Geopositioning Accuracy of an Autonomous Navigation System using Landmarks

An autonomous navigation system employing three-axis gyros, an earth sensor, star trackers, and sun sensors for attitude and orbit estimation is investigated via covariance analysis. Of primary interest is the ability of the system to determine the location in earth-fixed coordinates of features of interest observed by the earth sensor, i.e., the geopositioning accuracy. Known landmarks observed by the earth sensor are indispensible references for this application since they provide the only orbit information and also avoid problems arising from dynamic misalignments between this primary sensor and the secondary attitude sensors. The dynamic models employed and the measurement model for the earth sensor are discussed. Preliminary results indicate that the intrack orbit uncertainty provides the major component of the geopositioning error.