Abstract: The system consists of a satellite position and attitude reference system utilizing Global Positioning System data, an on board computer to analyze and generate position and attitude dependent instructions, an attitude control system to adjust the attitude of the space craft in response to instructions from the computer, an imaging system responsive to the computer to generate image data and transmit it, and a ground based, image data receiver and post processing system to assemble the image data, code the data and compile sequential images into a mosaic depicting the target. The on board computer delays the generation of attitude control instructions, during the process of capturing image data, in order to avoid image distortion due to attitude adjustment movement of the spacecraft.

Abstract: A method and apparatus for steering a low-earth-orbit communication satellite requiring sun-orientation for solar-power accumulation is disclosed. Momentum-bias both maintains nadir pointing and adds yaw-steering moments for sun-trackig attitude control, simultaneously. The method has two principal steps: 1) open-loop momentum decoupling, for correcting the calculated steering torque, and closed-loop attitude compensation, to correct for perturbations about the calculated attitude in accordance with one of two control law definitions. This combines the advantage of stable gyroscopic attitude control with those of open-loop yaw steering.