesive for space applications, the existing literature There are many commercial products available, most of which
should be reviewed for outgoing values when tested in accor- have high outgassing, poor reproducibility and reliability of
dance with Test Method E595. The actual mix ratio and cure properties, or unacceptable behavior at high or low
cycle of the tested samples must be taken into account and temperatures, or both, or have compatibility concerns when
comparedwithplannedprocessingconditions.Ifnooutgassing used with other materials. If shelf life is less than 180 days, it
data are available, the material should be tested and TLM and may be relatively expensive to purchase and stock supplies of
CVCM determined early in the test and evaluation phase for thesematerials.Itisinadvisabletouseadhesivesspecifiedtoa
the material. Elevated temperature outgassing testing is re- military or federal specification since they have no require-
quiredwhenservicetemperaturesareexpectedtoexceed85to mentsforoutgassingorshelflifecontrol.Inaddition,anumber
90°C since the normal screening temperature of 125°C is too of different materials may be on the QPI for various military
low to predict elevated temperature outgassing. A number of and federal specifications, but all of them may not be equally
acceptable for space use.
materials have been tested for outgassing at 200°C. or higher.
X3. SPECIFIC MATERIAL RECOMMENDATIONS—POTTING COMPOUNDS
X3.1 General —Potting compounds may be used to coat growth at higher temperatures. Thermal cycling of potting
magnetics, pot connector backshells, pot inserts, fill compounds can cause cracking or crazing and loss of physical
honeycomb, or encapsulate electronics. Most potting com- and mechanical properties.
pounds are epoxies, silicones, or polyurethanes. The same
X3.3 Corrosion and Compatibility—Compatibility of pot-
concerns discussed in Appendix X2 regarding changes in
tingcompoundsoradhesivesshouldbeestablishedbeforeuse.
properties at the glass transition point apply to these classes of
Sequence of use, and which potting compounds are used
materialswhentheyareusedforpotting.Inaddition,theremay
together, must be considered carefully. For example, if sili-
be significant differences in the coefficient of thermal expan-
conesareusedtosealsurfacesthatarethenpottedinepoxy,the
sion between potting compounds and items being potted,
epoxy will not adhere to the silicone and may interact
resulting in significant stresses on the parts or solder joints.
adversely with it. Amine-cured epoxies should be avoided in
Processingconditionsmustbecontrolledandrepeatable.There
contact with silicones. Moisture-curing systems, such as one-
are additional specific concerns when the materials are used in
part silicones, may be sealed from sources of moisture, if
potting applications.
overcoated, before they are cured. Curing agents may be toxic
X3.2 Mechanical and Physical Properties—In addition to
ormayattackothermaterials.ExamplesaretheMOCA-curing
the limits on thermal stability and functional suitability at high
agent, which is considered toxic, and dibutyl tin, which
and low temperatures, potting compounds may have exother-
corrodes copper.
mic reactions. Since they are used in larger quantities than
adhesives, the heating during cure could be enough to damage X3.4 Environmental Concerns—Foams and soft potting
compounds present a particular problem. They contain signifi-
components.Itmaybenecessarytocurethepottingcompound
in separate castings or in a controlled environment to reduce cant amounts of air or foaming agents. After launch, the
trapped gases can expand in vacuum and cause physical
thermal stresses during curing. Because the mass of potting
compoundsisgreaterthanadhesivesinmostapplications,high damage to components. Gases, which are emitted over time,
can cause arcing or multipacting if electrical equipment is
and low temperature exposure may result in noticeable dimen-
sional changes or component stresses as a result of potting turned on before all the gases have dissipated. It may be
E1997 − 15 (2021)
necessary to vacuum degas foams and potting compounds or be tested and qualified for the specific application of use. This
postcure them under vacuum. It is important to verify that the normallyrequireshardnessandmechanicalstrengthtestingand
particular foam under consideration has adequate stability,
evaluation.
does not crumble or generate particles, and is stable over the
temperature range of interest. Some foams may be susceptible X3.7 Preferred Materials—The clear preference is to use
materials that are well characterized, readily available, have
to biological attack before launch.
reproducible and reliable properties, have acceptable
X3.5 Outgassing —Materials that should be avoided in-
outgassing, are fabricated readily, will survive the anticipated
clude any with excessive outgassing, such as polysulphides or
environment, are compatible with other materials in the
nonspace-grade silicones. Some materials, such as nylons and
system, and have a history of successful use in the intended
inks, have high TML and may produce significant amounts of
applications.
water and solvents.They should be evaluated for each specific
application before they are approved and used. Potting com-
X3.8 Materials To Be Avoided—It is preferable to avoid
poundsthathavehighexothermalreactions,shrinkseverely,or
materials that undergo phase transformations in the expected
havehighcoefficientsofthermalexpansionshouldbeavoided.
servicetemperaturerange,havehighoutgassing,donothavea
history of successful use in similar applications, are not well
X3.6 Controls on Properties—It is a general requirement
that all materials used on spacecraft be identified fully and characterized, do not have dependable and reproducible
properties,aredifficultorexpensivetoprocure,orareunstable
uniquely. This identification is not possible for almost all
military or federal specification products. Any adhesive must or have short shelf lives.
X4. SPECIFIC MATERIAL RECOMMENDATIONS—TAPES
X4.1 General —Adhesive tapes have two materials of Optical properties of these tapes is of interest and should be
concern:boththebackingmaterialandtheadhesiveneedtobe verified.
evaluated. Backings should be selected from materials that are
X4.4 Corrosion and Stability—Corrosion is not applicable.
acceptable generally for space applications, such as polyimide
Adhesives on the tapes are age sensitive and must have
(Kapton), polyester (Mylar® ), fiberglass, metal foils, such as
shelf-life controls imposed. Over time, adhesives will lose
...