Mars Atmospheric Entry Guidance Design by Sliding Mode Disturbance Observer-Based Control

One of the demands for future Mars exploration is pin-point landing, in which the landing precision should be less than one hundred meters and is two orders of magnitude higher than the current level. In the process of the high-speed vehicle entering a rarefied atmosphere with highly uncertainties as the Mars atmosphere, the trajectory deviation caused by entry guidance can be the major part of the total landing errors. Due to modeling errors such as the atmospheric modeling error and the vehicle's aerodynamic model inaccuracy, the more the guidance law depends on the models, the larger the trajectory dispersion can be. To reduce the impact of model errors on guidance performance, a guidance law based on the second-order sliding mode variable structure control is developed for reference trajectory tracking. The guidance law which is tested in a real entry scenario is proved to be evident in reducing the control gain and the requirement for control ability. The proposed guidance law also shows accurate tracking for the reference trajectory and high precision of the landing sites, and thus has the potential to be applied to online guidance. (C) 2015 The Authors. Published by Elsevier Ltd.