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This study presents the design and implementation of a low-speed intrusion experiment under microgravity, with a strong motivation to support the pre-research of the Chinese asteroid exploration mission. In the experiment apparatus, we reconstructed an effective gravity of 10 - 2 g in a free-falling capsule in the drop tower. The simulant of regolith particles is processed using natural basalt and sorted using layered screens. The irregular shapes of the particles are retained to mimic the realistic regolith. A detailed description of the experimental system components and the full-cycle procedure is first presented, which gives 3.6 s of microgravity time for each trial. Repeatable controlled experiments are performed to characterize the dynamical responses of the simulant particles under centimeter-per second intrusion. The results reveal diverse responses that depend on different variables, and the mechanism of different responses is discussed based on theories of granular mechanics. This experimental study is expected to improve our understanding of the contact mechanics of regolith material, which will facilitate the operation design of future asteroid missions. [ABSTRACT FROM AUTHOR]

The research on particle size classification in lunar microgravity has gradually attracted the attention of scholars. Based on the discrete element method (DEM), this work proposes a double-layer auxiliary screening vibrating screen in the form of intermediate feeding, and takes the screening efficiency and screening time as the evaluation indicators. Firstly, the Helmholtz-Maxwell coil is used to simulate the force of particles under lunar microgravity, which verifies the reliability of the numerical simulation of particles under lunar microgravity based on the discrete element method. Then, the influence of the parameters of each screen on the comprehensive performance of screening was analyzed by a single-factor experiment. Finally, based on the BP (Back Propagation) neural network optimized by genetic algorithm, the evaluation model of screen parameters and screen performance is established, and the multi-objective genetic algorithm is used to optimize the screen parameters combination scheme with excellent performance. An efficient comprehensive model of screening is provided to improve the screening performance and the design of the screen machine under lunar microgravity. [ABSTRACT FROM AUTHOR]

• A compact electro-adhesive hexapod robot is designed and prototyped. • A novel convertible limb that integrates manipulation and locomotion is proposed. • An optimized foot-trajectory subject to velocity and acceleration is developed. • Extensive simulations and ground experiments are performed. Service space robotics can provide on-orbit maintenance for faulty spacecrafts to extend life and reduce economic losses. In many cases, spacecraft failures are minor and can be easily recovered by completing simple manipulations or by providing observations. In this study, we propose a spacecraft surface adhesion-crawling-manipulation hexapod robot that can provide such services. To avoid increasing the payload, both of the robot's forelimbs were designed to be convertible, integrating manipulation and locomotion capabilities; the manipulation methods for the novel convertible limb are analyzed. A novel foot trajectory generation method is proposed to reduce the contact force generated when the foot of the robot touches the spacecraft surface and increase dynamic stability. Theoretical and experimental analyses of our robot are presented. Kinematic analyses are performed to validate the manipulation methods using convertible forelimbs. The stability of the robot's static adherence and dynamic crawling are analyzed in a microgravity simulation environment. A physical ground test is conducted to demonstrate the mobility and manipulation capabilities of the robot. [ABSTRACT FROM AUTHOR]

• A ray-tracing algorithm is applied to melting PCM bridges. • Support material for the optical diagnosis of the MarPCM experiment. • The validation of the algorithm is performed via ground experiments. • Three reference bridge shapes are defined to account for volume changes. • A minimum of 60% liquid fraction is needed to accurately determine the front shape. A ray-tracing algorithm is developed to obtain synthetic images for tracking the melting of the phase change material (PCM) n-octadecane in a liquid bridge configuration. The translucent nature of the solid n-octadecane is modelled through a sigmoid function which provides a distance-dependent illumination intensity throughout the solid. The code is validated against two types of experiments: front shapes made of 3D-printed PLA and cast front shapes of solid n-octadecane. Comparison with these experiments allows the numerical constants involved in the model to be tuned to appropriate values. For application to the MarPCM microgravity experiment (Porter et al., 2023), the current study provides the expected images of the solid/liquid front obtained by the optical diagnosis module for three different values of the dimensionless volume (defined with respect to a perfect cylinder), V = 0.9 , 1, and 1.1, and two applied temperature differences, Δ T = 5 and 30 K. The solid/liquid front shapes are obtained numerically from a two-dimensional axisymmetric code as in Varas et al. (2021). The results reveal a strong dependence of image quality on the liquid fraction L. Visual inspection leads to the conclusion that, below L ≈ 60 % , an accurate determination of the front location may be difficult, particularly for the relatively shallow layer of liquid near the thermocapillary interface. [ABSTRACT FROM AUTHOR]

• The current progress and planning of SCBs exploration missions are reviewed. • The surface environmental characteristics of SCBs are analyzed. • Classic adhesion and locomotion technologies for exploring SCBs are studied. • Bionic adhesion and locomotion techniques for exploring SCBs are organized. • Critical issues and research directions of related technologies are presented. This paper attempts to present a comprehensive review of adhesion and locomotion technology for exploring small celestial bodies (SCBs). The long-term landing, adhesion, and locomotion of space robots on the surface of SCBs can maximize the scientific value of exploration missions. They can also provide technical reserves and support for future SCBs resource exploitation and crewed missions. Based on this background, the current progress and planning of SCBs exploration missions are first reviewed. Due to the special microgravity environment and complex surface characteristics of SCBs, adhesion and locomotion on SCBs surfaces are extremely difficult. The surface environmental characteristics of SCBs and their influences and limitations on the adhesion and locomotion of space robots are analyzed. The progress of classic adhesion and locomotion technology on SCBs is classified and studied, including anchoring adhesion, instantaneous adhesion, and locomotion technologies. Based on the research of climbing and soft robots, various bionic adhesion and locomotion techniques are introduced, with emphasis on their application prospects in SCBs exploration missions. Finally, according to the trend of future SCBs exploration missions, the critical issues and research direction of related technologies are presented, and concluding remarks are provided. [ABSTRACT FROM AUTHOR]

• A leg-type asteroid probe landing cushioning device is proposed based on electromagnetic damping. • The vertical landing speed and landing tilt angle will affect the cushioning characteristics. • The horizontal movement direction and the landing tilt direction have a coupling effect on the landing dynamics. • Soft landing media will cause the footpad to collide and bounce on the surface, thereby increasing the cushioning time. In-situ scientific exploration is of great significance to asteroid exploration, and resource development and utilization. The asteroid surface landing cushioning is the basis of in-situ scientific exploration of asteroids. Therefore, a leg-type asteroid landing cushioning device is proposed based on the principle of electromagnetic damping. A dynamic simulation model is used to study the cushioning dynamics of the cushioning device in a microgravity environment. For the proposed landing cushioning device, the simulation investigates the influence of vertical landing speed and landing vertical tilt angle on the dynamic characteristics and landing stability. The dynamics simulation method is also adopted to investigate the influence of the landing horizontal tilt angle and the horizontal movement direction on the landing stability of the three-legged asteroid probe. The horizontal movement direction and the landing horizontal tilt angle have a coupling effect on the landing cushioning dynamics. Finally, based on the developed simulation device of asteroid microgravity environment, landing cushioning experiments are conducted to investigate the influence of soft and hard landing media on the cushioning process and verify the feasibility of the landing cushioning device. The comparison and analysis of the experimental results and the simulation results verify the accuracy of the landing cushioning dynamics simulation method. [ABSTRACT FROM AUTHOR]

• Impossible experiments are performed in microgravity environment. • International collaboration/joint ventures are increasing in microgravity research. • Clinostats and RPMs simulate partial/reduced gravity conditions of Mars and Moon. • New microgravity analogs, models and simulators of better benefits can be developed. Gravity is always present on Earth. However, the influence of gravity can be modified or compensated. Generally, the products created under microgravity have important properties that usually surpasses the best terrestrial counterparts. Commercially, these products have striking features that aids marketing. Fast responding microgravity platforms can be used for short-term experiments, where the reactions or observations takes less time. This can be provided in drop towers, parabolic flights and sounding rockets. To study long-term effects of microgravity, human tended space laboratories have been used, such as the International Space Station. Scientists have developed various kinds of ground-based facilities and equipment for some of them to achieve the condition of functional weightlessness as a result of limited access to space laboratories. Slow responding microgravity platforms can be used for long-term experiments, where the reactions or observations takes more time. Microgravity analog, model or simulations are slow responding platforms and are able to provide long-term effects of microgravity. This includes long-duration bedrests, water immersions and in magnetic levitation, clinostats, random positioning machines, rotating wall vessels and even centrifuges. This study compares and gives an overview of currently known real, analog, model or simulated microgravity environments and platforms, and demonstrates their individual capacities, benefits and limitations. [ABSTRACT FROM AUTHOR]

• Influence of free surface heat transfer on the onset of oscillatory instability. • Thermo-capillary flow in curved liquid bridges under microgravity conditions. • Critical value for the onset of oscillatory flow instability. • 'Dynamic mode decomposition' technique to reveal the inherent flow dynamics. • Quantification of each characteristic mode. Three-dimensional and oscillatory thermo-capillary flow in a liquid bridge of 5 cSt silicone oil (Pr = 67) has been numerically investigated by performing dynamic mode decomposition (DMD) analysis applied to the time-resolved thermal data generated by the 'method of snapshots'. For various heat transfer conditions defined on the free surface of the curved liquid bridge, a series of dynamic modes has been extracted to unfold the underlying physical mechanism that governs the considered dynamical system. Unstable and neutral modes primarily accountable for the transition to the supercritical state established in the liquid bridge have been identified by decomposing the acquired temperature disturbances into spatial and temporal coherent structures. Under microgravity conditions, unsteady and three-dimensional computations are carried out in a liquid bridge of different volume ratios (VR = 0.9 and 1.1) using the finite volume method (FVM) to capture the dynamical evolution of temperature disturbances at the onset of oscillatory instability. The present numerical investigation is mainly aimed at providing broader insight into the complex fluid dynamic processes associated with the oscillatory thermal convection by determining the growth/decay rate and frequency of each characteristic mode with the help of DMD spectra. For each oscillation pattern, the dominant behavior of oscillatory thermo-capillary flow is revealed by its coherent structures. The characteristic modes having more energy content (dominant modes) are also analyzed by the norm of modes || ϕ || by demonstrating the frequency spectra of DMD analysis. [ABSTRACT FROM AUTHOR]