Investigation of Periodic-Disturbance Identification and Rejection in Spacecraft

Spacecraft periodic-disturbance rejection using a realistic spacecraft hardware simulator and its associated models is investigated. The effectiveness of the dipole-type disturbance rejection filter on the current realistic nonlinear rigid-body spacecraft model is validated. However, it is shown that the rejection filter is not robust to disturbance frequency uncertainty. Therefore, system identification techniques are needed if the disturbance frequency is unknown or changing. Based on experience with the current test bed, two simple closed-loop system identification methods are introduced to experimentally identify the disturbance frequency using data from the control input torque signal. It is shown that an incorrect filter frequency results in beating of the control input torque. Examination of the beat envelope leads to tuning of the rejection filter.