Research On Dynamics Analysis And Control Methods Of A Reentry Vehicle

Reentry vehicles launched by human, including reentry warheads and reentry modules, are a set of vehicles that return to atmosphere to accomplish their missions from outer space. Reentry vehicles attract attentions of all countries’ s cientific researches by their enormous commercial value and military value. Owing to their multidisc ciplinary design and high difficulty, the level of development of reentry vehicles represents the national scientific development and comprehensive national strength. Regarding the reentry maneuverable warhead with one moving mass as the research objective, several key technical problems of its dynamics and control are researched in this article.Reentry vehicle with signal moving mass roll control system(SMMRCS) is a classical multi-body system with asymmetric structure and aerodynamics, which makes its dynamics complex. First, the complete dynamics of the reentry vehicle with SMMRCS is modeled based on the theorem of momentum and moment of momentum theorems. Although the model can be adopted by the 7-freedoms controlled rigid body trajectory simulation, it is difficult to analyze the motion characteristics of the reentry vehicle via analytic methods for its large dimensions. Based on the complete dynamics model, the classic Euler angles are introduced and a 5-freedom sangular motions model is built in the light of the aforementioned problems. The reformatted model reduces the complexities of the dynamics, thus it lays the foundation of the analyses of the motion characteristic further.The angular motions model, regarding the classic Euler angles as the state variables, still has strong nonlinearity and coupling, which is difficult to adopt the mature linear system theory to analyze. Nonlinear analysis methods are introduced to research the open-loop attitude dynamics of the reentry vehicle with SMMRCS. Firstly, the angular motions of the reentry vehicle are demonstrated to be symmetrical to restrict the problems in a small region, and then the trim states are computed by some numerical calculation methods. The approximate analytic expressions to analyze the influences of system parameters on the trim states are reformatted by simplifying the model logically. The simulations illustrate that the approximate analytic expressions under small nutation angle conditions can coincide the numerical solutions better, which is convenient for computation and analysis of the trim states. Stability is of great importance to describe the qualitative behaviors of the dynamics system, and the local stability around the trim states is simulated by the first theorem of Lyapunov. The results present that the reentry vehicle has groups of trim states, and the angular motions will diverge or converge to the equilibrium points or limit cycles under different initial flight conditions. These stable trim states comprise both the expected states around the trim angle of attack, and the adverse states that include high nutation angle or high speed against flight control.The domains of attraction distributions of the attractors are obtained by numerical simulations, and accordinglya method is proposed to unlock the vehicle from the unexpected stable flight states.The bifurcation analysis method that is widely used for nonlinear system is introduced to manage the reentry vehicle attitude dynamics in the article. The simulation analyses that draw support from the MATCONT software are applied for limit point bifurcation and Hopf bifurcation. Besides, comparing the changing patterns of the bifurcation diagram under different structural parameters and aerodynamic parameters of the body, the relationship between the maximum stable offset distance and system parameters are obtained, thus it provides a basis for the optimal design of the system parameters.The reentry vehicle with SMMRCS realizes the trajectory maneuvering flight by controlling the roll channel. The roll autopilot therefore is an effective way to control the roll attitude. According to the transfer function model of the roll channel, the control parameters of the double loop feedback autopilotare designed by standard coefficient method and dominant poles assignment method respectively, which achieve superior results. The bifurcation analyses of the closed-loop system indicate that the stability of the trim states isameliorated though a roll autopilot, and then the maximum stable rotation rate boundary is increased. Besides, the Trajectory Linearization Control(TLC) method, a nonlinear control method, is used in the control of the reentry vehicle. The simulation results show the good control effect of the controller, which can effectively deal with the interference of aerodynamic uncertainty.