Satellite Position and Attitude Estimation Using an Extended Kalman Filter

Abstract

Free space laser communication is being proposed for a number of satellite-to-satellite and satellite-to-aircraft links. They provide high speed data transfer over the large distances involved between objects. Recently, the question has arisen as to whether these systems can be used for more than just communication. In order for two objects to communicate using lasers, they need some knowledge of the line of sight vector between them. Real time estimation techniques such as the extended Kalman filter can use this information to improve their accuracy. This paper studies a six satellite problem, five of which are in geostationary orbits, with the remaining satellite in a low earth orbit. The geostationary satellites are contained within the equatorial plane, while the orbit of the low earth satellite is not. Line of sight vectors and time of flight measurements are generated at each time step. The time of flight measurements are used to correct clock differences between the satellites and improve range estimates. Radio frequency communication between one geostationary satellite and an earth based tracking station is also included within the simulation. Results demonstrate that both position and attitude can be estimated using only the line of sight measurements. Time of flight measurements are shown to improve accuracy of both the position and attitude state estimates. Robustness to initial condition errors is also demonstrated.