NONLINEAR DYNAMICS AND CONTROL OF INSAT-II - APPLICATION OF A GENERALFORMULATION

The paper presents a general Lagrangian formulation capable of studyin g the nonlinear dynamics and control of spacecraft with interconnected members in a tree-type topology. The nonlinear control, based on the feedback linearization technique (FLT) is adopted. The simplicity of t he control algorithm and its applicability to both rigid and flexible spacecraft make the technique quite attractive. Application of the for mulation is illustrated using a spacecraft of contemporary interest, I Ndian SATellite-II (INSAT-II), a next generation of multipurpose commu nications spacecraft launched in August 1992. The uncontrolled dynamic s show the spacecraft to be in an inherently unstable equilibrium orie ntation. Control, based on the FLT, is then applied to restore the des ired attitude of the spacecraft. The performance of three sets of cont rol gains are compared. Even if the satellite is initially subjected t o a large disturbance of 1-degrees in pitch, roll, and yaw, the contro ller is successful in reducing the attitude error to less than 0.1-deg rees in about 2 minutes. The control scheme works remarkably well even with the inclusion of flexibility and thermal deformations of the app endages.