On-Orbit Identification of Flexible Spacecraft and Periodic Disturbance Based on Subspace Algorithm

A subspace -based system identification method is presente d to extract the disturbance free dynamics and unknown periodic disturbance mode s simultaneous ly, which is applicable to flexible spacecraft. The periodic disturbances are viewed as observable but uncontrollable states instead of inputs as usual. These dis turbances are then involved into an augmented system that comprise s disturbance -free dynamics and periodic disturbance modes. Without the knowledge of disturbance frequencies and waveforms, the augmented system can be identified only based on excitation in put and disturbance -corrupted output data through the application of subspace algorithm. With mode controllability criterion, the system dynamics and disturbance modes can be discriminated correctly from the augmented system. Two numerical simulations are conducted to illustrate the proposed scheme.