The lunar nearside has been investigated by many uncrewed and crewed missions, but the farside of the Moon remains poorly known. Lunar farside exploration is challenging because maneuvering rovers with efficient locomotion in harsh extraterrestrial environment is necessary to explore geological characteristics of scientific interest. Chang’E-4 mission successfully targeted the Moon’s farside and deployed a teleoperated rover (Yutu-2) to explore inside the Von Kármán crater, conveying rich information regarding regolith, craters, and rocks. Here, we report mobile exploration on the lunar farside with Yutu-2 over the initial 2 years. During its journey, Yutu-2 has experienced varying degrees of mild slip and skid, indicating that the terrain is relatively flat at large scales but scattered with local gentle slopes. Cloddy soil sticking on its wheels implies a greater cohesion of the lunar soil than encountered at other lunar landing sites. Further identification results indicate that the regolith resembles dry sand and sandy loam on Earth in bearing properties, demonstrating greater bearing strength than that identified during the Apollo missions. In sharp contrast to the sparsity of rocks along the traverse route, small fresh craters with unilateral moldable ejecta are abundant, and some of them contain high-reflectance materials at the bottom, suggestive of secondary impact events. These findings hint at notable differences in the surface geology between the lunar farside and nearside. Experience gained with Yutu-2 improves the understanding of the farside of the Moon, which, in return, may lead to locomotion with improved efficiency and larger range.

Micro-vibration has been a dominant factor impairing the performance of scientific experiments which are expected to be deployed in a micro-gravity environment such as spacelab. The micro-vibration has serious impact on the scientific experiments requiring quasi-static environment. Therefore, we proposed a maglev vibration isolation platform (MVIP) operating in six degrees of freedom (DOF) to fulfill the environmental requirements. In view of non-contact and large stroke requirement for micro-vibration isolation, an optimization method was utilized to design the actuator.Mathematical models of actuator's remarkable nonlinearity was established, so that its output can be compensated according to floater's varying position and system's performance may be satisfied. Furthermore, aiming to adapt to an energy-limited environment such as spacelab, an optimum allocation scheme was put forward.Considering actuator's nonlinearity, accuracy and minimum energy-consumption can be obtained simultaneously. In view of operating in six DOF, methods for nonlinear compensation and system decoupling were discussed, the necessary controller were also presented. Simulation and experiments validate system's performance. With a movement range of 10×10×8 mm and rotations of 200 mrad, the decay ratio of -40 dB/Dec between 1-10 Hz was obtained under close-loop control.

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A magnetic levitation isolation system applied for the active control of micro-vibration in space requires actuators with high accuracy, linear thrust and low power consumption. The magneto-force-thermal characteristics of traditional electromagnetic actuators are not optimal, while actuators with a Halbach array can converge magnetic induction lines and enhance the unilateral magnetic field. To improve the control effect, an accurate magnetic field analytical model is required. In this paper, a magnetic field analytical model of a non-equal-size Halbach array was established based on the equivalent magnetic charge method and the field strength superposition principle. Comparisons were conducted between numerical simulations and analytical results of the proposed model. The relationship between the magnetic flux density at the air gap and the size parameters of the Halbach array was analyzed by means of a finite element calculation. The mirror image method was adopted to consider the influence of the ferromagnetic boundary on the magnetic flux density. Finally, a parametric model of the non-equal-size Halbach actuator was established, and the multi-objective optimization design was carried out using a genetic algorithm. The actuator with optimized parameters was manufactured and experiments were conducted to verify the proposed analytical model. The difference between the experimental results and the analytical results is only 5%, which verifies the correctness of the magnetic field analytical model of the non-equal-size Halbach actuator.

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