Autonomous Orbit And Magnetic-Field Determination Using Magnetometer And Star Sensor Data

A batch filter has been adapted to autonomously determine spacecraft orbit and corrections to Earth's magnetic field model. It uses only magnetometer and star sensor measurements. This filter's aim is to improve the accuracy of magnetometer-based spacecraft orbit determination. Observability of the system is demonstrated through covariance analysis. The results of filtering data from a truth model simulation predict the methods accuracy. The truth model includes random magnetometer noise, random star sensor attitude errors, and high-spatial-frequency magnetic field uncertainties. System accuracy is highest for low altitude, about 500 km, and significant inclination, 45 deg or larger. Accuracies on the order of 200 m for position and 1 nT for field model coefficients are predicted by the study. The only unobservable situation is that of an orbit with zero inclination and zero eccentricity, but accuracy degrades markedly for nearly circular orbits with low inclination.