Estimation and Prediction of the GIOVE Clocks

Irene Hidalgo, R. Píriz, A. Mozo, G. Tobias, P. Tavella, I. Sesia, G. Cerretto, P. Waller, F. González, and J. Hahn

Abstract:	In preparation for the development of the Galileo system, the European Space Agency (ESA) launched in 2002 the development of an experimental ground segment (Galileo System Test Bed Version 1). Within the GSTB-V1 project, tests of Galileo algorithms were conducted processing GPS global data at the Ground Processing Center (GPC) located at ESA/ESTEC in The Netherlands. In December 2005 and then in April 2008, two experimental Galileo satellites called GIOVE-A and GIOVEB, respectively, have been launched. They mark the second step in the validation of the Galileo system to be completed with the deployment of the In-Orbit Validation (IOV) satellites. The vapor-cell rubidium (RAFS) atomic clock technology is common to both GIOVE satellites, and GIOVE-B carries also the first-ever orbiting passive hydrogen maser (PHM). The GIOVE Mission experimentation project is intended to mitigate the Galileo project risks by an early assessment of technical aspects like demonstration of the navigation service (including navigation message generation, uplink, and broadcast), validation of critical in-orbit technology (clocks), end-to-end analysis of the Galileo signal in space, assessment of Galileo Test Receiver performance, validation of on-ground algorithm prototypes, and overall testing of timeliness and operational aspects. The GIOVE Mission core infrastructure for experimentation consists of a network of 13 Galileo Experimental Sensor Stations (GESS) worldwide distributed that acquire and collect the GIOVE and GPS satellite signals and send pseudo-range and carrier-phase measurements to the upgraded GPC. Satellite Laser Ranging (SLR) stations track both GIOVE satellites as well. One of the GESS is installed at the Time Laboratory located at INRiM, Turin, connected to an active hydrogen maser, located in a controlled environment. The INRiM time reference is used as the basis for Experimental Galileo System Time (EGST). This paper presents and discusses up-to-date results from the GIOVE Mission experimentation, mainly focusing on the Orbit Determination & Time Synchronization (ODTS) technique and its validation with GIOVE data. After a short description of the GIOVE infrastructure and of the ODTS process, the results obtained with both RAFS and PHM are presented, which is followed by a discussion on the ODTS quality and validity.
Published in:	Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 4, 2008 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	361 - 374
Cite this article:	Hidalgo, Irene, Píriz, R., Mozo, A., Tobias, G., Tavella, P., Sesia, I., Cerretto, G., Waller, P., González, F., Hahn, J., "Estimation and Prediction of the GIOVE Clocks," Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2008, pp. 361-374.
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