Space Non-cooperative Target Research Articles

Autonomous relative navigation error compensation method for small body exploration based on sequence-images

<p indent="0mm">Deep-space small bodies are typical space non-cooperative targets. The autonomous relative navigation of space non-cooperative targets based on sequence-images is an important technical method to realize the small body exploration. Due to the complex on-orbit environment, it is inevitable that the camera will suffer the measurement deviations and the focal length deviation, which will severely affect the relative navigation state estimation accuracy. On the basis of making full use of the information of star sequence images in the field of view of the camera, the initial value of the camera on-orbit calibration is calculated by the least square method. Combined with the measurement deviation state transition model and the starlight angular distance measurement equation between two stars, the measurement deviations are expanded into state estimation parameters and the relative navigation state estimation model based on camera on-orbit error compensation is constructed. Combined with the unscented Kalman filter algorithm, the iterative estimation is carried out through comparing the information between the frames of sequence images. Then the camera measurement deviation and the relative navigation system state are obtained. In this way, the state estimation accuracy is improved. In the simulation analysis, the small body 2016HO3 is considered as the relative navigation target. The simulation results show the effectiveness of the method, which can effectively compensate the camera measurement deviation and achieve the high-precision estimation of the relative navigation system state. The research results provide certain technical support for the subsequent related tasks.

Design and Experimental Study of Space Continuous Robots Applied to Space Non-Cooperative Target Capture.

Space capture actuators face problems such as insufficient flexibility and electrical components that are vulnerable to extreme space environments. To address these problems, a centralized-driven flexible continuous robot based on a multiple scissor mechanism units is proposed in this study. The continuous robot body is composed of two scissor mechanism units coupled in series, and the base container’s three motors to drive the robot. The two scissor mechanism units ensure a wide range of flexible operations and the light weight of the robot. The centralized drive with three motors not only reduces the number of driving sources, but also ensures temperature control and protection of electrical components in the space environment. The kinematics and dynamics of the robot are analyzed, and the workspace and deformation performance of the robot are verified through experiments. Compared with other continuous robots, the proposed continuous robot retains the characteristics of continuous robots in a wide range of flexible operations. At the same time, the configuration is light and a small number of driving sources are used, which is suitable for extreme temperatures, vacuum, radiation, and strict resource-constrained environments in space.

Multi-spacecraft collaborative attitude determination of space tumbling target with experimental verification

The precise attitude determination of a tumbling non-cooperative space target is challenging. This paper proposed an attitude determination approach based on multi-spacecraft collaborative observation. The three-dimensional (3-D) point cloud data of the target is constructed in terms of the collaborative observation data. By virtue of the target features and point cloud matching between two adjacent frames, the attitude change information of the target is derived, and based on this, the attitude information of the tumbling target is estimated via Extended Kalman Filter (EKF). Numerical simulations and ground micro-gravity experiments are carried out to demonstrate the performance of the proposed collaborative observation method. The results show that the presented approach can successfully estimate the attitude of the tumbling target with no prior information, and avoid the presence of occlusion or data missing during the observation process.

Multi-view-based cooperative observation method for space non-cooperative target's attitude determination

The parameter identification of a non-cooperative target is a key problem of on-orbit servicing. Due to poor priori information about the motion and structure of non-cooperative targets, the traditional cooperative estimation architecture is inadequate. In addition, the existing method based on single observation spacecraft is difficult to ensure a good observation state for a long time. This paper proposes a method for observing and estimating attitude kinematic state of a non-cooperative space target based on multi-spacecrafts cooperative observation. The space target's 3D point cloud data is reconstructed based on the data with different viewpoints. The target's attitude change is calculated based on the 3D point cloud matching, and the kinematics information is estimated via EKF filtering. The simulation results demonstrate the efficiency of the proposed approach. As the proposed method does not require priori model, structural information or accurate motion information of the tumbling non-cooperative target, it can avoid the influence of occlusion or date missing in space observation, it is suitable for space on-orbit servicing with non-cooperative target in future.

Pose estimation of a fast tumbling space noncooperative target using the time-of-flight camera

This article proposes a pose estimation method for a fast tumbling space noncooperative target. The core idea of this method is to extract the target’s body-fixed coordinate system by using the geometric characteristics of the target’s point cloud and then by the body-fixed coordinate system to realize pose initialization and pose tracking of the target. In the extraction of the body-fixed coordinate system, a point cloud of the target, which can be obtained by a time-of-flight camera, can be divided into small plane point clouds firstly; then the geometric information of these plane point clouds can be utilized to extract the target’s descriptive structures, such as the target surfaces and the solar panel supports; and finally the body-fixed coordinate system can be determined by the geometric characteristics of these structures. The body-fixed coordinate system obtained above can be used to determine the pose of consecutive point clouds of the target, that is, to realize the pose initialization and the pose tracking, and accumulated bias often emerges in the pose tracking. To mitigate the accumulated bias, a pose graph optimization method is adopted. In the end of this article, the performance of the proposed method is evaluated by numerical simulations. Simulation results show that when the distance between the target and the chaser is 10 m, the errors of the estimation results of the target’s attitude and position are 0.025° and 0.026 m, respectively. This means that the proposed method can achieve high-precision pose estimation of the noncooperative target.

Motion Prediction of a Free-Floating Noncooperative Target Considering J2 Perturbation

Abstract Motion prediction of space noncooperative target is an important issue for spacecraft on-orbit service. After obtaining high-precision motion prediction results, the chaser can efficiently plan a motion trajectory to approach the target and then capture it. In this paper, a motion prediction method considering J2 perturbation is proposed for a free-floating noncooperative target. The core idea of this method is to identify dynamic parameters of the target, and then realize the motion prediction through a dynamic model of the target that considering J2 perturbation. In the identification of the dynamic parameters, inertia parameters of the target are preliminarily identified first, then a noise-adaptive unscented Kalman filter (UKF) is applied to roughly identify the dynamic parameters, and finally, the identification precision is further improved through optimization. At the end of this paper, the significance of considering J2 perturbation is demonstrated by numerical simulations, and the effectiveness of the proposed method is verified. Simulation results indicate that J2 perturbation has a great influence on the motion prediction of the target and that the proposed method can yield long-time high-precision motion prediction results. Specifically, under the simulation conditions of this paper, the predicted time obtained by the proposed method is longer than 200 s, and the errors of the motion prediction results of the target's attitude and position are less than 2 deg and 0.02 m, respectively.

Motion Prediction of Free-Floating Space Non-Cooperative Targets

Motion Prediction of Free-Floating Space Non-Cooperative Targets

Pose Measurement Method of Space Non-Cooperative Targets Based on TOF Camera

Pose Measurement Method of Space Non-Cooperative Targets Based on TOF Camera

Design and analysis of a deployable grasping mechanism for capturing non-cooperative space targets

Space targets capture is an essential issue for space missions. This paper proposes a novel deployable grasping mechanism (DGM) that can be folded into a compact configuration for convenient transportation and deployed into an extensive configuration for grasping non-cooperative space targets. The DGM mainly consists of a series of serially connected basic deployable modules (BDMs). Each BDM is designed with a scissor mechanism and two parallelogram mechanisms. In order to deploy the BDMs synchronously, a unique connection mechanism is designed. The decoupled deployment motion and grasping motion enables the DGM to perform the capture operation at any motion state. For the proposed DGM, mobility, kinematics and stiffness analysis are performed. The characteristics and performance studied in this paper provide a basis for further investigation of the DGM in the area of space applications.

Quantum Radar.

We propose a quantum metrology protocol for the localization of a noncooperative pointlike target in three-dimensional space, by illuminating it with electromagnetic waves. It employs all the spatial degrees of freedom of N entangled photons to achieve an uncertainty in localization that is sqrt[N] times smaller for each spatial direction than what could be achieved by N-independent photons or by classical light of the same average intensity.

Design of Parameter-Self-Tuning Controller Based on Reinforcement Learning for Tracking Noncooperative Targets in Space

Tracking space noncooperative targets, including disabled and mobile spacecrafts, remains a challenging problem. This article develops two reinforcement-learning-based parameter-self-tuning controllers for the following two different tracking cases: case A, tracking a disabled target, and case B, tracking a mobile target. An adaptive controller consisting of five model uncertainties is adopted for case A, and a modified PD controller is derived for case B. The actor–critic framework is employed to reduce the initial control accelerations for case A and to improve the terminal tracking accuracy for case B. Relations between control parameters and tracking errors are found through the fuzzy inference system. Finally, the reinforcement learning is used to select suitable control parameters for achieving desired purposes. Numerical experimental results validate the effectiveness of the proposed algorithms on reducing initial control accelerations for case A and improving the terminal tracking accuracy for case B.

Passive impact/vibration control and isolation performance optimization for space noncooperative target capture

On-orbit capture is an important technique for the space debris removal, refueling, or malfunction satellite repairing. While due to the uncertainty of the motion parameters of the space noncooperative target, the impact between the capture device and the noncooperative target during the capturing process is inevitable, which may bring strong vibration perturbation to the base satellite, and potentially alter the position and the attitude of the servicing spacecraft, or even cause failure of on-orbit tasks. This article presents a new and alternative method for passive suppression of spacecraft impact and perturbation during noncooperative spacecraft capture. The passive device based on bioinspired X-shape is installed between the satellite and the capture device. In the capture process, nonlinear damping of the passive isolation structure can significantly reduce impact/vibration perturbation. For performance analysis, dynamic equations of the isolation system are established. Based on which, the relationship between structure parameters and isolation performance is systematically analyzed. Experiments are conducted for verification of the effectiveness of the proposed method. Moreover, an optimal process using the non-dominated sorting genetic algorithm II optimization method is developed to minimize impact/vibration perturbation effect, and optimal solutions can provide useful reference for the passive isolation system design.

Predictive pursuit-evasion game control method for approaching space non-cooperative target

This paper designs the predictive pursuit-evasion game-based orbit control method for the chasing spacecraft to approach a space uncooperative maneuvering target. Firstly, the trajectory planning algorithm combines RRT⁎ and cubic splines to generate a feasible reference trajectory in the relative motion space for the chaser, which enables to deal with the boundary constraints and avoid collisions with the attachments of target. Then, based on the dynamics model, input constrains and objective functions, the pursuit-evasion game model between the target and the chaser is formulated, in which each one acts independently to satisfy its own objective function. With the game formulation, a predictive pursuit-evasion game controller for the chaser is designed to track reference trajectory. Under the frame of model predictive control, the multiple objective constraint optimization can be transferred into to quadratic programming problem to handle input constraints. By predicting opponent’s best move and changing its optimal strategy for its benefit iteratively, the saddle points of the game can be obtained without opponent’s maneuvering. Numerical simulations verify the effectiveness of the predictive pursuit-evasion game control method for approaching an uncooperative target.

Pose Estimation of a Noncooperative Target Based on Monocular Visual SLAM

This paper estimates the pose of a noncooperative space target utilizing a direct method of monocular visual simultaneous location and mapping (SLAM). A Large Scale Direct SLAM (LSD-SLAM) algorithm for pose estimation based on photometric residual of pixel intensities is provided to overcome the limitation of existing feature-based on-orbit pose estimation methods. Firstly, new sequence images of the on-orbit target are continuously inputted, and the pose of each current frame is calculated according to minimizing the photometric residual of pixel intensities. Secondly, frames are distinguished as keyframes or normal frames according to the pose relationship, and these frames are used to optimize the local map points. After that, the optimized local map points are added to the back-end map. Finally, the poses of keyframes are further enumerated and optimized in the back-end thread based on the map points and the photometric residual between the keyframes. Numerical simulations and experiments are carried out to prove the validity of the proposed algorithm, and the results elucidate the effectiveness of the algorithm in estimating the pose of the noncooperative target.

Design and optimization of a space net capture system based on a multi-objective evolutionary algorithm

Space net capture is an innovative concept for active debris removal that provides a prospective method for the removal of large, non-cooperative space targets. The design of a space net capture system must meet two basic requirements: maximizing the capture ability and minimizing the system cost. This paper presents an inexpensive multi-objective optimization framework to solve this design problem. In this framework, a design optimization approach using a lumped parameter modelling method as well as an improved inexpensive multi-objective optimization algorithm is proposed. The system mass and effective distance are chosen as objectives of this optimization problem. The simulation results reveal that the multi-objective optimization framework is feasible and effective for the design of a space net capture system, and the designer preferred solutions that enhance system design are reliably identified.

Fast-swirl space non-cooperative target spin state measurements based on a monocular camera

Measuring the motion state of space non-cooperative targets is in the fields of space on-orbit services and debris removal. This paper proposes a method for the measurements of the spin rate of fast-swirl non-cooperative targets through a monocular camera, for image features that have been degraded at a medium and long distance. First, the coordinate system between the tracking satellite and the target is established, and the relationship between the target spin period and its image projection angle is deduced. An image processing method which can extract the projection angle of the target image stably under complex illumination conditions is then proposed. Next, considering the characteristics of the sequence projection angle of the fast-spinning target at a long distance, the spin rate of the target is calculated using a sinusoidal polynomial fitting method. The proposed method is validated by simulated and on-orbit data. Experiment results show that the method has strong adaptability, measurement reliability and practical engineering application prospects.

Dynamics and control of a 7-DOF hybrid manipulator for capturing a non-cooperative target in space

This paper proposes a 7-DOF hybrid serial-parallel manipulator for capturing a non-cooperative target in space and discusses its dynamics and control. The hybrid manipulator is connected in a series by a 3-DOF parallel part with 1-PU&2-PUS configurations and a 4-DOF serial part with a 4R configuration. First, the UP-RRRR equivalent serial mechanism is presented for the kinematic analysis of the hybrid manipulator. Utilizing the Newton-Euler method, the dynamic model of the equivalent serial mechanism is derived in a recursive form. Then the dynamic equations of the parallel part in recursive form are also developed using the Newton-Euler method. Based on the complete dynamic model, we propose a control scheme for a hybrid robot to capture a non-cooperative target in a zero-gravity environment, including three modules: admittance control, motion estimation of the target satellite, and feedforward of the reaction forces. Finally, experimental results of full physical experiments based on air-bearing testbeds confirm the validity of the proposed control scheme for the hybrid robot to capture a non-cooperative target in space.

Actuation distribution and workspace analysis of a novel 3(3RRlS) metamorphic serial-parallel manipulator for grasping space non-cooperative targets

Capturing non-cooperative targets in space is a cutting-edge technology in the aerospace field. In this study, a novel n(3RRlS) metamorphic serial-parallel manipulator (MSPM) with multiple working conditions is proposed, which can serve as the fingers of a large-scale reconfigurable space multifingered hand (LSRSMFH). First, a limb combination coding method is proposed to describe the topological graph and determine the isomorphism of the n(3RRlS) MSPM. Subsequently, the topological graphs and the limb combination codes (LCCs) of the 1(3RRlS) MSPM, 2(3RRlS) MSPM and 3(3RRlS) MSPM are further analyzed, and the isomorphism of all the actuation distribution configurations (ADCs) and metamorphic configuration states (MCSs) is determined. Second, a two-actuator method is applied for the n(3RRlS) MSPM, and the workspaces of all MCSs of all ADCs of the 1(3RRlS) MSPM, 2(3RRlS) MSPM and 3(3RRlS) MSPM are analyzed using a transformation method. The results show that the n(3RRlS) MSPM can realize their respective functions of the LSRSMFH under three working conditions with the minimum number of actuators, which can reduce the number of actuators and the weight of the LSRSMFH and can gain benefits in multitask adaptability, simplified control, precision and rigidity improvement, energy saving and risk reduction.

A Pose Measurement Method of a Space Noncooperative Target Based on Maximum Outer Contour Recognition

The relative pose (position and attitude) measurement of space noncooperative targets is very important for on-orbit servicing activities, such as target tracking, approaching, and capturing. The traditional methods rarely consider the instability of feature extraction and image blurring caused by target tumbling. In this paper, a method based on the maximum outer contour (MOC) recognition is proposed to measure the pose of the target. Different feature extraction algorithms can simultaneously achieve close- and long-range measurement tasks. First, the trailing image is restored by the image enhancement method. Second, the “rough + fine” combination recognition method is used for contour extraction and connected component labeling of the restored image, and the target feature extraction time is reduced to one-third of traditional methods. Furthermore, the elliptical surface on the MOC is fitted by the least squares method (LSM), and the ellipse parameters (i.e., the center position, the long- and short-axes, and the deflection angle) are extracted. The accuracy of the target recognition is improved. Third, for the close-range measurement, based on the detected ellipse parameter, the pose of the noncooperative target is solved by the binocular imaging algorithm of the space circle; for the long-range measurement, the contour centroid of the target is calculated by the detected MOC, and the position of the target is solved by the LSM. Moreover, the effectiveness of the method is verified by the OpenSceneGraph numerical simulation system. Finally, an experimental system consisting of a binocular camera, a UR5 manipulator, and a satellite mockup was built. The experimental results verified the proposed method.

Pose Measurement and Motion Estimation of Space Non-Cooperative Targets Based on Laser Radar and Stereo-Vision Fusion

The pose (position and attitude) measurement of space non-cooperative targets is one of the key technologies in on-orbit service. Traditional stereo-vision-based methods are easily affected by illumination conditions, while the 3D laser radar has a good stability, but the point cloud is sparse. In this paper, a method based on the 3D laser radar and stereo-vision information is proposed to measure the pose and estimate the motion for non-cooperative targets. The proposed method can not only adapt to the harsh lighting conditions, but also has better robustness and higher precision. First, find the matching point corresponding to the binocular camera by using the stereo matching algorithm, and then, calculate the 3D coordinates of the matching points according to the least squares method. Combined with the fusion calibration result, the point cloud data acquired by the 3D laser radar is converted to the left camera frame. Second, integrate the point cloud data obtained by the above two sensors to obtain a complete point cloud model of the non-cooperative target. Third, the obtained point cloud model is registered, and the rigid transformation matrix of two adjacent point clouds is solved. Then, the relative pose and velocity (linear velocity and angular velocity) of the non-cooperative target are estimated by the extended Kalman filter (EKF) algorithm. Finally, an experimental system was built. It consists of a UR5 robot, a satellite mockup, two cameras, a 3D laser radar, and an API laser tracker (for evaluating the accuracy of measurement), was built. The experiment results verified the proposed method.