Precision spacecraft attitude estimators using an optical payload pointing system

The advancement of satellite program technology mandates that issues affecting future spacecraft system development cost be resolved, while continuing to meet smaller size, lower power, and more stringent mission requirements. In the specific area of the spacecraft attitude determination system, an optical payload pointing system can serve a dual purpose: to support the payload mission and to provide precise attitude information for the spacecraft functions, As a result, star trackers or other precise reference systems can be eliminated to reduce the development cost. Additional benefits include performance robustness to spacecraft motion or disturbance and potential cost saving due to weight reduction, e.g., launch cost. Attitude estimators using an optical payload pointing system and strap-down gyros are derived in detail for two distinct formulations: spacecraft body and inertial formulations. Alternative Kalman filter equation derivations are shown using the skew symmetric matrix properties of the attitude kinematics equation. It is also shown that both formulations produce identical solutions. However, the body formulation is conceptually easier to understand, and the inertial formulation requires less processing time. To shelf the spacecraft attitude estimator performance using an optical payload pointing system, an example is shown for an agile low-Earth-orbit satellite.