Demonstration of Adaptive Extended Kalman Filter for Low-Earth-Orbit Formation Estimation Using CDGPS
Franz Busse, Jonathan P. How, JAMES SIMPSON · NAVIGATION Journal of the Institute of Navigation · 2003
ABSTRACT: Carrier-phase differential GPS is an ideal sensor for formation flying missions in low earth orbit since it provides a direct measure of the relative positions and velocities of the vehicles in the fleet. This paper presents results for a relative navigation filter that achieves centimeter-level precision using a customized GPS receiver. A precise, robust extended Kalman filter estimates the relative states based on simple measurement models and a linear Keplerian propagation model. To increase the filter robustness in the face of environment uncertainty, adaptive method of maximum likelihood estimation (MMLE) algorithms are implemented. The adaptive filter accurately identifies the process and sensor noise covariances for the system. Despite the simplicity of the filter, hardware-in-the-loop simulations performed on the Formation Flying Testbed at Goddard Space Flight Center demonstrated that this filter can achieve ≅2 cm relative position accuracy and <0.5 mm/s relative velocity accuracy for a range of low-earth-orbit formation.