Abstract: An automatic, on-board system for orbiting spacecraft that controls yaw excursions caused by solar torques and thruster firings, which system combines inputs indicative of roll and yaw momentum increases and inputs containing information comprising the unbiased roll error from the earth sensor, yaw momentum measured from the wheel speeds, and commanded yaw momentum output from the wheel controller, and produces therefrom output signals indicative of the yaw estimate and the yaw momentum estimate. These output signals are combined and processed in a controller with a mimimum yaw error and roll thrust yaw controller gain and a miminmum yaw error and roll thrust yaw momentum controller gain, and a signal is produced therefrom for commanding roll thruster firings to change roll momentum, and, in turn, control yaw attitude and yaw excursions.