Projectile attitude and position determination using magnetometer sensor only

A priori information given by the complete modelling of the ballistic behavior (trajectory, attitude) of the projectile is simplified to give a pertinent reduced evolution model. An algorithm based on extended Kalman filters is designed to determinate : center dot position : x,y,z references in earth frame. center dot value and direction of the velocity vector; its direction is given by 2 angles (eta and theta). center dot attitude around velocity vector given by 3 angles : roll angle in the range [0, 2 pi], angle of attack a and side-slip angle beta in the range of few milliradians. The estimation is based on the measures of the magnetic field of the earth given by a three-axis magnetometer sensor embedded on the projectile. The algorithm also needs the knowledge of the direction of the earth magnetic fields in the earth frame and aerodynamics coefficients of the projectile. The algorithm has been tested on simulation, using real evolution of attitude data for a shot with a 155 mm rotating projectile over a distance of 16 km, with wind and measurement noise. The results show that we can estimate milliradians with non-linear equations and approximations, with good precision.