Zhongjie Meng

Adaptive Postcapture Backstepping Control for Tumbling Tethered Space Robot–Target Combination

a = positive parameter atx aty atz T = linear acceleration due to the tether tension, m · s−2 ax ay az T = linear acceleration of the gripper’s thruster force, m · s−2 C k = matrix in coordinated desaturation controller d = position vector of the capture position, m Fl = tether tension, N I = inertia matrix of the combination, kg · m I0 = nominal value of combination’s inertia matrix, kg · m Kξ = positive-definite design matrix k2 = positive-definite design matrix m = mass of tethered space robot–target combination, kg Oxlylzl = space tether frame Oxpypzp = space platform orbital frame Oxtytzt = combination orbital frame Ox 0 t y 0 t z 0 t = combination body frame P = positive-definite design matrix R = transformationmatrix from platform orbital frame to combination body frame S k = constant positive weighting matrix Tl = tether control torque, Nm x y z T = centroid position of the combination in the platform orbital frame, m ΔI = inertia matrix uncertainty, kg · m e = positive parameter λ k = Lagrange multiplier λL = upper bound of disturbance λL = estimation values of disturbance μ = positive design parameter ξ = state of the auxiliary design system σ = modified Rodrigues parameters σd = desired modified Rodrigues parameters τ k = vector of optimal thruster force and tether tension τc = control torque of the combination, N · m τd = disturbing torques, N · m τt = control torque of the thruster, N · m τl = control torque of the tether, N · m ω = absolute angular velocity of the combination, rad · s−1 ωd = desired angular velocity of the combination, rad · s−1

Impact Dynamic Modeling and Adaptive Target Capturing Control for Tethered Space Robots With Uncertainties

Target capturing is an essential and key mission for tethered space robot (TSR) in future on-orbit servicing, and it is quite meaningful to investigate the stabilization method for TSR during capture impact with target. In this paper, the stabilization control of TSR during target capturing is studied. The space tether is described by the lumped mass model, and the impact dynamic model for target capturing is derived using the Lagrange method with the consideration of space tether length, in/out-plane angles, and gripper attitude. Given the structure of the TSRs gripper, a position-based impedance control method is proposed for target capturing operation. The neural network is used to estimate and compensate the uncertainties in the dynamic model of TSR, and an adaptive robust controller is designed to overcome the influence of the space tether and track the desired position generated by impedance controller. Numerical simulations suggest that the proposed controller can realize the stabilization of TSR during target capturing; besides, the uncertainties of the TSR can effectively be compensated via adaptive law and the influence of the space tether can be suppressed via the robust control strategy, which lead to smaller overshoot, less convergence time, and higher control accuracy during capturing operation.

Reconfigurable spacecraft attitude takeover control in post-capture of target by space manipulators

Abstract Most current research on reconfigurable control system puts emphasis on reconfiguration for adapting to actuator failures. However, the reconfigurable control system is necessitated for spacecraft attitude takeover control in the application of capturing target spacecraft whose fuel is exhausted to extend its operational lifetime by supplying them propulsion, navigation and guidance services. In this scenario, the capture of target spacecraft by space manipulators will cause a large shift in the dynamics of the service spacecraft. Not only do the mass properties change, but also does the thruster configuration. The changes in the mass, center of mass and inertia of the combined spacecraft will cause changes in the equivalent force exerted by each thruster. In this paper, considering the changes of thruster configuration and the control reallocation, a reconfigurable control system is designed for spacecraft attitude takeover control in post-capture of target by space manipulators in order to adapt to changes in the mass properties. The unknown inertia properties of target spacecraft in the system constitute a formidable technical challenge for controller design. Therefore, a modified adaptive dynamic inverse controller is proposed to provide global asymptotic stability in the presence of model uncertainties and nonlinearities. Moreover, by the null-space intersections control reallocation method, the thrust forces of service spacecraft can be redistributed and satisfy some constraints. Numerical simulations validate the feasibility of reconfigurable spacecraft attitude takeover control with large center of mass shifts and unknown inertia properties.

Coordinated stabilization of tumbling targets using tethered space manipulators

Tethered space robots (TSR) have wide application prospects in future on-orbit missions such as debris removal. However, its rather complex and difficult for TSR to realize stabilization of tumbling combinations after target capture. Therefore, this paper addresses a novel control scheme for achieving attitude stabilization by coordination of the tethered space manipulator (TSM), the tether itself, and thrusters accommodated on the base of the TSM. Simulation results validate the feasibility of the attitude control scheme in the postcapture phase.

Post-capture attitude control for a tethered space robot–target combination system

This paper presents a novel scheme for achieving attitude control of a tumbling combination system in the post-capture phase of a tethered space robot (TSR). Given the combination rotation characteristics, tether force is applied to provide greater control torques for stabilising the attitude. The proposed control scheme involves two attitude controllers, which coordinate the controller of the tether force and thruster force and the controller of single thruster force. The numerical simulations include a comparison between this coordinated control and the traditional thruster control and a sensitivity analysis on initial values of parameters. Simulation results validate the feasibility of the attitude control scheme for a tumbling combination system, and fuel consumption of the attitude control is efficiently reduced using the coordinated control strategies.

Dynamics Analysis and Controller Design for Maneuverable Tethered Space Net Robot

Space robots are considered as a promising solution to active space-debris capture and removal. In this paper, a brand new space robot system called the maneuverable tethered space net robot is proposed. In addition to the advantages inherited from the tethered space net, extra maneuverability in the tethered space net robot allows for wider possibilities for debris capture. The motion equations of the system are derived, and both symmetrical and asymmetrical configurations are analyzed. According to the specific vibration analysis, a modified adaptive supertwisting sliding-mode control scheme is proposed. The proposed adaption law is a function of the disturbance, which is considered as the sum of all the adjacent forces working on the controller plant: that is, the maneuverable unit. Both symmetrical and asymmetrical cases are simulated to verify that the tethered space net robot can fly toward active space debris steadily under the proposed control scheme.

Twist Suppression Method of Tethered Towing for Spinning Space Debris

AbstractTowing spinning debris in space is subjected to the risk of twist, increasing the likelihood of collision. To reduce the twist potential, a twist suppression method is proposed for the visc...

Dynamics modeling and model selection of space debris removal via the Tethered Space Robot

This work proposes a scheme to select a proper dynamics model for space debris removal which is captured by a Tethered Space Robot. A proper dynamics model is crucial for the parameters estimation and controller design in a Tethered Space Robot mission, in particular, for the retrieval or de-orbiting of uncooperative target. A new dynamics model of the system is derived by treating the base satellite and the space debris as rigid bodies in the presence of offsets, and with the effect of the tether’s flexibility and elasticity. Then the equations of motion are simplified based on the attitude analysis and numerical simulations in different cases. It is concluded that in the Tethered Space Robot’s mission, the strong coupled attitude motions among the base, target satellites, and the tether cannot be ignored during the retrieval, which is totally different from the traditional tethered satellite system. The attitude motions of the system in different conditions are discussed respectively, and a method of the model selection of the system during post-capture and retrieval/de-orbiting phase is proposed, which is a balance of the accuracy and facility. Finally, a control scheme is used to prove this conclusion.

Autonomous Rendezvous and Docking with Nonfull Field of View for Tethered Space Robot

In the ultra-close approaching phase of tethered space robot, a highly stable self-attitude control is essential. However, due to the field of view limitation of cameras, typical point features are difficult to extract, where commonly adopted position-based visual servoing cannot be valid anymore. To provide robot’s relative position and attitude with the target, we propose a monocular visual servoing control method using only the edge lines of satellite brackets. Firstly, real time detection of edge lines is achieved based on image gradient and region growing. Then, we build an edge line based model to estimate the relative position and attitude between the robot and the target. Finally, we design a visual servoing controller combined with PD controller. Experimental results demonstrate that our algorithm can extract edge lines stably and adjust the robot’s attitude to satisfy the grasping requirements.

Approach Modeling and Control of an Autonomous Maneuverable Space Net

The autonomous maneuverable space net, which consists of a flexible net and several maneuverable units, is a promising solution for the active removal of space debris. A novel dynamics model and a corresponding controller are proposed in this paper to resolve the approach control problem. Given that the net tethers cannot be elongated, interval functions and corresponding constraint forces are exploited to model the unilaterally constrained tethers. The proposed approach dynamics model, which is based on the Hamilton principle, includes distinctive velocity jump phenomena. A dual-loop control scheme with double optimization pseudo-dynamics inversion and sliding mode control is also established. Simulation results validate the feasibility of the proposed control scheme. The net can fly along the expected trajectory without suffering unexpected net deformation or orbital radial movement.