Parameter convergence analysis in adaptive disturbance rejection problem of rigid spacecraft

The asymptotic rejection of rigid spacecraft systems under multi-tone sinusoidal disturbances with unknown frequencies was studied recently. It was shown that the problem can be solved via an adaptive control approach. However, the convergence issue of the estimated frequencies to the unknown frequencies has not been investigated. In this paper, we further give some sufficient conditions for guaranteeing the convergence of the estimated frequencies to the unknown frequencies.