Abstract:The guidance problem with fixed time convergence characteristics of Mars entry is investigated in this paper. First of all, aiming at lateral motion, the azimuth angle error threshold which is linear with the velocity is given, and the inversion logic of the bank angle is designed. Compared with the inversion logic of cross-range threshold, this logic in this paper has less computation and is more suitable for aerospace computers. Compared with the inversion logic of fixed azimuth angle error threshold, this logic can avoid frequent switching of the bank angle at high velocity and increase the probability of mission success. Secondly, for longitudinal motion, the RBF neural network is used to compensate the saturation of the bank angle, and a drag-based anti-saturation fixed time tracking guidance law is designed by using integral sliding mode. This guidance law can effectively eliminate the chattering problem of sliding mode control, and two different forms of tracking error which are introduced into the guidance law can rapid convergence and ensure that the tracking error converges to zero within a finite time. Finally, to show the feasibility of the proposed method, simulation results are included for illustration. It is proved that the bank angle inversion logic and guidance law presented in this paper can ensure that the Mars detector can track the nominal entry trajectory and has high guidance accuracy.