Control of Relative Attitude Dynamics of a Formation Flight Using Model-error Control Synthesis

Book excerpt: A robust approach to control, called Model Error Control Synthesis (MECS), is applied to the relative attitude between a formation-flight of spacecraft. This technique combines a nominal controller with a model error estimator, where the model error estimate is used to cancel the effects of disturbance inputs and model errors. Two separate controllers are tested and compared. The model error estimate is determined using a Predictive filter. State estimation is performed by a modified extended Kalman filter. MECS is shown to be effective in canceling the effects of parametric model errors and external disturbances. The type of nominal controller has no effect on the ability of MECS to function. Accurate tracking of the desired trajectories and final attitude is achieved in each case. One negative aspect observed is that MECS tends to amplify acceleration level effects such as measurement noise.