Impact of Flexibility on the Clock Controller of the Galileo Spacecraft

This paper presents a study of the effects of structural flexibility on one of the control loops that constitute the Attitude and Articulation Control Subsystem of the Galileo Spacecraft. Both stability analysis and time domain simulation studies are discussed. Results obtained indicate that the control loop of interest—the Clock Controller—will interact stably with the spacecraft structure as long as the spacecraft scan platform boresight points at least 30 deg away from the spacecraft spin axis (poles). Flexibility effects become more and more pronounced with proximity of the bore-sight to the poles as several structural modes become excitable to resonance.