Laboratory measurement of the charge and adhesion forces of lunar regolith simulants

During the Apollo missions, it has been well understood that the abrasive and adhesive nature of the lunar regolith was an impediment to the success of future robotic and manned missions. In recent years, many studies focus on understanding dust behaviour under a representative environment. VUV is used to mimic the side of the Moon that is illuminated by the sun, whereas electron irradiation is used to mimic the dark side of the Moon. One major topic that is currently addressed is the assessment of the electrical charge of the lunar regolith under VUV and electron irradiation. The main objective is to study its electrical properties and estimate its adhesion forces. On Earth, different simulants are used and compared to each other. Therefore, the adhesion forces are not only charge and environmental (topography, irradiation conditions, etc) dependent, but also simulant dependent. Studying a large range of dust simulants thus helps us to refine our understanding of the behaviour of the lunar regolith. This will help define and design mitigation techniques that will protect scientific instrument and, more generally, ensure the safety of future lunar missions.

For future lunar missions, it is important characterize the charge and size of dust particles to assess their adhesion forces. Measuring the particles’ charge and size allows us to derive whether the charge of dust particles depends on its size or if it is merely a consequence of the environment and local topography. These measurements will also allow us to compare the significance between the lunar regolith and the different dust simulants (JSC-1A, LHS-1, LMS-1, etc), making it easier to extrapolate the behaviour of the lunar regolith. Additionnally, refining our understanding of the electrical properties of the lunar regolith through experimental analysis will contribute to the improvement of simulating tools, such as SPIS ([1]), and allow us to anticipate future critical cases on the Moon.

Previous studies that have been led at ONERA with BIRA-IASB have shown that lunar dust simulant JSC-1A is charged negatively and positively under VUV irradiation [2]. This behaviour shows that emitted photoelectrons tend to differentially charge neighbouring grains. According to the patch charge model, deeper layers are charged negatively whereas layers at the surface are predominantly charged positively. In this study, it was shown that 50% of particles have a charge lower than +/- 10 fC. This is valuable information for the design of future mitigation techniques, as it gives a good overview of the electrostatic force that could be applied to extract dust particles from their substrate, or simply prevent them from adhering. Other simulants have also been tested but displayed quite different behaviour. LHS-1 has been tested under VUV and electron irradiation, but few dust grains were detected. This indicates that LHS-1 and JSC-1A have quite different electrical properties, that lead to very distinct behaviours under irradiation.

 

[1]          P. Oudayer et al., « Multiscale Modeling of Dust Charging in Simulated Lunar Environment Conditions », IEEE Trans. Plasma Sci., vol. 47, n^o 8, p. 3710‑3716, août 2019, doi: 10.1109/TPS.2019.2919932.

[2]          R. Pacaud, J.-C. Matéo-Vélez, S. Hess, et S. Ranvier, « Measurement of bipolar charge distribution of lunar dust simulant under VUV irradiation », Planetary and Space Science, vol. 263, p. 106120, sept. 2025, doi: 10.1016/j.pss.2025.106120.