Lunar dust poses a significant challenge for long-term lunar missions, and researchers have developed a groundbreaking model to understand how charged lunar dust particles interact with spacecraft. This model, created by scientists from Beijing Institute of Technology, China Academy of Space Technology, and the Chinese Academy of Sciences, focuses on the electrostatic forces and contact mechanics that determine whether dust grains adhere to or escape from spacecraft surfaces. The study aims to address the issue of dust accumulation on spacecraft and spacesuits, which is a critical constraint for surface operations and plans for permanent lunar stations.
The model begins by analyzing the electrostatic environment around the spacecraft and the lunar regolith. On the sunlit dayside, solar radiation generates photoelectrons, charging both the spacecraft and the regolith positively. This creates a photoelectron sheath above the surface. Conversely, on the nightside, the spacecraft and regolith are negatively charged due to electron collection from the ambient plasma, forming a Debye sheath. The model also considers additional charging from the solar wind, lunar plasma wake, and plasma in the magnetotail lobes and plasma sheet.
To simplify the complex interactions, the spacecraft is approximated as an infinite conducting plane coated with a dielectric layer. A single dust particle is treated as a dielectric sphere with a uniform surface charge density and permittivity. The distance from the coating surface to the outer sheath boundary is set to three times the Debye length, and the potential in the sheath decays exponentially. The total electrostatic force on the particle is calculated by considering the electric field force, dielectrophoretic force, and multipole image force, taking into account the particle's position and charge.
The second part of the study explores the adhesive-elastic-plastic collision mechanics that determine whether dust grains stick after impact. Despite the challenges posed by the small size, irregular shapes, and high hardness of lunar dust, the particles are represented as spheres for the normal contact problem. The spacecraft coating is modeled as a Kapton layer. The Johnson-Kendall-Roberts (JKR) model is used to describe adhesion, and plastic deformation of the coating is incorporated to account for energy losses during low-velocity collisions.
The impact process is divided into three stages: adhesive-elastic loading, adhesive-elastic-plastic loading, and adhesive-elastic unloading. The pressure distribution over the contact area evolves through these stages, with the first stage relating to JKR pressure, relative compression, and contact force. The second stage defines a normal contact force that accounts for plasticity, and the unloading stage expresses the contact force as a function of contact radius. Parametric calculations reveal how coating properties and particle characteristics influence the electrostatic force and post-collision outcomes.
The research highlights the roles of electrostatic and van der Waals forces during low-speed encounters. When the dust surface charge density is below a certain threshold, adhesive van der Waals forces dominate over electrostatic attraction. Coatings with low interface energy, achieved through the selection of low-surface-energy materials and increased surface roughness, make it easier to remove dust from spacecraft surfaces. For charged grains, long-term adhesion depends on the initial impact velocity and whether it falls within critical adhesion and escape thresholds defined by the combined electrostatic and contact mechanics model.
The theoretical framework has broader implications beyond lunar applications. It can be extended to other systems where charged dust accumulates on solid boundaries, such as electrostatic precipitators and the adhesion of energetic powders to mixer walls. This model can support design strategies to mitigate dust buildup. Future research will enhance the interaction model by incorporating realistic irregular dust shapes, more detailed plasma environments, and solar radiation effects to better represent natural conditions on the Moon and in related dusty plasmas.
