Terminal Guidance Law Design Considering Ternimal Constraints

In order to increase the damage degree of reentry vehicles as much as possible, it requires taking terminal constraints into consideration in the design of terminal guidance law. This paper mainly focuses on the terminal guidance problem for reentry vehicles with terminal angle and velocity constraints.Firstly, the motion characteristics of reentry vehicles are studi ed, the centroid kinematics and dynamics are established, and the calculating formulas of velocity, trajectory inclination angle, trajectory azimuth angle, atmospheric density, altitude are derived in this paper. Moreover relative motion equations of the d ive plane and turning plane are described, and navigation calculation model is given using the relative motion information of the aircraft and the target. The above mathematical model is the basis of the following study.Secondly, as for the terminal guidance problem for reentry vehicles with terminal angle constraints, an optimal finite time convergent guidance law is proposed which includes guidance equations in both dive plane and turn plane in this paper. On the basis of the above relative motions, the optimal guidance law is then used to calculate the line-of-sight(LOS) angular rate of optimal state, which subtracts the LOS angular rate of current state to get a deviation. Then, based on finite time control theory, a guidance law is designed to compens ate the deviation. In doing so, a correction term is introduced in the optimal guidance law, enabling the system to achieve high precision, rapid convergence and strong robustness. Compared with optimal guidance, sliding mode variable structure guidance an d optimal guidance law with sliding-mode variable structure, simulation results show that the guidance law developed in this paper has strong robustness against disturbances.Thirdly, the terminal guidance problem for reentry vehicles with terminal velocity constraints is developed in this paper. First of all, a desired velocity curve is designed according to the features of the reentry vehicles. Then the velocity is controlled to the designed curve by increasing the angle of attack. The proposed guidance law includes guidance equations in both dive plane and turn plane. Velocity control is introduced into the proportion navigation guidance law so that the closed-loop system can achieve the desired velocity. Simulation results show that the guidance law developed in this paper has good performance in the guidance process.Finally, combining the proposed guidance law with terminal angle and velocity constraints, this paper takes simulations of the whole process of terminal guidance. It can be seen from the simulations, the proposed optimal finite time convergent guidance law in combination with velocity control, can achieve relatively high accuracy at the requirements of angle and velocity with good robustness.