Research On Estimate Algorithm Of Free Flight And Re-Entry Phase Trajectory Based On Space-Based Early Warning System

Research of the state and covariance estimation for ballistic missile and the way of tracking missile using early warning satellite is an important technology. In this paper, detecting and surveillance process of ballistic missile with low satellite of SBIRS is studied deeply. The main contributions are as follows:First, geometry algorithm for determining position with two satellites is studied. Three parameters including intersection angle, pitching angle and visual angle are selected to describe the geometric relationship of observation intersection. With measurements through reasonable satellites position, the trajectory parameters of the ballistic missile are estimated using the extended Kalman filter. Trajectory parameters EKF estimation result based on two satellites positioning is given by Monte Carlo simulation.Secondly, aiming at measurement being only from one satellite and the EKF being not stable, the measure equation is improved. Transforming the form of angle measurements by the imaging theory, linearization of measure equation is realized by fake data of measurement. Parameter of ballistic missile trajectory is estimated by using EKF, and the simulation shows that the unstabilization problem of EKF with true measurements is solved by using EKF with fake measurements.At last, two kinds of method of estimating the impact point are investigated. Case one: ignoring atmosphere resistance, the impact point is estimated using the ellipse theory with the data of angle measurement . Case two: considering atmosphere resistance, the coefficient of missile trajectory is estimated by EKF and the impact point is estimated using missile's dynamic model. A simple model of atmosphere is described for reducing computation load and economizing the EMS memory. The precision of two kinds of method is validated by Monte Carlo simulation.