Control Structure Interaction of Multi-Flexible-Body Space Station and RCS Attitude Control

Space Station Freedom (SSF) attitude control represents a challenging Control Structure Interaction (CSI) problem. NASTRAN data show that flexure modes are densely packed in a narrow frequency band with a significant mode at very low frequency as low as 0.08 Hz. Furthermore, modal characteristics are dynamically changing due to articulation of substructures. Under these inherent structural conditions, the Space Station Attitude Control System (ACS) must provide stable attitude and attitude rate control during all phases of buildup and operations for assembly flights. Interaction between the flexible Station bending modes and attitude control system is of concern. This paper describes control structure interaction of the flexible Space Station and the Reaction Control System (RCS) under the influence of the elastic vehicle motion.