Orbit Estimation Using a Horizon Detector in the Presence of Uncertain Celestial Body Rotation and Geometry

This paper presents an orbit estimation using non-simultaneous horizon detector measurements in the presence of uncertainties in the celestial body rotational velocity and its geometrical characteristics. The celestial body is modelled as a tri-axial ellipsoid with a three-dimensional force field. The non-simultaneous modelling provides the possibility to consider the time gap between horizon measurements. An unscented Kalman filter is used to estimate the spacecraft motion states and estimate the geometric characteristics as well as the rotational velocity of the celestial body. A Monte-Carlo simulation is implemented to verify the results. Simulations showed that using non-simultaneous horizon vector measurements, the spacecraft state errors converge to zero even in the presence of an uncertain geometry and rotational velocity of the celestial body.Comment: 17 pages, 7 figures, accepted for publication in Acta Astronautic

Low-Earth Orbit Determination from Gravity Gradient Measurements

International audienceAn innovative orbit determination method which makes use of gravity gradients for Low-Earth-Orbit satellites is proposed. The measurement principle of gravity gradiometry is briefly reviewed and the sources of error are analyzed. An adaptive hybrid least squares batch filter based on linearization of the orbital equation and unscented transformation of the measurement equation is developed to estimate the orbital states and the measurement biases. The algorithm is tested with real flight data from the European Space Agency’s Gravity field and steady-state Ocean Circulation Explorer (GOCE). The orbit determination results are compared with the GPS derived orbits. The radial and cross-track position errors are on the order of tens of meters, whereas the along-track position error is over one order of magnitude larger. The gravity gradient based orbit determination method is promising for potential use in GPS-denied navigation and in outer space planetary exploration