Robust terminal area energy management guidance using flatness approach

This study deals with the design of a guidance scheme based on flatness theory and dedicated to the terminal area energy management phase of a reusable launch vehicle. The proposed guidance strategy is based on a non-linear dynamic inversion technique to handle the large flight envelope that characterises the reentry mission. This inversion takes advantage of a particular choice of linearising terms called flat outputs, that are used to perform an input-to-state linearisation. First, it is shown that the coupled in-plane and out-of-plane vehicle dynamics admits a set of flat outputs. The flatness property of this model is then used to compute the nominal control input profiles corresponding to a single reference trajectory computed off-line. Based on the linearised model obtained by dynamic inversion, a linear tracking controller is then designed so as to circumvent off-nominal flight conditions. Finally, robustness and performances of the proposed guidance scheme are assessed by performing Monte Carlo runs within an industrial simulation environment.