Fidelity - Progress Report on Delivering the Prototype Galileo Time Service Provider

The Fidelity consortium is currently implementing and will operate the Galileo Time Service Prototype Facility (GTSPF) in order to deliver Coordinated Universal Time (UTC) services to the Galileo satellite system during its in-orbit validation phase (due to begin in 2008). A key element of this plan is to integrate the Galileo timing activities into the wider time and frequency community, including the Bureau International des Poids et Mesures (BIPM). The main function of the GTSPF is to provide parameters for steering Galileo System Time (GST), as realized at the Galileo Precise Timing Facility (PTF), to UTC (modulo 1 s). This will be achieved in a three step process. First, the GST (as realized in the Galileo PTF from an ensemble of atomic clocks (active H-masers, high performance Caesium standards) with dedicated measurement equipment and clock ensemble algorithm) is compared against the participating UTC(k) time scales by Two-Way Satellite Time and Frequency Transfer (TWSTFT) and GPS P3 techniques. These raw data are sent to the GTSPF for processing. The Fidelity consortium is responsible for the calibration of the time transfer equipment. Second, the GTSPF generates a prediction of the difference UTC -GST (modulo 1 s) by means of an intermediate composite clock obtained from an ensemble of atomic standards maintained in the PTFs and in the participating European National Metrology Institutes (NMIs), and using the data of UTC -UTC(k) as computed by the BIPM. The benefits of the composite clock include enhanced stability and integrated integrity monitoring. Third, the GTSPF sends daily steering parameters to the PTF to be used to align the physical realization of GST against UTC (modulo 1 s) as required by the Galileo system specifications. The specification and design phase of the implementation of the GTSPF was concluded in August 2006 with the successful completion of the Critical Design Review (CDR). This included the functional and physical design of the GTS- PF and the verification of the uncertainty budget by means of extensive simulations. The design and functions of the GTSPF currently being implemented are detailed in this paper. The algorithm to be used for the prediction of UTC - GST is described. The time transfer link calibration activities under the responsibility of Fidelity are detailed. The PTF interactions with the GTSPF are described. A possible relationship between the GTSPF and EGNOS, the first step of European navigation satellite systems, is proposed. Finally, this paper gives a summary of the current status of the GTSPF implementation and the planned future activities of the Fidelity consortium.