Abstract

A method for acquiring Earth-pointing attitude of a three-axis, body-stabilized spacecraft orbiting the Earth in a prescribed orbit plane, e.g. a geosynchronous communications satellite, including the steps of aligning the roll axis of the spacecraft with the sun line (which is the vector directed from the spacecraft to the Sun); then, orienting the spacecraft such that the angle formed between the yaw axis and the sun line is equal to the Earth-Sun angle (which is the angle formed between the sun line and a vector directed from the origin of the spacecraft internal coordinate system to the Earth); then, orienting the spacecraft such that the yaw axis is aligned with the center of the Earth; and finally, rotating the spacecraft about its yaw axis until its pitch axis is oriented at a desired attitude relative to the orbit plane, e.g., normal to the orbit plane, to thereby complete acquisition of the Earth-pointing attitude.