2.5 THE WEST PROJECT: AN HYBRID CONSTELLATION DEDICATED TO THE UBIQUITOUS ACCESS OF THE 'INFORMATION SOCIETY'

摘要

At the beginning of the 21st century, the power of a country will be related to its capability to communicate and to access efficiently the so-called 'Global Information Infrastructure' (GII). Several terrestrial alternatives are available for broadband communications, but all are subject to some limitations (cost, availability of the infrastructure, time to install). Satellites appear to be the right answer to complement these terrestrial networks.rnWEST is a Matra Marconi Space initiative answering this need for multimedia services. WEST is satellite infrastructure based initially on several geostationary satellites and complemented by a constellation of satellites in Medium Earth Orbits (MEO).rnThis paper first describes the WEST system and its environment. Then, the optimisation process of the MEO constellation is presented, maximising the performances over the target areas identified by the market studies. These performances are for instance the elevation angle of user's terminals, the availability induced by rain and interference mitigation and the related need of multiple visibility, the robustness of the overall constellation, the station keeping cost, etc. Finally, station keeping of the WEST MEO constellation is presented. After the definition of the operational requirements and the analysis of the orbit perturbations, a station keeping strategy is proposed and analysed.