Attitude tracking of rigid spacecraft subject to disturbances of unknown frequencies

The asymptotic rejection of spacecraft systems under multi-tone sinusoidal disturbances has been studied recently for the case where the frequencies of the disturbance are known. In this paper, we further consider the case where the frequencies of the disturbance are unknown. We show that this case can be solved by an adaptive regulation technique. We also present some analysis on the convergence issue of the estimated frequencies to unknown frequencies.