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.
展开▼
