Abstract: Considering parameter identification of onorbit closedloop spacecraft, the periodically timevarying modal parameters and controller gain parameters of a large closedloop spacecraft are identified utilizing subspace method. The coordinate transformations of controller gain matrix in the state space equation are discussed. This approach is used to indentify modal parameters and controller gain matrix of the established ETSⅧ model. The results show that the proposed algorithm is effective in the closedloop identification of modal parameters via verifying closedloop response results in the simulation.

Key words: modal parameter identification, periodical time-varying system, closed-loop system identification, large flexible spacecraft, coordinate transformation