Research On Trajectory Tracking Control Methods For Mars Entry Vehicles

The trajectory tracking control problems of Mars entry vehicles subject to the large uncertainty, strong coupling, serious nonlinear, initial state errors and a large parameter perturbations in the ?ight control. Due to the harsh and complex Mars surface environment, the pin-point Mars landing is a signi?cant demand for future Mars missions.Meanwhile, trajectory tracking for Mars entry vehicles system is the key element to reduce the delivery ellipse size at parachute deploy, guarantee the pin-point Mars landing mission.Thus, the study on Mars entry trajectory tracking control is important. In this thesis,sliding mode control(SMC) combined with some uncertainty estimation methods to design several compound control strategies, to provide the robustness, accuracy and rapidity for Mars entry trajectory tracking.Considering the Mars entry vehicles system, the main content of this thesis can be summarized as follows:1. For the problem of the Mars atmospheric uncertainties, we investigate the fast and high-precision trajectory tracking control problem for Mars entry vehicles. According to the analysis of the Mars atmospheric model, nonlinear dynamic models for controller design are established. The sources of uncertainty in the Mars entry are summarized, and the trajectory tracking control strategy is designed for Mars entry vehicles based on the SMC combined with active disturbance rejection control(ADRC), using extended state observer(ESO). Due to accurate estimation of uncertainties and disturbances by extended state observer and fast response provided by SMC, the compound control law that is composed of SMC and ESO can achieve high-performance trajectory tracking control for Mars entry vehicles. Furthermore, the disadvantages of SMC, which su?er chattering, and ESO, of which the uncertainties and disturbances may be beyond the observability, can be remedied by each other.2. Based on high-order sliding mode control(HOSMC) and ADRC, we also study on the fast, robust and high-precision trajectory tracking control problem for Mars entry vehicles under the Mars atmospheric and uncertainties aerodynamic parameter disturbances.The control law combined HOSMC and DO can provide the ?nite-time stability of the trajectory tracking control for Mars entry vehicles during the entry phases. According to the analysis of the Mars atmospheric uncertainties, aerodynamic parameter disturbances and initial state errors, the control strategy combined with the ADRC can provide highperformance tracking during accurate estimation of uncertainties and disturbances by extended state observer.3. Based on nonsingular chattering-free full-order terminal sliding mode control(NCFTSMC) and ESO, we investigate the ?nite trajectory tracking control problem for Mars entry vehicles under the Mars atmospheric uncertainties, aerodynamic parameter disturbances and initial state errors. NCFTSMC is proposed to provide ?nite time stabilization for trajectory tracking system of Mars entry vehicles. According to the analysis of the impact on Mars atmospheric uncertainties, aerodynamic parameter disturbances and initial state errors, ESO is applied to estimate and compensate the tall disturbances. Due to the robust and fast of NCFTSMC, the proposed control law can achieve ?nite-time trajectory tracking control for Mars entry vehicles under the the harsh and complex Mars surface environment, reduce the delivery ellipse size at parachute deploy and guarantee the pin-point Mars landing mission.4. For the problem of the Mars atmospheric uncertainties, aerodynamic parameter disturbances, initial state errors and model bias, we investigate the robust and high-precision trajectory tracking control problem for Mars entry vehicles, based on the nonsingular chattering-free full-order terminal sliding mode control(NCFTSMC) and di?erential observer(DO). According to the analysis of the impact on Mars atmospheric uncertainties,aerodynamic parameter disturbances and initial state errors, the trajectory tracking control strategy for Mars entry vehicles can achieve ?nite-time tracking during the entry phase.Compared with traditional sliding mode control method, the proposed control law based on NCFTSMC combined with DO exhibits strong robustness against the Mars atmospheric uncertainties, aerodynamic parameter disturbances, initial state errors and model bias.5. Simulation results are presented to illustrate the e?ectiveness of the control strategies. Meanwhile, digital simulation results verify the e?ectiveness of the proposed controllers utilizing the “MSL” lander as the model.In the end, main results in this thesis are summarized, and the prospects for the future research are presented.