Tomoyuki Nagashio

Design and implementation of robust symmetric attitude controller for ETS-VIII spacecraft

To meet increasing mission requirements, communication satellites are being equipped with large flexible antenna reflectors and solar paddles. A typical such satellite, the Engineering Test Satellite VIII (ETS-VIII) spacecraft, was launched into geostationary orbit by the Japan Aerospace Exploration Agency (JAXA) in December 2006. The main mission of ETS-VIII is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar paddles that rotate around the pitch axis. The authors are planning to perform on-orbit attitude control experiments using ETS-VIII at the end of its mission life, aiming to develop a baseline for future controller design for this class of satellite using advanced control theories. This paper proposes two degrees-of-freedom control based on robust direct velocity and displacement feedback as a candidate controller technology. The spacecraft modeling and controller synthesis methods are discussed, and a controller implementation for an on-orbit control experiment is presented with simulation results.

Robust Control of Flexible Mechanical Systems by Utilizing Symmetry and Its Application to Large Space Structures

The control of flexible mechanical systems has been extensively studied in a variety of fields. For mechanical systems with collocated sensors and actuators, the use of symmetric controllers is known to be effective. The symmetric controller guarantees the robust stability of the closed-loop system irrespective of the system parameters by virtue of the structure of the dynamical equation having positive definite or semidefinite symmetric coefficient matrices. Although this controller is superior to existing parametric approaches, systematic procedures for obtaining specific control performance other than the stability of the closed-loop system have not yet been fully established. This paper proposes an optimal design method for symmetric controllers in the sense of the H infin norm by solving the linear matrix inequalities reduced from the bounded real lemma under the symmetry constraint. This method is then extended to static output feedback control and gain-scheduled control. Finally, the design method is applied to a flexible spacecraft attitude control problem, and its validity is confirmed.

GAIN SCHEDULING CONTROLLER DESIGN FOR ENGINEERING TEST SATELLITE-VIII

Abstract In this paper a new design method of a gain scheduling controller is described and a design procedure for Engineering Test Satellite (ETS)-VIII is explained. The derived gains are easy to be scheduled since the scheduling law consists of small number of grid points and requires just linear interpolation calculation. Using this method, stability and performance are guaranteed at each parameter value (paddle angle in this case). Some simulation results are provided to show the effectiveness of our controller.

Asymptotic stability of second-order linear time-varying systems

M ANY mechanical systems belong to a special class of dynamical systems that are generally described by a secondorder linear matrix differential equation after linearization about an equilibrium condition. When the system characteristics change with time, the coefficient matrices of the equation are time-varying. Examples can be found in all fields of engineering, a space station carrying a mobile crane and a space structure extended in orbit being typical examples from space engineering. This study is motivated by the latter, where the stabilization of a spacecraft undergoing a configuration change in a gravity gradient torque was investigated [1]. In this paper, we investigate the stability of the following secondorder multidimensional linear time-varying system:

Symmetric Controller Design for Symmetric Plant Using Matrix Inequality Conditions

For symmetric systems, the useage of symmetric controllers is known to be effective. The existence conditions of the controller have been shown in several studies. They require the symmetry of the plant as well as the control specifications. This paper describes the condition by matrix inequalities and relaxes it to be applicable to the case of non-symmetric sepcifications for the symmetric H∞controller design. Additionally, the optimal symmetric controller design for mechanical systems is investigated as a special case.

On Stability of Large Space Structures using DVDFB Controller with Nonlinear Sensor and Actuator

It is known that DVDFB controller has salient robust stability properties independent from parameter values. It belongs to a class of static output feedback control of velocity and displacement by the collocated sensors and actuators. However, all discussions on the stability have ignored the undesirable nonlinear properties of sensors and actuators such as saturation, despite of their practical importance. Viewing this, this paper studies the robust stability by taking into account of saturations of sensors and actuators. Some simulations using flexible spacecraft are shown

Robust control of flexible mechanical system by utilizing symmetry and its application to large space structures

The control issues of the flexible mechanical systems have been extensively studied in a variety of fields. For the mechanical systems with collocated sensors and actuators, it is known to be effective to use a symmetric controller. The symmetric controller guarantees robust stability of the closed loop system, independently from the system parameters, by virtue of the structure of the dynamical equation having positive definite or positive semi definite symmetric coefficient matrices. Although the controller has the advantage over the existing parametric approaches, almost all research works have been concentrated to the stability analysis without discussing the synthesis problems. This paper proposes an optimal design method of the symmetric controller in the sense of H/sub /spl infin// norm, by solving the linear matrix inequalities reduced from the bounded real lemma. Finally, we apply the design method to a flexible spacecraft mathematical model and its validity is confirmed.

Design and Implementation of Robust Symmetric Attitude Controller for ETS-VIII Spacecraft

This paper studies the robust attitude control of the large flexible communication satellite ETS-VIII. As a controller candidate, we propose a two-degrees-of-freedom control based on robust direct velocity and displacement feedback, in order to develop a baseline of future controller design technology for this class of spacecraft. For this purpose, the spacecraft modeling and controller synthesis methods are discussed. Then, the controller implementation for on-orbit control experiment is shown with some simulation results.

Formation Flight of Spacecraft in Earth Orbit via MPC

In the future space development, the formation flights of multiple spacecraft in earth orbit are planned for science or engineering missions. For the purpose, this paper proposes to use model predictive control (MPC). Although there are many control problems, this paper focuses on four key issues, i.e., the orbit eccentricity, the pulsive thruster features, the spacecraft mass changes and the length of sampling periods. We intend to overcome these problems in MPC framework. In this paper, the simple control schemes are shown and some numerical simulation results are illustrated in order to evaluate their feasibility

An optimal design of symmetric H ∞ static output feedback controller using LMI for collocated second-order linear system

The symmetric control systems have some interesting properties. This paper studies a class of symmetric system consists of a collocated second-order plant and a static output feedback controller. For the system, it is known that the internal stability and the robustness of the closed-loop system are guaranteed based only on the non-parametric structure condition. Our objective is to propose an optimal H∞ symmetric controller design method under a generalized non-symmetric control specification for disturbance attenuation. For this purpose, we investigate an existence condition of the symmetric controller for the bounded real lemma, and propose a convex optimization method using linear matrix inequalities.