A measurement method of nonlinear strength for dynamical model of SRLV

In the re-entry process of a suborbital reusable launch vehicle (SRLV), the strong nonlinear and uncertainty have a negative impact on the dynamical modelling and control system design. The paper introduces a nonlinearity index method to analyse the dynamical model of SRLV. The nonlinearity index method was first developed to control error propagation in a nonlinear system. The nonlinearity indices access the boundary between the strong and the weak nonlinearity of the system model. Applying this method on SRLV dynamics is an effective way to measure the nonlinear strength of dynamics model over the full flight envelope. The algorithm of nonlinearity index according to engineering applications is first proposed in this paper. The expressions of static and dynamic nonlinearity indices are given, which can qualitatively and quantitatively measure the nonlinear strength of dynamical model in the re-entry phase. The simulation results show the method is correct and appropriate.