Practical relativistic clock synchronization for high-accuracy space astrometry

International audienceFuture high-accuracy space astrometry missions, such as Gaia and SIM, will need a time-tagging of observations consistent with General Relativity nowadays used as standard background for global data processing scheme. In this work, we are focusing on the realization of the onboard time scale. The onboard clock, being not ideal and consequently tainted with systematic biases, has to be carefully calibrated to the ideal relativistic proper time of the satellite. We present here a modeling of this essential step to provide a reliable relation between the onboard time and TCB, a time scale suitable for global data processing

The Astronomical Virtual Observatory and application to Earth's sciences

International audienc

Multipath effect evaluation

International audienceACES-TN-SYRTE-FM-00

The Astronomical Virtual Observatory and application to Earth's sciences

International audienc

Determining the relativistic parameter γ using very long baseline interferometry

International audienc

Determining the relativistic parameter γ using very long baseline interferometry

International audienc

On general relativity tests with the VLBI

International audienceRelativistic bending in the vicinity of a massive body is characterized only by the post-Newtonian parameter gamma within the standard parameterized post-Newtonian formalism, which is unity in General Relativity. To estimate this parameter, we use very long baseline interferometry (VLBI) to measure the gravitational deflection of radio waves by Solar System bodies emitted by distant compact radio sources

Multipath effect evaluation

International audienceACES-TN-SYRTE-FM-00

Numerical study of relativistic frequency shift for cold-atom clock experiments in space

International audienceThis paper is motivated by the development of several space missions using an Earth-orbit laser-cooled atomic clock, providing a time-keeping accuracy of the order of 10−1610−18 in fractional frequency. We focus here on a particular part of the future data processing, namely the relativistic effects on frequency shift. These effects appear to be numerous and intricate, and it is important to precisely quantify their order of magnitude. Obviously, at this level of accuracy, a detailed analysis of all natural or artificial potential sources of error is required, and such a study is still missing at this time. We present here a numerical study of one-way relativistic frequency shifts of orders 1/c2, 1/c3 and 1/c4. These shifts are computed in the case of the ACES mission, i.e. a clock aboard the International Space Station and passing above a mid-latitude observing site. We obtain orders of magnitude for all interesting relativistic effects. We show that the influence on frequency shift of the mass quadrupole moment J2 of the Earth at the order 1/c3 has an amplitude around 10−18, below the expected sensitivity of ACES but close to the one of future missions such as RACE

On general relativity tests with the VLBI

International audienceRelativistic bending in the vicinity of a massive body is characterized only by the post-Newtonian parameter gamma within the standard parameterized post-Newtonian formalism, which is unity in General Relativity. To estimate this parameter, we use very long baseline interferometry (VLBI) to measure the gravitational deflection of radio waves by Solar System bodies emitted by distant compact radio sources