Terminal Guidance Law For Moving-mass Reentry Vehicle

Compared with the aerodynamic control reentry vehicle and direct force control reentry vehicle, the moving-mass control reentry vehicle has some advantages, such as simple structure and good aerodynamic shape. This paper mainly focuses on the terminal guidance law for the reentry vehicles with accuracy, velocity and terminal angle constraints.Firstly, the motion characteristics of moving mass control reentry are studied, and the status of force bearing analysis on the system is given. The kinematics equations of the centroid, dynamics equations of the centroid, the kinematics equations around the centroid and the dynamics equations around the centroid are established. Moreover the calculating formulas of velocity, trajectory inclination angle, trajectory azimuth angle, the flight height model, atmospheric density, range model, equation of Coriolis force, equation of transport acceleration and relation equations are given.Secondly, the design method of the terminal guidance law of moving mass control reentry vehicle is studied. Taking the consideration of the difference among the different stages during the whole flight, the method of segme ntation is adopted. What’s more, the basis of segmentation is given. During the low altitude area, the rolling guidance law considered the influence of gravity is adopted. With the appropriate parameters chosen and some compensation, the reentry vehicle ca n reach the target with high accuracy, appropriate velocity and angle under the nominal case. What’s more, with the design of segment points, the range of flight can be changeable, which means the accuracy can be guaranteed when the position of the target changes.Then, the problem of terminal guidance law when the system has uncertainties is studied. To solve the problem, the predict-correction method is adopted. Firstly, some physical quantities which are easy to measure are chosen to represent the influence of the uncertainties. Secondly, the sensitivity matrix between the physical quantities and the parameters in the guidance law is calculated with the method of iteration. In this way, the variation of the parameters can be got. Finally, the method of predict-correction is added to the terminal guidance law to make the robustness better.Finally, with the combination of two kinds of guidance law, the simulation program is compiled to verify the terminal guidance law designed for the moving mass control reentry vehicle. The simulation results show that with the terminal guidance law designed, the reentry vehicle can reach the target with high accuracy when the system has uncertainties and the target position changes.