Adaptive reentry guidance based on on-board trajectory iterations

An adaptive method for on-board generation of entry trajectory is presented to effectively tackle the discontinuity of the input data of the guidance system, as the traditional trajectory-tracking guidance method cannot well adapt to saltatorial conditions such as the switch of navigation modes. By real-time polynomial fitting and iteration, the desired altitude-versus-velocity profiles satisfying the final constraints are determined, and then the corresponding angle of attack and bank angle commands are obtained, which guide the vehicle to safely and accurately reach the terminal area of energy management. This method enables the iterations to be fast-converging, as it takes the advantage of building analytical relations between velocity and the state variables including energy, altitude, flight-path angle and range-to-go. Numerical simulations indicate that this method has a strong adaptability against uncertainties such as the error and the saltation of the input data, as well as a better accuracy than the traditional method under various dispersion conditions. It is also proved that this method significantly enhances the autonomy and adaptability of entry guidance under practical application circumstances, compared to the traditional trajectory-tracking guidance method.