Earth-pointing recovery

A geometrical approach for Earth pointing recovery that eliminates waiting for the orthogonal conditions is discussed. The three-axis control is achieved using an Earth scan sensor mounted to measure the Earth chord about the roll and pitch axis. The loss of Earth pointing happens due to various reasons such as earth sensor failure or dazzle, thruster failure, control glitch. The mathematical treatment, simulation, and onboard version based on the deal sun direction without the need for sun vector measurements in the spacecraft body frame are the novel developments of the technique presented. The first attitude maneuver is to obtain an orientation wherein the sun vector in the body frame is identical to the sun vector in the orbit reference frame corresponding to the Earth pointing orientation at the epoch of recovery.