Panfeng Huang

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.

Releasing Dynamics and Stability Control of Maneuverable Tethered Space Net

The issue of space debris capture and removal has become extremely urgent, due to the huge amounts of passive (or active) space debris along operational orbits. As a promising solution, space tethered net is low cost and executable. Based on this kind of nonmaneuverable space net, a new solution for space debris capture and removal is proposed in this paper, named maneuverable tethered space net (MTSN). We first describe the structure of the MTSN in detail, and then give a typical mission scenario. Then, the kinematics and dynamics model of the MTSN is derived under some basic conclusions of single space tether. An appropriate initial condition is decided after the analysis of releasing characters, including folding pattern, shooting angle, and shooting velocity. Considering the longitudinal elasticity of tether and the uncertainties from space environment, an adaptive second-order supertwisting sliding mode control scheme is employed for the stability control of the MTSN. Finally, we verify the controller by both theoretical proof and numerical simulations.

PSO-Based Time-Optimal Trajectory Planning for Space Robot with Dynamic Constraints

It is significant to increase the efficiency of space robotic operation in on-orbital services, to plan the time-optimal trajectory becomes an important and necessary problem. As well known, any motion of space manipulator will disturb its base due to the dynamic coupling between the base and manipulator, Especially, for free-floating space robot, when robotic manipulator moves from initial point to the end point, the shorter the motion time is, the greater the disturbance to the base will be. Thus, the space robot will be damaged or uncontrolled if this disturbance is beyond the its constraints. Therefore, it is a challenging problem to plan time-optimal or suboptimal trajectory for space manipulator with dynamics constraints, such as disturbance forces and limited torques. In this paper, we proposed a particle swarm optimization (PSO) to search the global time-optimal trajectory for space manipulator. For the formulation, we define the some inter-knots of joint trajectory as optimal parameters. These inter-knot parameters mainly include joint angle and joint angular velocities. Finally, we use an illustrative example to verify that PSO-based time-optimal trajectory planning method has satisfactory performance and real significance in engineering.

Optimal Path Planning for Minimizing Disturbance of Space Robot

Any motion of robotic manipulator will disturb its base in space due to the dynamic coupling. Such a disturbance will produce the serious impact between the manipulator hand and the object. Moreover, the disturbance will affect the communication with the ground and power supply for the space robot. On the other hand, compensating the disturbance using the attitude control system will consume large fuel which is limit in space. Therefore, a novel approach based on genetic algorithms (GA) is developed to find a global optimal path of a space robotic manipulator in joint space in order to minimize the disturbance to the base of space robot. The planning procedure is performed with respect to all constraints, such as joint angle constraints, joint velocity constraints, joint angular acceleration and torque constraints, and so on. We use GA to search the optimal joint inter-knot parameters in order to realize the minimum disturbance. These joint inter-knot parameters mainly include joint angle and joint angular velocities. We use an illustrative example to verify that GA-based optimal path planning method has satisfactory performance and real significance in engineering

Tracking Trajectory Planning of Space Manipulator for Capturing Operation

On-orbit rescuing uncontrolled spinning satellite (USS) using space robot is a great challenge for future space service. This paper mainly present a trajectory planning method of space manipulator that can track, approach and catch the USS in free-floating situation. According to the motion characteristics of USS, we plan a spiral ascending trajectory for space manipulator to approach towards USS in Cartesian space. However, it is difficult to map this trajectory into the joint space and realize feasible motion in joint space because of dynamics singularities and dynamics couple of space robot system. Therefore, we utilize interval algorithm to handle these difficulties. The simulation study verifies that the spiral ascending trajectory can been realized. Moreover, the motion of manipulator is smooth and stable, the disturbance to the base is so limited that the attitude control can compensate it.

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.