Abstract: This research focuses on the transient impact response and deployment dynamics of reusable launch vehicles with high center-of-gravity and high slenderness ratio landing legs. A transient dynamics model of the rocket incorporating the nonlinear characteristics of damper is developed using the finite element method (FEM). Simulations of four-leg symmetric and single-leg limit landing conditions, as well as drop tests, are performed for verification. Results indicate that the FEM demonstrates higher accuracy than rigid-flexible coupling methods in predicting key parameters such as cushion stroke, main strut loads, and vehicle overloads, especially within the landing speed range of 0.89-1.88 m/s, where dynamic responses align more closely. In the single-leg limit condition, the auxiliary beam exhibits alternating tension-compression characteristics, with the connection between the auxiliary beam the and footpad experiencing peak moments. This moment could be reduced by decreasing the eccentricity between the footpad and the auxiliary beam axis or by using a spherical hinge connection. A sensitivity analysis of the ground friction coefficient reveals that the dynamic friction coefficient is the dominant factor affecting landing stability, with an appropriate dynamic friction coefficient enabling optimal balance between vehicle vertical overload and cushion loads. Deployment dynamics research indicates that the main source of sleeve locking impact loads is the collision of the locking sleeve end face. The equivalent simplification method of contact pairs can enhance computational efficiency with minimal error. When the initial vehicle tilt angle is less than half of the landing leg deployment dead angle, the four-leg deployment time deviation is small enough to meet engineering requirements. These findings provide support and guidance for the optimal design of reusable rocket landing mechanisms.

Key words: reusable launch vehicle, finite element method, transient dynamics, landing leg, load