The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital ...The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.展开更多
This paper studies the thrust regulation of the tethered space-tug in order to stabilize the target towed by a flexible tether.To compromise between model accuracy and simplicity,a rigid-flexible coupling multi-body m...This paper studies the thrust regulation of the tethered space-tug in order to stabilize the target towed by a flexible tether.To compromise between model accuracy and simplicity,a rigid-flexible coupling multi-body model is proposed as the full model of the tethered space-tug.More specifically,the tug and the towed target are assumed as rigid bodies,whereas the flexible tether is approximated as a series of hinged rods.The rods are assumed extensible but incompressible.Then the equations of motion of the multi-body system are derived based on the recursive dynamics algorithm.The attitude motion of the towed target is stabilized by regulating the thrust on the tug,whereas the tether-tension-caused perturbation to the tug's attitude motion is eliminated by the control torque on the tug.The regulated thrust is achieved by first designing an optimal control trajectory considering the simplified system model with constraints for both state variables and control input.Then the trajectory is tracked using a neural-network based terminal sliding-mode controller.The radial basis function neural network is used to estimate the unknown nonlinear difference between the simple model and the full model,while the terminal sliding mode controller ensures the rapid tracking control of the target's attitude motion.Thrust saturation and tether slackness avoidance are also considered.Finally,numerical simulations prove the effectiveness of the proposed controller using the regulated thrust.Without disturbing orbital motion much,the attitude motion of the tug and the target are well stabilized and the tether slackness is avoided.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11002068 and11202094)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(No.0113Y01)the Priority Academic Program of Jiangsu Higher Education Institutions
文摘The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.
基金The authors acknowledge the support of the National Natural Science Foundation of China(Grant No.11402009).
文摘This paper studies the thrust regulation of the tethered space-tug in order to stabilize the target towed by a flexible tether.To compromise between model accuracy and simplicity,a rigid-flexible coupling multi-body model is proposed as the full model of the tethered space-tug.More specifically,the tug and the towed target are assumed as rigid bodies,whereas the flexible tether is approximated as a series of hinged rods.The rods are assumed extensible but incompressible.Then the equations of motion of the multi-body system are derived based on the recursive dynamics algorithm.The attitude motion of the towed target is stabilized by regulating the thrust on the tug,whereas the tether-tension-caused perturbation to the tug's attitude motion is eliminated by the control torque on the tug.The regulated thrust is achieved by first designing an optimal control trajectory considering the simplified system model with constraints for both state variables and control input.Then the trajectory is tracked using a neural-network based terminal sliding-mode controller.The radial basis function neural network is used to estimate the unknown nonlinear difference between the simple model and the full model,while the terminal sliding mode controller ensures the rapid tracking control of the target's attitude motion.Thrust saturation and tether slackness avoidance are also considered.Finally,numerical simulations prove the effectiveness of the proposed controller using the regulated thrust.Without disturbing orbital motion much,the attitude motion of the tug and the target are well stabilized and the tether slackness is avoided.
