Enabling & Support
04/05/2026
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Space mechanisms rely on liquid lubricants to keep rotating and moving parts functioning reliably over missions that may last many years. In the vacuum of space, however, those lubricants present a hidden hazard: they evaporate, and the molecules that escape can migrate and contaminate sensitive optical or electronic surfaces. A recent ESA Discovery project led by Brno University of Technology investigated how to keep those molecules in check.
One widely used passive containment solution is a labyrinth seal: a narrow gap placed around a bearing or shaft that forces evaporated lubricant molecules to navigate a maze-like path, making it unlikely that they will escape into the wider mechanism. The performance of such non-contacting seals depends on their geometry, but the relationship between design choices and sealing performance has not been fully understood.
The ESA Discovery activity ‘Effect of local geometrical changes and polarization of labyrinth seal surfaces on the evaporation rate of liquid lubricants in space applications‘ set out to change that, developing a rigorous, design-oriented framework for predicting and minimising lubricant loss in mechanisms such as attitude control systems, solar array drive mechanisms, and the coarse pointing assemblies that orientate a payload towards a target.
The geometry of sealing
“My activity targets a practical gap in contamination control for fluid lubricated space mechanisms, where evaporated lubricant molecules can migrate and deposit on sensitive surfaces,” says Principal Investigator Dr Josef Pouzar of the Faculty of Mechanical Engineering, Brno University of Technology. “The outcome is a more predictive, design-oriented basis for reducing contamination risk at the design stage rather than through late-stage testing.”
In space, residual gas pressures are so low that lubricant molecules travel in straight lines and interact primarily with boundary surfaces rather than with each other – a behaviour known as molecular flow. The project combined analytical modelling, computer simulation using the COMSOL Multiphysics and MolFlow+ software packages as well as physical experiments in custom-built vacuum test rigs to characterise the behaviour of labyrinth seals across a range of design and operating parameters.
Testing three seal geometries – short (1.5 mm gap length), long (10 mm gap length) and stepped path – the research team was able to confirm the strong effect of gap length and the introduction of a step (lubricant mass loss reduced by about 20% and 40%, respectively, compared to the short seal). Local geometry modifications such as relief grooves and dead-end pockets offered further reductions of around 4% each. Surface roughness proved significant: a rougher internal surface reduced evaporative losses by around 13% compared to a smooth one, and the team showed that deliberately increasing roughness could allow seal length to be reduced by up to 40% without any loss of sealing performance – an important consideration where mass and space are at a premium. Rotation too played a role, with seals spinning at 2,000 rpm losing approximately 10% less lubricant than static ones.
A second phase explored whether electrostatic fields could further reduce lubricant migration. Applying 50 V across the seal produced measurable reductions, up to about 4%, for perfluoropolyether (PFPE) and ionic liquid type lubricants, though the effect was negligible for non-polar lubricant molecules. The team concluded that an electrostatic field can fine-tune seal performance, but is no substitute for good seal geometry.
From lab to orbit
“ESA Discovery’s support enabled me to perform the experimental and modelling work needed to validate the concepts, including vacuum testing and molecular flow simulations,” says Pouzar. “Overall, it accelerated my research and helped translate it into results that are easier to transfer to the space mechanisms community and industry.”
“Many space mechanisms need to function reliably for the entire duration of a mission, and lubricant loss is one of the key risks that may cause mechanism failure,” says René Seiler, Senior Mechanisms Engineer and ESA lead on the project. “This research has given us a much better understanding of how labyrinth seal design choices translate into real sealing performance, and the results will make it easier for engineers to guarantee long-life lubrication and to design contamination control into mechanisms from the outset rather than discovering problems in the course of full-scale equipment tests or in-flight operation.”
The project has produced four publications, including papers in Vacuum and Results in Engineering, and a presentation at the 21st European Space Mechanisms and Tribology Symposium (ESMATS) in 2025. Pouzar also sees commercial potential: the validated models could underpin a software tool allowing engineers to compare seal concepts early in the hardware development process and streamline the associated qualification effort.
The next step will be in-orbit validation. Brno University of Technology is contributing a labyrinth seal experiment to a 3U CubeSat mission led by the Czech Aerospace Research Centre, Spacemanic CZ, and Brno Observatory, with launch planned for late 2027. It is a fitting conclusion for a research project that began as a blue-sky idea submitted through ESA’s Open Space Innovation Platform (OSIP) and was funded by the Discovery element of ESA’s Basic Activities.
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