Attitude determination system and method

An attitude control system for controlling an attitude of a spacecraft comprising:

• a star tracker coupled to said spacecraft having a star catalog associated therewith;
• a sun sensor coupled to said spacecraft;
• an actuator coupled to the spacecraft for adjusting spacecraft orientation with respect to an inertial frame;
• a control processor coupled to the star tracker and said sun sensor, said processor obtaining a star data using a star tracker and an on-board star catalog, generating a coarse attitude estimate of said spacecraft as a function of said star data;
• establishing a track on at least one star in said on-board star catalog;
• calculating a sun tracking rate;
• and obtaining a normal phase attitude estimate after the step of establishing a track as a function of a sun tracking rate, said star data and said coarse attitude;
• commanding said actuator to adjust attitude in response to said normal phase attitude.