Modified State Observer for Orbit Uncertainty Estimation

A novel technique for estimating uncertainties caused by gravitational perturbations is presented. The approach, called the Modified State Observer (MSO), allows for the estimation of uncertainties in nonlinear dynamics while in addition providing estimates of the system states. The observer structure contains neural networks whose outputs are the uncertainties in the system. A useful and important application of this observer is the problem of determining uncertainties with an inaccurate gravity mode that a satellite may experience when orbiting a body. With future space missions involving other bodies such as asteroids that produce gravitational perturbations which are highly uncertain and are subjected to unknown physical influences, the MSO can be used not only to estimate the states of the satellites, it can be used to estimate the uncertainties that could further be analyzed further in understanding the physical phenomena. To demonstrate the utility of the MSO for this class of problem, the technique is applied for three cases: estimating the uncertainty caused by the J2 perturbation for Earth and Mars orbiters, and estimating the uncertainty in an asteroid's gravitational field. Simulations are presented which indicate that the observer can accurately estimate both the periodic nature of these perturbations as well as the magnitudes. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.