Giove-A Apparent Clock Assessment and Results
Abstract
The performance of the Galileo space-borne clocks is of importance for navigation and integrity at the corresponding user level. Clock estimation and prediction errors are directly mapped into the User Equivalent Range Error (UERE). The clock quality also affects the integrity performance of the Galileo system: clock "feared events," such as frequency and phase jumps, have to be characterized and adequate barriers built against them. In addition, the clocks operate in the harsh MEO-orbit radiation environment, and performance has to be guaranteed in all satellite mission phases, including eclipses. Two Rubidium Atomic Frequency Standard (RAFS) units developed by Spectratime (former Temextime) were launched on the first experimental Galileo satellite, the Galileo In-Orbit Validation Element A (GIOVE-A). The RAFS already demonstrated excellent performance during on-ground qualification and acceptance tests. To verify its performance onboard, an experiment was carried out as part of the GIOVE Mission Segment. Under this Mission, an infrastructure was deployed, including a network of 13 Galileo Experimental Sensor Stations (GESS) monitoring continuously the GIOVE-A signals. Using dedicated network adjustment techniques, the processing of these observables allows the restitution of the phase difference between the onboard clock and a ground reference. Such restitution, however, is affected by the noise of the measurement system (e.g., onboard and averaged on-ground group delays, etc.), therefore the "apparent" clock denomination. This paper will present the GIOVE-A apparent clock results obtained since the ground infrastructure became operational for both the nominal and the redundant onboard clocks and for various signal configurations. These results will be complemented by relevant onboard telemetry data. Finally, the assessment of the onboard clock performance will be discussed, together with the contribution of the measurement system noise.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2007
- Accession Number
- ADA483828
Entities
People
- Alvaro Mozo
- Daniel Navarro-reyes
- Francisco Gonzalez
- Ilaria Sesia
- Joerg H. Hahn
- Marta Cueto
- Patrizia Tavella
- Pierre Waller
- Ricardo Piriz
- Virginia Fernandez
Organizations
- European Space Agency