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.
Tethered aircraft system has been widely investigated because of its extensive application in hose-drogue autonomous aerial refueling, aerial towed decoy, and towed aerial recovery drogue, etc. Yet, ...due to the system nonlinearity, unknown airflow disturbances and unmeasurable tether tension, the anti-disturbance control of the tethered aircraft system is still a difficulty, which has not been well solved in the existing literature. In this paper, by introducing the elasticity and length variation of the tether, the system model composed of the multi-link tether model and the 6-degree-of-freedom dynamics of the tether aircraft is accurately established, and the reachable domain of the tethered aircraft is carefully analyzed. Then, the system nonlinearity is handled by applying a new coordinate transformation, and the lumped disturbances are estimated by extended state observers. Finally, an extended state observer-based adaptive dynamic surface control approach is employed to guarantee the accurate tracking of the tethered aircraft under airflow disturbances. In comparison with PID method and active disturbance rejection control method, simulation results demonstrate that the proposed control method has better tracking ability under airflow disturbances, specially gust.
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 TSR's 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.
In this paper, we systematically introduce a novel geostationary orbit (GEO) space debris removal system called dexterous tethered space robot (DTSR). The DTSR has three notable characteristics: ...dexterity, lightweight, and cost effectiveness. We first describe the system's design and a typical mission scenario, and then present its two core technologies (vision-based pose measurement and coordinated controller design) in detail. Finally, we present the extensive simulations and ground semiphysical experiments to verify that the DTSR is a feasible solution to effectively remove the GEO space debris.
Bilateral synchronization control problem for networked teleoperation space robot system (NTSRS) with unknown gravity and asymmetric, random delay as well as communication intermittent interruption ...is discussed in this paper. To make full use of limited operation window time, improve telepresence, and realize continuous teleoperation, a special mode switching-based symmetric predictive control mechanism is designed, where the mode switching idea is to make full use of limited operation time. Meanwhile, among this mechanism, the symmetric predictive control structure is to improve telepresence and realize continuous teleoperation, besides the same function that mode switching idea provides. The structure of this mechanism for the master side is composed of a predictor and corresponding controller, and symmetric configurations for slave side. Combining with the homomorphic model idea and utilizing the predictive and estimation capability of neural network (NN), novel predictor design method is proposed. In designing the predictor, unlike the traditional model predictive control where predictor is coupled with the controller, this method is independent with the corresponding controller in structure, which is helpful for parameter adjustment and analysis. For unknown gravity, estimation ability of NN is utilized to solve it. With the adaptive method, estimation errors can be kept at a lower level. Subsequently, an analogous proportional-derivative controller with gravity compensation term is designed to realize asymptotical stability and synchronization control of the NTSRS. Finally, effectiveness of the proposed method is verified by some simulation examples.
Tethered space robots (TSR) have wide application prospects in future on-orbit missions such as debris removal. However, it's 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.
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.
•The dynamic model and contact dynamic model of tethered space net robot are derived.•The contact dynamics of tethered space net robot in an unideal capture case are analyzed.•An integral version of ...Super-Twisting Adaptive Sliding Mode Control scheme is designed for tethered space net robot to complete the net closing action.•Natural and controlled net capture cases are simulated. Compared with the nonlinear integral sliding mode control with equivalent control technique and the original Super-Twisting algorithm, the designed control method shows a better performance to close the net in this unideal case.
Tethered Space Net Robot (TSNR) is proposed as a hopeful solution for space debris capturing. An unideal case of net capture is studied in this paper, in which the net does not contact the target in the center of the net. For this case, the net cannot naturally close to wrap around the target completely after collision due to the asymmetric net configuration. Therefore, an integral adaptive Super-Twisting sliding mode control (IASTSMC) is designed to close the net. The control algorithm consists of a nonlinear integral sliding surface and adaptive Super-Twisting sliding mode control (ASTSMC), which not only has the property of “saturate the large error, magnify the small error”, but also provides a positive chattering alleviation effect. Compared with the nonlinear integral sliding mode control (ISMC) with equivalent control technique and the original Super-Twisting algorithm (STA), the proposed control method shows a better performance to close the net in this unideal case.
Active debris removal (ADR) technology is an effective approach to remediate the proliferation of space debris, which seriously threatens the operational safety of orbital spacecraft. This study aims ...to design a controller for a dual-arm space robot to capture tumbling debris, including capture control and detumbling control. Typical space debris is considered as a non-cooperative target, which has no specific capture points and unknown dynamic parameters. Compliant clamping control and the adaptive backstepping-based prescribed trajectory tracking control (PTTC) method are proposed in this paper. First, the differential geometry theory is utilized to establish the constraint equations, the dynamic model of the chaser-target system is obtained by applying the Hamilton variational principle, and the compliance clamping controller is further designed to capture the non-cooperative target without contact force feedback. Next, in the post-capture phase, an adaptive backstepping-based PTTC is proposed to detumble the combined spacecraft in the presence of model uncertainties. Finally, numerical simulations are carried out to validate the feasibility of the proposed capture and detumbling control method. Simulation results indicate that the target detumbling achieved by the PTTC method can reduce propellant consumption by up to 24.11%.
Most convolutional neural network based grasp detection methods evaluate the predicted grasp by computing its overlap with the selected ground truth grasp. But for typical grasp datasets, not all ...graspable examples are labelled as ground truths. Hence, directly back propagating the generated loss during training could not fully reveal the graspable ability of the predicted grasp. In this paper, we integrate the grasp mapping mechanism with the convolutional neural network, and propose a multi-scale, multi-grasp detection model. First, we connect each labeled grasp and refine them by discarding inconsistent and redundant connections to form the grasp path. Then, the predicted grasp is mapped to the grasp path and the error between them is used for back-propagation as well as grasp evaluation. Last, they are combined into the multi-grasp detection framework to detect grasps with efficiency. Experimental results both on Cornell Grasping Dataset and real-world robotic grasping system verify the effectiveness of our proposed method. In addition, its detection accuracy keeps relatively stable even in the circumstance of high Jaccard threshold.
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