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.
This paper investigates spacecraft disturbance rejection filtering for both persistent and decaying disturbances. The current study both validates the previously developed "dipole" disturbance rejection filter on a realistic non-linear spacecraft model, and extends the results to a new class of decaying disturbances. Although not designed specifically for decaying disturbances, prior investigations have demonstrated that the traditional "dipole" disturbance rejection filter attenuates both persistent periodic disturbances and decaying disturbances. Here we introduce a new filter which we call the decaying disturbance rejection filter, which has greater attenuation than the traditional filter for decaying disturbances. The new filter is also based on the internal model principle like the traditional filter. Also, it is shown that both the traditional and the new filter are not robust to frequency uncertainty. As a result, new closed-loop system identification methods are introduced to experimentally identify the disturbance frequency to be used within the filter design for both filter types.
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