Research On Mars EDL Dynamic Modeling,Guidance And Control Method

The key stage that affects the successful landing of the Mars lander is the process of the lander entering the Martian atmosphere and safely landing on the surface of Mars,that is,the process of Mars entry,descent and landing(EDL).Based on the background of China's first Mars exploration mission "Tianwen-1" in 2020,this paper studies the dynamics,guidance and control methods of Mars EDL,and performs simulation and optimization design.The main research contents are as follows:Firstly,the common coordinate system and motion variables and conversion relations are established.The geometric configuration of China's first Mars exploration lander and parachute is introduced.Based on the Mars atmospheric model and the corresponding uncertainty model,The mechanical environment of lander has been modeled,including Mars gravitation,different aerodynamic models experienced by landers and parachutes at different stages and control force model.Then,a high-precision dynamics model of the whole process of Mars EDL is established.The dynamics of the process of atmospheric entry,Trim-Flaps opening,parachute deployment,inflation,aero oscillations,heatshield separation,backshell separation,power descent are modeled.For the Mars entry and landing process,a sixdegree-of-freedom rigid body dynamics model is established.For the Mars parachute descent process,a parachute rigid-flexible coupling model,a parachute-lander combination dynamics model,and a parachute-lander-heatshield(backshell)multibody dynamics model are established.In addition,for different stages of EDL,the corresponding guidance and control methods are designed.About the guidance method,the atmospheric entry process uses e entry terminal point controller to reduce the landing point spread,and the power descent process uses polynomial guidance,hovering,maneuvering and landing guidance to make the lander land safely.About the control method,PID/PI control and pseudo rate control algorithm are used,and the disturbance torque is compensated by the disturbance observer,and the pulse width is adjusted to obtain the pulse thrust.Finally,through the environmental model,dynamic model and guidance and control methods of Mars EDL process,the integrated simulation of EDL process is carried out,which can simulate,analyze and optimize the various stages of entry,descent and landing.In the entry stage,the trigger of parachute deployment is optimized,the parachute deployment conditions and landing point dispersion are analyzed;In the parachute descent process,the trigger conditions of heatshield separation are optimized,the deceleration process of parachute system,the height and speed of parachute are analyzed;In the process of power descent and landing,the guidance law,control strategy,and backshell avoidance strategy at this stage are optimized,and the land accuracy and propellant consumption are analyzed.It provides a high-precision test platform for future Mars missions,which can be used to test the precise landing and hazard avoidance.