Dongping Jin

Infinite-Horizon Control for Retrieving a Tethered Subsatellite via an Elastic Tether

This paper presents a nonlinear optimal control scheme for the retrieval of an elastically tethered subsatellite model. The scheme accounts for in-plane and out-of-plane motions. The control design is formulated over an infinite horizon by using a domain-transformation technique and all the nonlinearities in the system model are taken into consideration. Two Legendre pseudospectral algorithms are explored to find an optimal trajectory that guides the subsatellite from an initial position far from the spaceship into a final position close to the spaceship. The first approach involves direct transcription and nonlinear programming, and the second one is based on the method of quasi linearization and matrix algebra. The case studies in the paper well demonstrate the effectiveness and dominant real-time merits of the proposed strategies.

Three-dimensional optimal deployment of a tethered subsatellite with an elastic tether

This paper presents the nonlinear optimal control for the deployment process of an elastically tethered subsatellite model, which involves not only the usually addressed in-plane motion, but also the out-of-plane motion. All the nonlinearities in the system model and the mission-related state-control constraints are taken into consideration. Instead of the commonly used state-space model, a second-order differential inclusion formulation is exploited in this paper to achieve a significant reduction of the number of system variables. The optimal control is solved by discretizing the optimal control problem first and then solving the resulting large-scale optimization problem. The case studies in the paper demonstrate well the performance of the proposed strategy.

Distributed finite-time tracking for a team of planar flexible spacecraft

The paper presents a distributed finite-time controller for multiple under-actuated spacecraft with flexible appendages to track a virtual leader with stationary states under an undirected communication graph. Each spacecraft of concern is simplified as a free-floating hub-beam system, which is an under-actuated Euler-Lagrange system by nature since only the hub is driven. In the undirected communication graph, it is assumed that only one spacecraft can receive the information from the virtual leader. A distributed finite-time control law is presented for such a multi-agent system. The closed-loop system is proven to converge to the desired states within a finite time via Lyapunov theory and homogeneous method. Finally, a comparison is made between the proposed controller and the PD controller to show the better performance of the proposed controller.

Boundary Control of a Flexible Manipulator Based on a High Order Disturbance Observer with Input Saturation

This paper studies a new boundary control strategy for a flexible manipulator subject to unknown fast time-varying disturbances. The flexible manipulator essentially is an infinite dimensional continuum. Hence, a continuous function of space and time can be employed to describe the position of such a distributed parameter structure, the motion of which can be described by partial differential equations (PDEs). To cope with fast time-varying external disturbances, a high order disturbance observer is adopted. A control strategy based on such a disturbance observer is proposed for the rest-rest maneuvering of the flexible manipulator. Moreover, a smooth hyperbolic function is included in the controller to satisfy the requirement of input saturation. The stability of the boundary control is analyzed using LaSalle’s invariance principle. Finally, the performance of the presented boundary controller is verified through comparison with that of employing a constant disturbance observer via numerical simulations.