Autonomous landing on small celestial bodies poses significant challenges due to irregular surface geometry, weak gravity, and limited navigational observability. This paper presents a shadow-assisted visual-inertial navigation framework that enhances localization performance during descent by incorporating shadow geometry as an additional visual constraint into a tightly coupled nonlinear optimization process. A joint optimization strategy is introduced to simultaneously estimate navigation states and beacon map errors, effectively reducing the impact of beacon uncertainty. Additionally, an adaptive weighting mechanism is proposed to modulate the influence of visual features based on observation redundancy, improving convergence robustness. Adequate numerical simulations demonstrate that the proposed method significantly improves the accuracy and stability of position, velocity, and attitude estimation. These results support the framework’s potential for enabling precise, autonomous landing in future small-body exploration missions.

The longest known Aletai meteorite belt presents a unique phenomenon in meteoroid dynamics. To investigate its formation mechanism, this study introduces a bilobate-shaped meteoroid model, emphasizing aerodynamic interactions and structure evolution. The sintered bond model is applied to simulate the tensile, compressive, and shear strengths of the bilobate-shaped meteoroid. Its disintegration is analyzed under the combined effects of aerodynamic forces and self-rotation. After disintegration, the transverse velocity of the sub-spherical fragments is applied to track their dispersal trajectories and calculate the resulting strewn field of meteorites. The influence of aerodynamical shock wave and mass ablation is considered throughout the descent process. Numerical simulations are conducted with varying initial entry conditions, particularly focusing on the initial rotation of the bilobate-shaped meteoroid. The study focuses on the mechanism of the skipping trajectory and the associated strewn field during the meteoroid's dynamical evolution. The results highlight the critical role of bilobate-shaped meteoroids in generating skipping trajectories and provide new insights into the formation of Aletai-like ultra-long meteorite belt.

Rotational intrusion into granular media is crucial for small body sampling but remains less studied than its non-rotational counterpart. Using a GPU-accelerated discrete element method, we investigate the resistance of a rotating cylindrical penetrometer as a function of the Froude number. Unlike quasi-static intrusion, which creates a stagnant zone ahead of the intruder, rotation disrupts this structure, inducing shear dilation both in front of and around the intruder. This results in a thin, highly mobilized layer of particles, causing the slope of the force-depth to decrease following a negative power-law relationship with increasing Froude number. As rotation intensifies, the rate of resistance reduction slows, and sliding friction becomes negligible, while rolling and torsional resistances remain significant. Furthermore, introducing cohesion shifts the granular medium's response from plastic to elasto-plastic, significantly altering the force-depth relationship and leading to resistance saturation. A brief gravity scan shows that weaker gravity modestly increases the depth-dependence of relative resistance and amplifies the influence of rotation. These findings enhance the understanding of rotational intrusion mechanisms under micro-gravity.

This study investigates the energy dissipation mechanism of particle-damping artificial landmarks during their deployment on planetary surfaces. Deploying inertial artificial landmarks under microgravity conditions poses significant challenges, as minimal rebound velocities can result in significant rebound or direct escape from the planetary surface. Successful deployments of artificial landmarks in Hayabusa and Hayabusa2 missions of JAXA have attracted much attention from space community. However, the underlying mechanism of the relationship between damping performance and the physical parameters of damping particles has not been thoroughly elucidated. In this study, the discrete element method is adopted to create a simulation platform within the Compute Unified Device Architecture (CUDA) framework, where its reliability is validated through ground experiments. Parametric simulations are conducted by taking damping particles and regolith particles into account. How the radius and amounts of the inner particles in the damper shell affecting the energy dispassion are investigated in detail. The research findings demonstrate that the quantity, radius, and density of particles in the damping device are crucial factors in determining damping performance. Additionally, the cohesion coefficient of the planetary regolith surface influences the effectiveness of damping as well. Such a study can provide a detailed design guideline for future particle damping landmarks.

This paper proposes a practical design of an autonomous optical navigation system for ultra-low orbit vehicles, offering an innovative solution to address the accumulation of satellite ephemeris errors. An emerging scenario is treated in which only one individual near-Earth satellite can be captured during each encountering period through a star tracker. When background stars are used to determine the attitude, the line-of-sight measurements of the observed satellite are extracted for flight vehicle positioning. To overcome the problem of gradually increasing satellite ephemeris errors over time, a method through sequential two-pass observations of a single satellite is proposed, which enables simultaneous estimation of the vehicle state and correction of the satellite position error. Some representative scenarios are simulated to illustrate the performance of the proposed algorithm. Results show that the autonomous optical navigation system can achieve sufficient accuracy using the very short-arc observations of a single target satellite. Copyright (c) 2025 The Authors.This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)

Precise landing navigation on small celestial bodies poses significant challenges due to low-gravity environments, rugged terrains, and harsh illumination conditions. This paper proposes a tightly coupled multi-source navigation framework integrating inertial sensors and navigation cameras, enhanced by shadow constraints, to achieve high-precision planetary landing. A nonlinear sliding-window optimization strategy is developed, where landmark position errors are treated as additional state variables, and an adaptive residual weighting scheme is introduced to improve the robustness and convergence rate of the estimator. Furthermore, a novel tightly coupled shadow measurement model is formulated to exploit the geometric regularity of spacecraft shadows under parallel sunlight. Simulation results demonstrate that proposed method significantly enhances positioning accuracy compared to traditional approaches, achieving sub-meter level precision during the final descent phase.

Landing on small bodies presents significant challenges due to the structural and dynamic inhomogeneity of their gravel layers, further complicated by microgravity conditions. These factors lead to highly nonlinear interactions between the lander and the gravel. In this study, the non-spherical discrete element method is applied to investigate the landing dynamics, focusing on the macroscopic behavior of the lander through the evolution of mesoscale force chains within the gravel. Our results show that the force chains quickly form during the initial penetration phase, causing a sharp increase in resistance, which is subsequently reduced as energy is dissipated. A key finding is the decoupling between peak resistance and the onset of rebound, which highlights the temporal discrepancy in the interactions between the lander and the particles. The study also finds that the particle size significantly affects the force chain structure and landing stability: larger particles form stronger force chains, resulting in higher resistance and rebound, while smaller particles dissipate more energy, promoting more stable landings. These findings offer new insights into the mechanics of asteroid surfaces and suggest practical strategies for optimizing landing procedures, such as selecting regions with smaller particles and minimizing lateral velocity to reduce rebound.

This study investigates the landing dynamics of a telescopic-legged robotic rover on granular surfaces of small celestial bodies, addressing the challenges posed by its high-degree-of-freedom structure. Using a custom module within the PolyDEM discrete element framework, the interaction between complex rigid bodies and nonspherical particles was accurately simulated and validated through ground-based experiments. The results reveal that retracted legs exhibit superior damping performance on coarse gravel layers by increasing localized contact area, enhancing friction, and promoting internal particle rearrangement. Conversely, extended legs perform better on fine-grained regolith by increasing penetration depth and enabling multi-point interactions, which amplify energy absorption. Additionally, this study examines the effects of impact velocity and angle on rover stability, providing actionable insights for terrain-specific deployment strategies. These findings advance our understanding of high-DOF robotic systems in extraterrestrial environments and offer practical guidance for future mission planning.

A novel method for simulating the disintegration of bilobate-shaped meteoric fragments is presented, which integrates aerodynamic interactions, rotational dynamics, structural strength, and ablation into the analysis. A disintegration criterion is proposed in this method, based on a comparison between the mechanism strength of the sintered bond and the required contact force to maintain the integrity of the bilobate shape. The disintegration of fragment 109 from the Moravka meteoroid, which deviates from the Weibull-like scaling law, is explained physically by applying this approach. Predictive numerical simulations are conducted by varying the initial attitudes, geometries, strengths, and angular velocities of the bilobate-shaped fragments. During atmospheric entry, variations in attitude, landing positions, and residual masses are analyzed as indicators of characteristics in the dynamical evolution.

The extremely weak gravity on small bodies makes landers prone to rebound and uncontrolled drift. To mitigate this, the Hayabusa2 mission employed a particle-filled flexible shell, but the coupled dynamics of shell deformation and internal particle dissipation remain unclear. We develop a computational model representing the flexible shell as a spring-mass network and fully resolve particle collisions, friction, and interactions with granular beds. Results show the flexible shell-granule system dissipates over 90 percent of impact energy, far exceeding rigid shells. Energy loss arises from shell-particle coupling, with the particle filling ratio dominating. Impacts on rigid planes produce large shell deformation, while granular beds limit deformation. Scaling and velocity analyses reveal distinct dissipation regimes. These findings clarify energy transfer mechanisms and inform the design of microgravity impact mitigation devices.

The hopping rover, especially the internal-torque-actuated (hopping) rover, is currently recognized as one of the most suitable types for asteroid surface exploration. Although such rovers have been successfully demonstrated in the Hayabusa 2 mission, their dynamical and control problem of its hopping motion has not been studied enough. Consequently, this article first builds the rover's hopping dynamical model based on the polygonal contact model in considering the flywheel braking process. The hopping motion is then numerically simulated on two kinds of planes, including an ideally flat plane and a complex rocky terrain. Furthermore, the parametric studies of the rover's hopping process are implemented by considering the flywheel's nonconstant reaction torque during braking, the multicontact cases, the surface deformation, and the slip cases. Particularly, the phenomenon of multiple microcontacts between the rover and the asteroid surface before departure is discovered. The effect of the flywheel's braking process, contact stiffness, and friction coefficient on the hopping characteristics of the rover is investigated. Moreover, their intrinsic dynamical mechanisms are also illustrated. This study could provide a reference for future missions that require roving on the surface of a small celestial body.

Meter-sized meteoroids typically exhibit asymmetric light curves with multiple peaks due to fragmentation and heterogeneous properties. This study proposes a systematic simulation method for modeling the trajectory, attitude, and structural evolution during their luminous atmospheric entry. The N-body meteoroid model incorporates irregular geometry, porous structure, and heterogeneous materials. In this approach, a cohesive contact model is employed to simulate the meteoroid's structural disintegration. Differential ablation and asymmetrical volume changes are applied to simulate the kinetic energy loss and reproduce the light curve. The equivalent crosssectional diameters of the valid granules at the light curve peaks are calculated to quantify the expansion of fragments. The effectiveness of the proposed method is validated through its application to two meteoroid cases: the 2023 Beijing meteoroid and the asteroid 2024 BX1. The multiple light curve peaks observed for both meteoroids are successfully reproduced using the new approach. For large meteorites from 2024 BX1 with masses exceeding 100 g, the method predicts landing positions with an accuracy of approximately 1 km. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The tradeoff between accuracy and efficiency in gravitational field modeling for binary asteroid landing is one of the challenges in dynamical analyses. Four representative gravitational modeling methods are employed and compared in this study. These are the sphere–sphere model, ellipsoid–sphere model, inertia integral-polyhedron method, and finite element method. This study considers the differences between these four models, particularly their effects on the landing dynamics of a lander. A framework to simulate the coupled orbit–attitude motion of a lander in a binary system is first established. Numerical simulations are then performed on the natural landings on the second primary of the (66391) Moshup–Squannit system. The results show significant differences in the final landing dispersions, settling time, and sliding distance when applying the simplified models. On the basis of the modeling accuracy and computational efficiency, the finite element method should be chosen for future missions.

Cubic rovers that traverse by hopping systems are promising in low-gravity environments. Although several analyses of the control methods and mobility of the cubic rover are available, investigations of its attitude-adjusting behavior are still limited. This study derives the dynamic equations of the two attitude-adjusting modes of the cubic rover, referred to as walking and twisting. The relationships between the speed threshold and rotation angle of the cubic rover were investigated in both rigid and regolith environments using a self-designed low-gravity testbed. Comparative studies were conducted by considering the experimental and simulated outputs. The results of this study can be interesting for roving mission planning when exploring planetary moons and small celestial bodies.

Meteoroid disintegration in the atmosphere can produce airbursts that pose regional/global threats to the Earth. Precise dynamical simulation of hypersonic meteoroids is necessary for human safety. An analysis model that includes spatial structures and non-uniform ablation is needed to understand the evolution of meteoroids and provide inference for the deviation of fragments. This paper proposes a new meteoroid entry method to simulate their trajectory, attitude, ablation, fragmentation, and detonation. N-body configurations of deformable polyhedral granules that can alter the structures of heterogeneous meteoroids are introduced. By manipulating the polyhedron vertices, the rugged surfaces of the meteoroid and the volume change under ablation are described quantitatively. The pressure of the concentrated detonation products is modeled using the Jones-Wilkins-Lee equation of state. To verify the effectiveness of the new method, the expansion of the concentrated detonation products is numerically simulated for the Chelyabinsk meteoroid. Different detonation cases are obtained and presented to demonstrate the laterally/vertically-ejected fragments. Characteristics of both the fragments’ trajectories and the remained terminal masses satisfy the observed results well.

One of the potentially catastrophic risks to human survival is the impact of a meteorite on Earth. When a meteoroid enters the atmosphere at an ultra-high speed, a series of complex evolution processes occur, mainly including ablation, fragmentation, airburst, and ground impact. This paper proposes a new systematic dynamical method for simulating the entire process of a meteoroid entering the atmosphere. In the new method, the DEM (Discrete Element Method) model is utilized to describe the initial structure and shape of a rubble-pile meteoroid. A combination of an aerodynamic trajectory model, a thermal ablation model, and an airburst model is introduced to simulate the entry process. Particularly, the Jone-Wilkins-Lee state equation is employed to characterize the large-scale airburst phenomenon caused by the internal expansion of the meteoroid. Referring to the observational data of the Chelyabinsk meteorite event, this paper parametrically simulates the trajectories, ablation, fragmentation, and airburst, and predicts the strewn field of different-shaped meteoroids. Compared with existing debris cloud models, this method considers the shape effect of rubble-pile meteoroids and can obtain the strewn field as a side effect. Numerical validation is carried out, indicating the result of the new method is more in line with the actual scenarios.

This paper presents a finite element method to search for equilibrium points around a heterogeneous small body, which degenerates from the full two-body problem in finite element form. The gravitational potential, acceleration, gravitational gradient matrix, and the linearized perturbation equation, which are key formulas for solving the equilibrium points and discriminating their stabilities, are interpolated by the tetrahedral model nodes of the small body. The finite element method could capture the complex internal structures of small bodies and provide a uniform and simple formula for various configurations. The method is applied to the Kuiper Belt Object (486958) Arrokoth, which is a contact binary asteroid. Three types of heterogeneous structures are hypothesized to investigate the evolutions of equilibrium points, namely density disparity of two sub-lobes, hardcore structure, and cavity structure. Under the condition of constant Arrokoth mass, the density disparity of the two sub-lobes greatly influences the local gravitational field. It thus has a significant influence on the positions of equilibrium points. The hardcore and cavity structures have less impact on the equilibrium points. These three simulation groups verified that the equilibrium points of a heterogeneous small body are quite different from those of a homogeneous small body. Such investigation of the equilibrium points may give an in-depth understanding of the dynamical environment around the heterogeneous small body, which is significant for future deep-space missions.

This paper presents an efficient CUDA-based implementation of a nonspherical discrete element method where irregular particles are described by using polyhedrons. Two strategies are employed to exploit the parallelism of the numerical method. One is to perform contact detection based on the contact pair level instead of the traditional particle level. The second is to reduce the computational burden of each kernel function by allocating thread blocks reasonably. Contact detection between potential contact pairs is the most complicated, time-consuming, and essential process for the polyhedral discrete element method. The linear bounding volume hierarchies are introduced to fix this issue. The hierarchies of the bounding volume tree are organized in a spatially coherent way. Such a structure can minimize branch divergence and is very suitable for parallel implementation with GPU. Two numerical examples are presented to show the performance of the code. It is found from the scenario of two sphere collision that improving the mesh resolution of polyhedral particles can reduce the computational error while slowing down the computational speed correspondingly. A trade-off must be made between accuracy and efficiency. The other example of self-gravitating aggregation demonstrates the code is convergent, stable, and highly efficient. Particularly, with a mainstream GPU, the proposed method easily performs hundreds of times faster than the serial CPU code that does the same function.

Particle mixtures of different sizes can segregate upon external excitation, which is called the Brazil nut effect (BNE). Since the BNE is a possible reason for large boulders depositing at the small body surface, the conditions and mechanisms regarding BNE have aroused broad concern in planetary science. Different from previous works, this paper further investigates this effect by using nonspherical polyhedral particles at different gravity levels. Numerical results of size segregation are presented to validate that a nonspherical polyhedral BNE is scalable if van der Waals cohesive interactions are not involved. Additionally, the attitude adjustment of the intruder would bring uncertainties to BNE, but it is eliminated upon the intense external vibration. The influence of the van der Waals force on BNE is also investigated. The van der Waals force strongly increases the stability of the particle system under a microgravity environment; therefore, the van der Waals force suppresses the BNE, and the scaling law is not applicable. However, when the particle system is under the Earth's gravitational environment with intense vibration, the van der Waals force benefits the BNE. The reason is that the cohesion force will increase the convective effect of the loosely structured particle system. Different shapes of intruders are also created. The intruder's oblateness influence on the BNE is further studied. It is difficult for the intruder to reorient the posture vertically as its increasing oblateness decreases the contact area, thus weakening the BNE.

This paper investigates the motion of a lander in a fully coupled spin–orbit binary system. The full dynamical equations are established, including the states of the lander and the two small celestial bodies. The binary companions are represented by tetrahedral meshes when propagating their states; therefore, their irregular shapes are preserved. The mutual gravitational interactions between the two bodies and the attraction of the lander in this binary system are evaluated by the finite element method. The contact motion between the lander in arbitrary shapes/inertia and the asteroid surface is processed by the polygonal contact model. The resulting framework is applied to the binary asteroid system, 66391 Moshup. The deployment simulations of four typical initial positions near the secondary body suggest the lander release should avoid polar regions. The dynamical effect of the primary body on the lander is also investigated. The numerical results show that the accumulative effect of the weak tidal force from the primary body is nonnegligible. In addition, four different internal structures of the secondary body are constructed by operating the tetrahedron mesh. The touchdown positions and settling time of the landing trajectories on these four models are summarized and compared. The results indicate that variations of the internal structure have a nonnegligible effect on the local gravitational field around the secondary body, and therefore affect the locomotion of the lander.