Introduction
Material outgassing is the release of gases, vapours or volatile compounds from a material when it is exposed to reduced pressure or vacuum. The effect is particularly important in spacecraft because released molecules can migrate through the vacuum environment and condense on colder or contamination-sensitive surfaces.
Adhesives, coatings, polymers, lubricants, tapes, composite materials, elastomers, inks and some additively manufactured materials can release water, residual solvents, plasticisers, oils or other volatile substances. These contaminants can deposit on optics, detectors, thermal-control surfaces, solar cells, electrical contacts and precision mechanisms.
Material outgassing is therefore not simply a chamber-cleanliness concern. It is a materials-selection, design, contamination-control and mission-assurance issue.
ECSS addresses outgassing principally through the product-assurance and contamination-control framework. ECSS-Q-ST-70-02 defines a thermal-vacuum outgassing screening method for space materials. ECSS-Q-ST-70-01 addresses cleanliness and contamination control across the project lifecycle. ECSS-E-ST-10-04 provides wider space-environment context, including the induced molecular environment created by the spacecraft itself.
Outgassing evidence can support material approval, Declared Materials List review, contamination analysis and thermal-vacuum campaign planning. It does not prove complete spacecraft suitability on its own. The applicable limits depend on the material quantity, location, operating temperature, nearby sensitive surfaces, mission environment and customer requirements.
Important: A material passing a screening limit is not automatically suitable for every spacecraft application. Location, quantity, geometry, temperature, view factors and contamination sensitivity still matter.
What Is Material Outgassing?
Definition
Material outgassing is the release of gaseous or volatile species from a material.
In vacuum, molecules that were absorbed, adsorbed, trapped or chemically retained can leave the material. The released species can travel through the vacuum environment and:
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Leave the spacecraft.
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Remain temporarily within an enclosed volume.
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Strike another surface.
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Condense on a colder surface.
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Re-evaporate when the receiving surface becomes warmer.
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Become altered by ultraviolet radiation or atomic oxygen.
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Contribute to a wider molecular-contamination environment.
Outgassing, Offgassing and Contamination
These terms are related but should not be used as if they are identical.
| Term | Practical meaning |
|---|---|
| Outgassing | Release of gaseous or volatile material, particularly under vacuum. |
| Offgassing | Release of substances in atmospheric or higher-pressure conditions. |
| Molecular contamination | Unwanted molecular material present on, or transported towards, a sensitive surface. |
| Particulate contamination | Unwanted solid particles suspended in air or deposited on hardware. |
| Condensable material | Released material capable of condensing on a cooler collection surface. |
| Bakeout | Controlled heating used to reduce removable volatile content before integration, testing or flight. |
Outgassing is a source mechanism. Contamination is the potential consequence.
Purpose of Outgassing Control
Outgassing control aims to:
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Select materials appropriate for vacuum service.
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Reduce molecular-contamination sources.
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Protect optics, sensors and thermal-control surfaces.
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Support contamination modelling.
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Maintain chamber and hardware cleanliness.
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Prevent unacceptable functional or performance degradation.
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Generate traceable evidence for material approval and verification.