Inmarsat-4 First L1/L5 Satellite: Preparing for SBAS L5 Services

摘要

The new Inmarsat-4 GEO satellites carry dedicated navigation transponders which have been designed to provide Satellite Based Augmentation System (SBAS) Signals-In-Space, at both GPS L1 (1575.42 MHz) and L5 (1176.45 MHz) frequencies. The launch of the first of those satellites (Inmarsat-4F1) in March 2005 and subsequent in orbit test marked an important milestone for satellite navigation: for the first time a navigation signal at L5 frequency is broadcast from the space, paving the way for the introduction of the second civil frequency for SBAS systems. As for the previous Inmarsat satellite generation, the so-called Inmarsat-3s, which are used in both EGNOS (European Geostationary Navigation Overly System) and WAAS (Wide Area Augmentation System) systems, the Inmarsat-4 navigation transponders undergo a comprehensive series of tests aiming at verifying their suitability for the mission they have been conceived for. Each transponder has been subjected to pre-flight (ground) tests and are further tested once the satellites are in orbit (in-orbit tests) to ensure compliance with specifications. Data collected from these tests is useful not only for the verification of the transponder, but to predict the ability of the overall system to provide high quality user ranging and timing signals. The European Space Agency (ESA) is currently considering the use (preliminary use) of Inmarsat-4F1 satellite, which will be located at Inmarsat's designated Indian Ocean Region (IOR), to test the potential extension of EGNOS in Africa, and to investigate the potentialities provided by the availability of an SBAS L5 signal. The uplink of signals will be based on the experimental NLES Uplink Station proposed by Telespazio and Inmarsat to be based at Fucino. This paper reports on the test results and observations for the Inmarsat-4F1 navigation transponder and the ESA proposed experimentation strategy for L5, including support to SBAS L5 standardization activities. EGNOS long-term modernization plans, in terms of coverage extension and SBAS L5 service provision, will also be described.