Docking Ring Research Articles

WDICD: A novel simulated dataset and structure-aware framework for semantic segmentation of spacecraft component

The identification and localization of non-cooperative target, especially for the components such as solar panel and docking ring, is crucial for missions involving the on-orbit space services, navigation, and positioning. However, on-orbit spacecraft images are difficult to obtain, and it requires substantial effort to label them with pixel-wise accuracy for semantic segmentation. To address the above problems, we construct a simulated Wide-Depth Illumination-Composite Dataset (WDICD) and introduces an automatic pixel-level semantic annotation method. Furthermore, this paper proposes a structure-aware framework for semantic segmentation of spacecraft component, which introduces a boundary-aware auxiliary task and constructs a boundary-distance-aware contrast loss based on batch-wise grouping. The related boundary-aware tasks alleviate the prediction error of semantic segmentation near the boundary. Experimental results demonstrate that the proposed method achieves SOTA mIoU results in spacecraft component segmentation against complex backgrounds on two datasets. Particularly, the test results on spaceborne device show that the proposed framework balances precision and efficiency without generating additional computational complexity.

Two-phase visual servoing for capturing tumbling non-cooperative satellites with a space manipulator

In this paper, a visual servoing approach is developed to capture the docking rings of tumbling non-cooperative satellites with a space manipulator. The primary challenge addressed is the potential for the docking ring to leave the monocular camera’s field-of-view as the manipulator approaches the target, due to the ring’s large size. To solve this issue, a two-phase visual servoing scheme combining a monocular camera and a three-line structured light vision system is proposed. In an effort to augment the success rate and safety of capture operations, several constraints are formulated, encompassing manipulator’s kinematics, monocular camera’s field-of-view, obstacle avoidance, structured light’s breakpoints and smooth capture. Subsequently, a nonlinear model predictive controller is proposed to manage these constraints in real-time and regulate the system. System models are established based on image moments and pose for each phase, selecting these features as visual feedback to simplify the formulation of servo constraints and avoid the complex circle-based pose measurement. Furthermore, to ensure unbiased predictions, the model disturbances arising from the imprecise estimation of target motion parameter are observed using an extended Kalman filter, which are then incorporated into the predictive control framework. The simulation results demonstrate the effectiveness of this scheme.

Image Segmentation Solutions for Improved Non-Cooperative Target Recognition

The number of failed satellites in space is increasing, and they need to be fueled through space docking to extend their life or clean them out of orbit. Visual measurement is widely used in the docking session because of its real-time performance and economy, but the collected images will have background interference, which directly leads to the degradation of the accuracy of visual measurement. Reduce the difficulty of subsequent image processing by solving these problems. For the non-cooperative target of the star-arrow docking ring and the solar sail panel, which are two significant targets, this paper is based on target detection, according to the image difference, binarization, morphological operations and other methods to complete the accurate segmentation of the two targets, which can be more accurately complete the target detection, and the image segmentation effect is obvious. The target image obtained by image segmentation does not contain background interference, which is convenient for feature extraction and matching of the image.

Circular-Feature-Based Pose Estimation of Noncooperative Satellite Using Time-of-Flight Sensor

This paper develops an end-to-end circular-feature-based pose estimation using the time-of-flight (TOF) camera for capturing serviced satellite. First, the docking ring is chosen as the recognized object for pose measurement. Second, a new ellipse detection method is proposed to detect the docking ring. Third, the circular feature is used to estimate the six-degrees-of-freedom pose with the aid of a reflective block. Combined with the range at each pixel location from TOF, the pose duality can be eliminated, and the roll angle is recovered through the geometric constraint. Ground physical experiments validate the effectiveness and efficiency of the proposed method. The on-orbit application demonstrates that the proposed algorithm can accurately and robustly estimate the relative pose of the noncooperative satellite, providing reliable navigation information for the chaser spacecraft with the relative pose estimation errors less than 2 deg and 5 cm.

A stereo visual navigation method for docking autonomous underwater vehicles

AbstractRecovering and recharging autonomous underwater vehicles (AUVs) on a regular basis allows for long‐term underwater activities. This research provides a vision‐based navigation strategy for AUVs to independently identify and reconstruct the docking station (DS). The proposed framework includes a light beacon detection approach, a filter‐based light beacon matching method, and a fusion pose estimation method for DS positioning. Four green LED light beacons are mounted symmetrically on the docking ring, enabling the stereo camera to observe them from close range. A method for detecting light beacons is proposed that assures detection accuracy by identifying false positives. On a single frame from a stereo camera, filter‐based matching follows the light beacons precisely. In addition, we construct a position estimate method that significantly improves accuracy and efficiency by consisting of analyzation and iteration. A series of virtual and real‐world experiments demonstrate that our methodology can provide AUVs with reliable docking navigation.

A collision-free visual servoing method for two space manipulators capturing tumbling satellites

A novel visual servoing method is proposed to synchronously capture a malfunctional satellite’s docking ring by two space manipulators. Due to the lack of conspicuous visual marks, structured light is implemented to estimate the ring’s pose. To ensure the capturing process’s security, two aspects are investigated. Spatially, capturing target points for two manipulators are planned together by considering the chaser’s orientation. As a consequence, collision risk between two manipulators is eliminated. Temporally, by adding duration parameters in trajectory generation algorithm, capturing synchronism for two manipulators is guaranteed. Experimental results show that, by the proposed method, a tumbling target was successfully captured by two space manipulators. Compared to existing methods, the collision risk between two manipulators is thoroughly eliminated and the capturing synchronism is improved remarkably.

Improved Lightweight YOLOv5 Using Attention Mechanism for Satellite Components Recognition

Recognizing typical components of the satellite is a challenging task for on-orbit services. This article proposes a YOLOv5-based satellite components recognition model (YSCRM) on a computationally limited platform. In particular, feature fusion layers and selective kernel networks (SK-Nets) are introduced to handle the complex multimodal recognition problem of the components, improving the model’s feature selection and representation capability and significantly increasing the recognition accuracy. The transformer encoder modules are used at the end of the Yolov5 Neck to explore the prediction potential with the self-attention mechanism. The channel sparseness training method is implemented to reduce the model size to deploy the model on an embedded platform. Moreover, for the purpose of enlarging the training datasets and their diversity, a data generation approach based on the synthetic images generated by 3ds Max and a data augmentation method based on cycle-consistent adversarial network (Cycle-GAN) are presented in this research. The proposed hybrid dataset is used for training and testing, and extensive qualitative and quantitative experiments are performed. The results demonstrate that the YSCRM has significant recognition performance, and the five typical components, solar panel, body, tripod, nozzle, and docking ring, can be recognized with high accuracy, which indicates that the proposed model can be used for real-world scenarios.

Pose measurement and motion estimation of non-cooperative satellite based on spatial circle feature

Malfunctioned satellites have seriously threatened orbital safety, and the capture of these satellites is of great significance. The pose measurement and the motion estimation of the tumbling satellite is the premise of capture. In this paper, the docking ring of the satellite is identified, which is equivalent to a spatial circle. Combined with the nozzle feature, the pose duality of the spatial circle can be eliminated. And the measurement accuracy is improved by minimizing the reprojection error of the docking ring and the nozzle. Due to the symmetry of the docking ring, the measured pose has only five degrees of freedom, losing the degree of freedom of rotation around the normal vector. In the motion estimation algorithm, the observability of the tumbling motion is firstly analyzed, then an error-state Kalman filter with inertia ratio constraints is designed. To improve the convergence speed and stability of the filter, a rough estimation algorithm of filter initial value based on linear term extraction and particle swarm optimization is proposed. The effectiveness of the pose measurement and motion estimation method is verified by simulations.

Predictive motion control for autonomous capture of a tumbling target with a space manipulator

In this study, an autonomous capture framework was proposed for a tumbling target satellite with a space manipulator. First, the motion model of a tumbling target was constructed and the motion properties were analyzed. Subsequently, a predictive motion control method was introduced to compensate for the time delay owing to image processing and to predict the tumbling motion of the target. Stability analysis was conducted using a Lyapunov function. To address the problem of large position and attitude deviations of the tumbling target, different autonomous capture strategies, that is, non-fixed-point position-based capture and area-based capture, were proposed to capture different parts of the target, such as the docking ring and side surfaces, which are important for practical applications. The capture conditions were created and compared, where the non-fixed-point position capture strategy and area-based capture strategy had a larger pose tolerance than the traditional fixed-point position methods. Finally, the framework was tested using Adams/Simulink co-simulations. The results validated the autonomous capture process and proposed alternatives for practical applications.

Research on docking ring pose estimation method based on point cloud grayscale image

The star-arrow docking ring is a ubiquitous structure on space vehicles and is often used as a feature component for pose measurement and capture in non-cooperative space capture missions. When the capture task is performed at a close distance of 0.5 m, due to the high radiation and high light intensity of the space and the coating of the satellite surface with thermal control multilayer materials, the lighting environment is complex, and the grayscale image processing is difficult. The point cloud grayscale image contour feature localization detection method converts the point cloud image into a grayscale image and then estimates the relative pose of the docking ring. Aiming at the problem of fast pose estimation in the case of relative motion, the algorithm adds a fast positioning module of frame image feature area based on the motion model on the original basis, which effectively reduces the feature retrieval area and improves the real-time performance of the algorithm. It is verified by physical simulation experiments. The results show that the method can effectively reduce the influence of stray light and eliminate noise contours. The pose estimation results of the docking ring are accurate and stable, the relative position calculation error is less than 1.5 mm, and the relative pose error is less than 0.45°. The frequency is better than 2 Hz, which meets the needs of real-time capture by space robotic arms.

Investigation on a new type of latching mechanism on the satellite-rocket docking system and locking dynamic analysis

To meet the in-orbit maintenance requirements of malfunctioning satellites and maintenance satellites rigid connections, a new type of latching mechanism based on satellite-rocket docking ring is proposed, which has light weight, good structural stiffness, simple motion and locking mechanism, simple control logic, high reliability and large range of docking ring size adaptation. A multi-body dynamic model of the docking ring latch mechanism, malfunctioning satellite and maintenance satellite were established, the maximum locking force and maximum friction of the latch mechanism and the maximum stress of the latching joint and crank of the direct force component were analyzed, and the change of locking force and friction under the three typical in-orbit maneuvering conditions were studied. The results show that: the maximum locking force and maximum friction of the latch mechanism on the docking ring is 1300N and 320N, respectively, stable locking force and friction are 300N and 80N, respectively, the maximum stress occurs on connecting rod which is 865 MPa; In-orbit maneuvering has little effect on the locking force and friction of the docking ring latch mechanism, and the docking ring latch mechanism can always lock the malfunctioning satellite steadily and reliably.

Satellite Pose Estimation via Only a Single Spatial Circle

To estimate the pose of satellites in space, the docking ring component has strong rigid body characteristics and can provide a fixed circular feature, which is an important object. However, due to the need for additional constraints to estimate a single spatial circle pose on the docking ring, practical applications are greatly limited. In response to the above problems, this paper proposes a pose solution method based on a single spatial circle. First, the spatial circle is discretized into a set of 3D asymmetric specific sparse points, eliminating the strict central symmetry of the circle. Then, a two-stage pose estimation network, Hvnet, based on Hough voting is proposed to locate the 2D sparse points on the image. Finally, the position and orientation of the spatial circle are obtained by the Perspective-n-Point (PnP) algorithm. The effectiveness of the proposed method was verified through experiments, and the method was found to achieve good solution accuracy under a complex lighting environment.

Feature-extraction and motion-measurement method for noncooperative space targets

<p indent="0mm">Space targets served on the orbit have a noncooperative characteristic. Thus, it is difficult to extract their features and measure their motions. To resolve this problem, a feature-extraction and motion-measurement method for noncooperative space targets is proposed in this paper. First, threshold segmentation is performed with the images captured using the binocular camera to separate the satellite-rocket docking ring section from the surrounding background. Additionally, the Canny operator method is used to detect the edge of the satellite-rocket docking ring. Based on the analysis of the characteristic of the edge’s shape, Hough transformation is employed to extract the line feature of the cross. The contour of the satellite-rocket docking ring is fitted using the least square method. Furthermore, the parallel equivalent projection and the epipolar line alignment methods are used to match the images of the left and right cameras in the convergence binocular vision. Finally, the relative position of the satellite-rocket docking ring is obtained through a three-dimensional reconstruction of the feature points on the satellite-rocket docking ring and cross. Additionally, the dual-vector pose-determination method is employed to obtain the relative pose of the satellite-rocket docking ring. The ground simulation test shows that this algorithm can measure the relative position and pose of the satellite-rocket docking ring effectively. At a distance of <sc>1.5 m</sc> from the target, the precision of the relative position is <sc>15 mm,</sc> and that of the relative pose is 1.12°. This research can achieve an accurate measurement of the relative position and pose of the noncooperative target’s docking ring, providing the measurement basis and important support for on-orbit service missions, such as the grasping, repairing, refueling, and module replacement of noncooperative space targets; thus, it has important practical application value.

SSWS: An edge detection algorithm with strong semantics and high detectability for spacecraft

Space tasks such as docking, capture and maintenance of spacecraft in orbit are increasingly dependent on visual system. High-order features extraction, target recognition and spacecraft pose measurement are essential image processing technologies to accomplish above tasks, for which image edge detection is one of the most critical and basic techniques. Traditional edge detection algorithms such as Canny have good extraction effect, but cannot extract and obtain semantic information. Besides, most of the edge detection algorithms based on deep-learning rely on a large number of annotation labels and require huge workload. Therefore, they cannot be applied to non-cooperative space targets. In this paper, we propose an edge detection algorithm with strong semantics and weak supervision (SSWS) to combine edge detection with image semantic segmentation. By learning geometric boundaries of ellipse and quadrilateral for docking ring and solar panel of spacecraft, and using the training method of weak supervision, our algorithm achieves effective boundary detection of important parts of spacecraft from images regardless of the background interference and light intensity. Real image experiments show that SSWS can effectively extract the boundary of important parts of spacecraft and filter out the background information and noise. In the performance verification experiment of BSDS500 dataset, with weakly supervised annotation tags, SSWS obtains the best OIS (0.831), in comparison with traditional edge detection algorithms and excellent recent deep-learning edge detection algorithms in recent years; in the contrast experiment of image segmentation in PASCAL VOC 2012 test set, SSWS gets the best mIoU value (66.9%).

Two AUVs Guidance Method for Self-Reconfiguration Mission Based on Monocular Vision

In this work, we propose a method for AUV to reconstruct the docking ring autonomously under the guidance of visual information. The proposed method is based on the knowledge of self-reconfiguration of two AUVs in underwater environment. In order to enable long distance performance, we make use of blue-green light beacons. The light beacons are detected by using YOLO V3 algorithm. In addition, P4P algorithm is applied to resolve the problem of relative poses of AUVs. In case of short distances, we use Aruco marker to precisely guide the AUV towards the docking ring. In addition, we use KCF algorithm to shorten the recognition time, and Kalman filter method to eliminate the interference of occlusions and jitters. The feasibility of the proposed method is verified by performing multiple experiments. Under the reasonable control flow and visual algorithm, the proposed solution avoids the situation where the accuracy of long-distance monocular recognition is low and is easy to be misjudged. The underwater multi-target integrated guidance method based on monocular vision is convenient for the recovery of underwater AUV, and can effectively take into account the advantages of wide effective guidance range and high precision of close range guidance.

Extension velocity limiter for the ring of an elastically adaptive peripheral docking mechanism

The docking ring of an elastically adaptive docking mechanism on the initial contact signal is extended by spring-loaded mechanisms of the rods in order to improve capture conditions. In the process, it reaches a high velocity, which applies unacceptably high impact loads to the docking interface. This paper discusses an extension velocity limiter for the docking ring, its analytical model, and a brief procedure for calculating its parameters. It describes a simplified model for ring extension during initial contact, and a method for determining viscous friction coefficient of the ball-screw pair of the docking mechanism, which is a parameter in the model. It presents the procedure, results and comparison of simulations of the docking ring extension both with the use of the proposed retarder and without it. It is demonstrated that the use of the velocity limiter permits to meet the requirements of the International Standard for pulsed loads on the passive interface. The paper describes a design option for velocity limiter that has acceptable mass and dimensions. Keywords: spacecraft docking, elastically adaptive docking mechanism, retraction device, velocity limiter, mechanical governor

Nonlinear Static Analysis and Structural Optimization of Rigid Clamp Band Connection Device between Launch Vehicle and Satellite

The Rigid Clamp Band Connection Device (RCBCD) is a novel satellite-rocket connection method adapted to the heavy lift trend of the launch vehicle. The static analysis model for the Rigid Clamp Band (RCB) and the Docking Ring (DR) under preloading state is established, and the structural strength and connection stiffness characteristics under the axial loading are analyzed, and the axisymmetric equivalent and parametric modeling techniques are combined to optimize the section shape parameter, which improves the overall connection performance. The results show that the structural stress concentrated on the "line-to-face" contact position between RCB and DR. Increasing the axial dimension of RCB, reducing the V-type angle and deepening the occlusion depth of RCB and DR can effectively improve the connection rigidity of RCB. By optimizing the section shape, the connection performance of RCBCD can be improved by above 70% under the structural strength and mass constraints.

FPGA - Based Docking Mechanism Prototype Docking Ring Control Research

Space Docking Mechanism makes two spacecrafts combine in the space orbit and connect as a whole in the structure. The prototype of docking mechanism scaling made of aluminum alloy is to scale the space docking mechanism according to 1:2, and verifies the function of multi-motor combined control to realize the action of the docking ring. This paper, based on the theoretical analysis of the control system of the scaled prototype and the action of the multi-motor combined drive butt ring, builds the control drive system for the experimental analysis. By this way the feasibility of realizing the action of the butt ring with the multi-motor combined control is verified.

SPACECRAFT DOCKING DYNAMIC FEATURES BY USING A PERIPHERAL MECH-ANISM WITH ACCUMULATION OF APPROACH KINETIC ENERGY

Up to now, several docking systems have been developed under the International Docking System Standard (IDSS) by national space agencies and private companies. Docking mechanisms of these systems are based on different design and control principles. Thus a new peripheral docking mechanism, with more simple kinematics and design than that used in previous APAS docking unit, has been developed by Rocket and Space Corporation «Energia». An accumulation of spacecraft approach kinetic energy instead of traditional damping is used in this mechanism. It allows to move forward the docking ring for capture improvement and to ensure slowdown. Main features of spacecraft docking dynamic process with the use of this mechanism are described in this paper. Key words: spacecraft, docking mechanisms, docking dynamics.

Real-Time Docking Ring Detection Based on the Geometrical Shape for an On-Orbit Spacecraft.

Docking ring is a circular hatch of spacecraft that allows servicing spacecraft to dock in various space missions. The detection of the ring is greatly beneficial to automatic capture, rendezvous and docking. Based on its geometrical shape, we propose a real-time docking ring detection method for on-orbit spacecraft. Firstly, we extract arcs from the edge mask and classify them into four classes according to edge direction and convexity. By developing the arc selection strategy, we select a combination of arcs possibly belonging to the same ellipse, and then estimate its parameters via the least squares fitting technique. Candidate ellipses are validated according to the fitness of the estimation with the actual edge pixels. The experiments show that our method is superior to the state-of-the-art methods, and can be used in real time application. The method can also be extended to other applications.