Patent ID: 7874519

Claim:
A method for orienting a spacecraft orbiting about a celestial body, said method comprising the steps of: determining a set of actual conditions of the spacecraft, said set of actual conditions comprising (i) a position of the spacecraft in inertial space as a function of time, (ii) a set of angular rotation rates of the spacecraft, said set of angular rotation rates being described with respect to a coordinate frame of the spacecraft, and (iii) an actual instantaneous direction of the sun, said actual instantaneous direction being described with respect to the coordinate frame; propagating an estimated sun direction, described with respect to the coordinate frame, said estimated sun direction being an estimate of the actual sun direction propagated as a function of time based on the previously determined set of angular rotation rates and the actual instantaneous direction of the sun; determining a desired sun direction, said desired sun direction varying as a function of time and being described with respect to the coordinate frame using orbital ephemeris data and actual time with respect to a known epoch; rotating the spacecraft and adjusting angular rotation rates of the spacecraft so that (i) an actual angle between the spacecraft coordinate frame and the sun substantially coincides with the desired sun direction with respect to the coordinate frame, and (ii) said actual angle and said desired sun direction vary as a function of time in a substantially similar manner; and, rotating the spacecraft around an axis defined by a line between the sun and the spacecraft until the celestial body is observed by a celestial body sensor of the spacecraft.