Simulation And Analysis Of Mars Entry Parachute Descent Phase Dynamics

Mars entry stage(Entry, Descent and Landing) is the most challenging and easily prone to failure stage in Mars exploration mission. The Mars entry stage consists of atmospheric entry phase, parachute descent phase, powered descent phase, and landing phase. Parachute descent phase is the most important phase in the whole mission. Many missions failed because of failure in parachute descent phase. In parachute descent phase, the entry capsule deploys parachute if the condition for parachute deployments in satisfied, followed by suspension line stretch, parachute inflation, area oscillation, and stable descent. Then the heatshiled is ejected by the capsule to open the lidar for the navigation of powered descent phase. At the end of parachute descent phase, backshell and parachute separate with the lander and the lander will deceleration again to guarantee a safe landing.As the most two important technological operations, heatshield separation and backshell separation become the critical design factors in parachute descent phase. Because the aerodynamic couple during heatshield separation, there is an attraction between heatshield and lander-backshell combination, which brings difficulty in heatshield separation; similarily, as the heatshield and lander-backshell have different mass and aerodynamic characters, the ballistics parameters of them are different. We should design an appropriate ballistic parameter difference to guarantee a positive separation. During backshell separation, the velocity is small and the aerodynamic couple is not obvious. What’s more the mass of lander is larger than the backshell, which can guarantee the ballistic parameter of lander is larger than the backshell-parachute combination. Thus for backshell separation we consider only the initial value constraint of powered descent phase.In this paper, a rigid-flexible coupling dynamic model of capsule-parachute combination in parachute descent phase is established to analyze the dynamic law of parachute descent phase, including the model of probe and the parachute model at different phases(suspension line stretch, inflation, area oscillation, and full inflation). The dynamics of capsule-parachute combination in parachute descent is analyzed. By the research of relationships between total parachute force and parachute pull angle, we got the force at different pull angle. The maximum value of total parachute force and force in every bridle is calculated. The distribution law of the total parachute force and single bridle force is analyzed by statistics. The dynamic character of the capsule is also analyzed by statistics. Then triggers of the two key operations, heatshield separation and backshell separation, in parachute descent phase is analyzed and designed. We proposed the available Mach number uncertainty range and the necessary Mach number uncertainty range. Then the design of three triggers is present with the security criterion and the advantages and disadvantages of three triggers are analyzed. The backshell separation dynamics and the link between backshell separation and powered descent phase are analyzed and got the design method of backshell separation. A Monte Carlo simulation is done to verify if the design is correct and it shows that the triggers can satisfy the requirement of safe separation.