Risk of Collision for the Navigation Constellations: The Case of the Forthcoming Galileo
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Risk of Collision for the Navigation Constellations: The Case of the Forthcoming Galile0 1 A. Rossi", G. B. Valsecchi3, and E. Perozzi" Abstract The satellite global positioning systems presently in space are the American NAVSTARGPS and the Russian GLONASS. Within this decade the European system, Galileo, should be operational in the same altitude range, dubbed MEO, Medium Earth Orbit. In this paper the fragmentation of a spacecraft related to one of these three constellations was simulated and the collision risk faced by the operational satellites was analyzed. Both the intraconstellation and the inter-constellation risk have been studied. An improvement in the collision risk calculation method developed in Valsecchi [5], is described in the paper. The new method overcomes the limitation in the application of Opik's theory of planetary encounters, dictated by the assumption of random orientation of the argument of perigee of the projectiles, and allows its application to the Medium Earth orbital regime. In general terms it was
observed in this study that the flux following a generic fragmentation is by far larger than the low background flux in MEO. The strong potential interaction of the three constellations has been shown by analyzing the inter-constellation effects of the fragmentations. In particular the GPS and the GLONASS strongly interact, while the Galileo constellation, orbiting at somewhat higher altitude, is less affected by any unfortunate event happening in the two lower constellations.
Introduction Satellite global positioning systems have been deployed in the early 1990's as military support systems by the US and the former Soviet Union. Later on, the global positioning systems first became available for private use in 1995, providing an extremely accurate and valuable tool. They are currently used by a huge number of people for many different applications. The satellite positioning systems presently in space are the American NAVSTAR-GPS (Navigation System with 1Presented as Paper AAS 03-185 at the AAS/AIAA Spaceflight Mechanics Meeting, Ponce, Puerto Rico, February 9-13, 2003. 2ISTI-CNR, Via Moruzzi, 1,56124 Pisa, Italy. 3IASFC-CNR, Via Fosso del Cavaliere 100, 00133 Roma, Italy. "Ielespazio S.p.A., Via Tiburtina 965, 00156 Roma, Italy.
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Time and Ranging-Global Positioning System) and the Russian GLONASS (Globaluaya Navigatsionnaya Sputnikovaya Sistema). On March 26, 2002 the European Union Transport Ministers gave the final goahead on the Galileo project. Galileo, to be developed by the European Space Agency in collaboration with the European Union, is a civil system, designed to be operational in 2008. Galileo is a twenty-seven satellite Walker constellation (three planes with nine satellites each) plus three active in-orbit spares, at an altitude of about 23,600 km and an inclination of 56°. The goal of the Galileo project is to provide Europe, and in general, the world, with an accurate, secure, and certified satellite positioning system. Galileo will
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