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
This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionl...This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionless form. Further, a decoupled PD controller is proposed, and the local stability of the controller is analyzed by linearization technique. Parametric studies of the dynamics and de-spin control of a massive target are conducted to characterize the dynamic process of de-spin with the proposed control law. It is shown that the massive target can be de-span by a single and small space tug with limited thrust within finite time. The thrust tangent with the tether de-spins the target while the thrust normal to the tether prevents the tether from winding up the target. The tether length has a positive contribution to the de-spin of a target. The longer tether leads to a faster de-spin process.展开更多
A retrieval control strategy for failed satellite,which is connected to a servicing spacecraft by a tether,is studied.The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing sp...A retrieval control strategy for failed satellite,which is connected to a servicing spacecraft by a tether,is studied.The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing spacecraft,a tether and a failed satellite,is presented under the earth center inertia coordinate system,then model simplification is conducted under the assumption that the failed satellite’s mass is far smaller than the servicing spacecraft’s,meanwhile the tether’s length is far smaller than the size of the servicing spacecraft’s orbit.Analysis shows that the retrieval process is intrinsically unstable as the Coriolis force functions is a negative damping.A retrieval strategy based on only the tether’s tension is designed,resulting in the fastest retrieval speed.In the proposed strategy,firstly,the tether’s swing angle amplitude is adjusted to 45?by deploying/retrieving the tether;then the tether swings freely with fixed length until it reaches negative maximum angle–45?;finally,the tether is retrieved by the pre-assigned exponential law.For simplicity,only the coplanar situation,that the tether swings in the plane of the servicing spacecraft’s orbit,is studied.Numerical simulation verifies the effectiveness of the strategy proposed.展开更多
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.
基金supported by the Discovery Grant(No.RGPIN-2018-05991)of the Natural Sciences and Engineering Research Council of Canada
文摘This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionless form. Further, a decoupled PD controller is proposed, and the local stability of the controller is analyzed by linearization technique. Parametric studies of the dynamics and de-spin control of a massive target are conducted to characterize the dynamic process of de-spin with the proposed control law. It is shown that the massive target can be de-span by a single and small space tug with limited thrust within finite time. The thrust tangent with the tether de-spins the target while the thrust normal to the tether prevents the tether from winding up the target. The tether length has a positive contribution to the de-spin of a target. The longer tether leads to a faster de-spin process.
基金supported by the Fundamental Research Funds for the Central Universities(NUAA-NS2016082)
文摘A retrieval control strategy for failed satellite,which is connected to a servicing spacecraft by a tether,is studied.The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing spacecraft,a tether and a failed satellite,is presented under the earth center inertia coordinate system,then model simplification is conducted under the assumption that the failed satellite’s mass is far smaller than the servicing spacecraft’s,meanwhile the tether’s length is far smaller than the size of the servicing spacecraft’s orbit.Analysis shows that the retrieval process is intrinsically unstable as the Coriolis force functions is a negative damping.A retrieval strategy based on only the tether’s tension is designed,resulting in the fastest retrieval speed.In the proposed strategy,firstly,the tether’s swing angle amplitude is adjusted to 45?by deploying/retrieving the tether;then the tether swings freely with fixed length until it reaches negative maximum angle–45?;finally,the tether is retrieved by the pre-assigned exponential law.For simplicity,only the coplanar situation,that the tether swings in the plane of the servicing spacecraft’s orbit,is studied.Numerical simulation verifies the effectiveness of the strategy proposed.
