Robust EGNOS GEO Ranging with Electric Propulsion Satellite

H. Secretan, F. Mercier, S. Trilles, J. Mancuso, X. Berenguer

Abstract:	The main purpose of a Satellite Based Augmentation Systems (SBAS), such as EGNOS or WAAS, is to provide the civil aviation user community with reliable navigation services for different flight phases. To achieve its missions over ECAC area, EGNOS uses two Geostationary Earth Orbit (GEO) satellites for corrections broadcasting that enhances GPS standard positioning, and allow providing sufficient integrity, accuracy, availability and continuity for commercial aviation needs. Today, one EGNOS GEO platform has electric propulsion (PRN 126) for stations keeping manoeuvers, and in early 2015 the EGNOS GEO PRN 120 will be replaced by a new GEO platform (Astra4B) with electric propulsion also. To use EGNOS GEO as a ranging source, the user needs an accurate GEO pseudo-range modelling based on GEO ephemeris and time synchronisation broadcasted in MT#9 and associated fast corrections. This paper presents the results of GEO Ranging performances based on an experimentation made in real conditions and real time, using EGNOS SPEED Testbed, and aiming to validate the strategy for GEO orbit/clock determination optimised for electric propulsion manoeuvres plan. The important characteristic is that the manoeuvres have small amplitude and long durations (two burns of 1.5h duration every two days). But a constraint for EGNOS is that they are considered as unknown (beginning of the manoeuvre, direction, amplitude, end of manoeuvre …), due to operational constraints. The performance objective is to provide a GEO range error better than 2.5 m rms. The orbit determination algorithm has been defined by CNES, in a first step, with a theoretical performance analysis (covariance analysis), and validated in a second step using real data from EGNOS RIMS on EGNOS GEO PRN 126 satellite (Inmarsat4-F2) and a dedicated orbit determination software [1]. These preliminary studies have shown that it is possible to achieve the required performance using the real EGNOS RIMS measurements but with a specific processing which is not directly usable in the present EGNOS design. This paper develops the results obtained in a realistic environment. First, the algorithm has been improved, and applied on real internal data, produced by the SPEED Testbed (smoothed C1 pseudo-ranges, corrected by the ionosphere and troposphere delays, and the receiver clock synchronisation computed by the GPS/Glonass orbit determination module of SPEED). The first results show that it is possible to achieve a performance around 1 m rms for the User Range Error (residuals of the OD process on the reference stations). However, a more realistic performance test is to implement the GEO orbit determination algorithms in SPEED to verify that the generated correction messages reflect this performance. This implementation has been developed by TAS, and the complete SPEED SNK PF (equivalent to EGNOS CPF-PS) performance has been verified using the produced EGNOS messages. These new SPEED GEO Ranging experiment results are presented, and the performance achieved so far with respect to the EGNOS requirements and the plan for the implementation in the EGNOS operational system.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	3323 - 3330
Cite this article:	Secretan, H., Mercier, F., Trilles, S., Mancuso, J., Berenguer, X., "Robust EGNOS GEO Ranging with Electric Propulsion Satellite," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 3323-3330.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In