In an airborne optical imaging system, a key function is to command and control the observation direction or line of sight whose aim is to track various targets during a determined period. Indeed, the optical images will be affected by the residue of pointing.
Moreover, the airborne environment adds complementary difficulties on the line of sight control. The Line of sight command is composed of three phases : the "designation", the "hanging" and the "tracking" phases. Each of one is characterized by a specific control law. The first one allows to place the instrument line of sight following the provisional target trajectory. The second control law is optimized for the target acquisition and the third one is dedicated to track the target. The acquired imagery allows, after validation of the known target and/or rallying it by human intervention, to calculate an angular deflection for measurement of tracking error. According to the scientific objective of the imaging system, various types of targets could be observed. So the angular deflection measurement is calculated by barycentric or images correlation methods. This information is injected into the second control law which will be substituted, without unhooking, to the first performed for designation. The line of sight of the imaging system is realized with a gyro-mirror for the fine pointing in front of a camera and an independent mechanical framework, supporting the camera and the gyro-mirror. This pedestal offers to the instrument a wide angular field of view but a coarse pointing. These elements individually controllable are dimensioned for the design and realization for the control law. This paper presents each station to study needs for the definition and the realization of the control law for an airborne optical imaging instrument. This paper also describes an approach of the harmonization of the lines of sight of different instruments pointing the same target.