Hierarchical HAC∞/LAC vibration suppression for a flexible space telescope: SPICE

This paper describes the synthesis of a dynamic compensator for a flexible space telescope described by a 280^th order finite-element NASTRAN-based model. The control objective is to attenuate the induced LOS jitter by a factor of 40 dB over the open loop value. A combination of low authority control (LAC) followed by high authority control (HAC_∞) which utilizes the H^∞ optimal control methodology make up the hierarchical control system developed in this paper. The final design is shown to offer the required performance and robustness. The LAC loop is made up of two loops which provide broadband modal damping, modal spillover robustness, and actuator mode stabilization; all of which help in the design of the HAC_∞. The HAC_∞ loop controller order is reduced from 130-states to 60-states by applying frequency-weighted balanced truncation techniques. The resulting hierarchical HAC_∞/LAC controller is robustly stable against ±10% variation in actuator and sensor modeling.