CISLUNAR ANGLES-ONLY NAVIGATION USING HIGHER ORDER FILTERING

With the many impending cislunar projects such as the Artemis program and Lunar Gateway, traditional navigation methods (largely terrestrial) like the Deep Space Network (DSN) cannot accommodate the increasing demand. Moreover, terrestrial navigation methods rely on factors like geometric observability, signal availability, etc, which are particularly challenging for deep space missions. This necessitates the need for space-based navigation, which will both reduce dependency on terrestrial resources, as well as facilitate autonomous onboard navigation. Optical instruments onboard a spacecraft provide angles-only measurements, and are an attractive means for space-based navigation due to their low size, weight, power, and cost. This thesis examines angles-only navigation in cislunar space, with a target (Lunar Gateway) orbiting in the Southern L2 Near Rectilinear Halo Orbit (NRHO) and a chaser satellite orbiting in a close-by Quasiperiodic Orbit (QPO). Two scenarios are explored: the cooperative target scenario where chaser knows the target's state, and the uncooperative target scenario where both target and chaser states are estimated simultaneously. Angles-only measurements are weakly observable, requiring a robust filter for state estimation. This thesis studies higher order filtering methods, focusing specifically on the second-order Extended Kalman Filter (EKF2). Results show that the EKF2 is a consistent and robust state estimator in both the scenarios explored, and is a desirable alternative to the existing state-of-practice methods to facilitate spacecraft optical navigation.