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Next The Onboard Galileo Rubidium and Passive Maser, Status & Performance P. Rochat Temex Neuchatel Time Neuchatel, Switzerland F. Droz, P. Mosset, G. Barmaverain, Q. Wang, D. Boving Temex Neuchatel Time Neuchatel, Switzerland L. Mattioni, M. Belloni, M. Gioia Galileo Avionica Milan, Italy U. Schmidt, T. Pike EADS Astrium Munich, Germany F. Emma European Space Agency - ESTEC Noordwijk, The Netherlands
I. INTRODUCTION GALILEO is a joint initiative of the European Commission and the European Space Agency (ESA) for a state-of-the-art global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It will probably be inter-operable with GPS and GLONASS, the two other Global Navigation Satellite Systems (GNSS) available today. The fully deployed Galileo system consists of 30 satellites (27 operational and 3 active spares), stationed on three circular Medium Earth Orbits (MEO) at an altitude of 23 222 km with an inclination of 56º to the equator. Atomic clocks represent critical equipment for the satellite navigation system. The Rubidium Atomic Frequency Standard (RAFS) and Passive Hydrogen Maser (PHM) are at present the baseline clock technologies for the Galileo navigation payload. According to the present baseline, every satellite will embark two RAFSs and two PHMs. The adoption of a "dual technology" for the on-board clocks is dictated by the need to insure a sufficient degree of reliability (technology diversity) and to comply with the Galileo lifetime requirement (12 years). Both developments are based on early studies performed at the Observatory of Neuchatel (ON) from end of 1980s and Temex Neuchâtel Time (TNT) since 1995. These studies have been continuously supported by Switzerland within ESA technological programs especially since the set-up of the European GNSS2 program. The activities related to Galileo System Test Bed (GSTBV2) experimental satellite as well as the implementation of the In Orbit Validation phase are in progress. Two experimental satellites will be launched by the end of 2005 or beginning of 2006, to secure the Galileo frequency fillings, to test some of the critical technologies, such as the atomic clocks, to make experimentation on Galileo signals and to characterise the MEO environment. There will be one PHM and two RAFS on board the satellite supplied by Galileo Industries and two RAFS on the satellite supplied by Surrey Satellite Technologies Ltd. This article gives a general overview on the space RAFS and the PHM developments and evolution up to now, lifetime expectation and qualification status. II. DEVELOPMENT ACTIVITIES OF ON-BOARD CLOCKS A. Development & Qualification Activities of Rubidium Atomic Frequency Standard The RAFS development milestones are chronologically listed as below:
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