Nonlinear dynamics and control of orbiting structures: an approach with applications

A relatively general Lagrangian formulation for studying the nonlinear dynamics of spacecraft with interconnected flexible members in a tree-type topology is developed. The governing equations of motion are coupled, nonlinear, and nonautonomous; hence, nonlinear control, based on the Feedback Linearization Technique (FLT), is incorporated. Versatility of the formulation is illustrated through dynamical studies of the multipurpose telecommunications satellite, Indian Satellite II(INSAT-II) and Space Station based two-link Mobile Servicing System (MSS). The uncontrolled dynamics of the INSAT-II shows that the flexible spacecraft to be in an inherently unstable equilibrium orientation. Control, based on the FLT, is then applied to restore the desired attitude of the spacecraft. The performance of the MSS undergoing inplane and out-of-plane slewing maneuvers is compared. Results indicate that, in absence of control, the maneuvers induce vibration of the links as well as undesirable librational motion of the Space Station. Control is next applied to the Space Station. Once the altitude of the Space Station is controlled, the performance of the MSS improves significantly