On the Shape and Orientation Control of Orbiting Shallow Spherical Shell Structure

Abstract

The dynamics of orbiting shallow flexible spherical shell structures under the influence of control actuators is studied. Control laws are developed to provide both attitude and shape control of the structure. It is seen that the elastic modal frequencies for the fundamental and lower modes are closely grouped due to the effect of the shell curvature. The shell is also assumed to be gravity stabilized by a spring-loaded dumbbell type damper attached at its apex. Control laws are developed based on the pole clustering technique and it is assumed that the dumbbell state information may not be directly observable. Numerical results verify that a significant savings in fuel consumption can be realized by using the hybrid shell-dumbbell system together with point actuators. Other results indicate that for the less robust systems instability may result by not including the orbital and first order gravity-gradient effects in the plant prior to control law design.