In order to match image motion at focal plane produced by ground objects movement accurately

the image motion speed calculation method is realized

whose input parameters is the spacecraft location vector and velocity vector based on the WGS-84 coordinate system and spacecraft attitude angle and attitude angular velocity based on spacecraft orbital coordinate system. First of all

the inertial coordinate system is selected flexibly based on the original image motion speed calculation model

so the complexity of solving orbital inclined angel and descending node longitude is decreased. And the cosine value of central angel between spacecraft and descending node is solved by using cosine theorem of spherical Geometry

the cumbersome process of solving central angel cosine value between spacecraft and descending node is avoided by judging the flight direction of satellites and the latitude of sub-satellite point in original motion speed calculation model. Subsequently

the longitude and latitude of sub-satellite point and FLASH address are linked organically and skillfully

the cumbersome lookup process is avoided when elevation data is visited. Then the feasibility of image motion speed calculation model is evaluated by analyzing the impact of image motion speed residual on the camera MTF. Finally

the whole process which calculates the motion speed is realized on DSP from TI. Analyzing and experimental results indicate that the image motion speed calculation residual is 1.5‰

which result in a 1% decrease of the MTF. The time that is cost by Image motion speed calculation is less than 2ms. It can satisfy the system requirements of the camera on the calculation accuracy and computing time.