Kinematic modeling and analysis of novel eight-wheel lunar rover

A new kind of eight-wheel lunar rover is developed, which is a complex closed-chain system and has good capabilities of climbing slope, surmounting obstacles and adapting to uneven terrain. In this paper, the mechanical structure of the novel eight-wheel lunar rover is introduced, forward and inverse kinematic models of the rover are established according to the closed-chain coordinate transformation and instantaneous coincidence coordinate. Based on structural characteristics, its kinetic characteristics are analyzed. Wheel slippages are separated and calculated, and a method for closed-loop control modification using wheel slip estimation during the model establishment is proposed. The results can be applied to the motion control of lunar rover.

Wheel slip-sinkage and its prediction model of lunar rover

In order to investigate wheel slip-sinkage problem, which is important for the design, control and simulation of lunar rovers, experiments were carried out with a wheel-soil interaction test system to measure the sinkage of three types of wheels in dimension with wheel lugs of different heights and numbers under a series of slip ratios (0-0.6). The curves of wheel sinkage versus slip ratio were obtained and it was found that the sinkage with slip ratio of 0.6 is 3-7 times of the static sinkage. Based on the experimental results, the slip-sinkage principle of lunar's rover lugged wheels (including the sinkage caused by longitudinal flow and side flow of soil, and soil digging of wheel lugs) was analyzed, and corresponding calculation equations were derived. All the factors that can cause slip sinkage were considered to improve the conventional wheel-soil interaction model, and a formula of changing the sinkage exponent with the slip ratio was established. Mathematical model for calculating the sinkage of wheel according to vertical load and slip ratio was developed. Calculation results show that this model can predict the slip-sinkage of wheel with high precision, making up the deficiency of Wong-Reece model that mainly reflects longitudinal slip-sinkage.

Virtual Simulation System with Path-following Control for Lunar Rovers Moving on Rough Terrain

Virtual simulation technology is of great importance for the teleoperation of lunar rovers during the exploration phase, as well as the design of locomotion systems, performance evaluation, and control strategy verification during the R&D phase. The currently used simulation methods for lunar rovers have several disadvantages such as poor fidelity for wheel-soil interaction mechanics, difficulty in simulating rough terrains, and high complexity making it difficult to realize mobility control in simulation systems. This paper presents an approach for the construction of a virtual simulation system that integrates the features of 3D modeling, wheel-soil interaction mechanics, dynamics analysis, mobility control, and visualization for lunar rovers. Wheel-soil interaction experiments are carried out to test the forces and moments acted on a lunar rover’s wheel by the soil with a vertical load of 80 N and slip ratios of 0, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.6. The experimental results are referenced in order to set the parameters’ values for the PAC2002 tire model of the ADAMS/Tire module. In addition, the rough lunar terrain is simulated with 3DS Max software after analyzing its characteristics, and a data-transfer program is developed with Matlab to simulate the 3D reappearance of a lunar environment in ADAMS. The 3D model of a lunar rover is developed by using Pro/E software and is then imported into ADAMS. Finally, a virtual simulation system for lunar rovers is developed. A path-following control strategy based on slip compensation for a six-wheeled lunar rover prototype is researched. The controller is implemented by using Matlab/Simulink to carry out joint simulations with ADAMS. The designed virtual lunar rover could follow the planned path on a rough terrain. This paper can also provide a reference scheme for virtual simulation and performance analysis of rovers moving on rough lunar terrains.

Mechanical Analysis and Performance Optimization for the Lunar Rover’s Vane-Telescopic Walking Wheel

It is well-known that optimizing the wheel system of lunar rovers is essential.However,this is a difficult task due to the complex terrain of the moon and limited resources onboard lunar rovers.In this study,an experimental prototype was set up to analyze the existing mechanical design of a lunar rover and improve its performance.First,a new vane-telescopic walking wheel was proposed for the lunar rover with a positive and negative quadrangle suspension,considering the complex terrain of the moon.Next,the performance was optimized under the limitations of preserving the slope passage and minimizing power consumption.This was achieved via analysis of the wheel force during movement.Finally,the effectiveness of the proposed method was demonstrated by several simulation experiments.The newly designed wheel can protrude on demand and reduce energy consumption;it can be used as a reference for lunar rover development engineering in China.

Configuration Synthesis and Performance Evaluation Metrics of Lunar Rover Locomotion Systems

A method of topology synthesis based on graph theory and mechanism combination theory was applied to the configuration design of locomotion systems of lunar exploration rovers(LER).Through topology combination of wheel structural unit,suspension unit,and connecting device unit between suspension and load platform,some new locomotion system configurations were proposed and the metrics and indexes to evaluate the performance of the new locomotion system were analyzed.Performance evaluation and comparison between two LER with locomotion systems of different configurations were analyzed.The analysis results indicate that the new locomotion system configuration has good trafficability performance.

Configuration and kinematics analysis of locking-releasing mechanism for side-loaded lunar rover

In order to save space for storing precision equipments,lower the center of mass of Lander and reduce lunar rover's dimension constraint limited by mechanism of Lander,the locking-releasing mechanism of side-loaded lunar rover loaded outside Lander is presented,which is a kind of metamorphic mechanism.To ensure the working of this mechanism as the metamorphic process designed,configuration analysis of the locking-releasing mechanism is carried out,and topological structures are described by Huston lower numbered arrays.A kinematic mathematical model of the mechanism is established through homogeneous transformation matrix.The kinematic simulation validates the feasibility of the locking-releasing mechanism when the configurations are shifted from one to the other.

Calculation on the pitch angle of rocker of a rocker lunar rover in uneven terrain and path planning

For the concerted motion of rocker lunar rover, the pitch angle of rocker of a rocker lunar rover in uneven terrain must be calculated. According to the character of passive shape-shifting adaptive suspension of rocker lunar rover, the model of rocker lunar rover and the model of terrain were both simplified. The pitch angle of rocker was calculated using forward solving, reverse solving and the method of offsetting the curve of terrain respectively. Because of the banishment of the nonlinearity of equation sets of calculation by reverse solving, the calculation of the pitch angle based on reverse solving was programmed by means of MATLAB. Simulations were carried out by means of ADAMS. The result verified the validity of the calculation based on reverse solving. It provides the theoretical foundation for motion planning and path planning of rocker lunar rover. As applications of the calculation of pitch angle of rocker, the multi-attribute decision making of path based on the concerted motion planning and the predictive control on lunar rover based on the Markov prediction model were introduced.

Steering mechanical analysis for lunar rover wheel

Facing the requirement of establishing a steering mechanical model for the wheel configuration design,selection of steering motors, dynamic analysis and simulation of the lunar rover, shear force beneaththe steering wheel, bulldozing resistance acting on steering wheel rims and side surfaces respectively areconducted on the basis of the wheel-loose soil interaction. The quantitative relation between steering resistancemoment (SRM) and steering radius, dimension of the wheel, soil parameters is established. Tovalidate the model, a single-wheel test bed is employed to test the steering performance of a wheel with0.15735m radius and 0.165m width when the steering radius is 0.00m, 0.04m, 0.08m, 0.12m and0.16m, respectively. The SRM is approached asymptotically with the increasing steering angle and almostproportional to the steering radius. The theoretical results of SRM are compact with the experimental results,which shows that the steering model can predict the experimental results well.

Study on Running Performance of Flexible Wheels for Lunar Rovers： Relation between Stress Distribution of Flexible Wheel and Running Performance

On lunar exploration missions, the rovers which can move and explore directly are considered by various agency like NASA （National Aeronautics and Space Administration）, JAXA （Japan Aerospace Exploration Agency）, ESA （European Space Agency）. Lunar rovers are required to move on rough terrains such as craters and rear cliffs where it is scientifically very important to explore. However, there is a problem that the rovers have possibility of stack because of the lunar surface is covered with loose soil named Regolith. Therefore, this paper investigates a mechanism of kinetic behavior between the wheels of the exploration rovers and loose soil. And then, this paper proposed a flexible wheel to solve like that problems. The flexible wheel has the surface which can be changed flexibly toward rough terrain. Running experiments on loose soil which imitated regolith were carried out to observe the traversability of the flexible wheel using slip ratio. Traversality of flexible wheel was better than the circular rigid wheel. The authors believe that stress distribution is important. The stress distribution of the flexible wheels is horizontally long and stress value is small. However, the stress distribution can be changed by loaded more weight. Therefore, the relationship between the stress and the running performance was considered using this differential stress distribution. In experiments, the authors used the flexible wheel with simple structure （3 limbs）. From these considerations, the relationship between the stress of the flexible wheel and the running performance was described.

3D-Aided-Analysis Tool for Lunar Rover

3D-Aided-Analysis Tool （3DAAT） which is a virtual reality system is built up in this paper. 3DAAT is integrated with kinematics and dynamics model of rover as well as real lunar surface terrain mode. Methods of modeling which are proposed in this paper include constructing lunar surface, constructing 3D model of lander and rover, building up kinematic model of rover body. Photogrammetry technique and the remote sensing information are used to generate the terrain model of lunar surface. According to the implementation result, 3DAAT is an effective assist system for making exploration plan and analyzing the status of rover.

China Will Launch A Spanish Lunar Rover

China Great Wall Industry Corporation (CGWIC) and Barcelona Galactic Suite Moon Race S.L (GSMR) signed a launch contract in Paris to launch a Spanish lunar rover with a LM-2C launch vehicle. According to the contract, CGWIC will provide the launch service for the lunar rover developed by the Barcelona

Panoramic camera on the Yutu lunar rover of the Chang'e-3 mission

The Chang＇e-3 panoramic camera, which is composed of two cameras with identical functions, performances and interfaces, is installed on the lunar rover mast. It can acquire 3D images of the lunar surface based on the principle of binocular stereo vision. By rotating and pitching the mast, it can take several photographs of the patrol area. After stitching these images, panoramic images of the scenes will be obtained.Thus the topography and geomorphology of the patrol area and the impact crater, as well as the geological structure of the lunar surface, will be analyzed and studied.In addition, it can take color photographs of the lander using the Bayer color coding principle. It can observe the working status of the lander by switching between static image mode and dynamic video mode with automatic exposure time. The focal length of the lens on the panoramic camera is 50 mm and the field of view is 19.7？umination and viewing conditions, the largest signal-to-no×14.5？.Under the best illise ratio of the panoramic camera is 44 d B. Its static modulation transfer function is 0.33. A large number of ground testing experiments and on-orbit imaging results show that the functional interface of the panoramic camera works normally. The image quality of the panoramic camera is satisfactory. All the performance parameters of the panoramic camera satisfy the design requirements.

Relative position determination of a lunar rover using the biased differential phase delay of same-beam VLBI

When only data transmission signals with a bandwidth of 1 MHz exist in the rover, the position can be obtained using the differential group delay data of the same-beam very long baseline interferometry (VLBI). The relative position between a lunar rover and a lander can be determined with an error of several hundreds of meters. When the guidance information of the rover is used to determine relative position, the rover's wheel skid behavior and integral movement may influence the accuracy of the determined position. This paper proposes a new method for accurately determining relative position. The differential group delay and biased differential phase delay are obtained from the same-beam VLBI observation, while the modified biased differential phase delay is obtained using the statistic mean value of the differential group delay and the biased phase delay as basis. The small bias in the modified biased phase delay is estimated together with other parameters when the relative position of the rover is calculated. The effectiveness of the proposed method is confirmed using the same-beam VLBI observation data of SELENE. The radio sources onboard the rover and the lander are designed for same-beam VLBI observations. The results of the simulations of the differential delay of the same-beam VLBI observation between the rover and the lander show that the differential delay is sensitive to relative position. An approach to solving the relative position and a strategy for tracking are also introduced. When the lunar topography data near the rover are used and the observations are scheduled properly, the determined relative position of the rover may be nearly as accurate as that solved using differential phase delay data.

Geospatial technologies for Chang’e-3 and Chang’e-4 lunar rover missions

This paper presents a brief overview of the geospatial technologies developed and applied in Chang’e-3 and Chang’e-4 lunar rover missions.Photogrammetric mapping techniques were used to produce topographic products of the landing site with meter level resolution using orbital images before landing,and to produce centimeter-resolution topographic products in near real-time after landing.Visual positioning techniques were used to determine the locations of the two landers using descent images and orbital basemaps immediately after landing.During surface operations,visual-positioning-based rover localization was performed routinely at each waypoint using Navcam images.The topographic analysis and rover localization results directly supported waypoint-to-waypoint path planning,science target selection and scientific investigations.A GIS-based digital cartography system was also developed to support rover teleoperation.

The penetrating depth analysis of Lunar Penetrating Radar onboard Chang＇e-3 rover

Lunar Penetrating Radar（LPR） has successfully been used to acquire a large amount of scientific data during its in-situ detection. The analysis of penetrating depth can help to determine whether the target is within the effective detection range and contribute to distinguishing useful echoes from noise.First, this study introduces two traditional methods, both based on a radar transmission equation, to calculate the penetrating depth. The only difference between the two methods is that the first method adopts system calibration parameters given in the calibration report and the second one uses high-voltage-off radar data. However, some prior knowledge and assumptions are needed in the radar equation and the accuracy of assumptions will directly influence the final results. Therefore, a new method termed the Correlation Coefficient Method（CCM） is provided in this study, which is only based on radar data without any a priori assumptions. The CCM can obtain the penetrating depth according to the different correlation between reflected echoes and noise. To be exact, there is a strong correlation in the useful reflected echoes and a random correlation in the noise between adjacent data traces. In addition, this method can acquire a variable penetrating depth along the profile of the rover, but only one single depth value can be obtained from traditional methods. Through a simulation, the CCM has been verified as an effective method to obtain penetration depth. The comparisons and analysis of the calculation results of these three methods are also implemented in this study. Finally, results show that the ultimate penetrating depth of Channel 1 and the estimated penetrating depth of Channel 2 range from 136.9 m to 165.5 m（ε_r = 6.6） and from 13.0 m to 17.5 m（ε_r = 2.3）, respectively.

Relative position determination of a lunar rover using high-accuracy multi-frequency same-beam VLBI

Multi-frequency same-beam VLBI means that two explorers with a small separation angle are simultaneously observed with the main beam of receiving antennas. In the same-beam VLBI, the differential phase delay between two explorers and two receiving telescopes can be obtained with a small error of several picoseconds. The differential phase delay, as the observable of the same-beam VLBI, gives the separation angular information of the two explorers in the celestial sphere. The two-dimensional relative position on the plane-of-sky can thus be precisely determined with an error of less than 1 m for a distance of 3.8×105 km far away from the earth, by using the differential phase delay obtained with the four Chinese VLBI stations. The relative position of a lunar rover on the lunar surface can be determined with an error of 10 m by using the differential phase delay data and the range data for the lander when the lunar topography near the rover and the lander can be determined with an error of 10 m.

月球车驾驶运动感知特性研究

航天员月球车驾驶技能地面训练需要模拟逼真的运动感知特性,其关键在于掌握地面与月面驾驶运动感知的差异。笔者建立了高度逼真的月球车驾驶运动仿真场景,模拟月球车驾驶运动的地月差异;开发了以空间定向模型为框架的人体运动感知软件,仿真比较了月球车驾驶前向运动感知的地月差异。结果表明,月面环境下月球车加速度变化范围减小、加减速缓慢且易发生侧滑;视觉信息受限时动态俯仰角感知显著大于地面,而静态俯仰角感知则大大降低;这种地月差异在加入视觉信息后大幅度减少。揭示了月面与地面驾驶运动感知特性的差异,为月球车驾驶运动模拟策略的优化提供了依据。

考虑崎岖地形的月球车路径规划与跟踪控制研究

为优化月球车运动路径,避开月球陨石坑和高地等月面静态障碍物,以安全、高效抵达目标任务点,提出了一种结合A∗算法和人工势场法的融合算法。首先,利用A∗算法在栅格地图中生成从起点到终点的最优安全路径;然后,设计全局路径分割方法,按阶段进行基于人工势场法的局部路径规划,并基于Lyapunov稳定性理论设计了全局渐进稳定的轨迹跟踪控制律;最后,通过Blender软件制作仿真月表环境,并使用ROS Gazebo仿真平台进行轨迹跟踪仿真验证。仿真结果表明:提出的融合算法生成的移动路径相较于普通A∗算法路径更短,转折次数更少,并加入人工势场算法进行局部避障,极大提高了月球车运动安全性,验证了所提出算法的可行性和有效性。

载人月球车柔性太阳翼设计与分析

为满足载人月球车关于太阳翼的高刚度、可重复收展和轻量化的性能要求,在国内外星球车太阳翼、柔性太阳翼研究的基础上,提出了一种基于连杆机构的柔性太阳翼展开机构总体方案,根据能量守恒原理对太阳翼进行了展开运动学分析。将太阳翼结构简化为张拉索-梁模型,建立了柔性阵面和太阳翼的结构动力学分析模型,基于刚度需求对太阳翼结构进行轻量化优化设计,并通过ABAQUS有限元模型验证了结构优化设计的可行性和合理性。结果表明:太阳翼在涡卷弹簧驱动下展开到位时存在一定的冲击,但是对阵面影响较小。该张拉膜结构等效结构动力学模型可用于柔性太阳翼结构的快速迭代和优化设计,并实现柔性太阳翼支撑结构刚度和阵面张力的高效匹配。

基于模型的载人月球探测人机功能分配方法研究

针对载人月球探测任务飞行模式复杂、各阶段衔接紧密、活动间关联性强的特点,为确保人参与到系统中去,引入基于模型的系统工程(MBSE)对载人月球探测任务总体设计中人机功能分配进行设计与验证研究,提出了一种基于模型的载人月球探测人机功能分配方法。考虑载人月球探测活动中人机功能分配是一个不断反复、连续的决策过程,从人因需求指标体系出发,引入MBSE阐述载人月球探测任务系统建模方法,并基于系统模型实现月面科考载人月球车驾驶场景下的人机(航天员-月球车)功能分配合理化。通过模型化载人月球探测人机功能分配过程,合理分配人、机作业,使航天员处于合适的工作负荷状态,以简化系统设计、操作的复杂性,提高整个系统的机动灵活性和安全可靠性。