Time- and frequency-domain subspace identification of a nonlinear spacecraft

The present paper discusses the identification of the SmallSat spacecraft, a real-life nonlinear space structure developed by EADS-Astrium. To this end, two nonlinear subspace identification techniques formulated in the time and frequency domains are exploited, referred to as the TNSI and FNSI methods, respectively. The frequency response functions (FRFs) of the underlying linear spacecraft and the nonlinear coefficients are estimated by these approaches. The nonlinear component comprises an inertia wheel mounted on a support, the motion of which is constrained by eight elastomer plots and mechanical stops. This application is challenging for several reasons, which include high modal density, the discontinuous nature of the nonlinearities and order selection of the identified reduced model.