Abstract: To determine precise missile attitude from star observations in ballistic missile guidance system integrated with strap-down inertial navigation system and celestial navigation system(SINS/CNS),is a scaled unscented Kalman filter(SUKF) is to estimate real-time missile attitude.In the filter,build a set of missile attitude kinematics equations are built based on Rodrigues parameters,which avoids attitude quaternion normalizations.And measurement equation of Rodrigues parameters is designed based on quaternion estimation(QUEST) methods.A simulation with the SUKF application to a missile ballistic trajectory is done and the result shows that the method is available.