The Galileo Constellation Design: A Systematic Approach

Ricardo Píriz, Belén Martín-Peiró and Miguel Romay-Merino

Abstract:	The Galileo satellites will form a 27/3/1 Walker constellation with 27 active satellites in three orbital planes (plus three in-orbit spare satellites), and nine operational satellites in each orbital plane equally spaced along the orbit. The process leading to this constellation choice has been an iterative one in which many criteria have been taken into account, and many analyses and trade-offs have been made. This paper tries to review and summarize in a retrospective way the rationale behind the Galileo constellation, and proposes a systematic approach for GNSS constellation design. Three major technical areas are involved in the design decision process: performance, repeatability and stability. Performance refers to the navigation capabilities of the constellation in terms of user positioning accuracy (DOP, vertical accuracy…) Repeatability refers to the time interval for the satellite geometry to repeat on the sky for an observer on-ground, either with the same satellite or with satellites from other orbital planes. Stability refers to the ability of the constellation to maintain its geometrical properties in space throughout the mission lifetime, with the minimum number of maneuvers, and preferably no maneuvers at all. Stability and repeatability are to some extent conflicting objectives because of the phenomenon of resonance. The Galileo design takes into account all the criteria explained above in order to obtain a non-resonant, stable, and performing constellation with a short enough repeat period.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1296 - 1306
Cite this article:	Píriz, Ricardo, Martín-Peiró, Belén, Romay-Merino, Miguel, "The Galileo Constellation Design: A Systematic Approach," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1296-1306.
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