Experimental Assessment Of Galileo Clocks Performance In Space

Christophe Bourga, Bruno Lobert, and Michel Brunet

Abstract:	The GEM study, conducted by Alcatel Space Industries under CNES contract, has been performed to propose potential missions for an early flight experimentation of Galileo system. The design of the experimental satellite has been based on the Proteus platform developed by Alcatel. It has been recognised that one essential mission is the characterisation of the performance of the space clocks that could be considered for Galileo and that would be available in the very next years. The goal is to have at least one clock of each technology, hence three different space clocks have been envisaged : • RAFS (Rubidium Atomic Frequency Standard), developed under ESA contract • PHM (Passive Hydrogen Maser), developed under ESA contract • SCOP (Space Cesium clock with Optical Pumping), proposed by CNES. Several clock configurations have been analysed, the retained baseline for satellite design is 1RAFS +1PHM, because it is the most dimensioning configuration (in terms of power consumption, volume and mass) and also because the planning for SCOP is actually critical for 2004/2005 launch. This paper describes the system architecture proposed for one of the identified missions, namely clock Characterisation, with emphasis on the metrology aspects. This architecture relies on : • on-board phase comparisons • comparison of space clocks with a ground ultra- stable time scale through measurements performed with the navigation signal emitted by the experimental payload, using a world-wide sensor station network (similar technique to IGS) • comparison of space clocks with ground ultra- stable time scales through T2L2 measurements (Time Transfer by Laser Link) • monitoring of clock environment (radiation, magnetic field, temperature). The design of space segment and ground segment has been analysed. Finally, the performance of clock characterisation has been assessed as a function of system design (number of stations, error budget ...) and of experimentation duration.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2216 - 2224
Cite this article:	Bourga, Christophe, Lobert, Bruno, Brunet, Michel, "Experimental Assessment Of Galileo Clocks Performance In Space," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2216-2224.
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