To quickly and easily find the relative position and speed of a target spacecraft by using the structure of a target spacecraft, if almost in rotation symmetry.

A system includes a TV camera 1 for picking up the image of a target spacecraft almost structured in rotation symmetry and a computer device 3 for detecting an axis of rotation of the target spacecraft picked up on the acquired image, calculating the diameter of the axis of rotation and comparing the calculated diameter with the actual diameter of the target spacecraft to calculate a relative distance from a chaser spacecraft to the target spacecraft in such a manner that the relative distance is calculated in time intervals. The relative distance and speed of the target spacecraft can thus be directly found without requiring the attitude angle.