When an aircraft keeps flying for a long time,the external acceleration may affect the accelerometer output and result in lower position precision,even divergence problem of attitude and heading system,which is composed of low-precision gyroscope,accelerometer and magnetometer .To solve the problem,the external acceleration description is taken as current statistical model .The commonly used 6-state UKF is extended to 9-state,and the state variables include three modified Rodrigues parameters ( MRPs ),three-axis gyroscopes bias and three-axis external acceleration .The measurements include the outputs of three-axis accelerometer and three-axis magnetometer .The experimental results show that 9-state UKF can estimate the three-axis external accelerations and guarantee the accuracy of positioning measurement .%针对飞行器长时间飞行时，低精度陀螺、加速度计和磁强计组成的航姿系统容易受到运动加速度的影响而导致姿态精度较低，甚至发散的问题，将载体机动加速度描述为当前统计模型，将目前常用的6状态无迹卡尔曼滤波扩展为9状态，其状态变量包括3个修正罗德里格参数、三轴陀螺零偏误差和三轴载体机动加速度，量测量为三轴加速度计输出和三轴磁强计输出。实验结果表明，当飞行器长时间机动飞行时，9状态无迹卡尔曼滤波可以估计载体的机动加速度，保证姿态测量精度。
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