针对在轨运行的微小航天器发射过程的振动引起的结构变形和在轨太阳光照产生的结构热变形会使发射前对惯性恒星罗盘(Inertial Stellar Compass：ISC)标定的光学系统焦距偏离实际值，进而影响微小航天器的高精度姿态确定的问题，提出了一种基于姿态矩阵判据的ISC光学系统焦距在线快速标定方法。首先，分析了光学系统焦距与姿态矩阵的映射关系; 然后，利用任一时刻由滤波生成的姿态矩阵，结合姿态矩阵单位正交特性的这一判据，采用迭代法实现了ISC光学系统焦距的在线快速标定。实验结果表明：该方法对ISC光学系统焦距的标定精度同星点质心提取的像素精度相当，大约为0.01个像素。该方法可在轨随时进行光学系统焦距的标定，标定速度快，且不需要采集大量姿态测量传感器的数据，标定效果良好。

The structure deformation of a micro-spacecraft in orbit caused by launching vibration and its thermal deformation resulted from sunlight will change the optical focal length of an Inertial Stellar Compass ( ISC) in the calibration before launching. Furthermore, it will affect on the high-precision attitude determination for the micro-spacecraft. To improve the calibration, an online fast calibration method based on the attitude matrix criterion was presented. Firstly, this method was used to analyze the mapping relation between the optical focal length and the attitude matrix. Then, combining the attitude matrix generated by the filter in any time with the orthogonal unit features of attitude matrix, the focal length of ISC was calibrated online based on an iterative method. Experimental results indicate that the calibration precision by proposed method for the optical length of the ISC system is equivalent to the extracting precision by the stellar center of mass method, and it is about 0.01 pixel. This method can calibrate the focal length at any time in orbit, and have fast calibration speeds and better calibration results without capturing a large number of other attitude measurement data from sensors.