Flatness-based hypersonic reentry guidance of a lifting-body vehicle

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This paper deals with the design of a guidance algorithm for the hypersonic phase of a lifting-body vehicle. The guidance strategy is based on a particular kind of nonlinear dynamic inversion, the so-called flatness approach. The main advantage of this approach is that the longitudinal guidance law is in-flight self-adaptive to any feasible hypersonic trajectory and can be written in analytical form with a small set of design parameters. Therefore, the required on-board computational resources are limited, and a reduced off-line design effort is needed for the change of vehicle parameters. Moreover, the closed-loop longitudinal guidance commands are computed on-board in a coupled way without relying on an explicit deceleration profile. Consequently, the approach leads to an efficient management of the degree of freedom associated with the angle-of-attack. PID controllers are then designed based on the longitudinal flat model in order to circumvent uncertainties and parameters dispersions. The crossrange is controlled by a series of bank reversals determined by an azimuth error deadband. The robustness and performance of the proposed guidance law are assessed by performing Monte Carlo runs with various sets of dispersions.