Space robots as one of the enabling means to realize automatic and intelligent on-orbit operations, play a critical role in both manned and unmanned space scientific explorations. The engineering application status of several types of orbital space robots is firstly reviewed, including the International Space Station extravehicular and intravehicular robots, the Chinese Space Station robots, and some free flying space robots. First, the application status of two kinds of planetary robots successfully applied is also reviewed, including the lunar robots and the Mars robots. Secondl, in view of the increasingly complex task requirements for space robots, the technical challenges faced by space robots in mechanism configuration, actuator joints, end effectors, perception and cognition, mobility, dynamics and control are discussed. The exploration of some novel mechanism configurations for space robots in multi-arm, super redundancy,
The construction demands for large space platforms and infrastructures such as space stations, space telescopes, large communication antennas, space solar power stations, in-orbit supply stations, deep space exploration stations and extraterrestrial bases, which represent national scientific and technological capability, are constantly increasing. The autonomous construction of these projects in space remains a huge challenging task. Since large space infrastructures play a significant role in future space exploration missions, various investigations have been performed by different space agencies to cope with this issue. This paper presents an overview of in-space assembly studies, systematically summarizing the research status and technological development of in-orbit assembly. The technological progress of manned and unmanned in-orbit assembly is first analyzed, and the development roadmap, assembly levels and methods of in-orbit assembly technology summarized.
Planetary surface mobile exploration robots are multi-disciplinary, high-tech products, used in unstructured environments of planet surface exploration. These robots can effectively reduce the intensity of human work, protect human safety and replace humans to complete scientific research and exploration work in harsh environment with substantial economic and social benefits. This study conducts the statistics of the launched detectors, systematically sorting out the technical parameters, structure, and mechanism composition of the probe robots successfully landing on the moon and Mars. The technological status of space robots in different countries are compared comprehensively. Based on the present foreign and domestic research status and achievements, this paper focuses on the research of the mobile system of planetary surface mobile exploration robots.
Considering the requirements of integrated exploration tasks of landing and patrolling on the planet surface in the field of deep space exploration, this paper comprehensively reviews the history of these integrated tasks both in China and abroad, summarizing the methods of deceleration and buffering and the moving detection situations during the landing process, and further pointing out the limitations of traditional landing and moving systems such as complex configuration, low reliability, high proportions of the quality and volume of the landing buffer devices. The advantages of the integrated robots for landing inspections are then compared and analyzed. In addition, the research progress of legged mobile robots, wind driven spherical robots, small jumping robots and tensegrity robots with integrated landing and moving functions are reviewed respectively. The performance characteristics of all these robots are compared, their application scope given. Finally
Considering the requirements of integrated exploration tasks of landing and patrolling on the planet surface in the field of deep space exploration, this paper comprehensively reviews the history of these integrated tasks both in China and abroad, summarizing the methods of deceleration and buffering and the moving detection situations during the landing process, and further pointing out the limitations of traditional landing and moving systems such as complex configuration, low reliability, high proportions of the quality and volume of the landing buffer devices. The advantages of the integrated robots for landing inspections are then compared and analyzed. In addition, the research progress of legged mobile robots, wind driven spherical robots, small jumping robots and tensegrity robots with integrated landing and moving functions are reviewed respectively.
In view of the requirements of small-scale mobile robots as scientific component loads for large-scale landing explorers in deep space exploration (particularly lunar, Mars and asteroid explorations), this paper summarizes the worldwide development status of small-scale planet surface exploration robots, focusing on the mission requirements, basic configuration and prototype testing of representative small-scale robots for the lunar, Mars and asteroid explorations. Based on the systematic summary of the developing trend of small-scale planet surface exploration robots, suggestions for the future development and improvement in this field in China are put forward. The analysis shows that: for the exploration of lunar rugged terrains which are of high research value, the small-scale wheeled and legged robots with strong motion performance have attracted wide attention, with countries such as Japan, Britain.
The parabolic antenna, being an important part of spaceborne antennas, has been widely used in multiple disciplines such as deep space exploration, mobile communications, national defense, and meteorological monitoring. In recent years, with the rapid development of the above disciplines, the research of parabolic antennas has also gained increasing attention. In response to the development and demands of large spaceborne parabolic antennas, this article first systematically summarized the development status of foreign spaceborne parabolic spherical antennas, and rigid, mesh and inflatable spaceborne parabolic spherical antennas. The structure and performance of the spherical antennas are then described and analyzed, followed by a brief description of some domestic research results in this field. s.
A wheel-legged hexapod robot with high symmetries is designed for planetary exploration. With a structure both centrosymmetric in the body horizontal plane and symmetric about its body horizontal plane, this robot can realize two modes of locomotion: wheeled mode and legged mode. In the knee joint, a double parallelogram transmission mechanism is used to avoid the singularity of the traditional parallelogram mechanism, enlarging the motion range of the knee joint. Based on the motion planning in the exponential coordinate on SE(3), an adaptive gait is designed for this wheel-legged hexapod robot. Relying on the force sensor on the feet and inertial measurement unit on the body, this robot using this adaptive gait without the visual sensor and the global map can achieve a stable and continuous walk in an unknown environment.
To detect the joint failure of space manipulators in real time and obtain effective fault information, a fault diagnosis method based on state observers is proposed. Through the design of a sliding mode state observer based on the sliding mode control theory, the residual information of each running status for the manipulator is obtained. A comparison of the residual information and the preset threshold is then conducted to achieve joint failure detection. In addition, different failure modes are introduced to build a failure database with which the residual information of the manipulator caused by the actual joint failure is compared, thereby realizing the location and degree identification of the failure.
Aiming at the problem of trajectory planning for the Free Floating Space Robot (FFSR), this paper proposes an FFSR trajectory planning method based on the kinodynamic RRT* algorithm. The kinematics and dynamics model of the FFSR is first established with the pseudo linear system model reconstructed into the state space model and a weighted objective function designed considering both time and energy consumption of posture adjustment. Secondly, considering the obstacles between the initial and final positions of the manipulator, we propose a simplified obstacle avoidance method, formulating a two-level obstacle avoidance strategy for robotic arms and the manipulator to improve the collision detection efficiency.
Tethered mobile robots can be used to explore extreme terrains such as steep slopes, cliffs, and gullies. During the exploration process, the tethers of the mobile robots will inevitably contact or even wrap around the obstacles. The classic FastSLAM framework does not apply to the Simultaneous Localization and Mapping (SLAM) of tethered robots due to the dependence of the contact points between the obstacles and the robots, and the nonlinearity of the robot model. In this paper, a modified FastSLAM-based algorithm is proposed to solve the SLAM problem of the tethered robot, where an unscented filter and a particle filter are adopted to estimate the positions of the contact points and the pose of the tethered robot, respectively. An unscented transformation on the nonlinear observation model is utilized to simplify the updating of the particle weights.
Due to characteristics such as strong nonlinearity, strong coupling and strong time-variation, the subtle stability control of flexible space robots has always been a major challenge. Limited by space and weight, the joint flexibility of lightweight miniaturized robots cannot be ignored, which is mainly caused by the flexibility of the harmonic reducer and the torque sensor. Traditional kinematics control can keep it stable in no-load states, while has poor adaptability to large loads and fast movement. In serious situations, the manipulator shakes violently, or even diverges. In view of the above problems, this paper proposes a precise operation control method for on-orbit flexible joint space robots based on a nonlinear disturbance observer and dynamics pole assignment. The simulation results show that this method can effectively suppress the flexible excitation, and ensure the rapidity and accuracy of the response;
Combining teleoperation and multi-robot coordination, cooperative teleoperation is an important means to expand complex space robot tasks and improve reliability for space robot teleoperation. Based on a review of cooperative teleoperation technology, this paper first proposes the cooperative teleoperation method for robots with large time-varying delays, drawing on the advanced prediction characteristics of teleoperation systems. A description model of complex Multi-Master/Multi-Slave (MM/MS) teleoperation systems is provided, together with a tree-like timesharing grouping strategy of all operators and objects with its five prerequisites presented.
This paper proposes a load distribution method of the desired target external force for the multi-arm space robot after capturing the target in the form of soft-finger contact, which considers both the friction constraint and capability constraint of the manipulators. The dynamic equations of the space robotic system and the target are first constructed as the basis of load distribution. The soft-finger contact model between the end-effector of manipulators and the target surface is then established based on the research of ground robots, while the motion constraint between the two is also obtained. To simplify the optimization calculation, the friction cone constraint is linearized, and the capability constraint of manipulators considering the joint torque limit is established to transform the nonlinear optimization problem of the grasping force planning into a linear one.
Aiming at cross-scale and multi-target spatial capture tasks, this study analyzes the kinematics of composite capture systems by combining the folding and geometric characteristics of Bricard and 3RRS mechanisms. Based on the analysis of the freedom degree and configuration characteristics of the capture system, the kinematic decoupling of the system is realized by constructing the transformation relationship between Bricard and 3RRS. According to the six-prism model and with the introduction of the Bricard virtual vertex, a kinematic solution method for the composite space capture system is designed. The kinematic and dynamic models of the capture system are built in the simulation environment, and the trajectory tracking experiments conducted for the dynamic capture targets.
During planetary exploration, the rover demands the capability of terrain characteristic estimation for timely adjustment of control strategies to quickly adapt to terrain changes. For the parameter-coupled wheel-terrain interaction model with complex forms, the Sobol analysis method is adopted to quantitatively analyze the sensitivity of terrain bearing and shearing characteristic parameters in the model, respectively. In consequence, the sinkage exponent and internal fraction angle are selected as the dominant parameters reflecting significant changes in the terrain bearing and shearing characteristics. Based on the mechanics equilibrium equation of wheel-terrain interaction, the analytical model of the dominant parameters is further derived by simplifying the stress distribution formula.
An online self-learning trajectory planning method based on the deep reinforcement learning is studied for a six Degree-of-Freedom (DOF) space floating manipulator to capture moving objects. The DH(Denavit-Hartenberg) model of the manipulator is presented, and the kinematic and dynamic models of multi-rigid bodies established considering the mechanical coupling characteristics of the combination. An improved deep determination policy gradient algorithm is further proposed, and a multi-agent self-learning system established with each joint as a decision-making agent. Additionally, a training model of the space manipulator is built based on "offline centralized learning and online distributed execution", constructing a reward function with the variables of the target relative distance and the total operation time.
To promote the efficiency and safety of autonomous detection tasks of lunar rovers, a fast and safe path planning algorithm for large-scale autonomous detection based on the lunar surface digital elevation map is proposed. A terrain trafficability analysis method is firstly designed according to the lunar digital elevation map, and a Euclidean Distance Map (EDM) is generated to provide reference for safe path planning.
Space debris or failed satellites often spin around their main inertial axis. Despite their stable state, measurement of their motion state is more difficult than that of a three-axis stable target. Difficulties mainly involve loss of feature points, scale changes and rotation changes in a complex light field environment, and those caused by periodic entry and exit of the target observation surface, as well as increase of cumulative errors and non-convergence of the calculated position and attitude resulted from long-term continuous observation.
During lunar surface scientific explorations, high-accuracy self-localization of lunar rovers is a key problem to be solved. Aiming at accurate localization in the featureless environments on the lunar surface, we propose a new visual-inertial Simultaneous Localization and Mapping (SLAM) algorithm, which fuses the measurements of vision and the inertial sensor by pose-graph optimization to achieve high-precision self-localization. An optical flow tracking algorithm based on the quadtree method is proposed to address the unbounded front-end visual measurements correlation error in featureless environments.
This paper focuses on multiple Line-of-Sight (LOS) angles-only relative navigation of multiple collaborative space robots for non-cooperative targets. To improve the relative navigation performance by fusing multi-LOS information, we propose a multi-LOS relative navigation method based on observability optimization. A relative dynamic model and a state equation between the center robot and the non-cooperative target as well as the observation equation of the multi-robot LOS are firstly developed, and the multi-LOS angles-only relative navigation system is then studied. After that, the angle condition of the multi-LOS with optimal observability is obtained, and a method for the observation configuration optimization of multiple space robots is proposed, considering the observability and long-term natural maintenance.
The overseas space manipulator systems for on-orbit technology verification and engineering applications are reviewed, and the development trend of the space manipulator technology is analyzed from the aspects of task types, robot configurations, end effectors, and operation modes. Seven key technologies of space manipulators are summarized, including task planning, system control, path planning, visual perception, end effectors, teleoperation control, and ground verification. The on-orbit verification experiments of China space manipulators SY-7 and TianGong-2 are presented. Furthermore, the basic scheme of the Chinese space station manipulator system under development is introduced in detail. Finally, in view of the existing problems of the space manipulator technology, suggestions are put forward for the future development of the space manipulator technology in China.
The design and evaluation of the maintainability system for space manipulators are highly significant for the manipulator maintenance. In this paper, combined with the maintainability requirements of space manipulators, the maintainability design and evaluation systems for the whole cycle of "design-verification-design-evaluation" are established. According to the maintainability design system, the cycle management of maintainability design-verification-redesign is conducted. Based on the maintainability evaluation system, three types of evaluators simulate the on-orbit maintenance operation scenarios to respectively carry out maintenance evaluation. The unqualified items in the evaluation index are then redesigned and replaced. The evaluation system is verified by simulation and experimental results with the Central Controller as an example. The research results will provide systematic reference and engineering guidance for the maintainability design and evaluation of space manipulators.
Simultaneous Localization And Mapping (SLAM) can realize the localization and navigation of the lunar rover in the unknown complex lunar environment. The lunar surface is composed of undulating terrain such as craters and stones, lacking the salient features of ground such as trees and buildings. Point cloud data with insignificant features will affect the localization accuracy and real-time performance of the lunar rover. This paper proposes a method to extract salient feature point clouds for the lunar surface environment and an incremental optimization algorithm based on the curve localizability estimation. The information matrix calculates the curve localizability index, obtains the uncertainty measurement of the robot pose estimation, and uses the incremental SLAM scheme for optimization to improve the positioning accuracy and real-timeness. The performance of the algorithm is verified by testing in Gazebo (physical simulation platform) simulation scenario.
The Mars exploration mission requires the robot to be dynamically stable and adaptive to the unknown irregular terrain. This paper proposes a multi-target coordinated control strategy for a wheel-legged Mars exploration robot based on the inverse kinematics model, the vehicle body attitude and the wheel-to-ground contact force. Through kinematic modeling of vehicle attitude adjustment, the first-order low-pass filtering and leg impedance control algorithm, and the center of gravity height adjustment algorithm based on the leg motion hazard coefficient, we realize the tracking control of the vehicle body attitude, wheel-ground constant force contact control and the optimal control of the center of gravity height, thereby improving the self-adaptability, movement stability and the safety of the leg movement space when the wheel-legged robot passes unstructured topographies. The effectiveness of this control strategy proposed in this paper is verified by the joint simulation of MATLAB and UG.