New algorithms to estimate initial roll angle for in-flight alignment of GPS/INS guided munitions

When GPS/INS guided munition needs in-flight realignment after it is fired from a conventional platform, an initial roll angle is difficult to be acquired. To solve this problem, two new algorithms of initial roll angle were proposed with regard to the non-spin and low-speed spin of projectile. The relationships between the roll angle and the transverse angular rates and attitude angle rates were derived from attitude kinematics equations. The measured values of angular rate gyroscopes and GPS velocity were used to obtain optimal estimation of roll angle based on least squares estimation. Simulation results and performance analysis show that the random and constant wind during flight are the main factors affecting estimation accuracy. The estimated errors are less than 3° under different typical levels of measurement and flight conditions. The algorithm can be used to estimate the roll angle during in-flight coarse alignment.