EKF and UKF state estimation comparison for rotating rockets

Abstract

Increasing the accuracy of munitions can be accomplished in various ways. One method is to use on-board guidance systems that can steer a missile to within meters or less of its target. However, this approach is expensive. A less costly more inaccurate alternative is the spin stabilization approach. These systems lack close-loop flight control and many of the sophisticated sensor found in on-board guidance systems. The accuracy of spin stabilized rockets is affected by many factors including motor misalignments, tip-off error, and wind. With the goal of improving the flight trajectory (and thereby accuracy) of a spin stabilized ground launched ballistic missile, we evaluate the performance of an Extended Kalman Filter (EKF) and an Unscented Kalman Filter (UKF) for nonlinear state estimation. Performance is evaluated in terms of mean square error (MSE) and circular error probability (CEP). The modeled rocket is equipped only with MEMS gyroscopes for sensing and pyrotechnic thrusters for flight path correction. Due to properties of the modeled system, all state estimation and control must be performed in the early stages of flight. This allows many tasks to be performed off-line, which decreases the computational cost of the estimators.