Materials outgassing: impact of environmental conditions

Objectives :

As the consequences of degassing can be detrimental to the operation of on-board instruments, it is now necessary to accurately predict the risks of molecular contamination on sensitive surfaces in order to better consolidate the expected levels of cleanliness.

The first objective of this thesis is to improve the physico-chemical understanding of the phenomena of diffusion, desorption or even adsorption / absorption (uptake of humidity) of materials having undergone a thermal pre-treatment under vacuum on the ground and / or exposed to the space environment and in particular to UV.

The second objective is to improve the prediction models by modeling the phenomena analyzed.
The purpose of this thesis is then to model with more physical realism the levels of outgassing over the duration of a mission, taking into account all the phenomena induced on the ground and in flight (vacuum, radiation).

More details :

Assessing the outgassing of space materials, through elementary experiments and modeling the masses emitted and deposited, is essential to minimize the risks of contamination throughout the lifetime of a spacecraft. Although the first physical models have evolved little, based essentially on the classic laws of surface desorption of families of contaminants, recent experiments have shown the importance of taking into consideration the separation of degassed chemical species to account for a physical more realistic but also to study the mechanisms of diffusion in matter, considered until then as negligible.

Significant progress could then be made with new experimental protocols combining thermogravimetry and mass spectrometry to overcome certain limitations in the experiment/simulation comparison. If the results are very satisfactory on specific cases (EC9323-2 glue…), it is proposed here to exploit them more systematically with materials of various natures and shapes (paints, varnishes, glues, composites…) in order to validate proposed improvements regarding the fit of new data (particularly with long-term trials).

In addition, a very often neglected aspect concerns the experience of a material and the various ground / flight treatments it has undergone such as thermal cycling tests under vacuum or other thermal pre-treatments or even long-term storage under humidity, which can greatly affect the amount of contaminant available and therefore the prediction of outgassing during a space mission. Indeed, the input parameters of the degassing kinetics are obtained from most of the time freshly polymerized materials and the long-term prediction is therefore greatly modified.

The objective of this thesis is therefore to improve the understanding from a physical and chemical point of view of all the phenomena associated with the vacuum degassing of usual space materials and the consideration of their history in order to then validate the approaches recently developed in collaboration with ONERA. A hybrid approach to prediction combining Arrhenius-type desorption models with Fick-type diffusion models could be considered.
The informal partners potentially interested in this work are the prime contractors TAS and ADS as well as ONERA with whom we have been collaborating on related subjects for many years.

The National Centre for Space Studies (CNES; French: Centre national d'études spatiales) is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is under the supervision of the French Ministries of Defence and Research.

It operates from the Toulouse Space Centre and the Guiana Space Centre, but also has payloads launched from space centres operated by other countries. The president of CNES is Philippe Baptiste. CNES is a member of Institute of Space, its Applications and Technologies. It is Europe's largest and most important national organization of its type.

Chemistry of materials / polymers, simulation, analytical chemsitry, vacuum, space