Data Timing, Time Transfer and On-board Clock Monitoring for Space Astrometry with Gaia
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The paper discusses the problematic of data timing in the framework of the space astrometry mission Gaia. For various reasons related both to astrometry and to the measuring principles of the Gaia instrument it is mandatory to assign a highly stable and accurate time tag for each observational point. For this purpose Gaia has a Rb clock on board. That on-board clock is a free-running oscillator and must be regularly synchronized with TCB which is used as the underlying relativistic coordinate time scale in the whole Gaia data processing. To monitor the reading of the on-board clock with respect to TCB (or any other timescale) a one-way clock synchronization scheme is implemented. This scheme takes into account all known theoretical effects (e.g., relativity, tropospheric delay, etc.) and allows one both to monitor the health of the on-board clock and to create a clock model at the accuracy of better than 1 microsecond.
KeywordsGaia Astrometry Space mission Time synchronization Atomic clocks in space
This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The practical realization of the theoretical scheme for the time synchronization in Gaia is the work, which was prepared, discussed, organized and made possible by a large number of people from ESA and the DPAC. The help and fruitful discussion with Ulrich Bastian, Neil Cheek, Peter Collins, Sebastian Els, Rocio Guerra, Jose Hernandez, Arek Kowalczyk, David Milligan, Hassan Siddiqui, and Gary Whitehead are gratefully acknowledged. The work was partially supported by the BMWi grant 50QG1402 awarded by the Deutsche Zentrum für Luft- und Raumfahrt e.V. (DLR).
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