Effective Use of Magnetometer Feedback for Smart Projectile Applications

Abstract

: The use of magnetometers for orientation estimation on rapidly-spinning flight bodies is analyzed. Specifically, the effect of spin-induced magnetic field distortion is discussed, with particular attention to its implications for magnetometer-based orientation estimation. First, the nature of spin-induced field distortion is described and it is shown that, if not properly accounted for, distortion can lead to significant estimation errors in artillery projectiles. Then, an orientation estimator is constructed driven by magnetometer, gyroscope, and GPS feedback. A novel feature of this algorithm is its compensation for spin-induced distortion of the Earth's field. The algorithm also incorporates in-flight magnetometer calibration performed simultaneously with projectile orientation estimation. The comprehensive algorithm is built as a coupled set of Extended Kalman filters. Observability of the estimation problem is discussed and unobservable modes are identified. Finally, example results and Monte Carlo simulations compare estimation performance to algorithms which neglect spin-induced distortion effects or do not perform in-flight calibration. These results demonstrate that magnetometer-based systems on-board spinning projectiles should incorporate corrections for field distortion, and that overall accuracy is greatly enhanced by performing in-flight calibration.