Docking Ring Research Articles

Choice of energy accumulator parameters for a new peripheral docking mechanism

Spacecraft docking is a controlled on-orbit mechanical assembly process realized using active and passive docking units. The docking mechanism of the active unit provides capture conditions, attenuation of active spacecraft approach energy, alignment and retraction of the docking units before their hard connection. A kinematical scheme of a new peripheral docking mechanism is considered in this paper. Instead of energy damping, it is based on energy accumulation using springs with controlled recoil blocking. The blocking is activated before docking and keeps the docking mechanism in its initial position. On the first contact signal, the blocking is switched off releasing the energy of compressed springs for quick forward moving of the docking ring and improving capture. The blocking is activated again after capture and approach energy is accumulated by the springs without returning to the mechanical system. Avoiding contacts of docking mechanism links between each other and with the docking unit body is important for peripheral mechanisms due to their design. A procedure for choosing parameters of an energy accumulator that allows attenuating a max permissible energy without link contacts and without exceeding the max permissible value of the axial interface load is considered here. Key words: spacecraft, docking, docking mechanism.

Satellite Pose Estimation via Single Perspective Circle and Line

Pose estimation is vital for space robot to capture satellite. Dual poses including center position and normal direction can be obtained from a single perspective view of a radius-known circle such as docking ring of the satellite. To solve the duality and recover the roll angle, this paper presents here a new method called perspective circle and line (PCL), which is based on the perspective view of a single circle and line. First of all, the dual center positions and normal directions are recovered with the circle and the image. Then, the line is utilized to recover the roll angle of the circle analytically. By reprojecting a random point on the line to the image and verifying whether the projection lies on the image line, the false pose of the object is identified. Simulation and physical experiments show that the position and orientation of the circle can be recovered. But in practice they are affected by the accuracy of camera calibration and feature extraction. As a whole, PCL is robust to noise in pose estimation, especially in recovering the orientation.

Design and Kinematic Analysis of a Novel Hybrid Kinematic Mechanism With Seven-Degrees-of-Freedom and Variable Topology for Operation in Space

We propose a novel hybrid robot with seven degrees-of-freedom (DOF) and variable topology for operation in space. Design specifications of the space robot are presented for the type synthesis of hybrid mechanisms. Based on GF set theory, three design rules are given, thus providing the design method of the 7DOF hybrid space robot mechanism. Twenty-four combinations of the hybrid robotic mechanisms are obtained. The final synthesized configuration for the design of the space robot has a 3DOF parallel module and a 4DOF serial module with four revolute (RRRR) joints. The parallel module consists of a limb with universal-prismatic (UP) joints and two limbs with universal-prismatic-spherical (UPS) joints. The topology of the hybrid robot can be changed, and it will become an RPRR four-bar mechanism when it is folded for launch. The closed-form solution for the inverse displacement model is developed, and then the forward displacement equations are also obtained. After that, the Jacobian matrix is derived from the displacement model; the Jacobian matrix will analyze the singularity and workspace. We find that there are four singularities of mechanisms. The dexterous workspace of the hybrid robot is a good match for the grapple operation in space. An experiment with the prototype shows the present hybrid robot can grapple to a satellite-rocket docking ring and therefore validates the kinematic equations.

Vision-based position and pose determination of non-cooperative target for on-orbit servicing

For finding an effective measurement for space non-cooperative targets in close distance, a vision-based position and pose determination algorithm of non-cooperative target for on-orbit servicing is investigated. First, the satellite-rocket docking ring’s region is separated from the background environment by a selected grayscale thresholding method and the Canny operator algorithm is used to extract the edge of the satellite-rocket docking ring. Furthermore, the mathematical alignment of the image plane and binocular stereo matching are used to obtain the correspondence of 3D points. Finally, the model of 3D reconstruction is established to determine the relative position and pose of the satellite-rocket docking ring. The ground simulation test shows that our method can measure the relative position and pose of the satellite-rocket docking ring effectively. The precision of the relative position is 0.001 m and that of the relative attitude is 0.1 deg., which satisfies the requirements of the relative measurement for non-cooperative target in extra-close range.

Research on pose measurement between two non-cooperative spacecrafts in close range based on concentric circles

Conventional measurement of relative poses between two non-cooperative spacecrafts in close range is derived from the iteration of monocular vision or three-dimensional reconstruction of binocular vision, which introduces errors in the process of feature matching, and the timeliness and accuracy are poor. Regarding the issues above, this article tries to do some researches on measurement of relative poses between two non-cooperative spacecrafts in close range based on concentric circles. Here, 'concentric circles' means the spatial parallel but not coplanar positional relationship between docking ring and engine nozzle. Through the binocular vision measurement model, the angle adaptability and the applicability are improved. Then, the algorithm of this model is simulated, and the simulated results show that the accuracy of the algorithm can reach higher than 0.5°.

Research on Spacecraft Dynamic Interface Force Identification Based on Strain Detection

The static/dynamic interface force between spacecraft and rocket is an important reference for spacecraft structure design. The most conventional dynamic force identification method is finite element simulation combined with the telemeter acceleration data, which restricts the spacecraft design level owing to the large error. A dynamic force identification method according to the detected strain field of attachment and its optimization plans are proposed. Three-way strain rosettes are mounted outside the docking ring densely. And the six Degree Of Freedom force can be derived by strain field. Considering the requests of engineering application, under the premise that detection result would meet the accuracy requirement, an optimization plan which reduce the detecting point is proposed. Results of dynamic simulation show that, only X direction bending moment identification error is 19.8%, and other loads identification error are below 10%. The test results show that both identification errors of static and dynamic load are below 20%, which can meet the engineering requirements.

A mitofusin-dependent docking ring complex triggers mitochondrial fusion in vitro.

Fusion of mitochondrial outer membranes is crucial for proper organelle function and involves large GTPases called mitofusins. The discrete steps that allow mitochondria to attach to one another and merge their outer membranes are unknown. By combining an in vitro mitochondrial fusion assay with electron cryo-tomography (cryo-ET), we visualize the junction between attached mitochondria isolated from Saccharomyces cerevisiae and observe complexes that mediate this attachment. We find that cycles of GTP hydrolysis induce progressive formation of a docking ring structure around extended areas of contact. Further GTP hydrolysis triggers local outer membrane fusion at the periphery of the contact region. These findings unravel key features of mitofusin-dependent fusion of outer membranes and constitute an important advance in our understanding of how mitochondria connect and merge.