Pacôme Delva - Academia.edu (original) (raw)
Papers by Pacôme Delva
The Twelfth Marcel Grossmann Meeting, 2012
In this paper we analyze some aspects of the "relativistic glider" proposed by Gu\'... more In this paper we analyze some aspects of the "relativistic glider" proposed by Gu\'eron and Mosna more in detail. In particular an explicit weak gravity and low velocity expansion is presented, the influence of different initial conditions are studied and the behavior of the glider over a longer integration time is presented. Our results confirm that the system can be used as a glider, but is not able to stop or even revert the fall of an object. Comment: 5 pages, 7 figures; minor corrections
2012 European Frequency and Time Forum, 2012
The Atomic Clocks Ensemble in Space (ACES/PHARAO mission), which will be installed on board the I... more The Atomic Clocks Ensemble in Space (ACES/PHARAO mission), which will be installed on board the International Space Station (ISS), uses a dedicated two-way MicroWave Link (MWL) in order to compare the timescale generated on board with those provided by many ground stations disseminated on the Earth. Phase accuracy and stability of this long range link will have a key role in the success of the ACES/PHARAO experiment. SYRTE laboratory is heavily involved in the design and development of the data processing software : from theoretical modelling and numerical simulations to the development of a software prototype. Our team is working on a wide range of problems that need to be solved in order to achieve high accuracy in (almost) real time. In this article we present some key aspects of the measurement, as well as current status of the software's development.
Our team in SYRTE-Observatoire de Paris is currently working on a software prototype for the proc... more Our team in SYRTE-Observatoire de Paris is currently working on a software prototype for the processing and analysis of the data coming from the microwave link of the ACES (Atomic Clocks Ensemble in Space) mission. The goal of the mission is to realize, in space, a very accurate and highly stable time scale that will be compared to ground clocks. A critical part of this project is the time and frequency transfer between the ground and space stations: this will rely heavily on the microwave link, so it is critical to find a robust and accurate algorithm for this task.
Classical and Quantum Gravity, 2009
In this paper the effects of vibrations at high frequencies onto a freely falling two-body system... more In this paper the effects of vibrations at high frequencies onto a freely falling two-body system in Schwarzschild spacetime are investigated. As reference motion of the same system without vibrations a circular orbit around the central body is considered. The vibrations induce a perturbation on this motion, whose period is close to the orbital period, in agreement with the simpler situation of the Shirokov effect [1]. In general relativity the amplitude of the perturbation is dominated by high velocity effects, which grow linearly in the radius r of the circular orbit, while the leading term surviving the Newtonian limit decays as 1/r. Thus even for very large radii a significant difference between Newtonian physics and general relativity is found. We give an estimate of this effect for some molecular vibrations of a system orbiting around the Earth.
arXiv preprint arXiv:1106.3168, Jun 16, 2011
Abstract: A relativistic positioning system has been proposed by Bartolom\'e Coll in 2002. S... more Abstract: A relativistic positioning system has been proposed by Bartolom\'e Coll in 2002. Since then, several group developed this topic with different approaches. I will present a work done in collaboration with Ljubljana University and the ESA Advanced Concepts Team. We developed a concept, Autonomous Basis of Coordinates, in order to take advantage of the full autonomy of a satellite constellation for navigation and positioning, by means of satellite inter-links. I will present the advantages of this new paradigm and a ...
The need for defining our position in space and time is an ancient one and its realization has de... more The need for defining our position in space and time is an ancient one and its realization has developed in millennium according to human understanding of the world and according to technology available to further such understanding. The commonly used global coordinates, the geographic longitude and latitude, or the astronomical right ascension and declination were carefully defined with respect to Earth rotation axis and a point on the equator, conveniently chosen in such a way that it can be most easily and accurately realized by ...
Advances in Space Research, 2011
In this article we model a Global Navigation Satellite System (GNSS) in a Schwarzschild spacetime... more In this article we model a Global Navigation Satellite System (GNSS) in a Schwarzschild spacetime, as a first approximation of the relativistic geometry around the Earth. The closed time-like and scattering light-like geodesics are obtained analytically, describing respectively trajectories of satellites and electromagnetic signals. We implement an algorithm to calculate Schwarzschild coordinates of a GNSS user who receives proper times sent by four satellites, knowing their orbital parameters; the inverse procedure is implemented to check for consistency. The constellation of satellites therefore realizes a geocentric inertial reference system with no a priori realization of a terrestrial reference frame. We show that the calculation is very fast and could be implemented in a real GNSS, as an alternative to usual post-Newtonian corrections. Effects of non-gravitational perturbations on positioning errors are assessed, and methods to reduce them are sketched. In particular, inter-links between satellites could greatly enhance stability and accuracy of the positioning system.
PHYSICAL REVIEW LETTERS 1, 2018
We report on a new test of the gravitational redshift and thus of local position invariance, an i... more We report on a new test of the gravitational redshift and thus of local position invariance, an integral part
of the Einstein equivalence principle, which is the foundation of general relativity and all metric theories
of gravitation. We use data spanning 1008 days from two satellites of Galileo, Europe’s global satellite
navigation system, which were launched in 2014, but accidentally delivered on elliptic rather than circular
orbits. The resulting modulation of the gravitational redshift of the onboard atomic clocks allows the
redshift determination with high accuracy. Additionally, specific laser ranging campaigns to the two
satellites have enabled a good estimation of systematic effects related to orbit uncertainties. Together with a
careful conservative modelling and control of other systematic effects we measure the fractional deviation of
the gravitational redshift from the prediction by general relativity to be ð0.19 2.48Þ × 10−5 at 1 sigma,
improving the best previous test by a factor 5.6. To our knowledge, this represents the first reported
improvement on one of the longest standing results in experimental gravitation, the Gravity Probe A
hydrogen maser rocket experiment back in 1976
The Twelfth Marcel Grossmann Meeting, 2012
In this paper we analyze some aspects of the "relativistic glider" proposed by Gu\'... more In this paper we analyze some aspects of the "relativistic glider" proposed by Gu\'eron and Mosna more in detail. In particular an explicit weak gravity and low velocity expansion is presented, the influence of different initial conditions are studied and the behavior of the glider over a longer integration time is presented. Our results confirm that the system can be used as a glider, but is not able to stop or even revert the fall of an object. Comment: 5 pages, 7 figures; minor corrections
2012 European Frequency and Time Forum, 2012
The Atomic Clocks Ensemble in Space (ACES/PHARAO mission), which will be installed on board the I... more The Atomic Clocks Ensemble in Space (ACES/PHARAO mission), which will be installed on board the International Space Station (ISS), uses a dedicated two-way MicroWave Link (MWL) in order to compare the timescale generated on board with those provided by many ground stations disseminated on the Earth. Phase accuracy and stability of this long range link will have a key role in the success of the ACES/PHARAO experiment. SYRTE laboratory is heavily involved in the design and development of the data processing software : from theoretical modelling and numerical simulations to the development of a software prototype. Our team is working on a wide range of problems that need to be solved in order to achieve high accuracy in (almost) real time. In this article we present some key aspects of the measurement, as well as current status of the software's development.
Our team in SYRTE-Observatoire de Paris is currently working on a software prototype for the proc... more Our team in SYRTE-Observatoire de Paris is currently working on a software prototype for the processing and analysis of the data coming from the microwave link of the ACES (Atomic Clocks Ensemble in Space) mission. The goal of the mission is to realize, in space, a very accurate and highly stable time scale that will be compared to ground clocks. A critical part of this project is the time and frequency transfer between the ground and space stations: this will rely heavily on the microwave link, so it is critical to find a robust and accurate algorithm for this task.
Classical and Quantum Gravity, 2009
In this paper the effects of vibrations at high frequencies onto a freely falling two-body system... more In this paper the effects of vibrations at high frequencies onto a freely falling two-body system in Schwarzschild spacetime are investigated. As reference motion of the same system without vibrations a circular orbit around the central body is considered. The vibrations induce a perturbation on this motion, whose period is close to the orbital period, in agreement with the simpler situation of the Shirokov effect [1]. In general relativity the amplitude of the perturbation is dominated by high velocity effects, which grow linearly in the radius r of the circular orbit, while the leading term surviving the Newtonian limit decays as 1/r. Thus even for very large radii a significant difference between Newtonian physics and general relativity is found. We give an estimate of this effect for some molecular vibrations of a system orbiting around the Earth.
arXiv preprint arXiv:1106.3168, Jun 16, 2011
Abstract: A relativistic positioning system has been proposed by Bartolom\'e Coll in 2002. S... more Abstract: A relativistic positioning system has been proposed by Bartolom\'e Coll in 2002. Since then, several group developed this topic with different approaches. I will present a work done in collaboration with Ljubljana University and the ESA Advanced Concepts Team. We developed a concept, Autonomous Basis of Coordinates, in order to take advantage of the full autonomy of a satellite constellation for navigation and positioning, by means of satellite inter-links. I will present the advantages of this new paradigm and a ...
The need for defining our position in space and time is an ancient one and its realization has de... more The need for defining our position in space and time is an ancient one and its realization has developed in millennium according to human understanding of the world and according to technology available to further such understanding. The commonly used global coordinates, the geographic longitude and latitude, or the astronomical right ascension and declination were carefully defined with respect to Earth rotation axis and a point on the equator, conveniently chosen in such a way that it can be most easily and accurately realized by ...
Advances in Space Research, 2011
In this article we model a Global Navigation Satellite System (GNSS) in a Schwarzschild spacetime... more In this article we model a Global Navigation Satellite System (GNSS) in a Schwarzschild spacetime, as a first approximation of the relativistic geometry around the Earth. The closed time-like and scattering light-like geodesics are obtained analytically, describing respectively trajectories of satellites and electromagnetic signals. We implement an algorithm to calculate Schwarzschild coordinates of a GNSS user who receives proper times sent by four satellites, knowing their orbital parameters; the inverse procedure is implemented to check for consistency. The constellation of satellites therefore realizes a geocentric inertial reference system with no a priori realization of a terrestrial reference frame. We show that the calculation is very fast and could be implemented in a real GNSS, as an alternative to usual post-Newtonian corrections. Effects of non-gravitational perturbations on positioning errors are assessed, and methods to reduce them are sketched. In particular, inter-links between satellites could greatly enhance stability and accuracy of the positioning system.
PHYSICAL REVIEW LETTERS 1, 2018
We report on a new test of the gravitational redshift and thus of local position invariance, an i... more We report on a new test of the gravitational redshift and thus of local position invariance, an integral part
of the Einstein equivalence principle, which is the foundation of general relativity and all metric theories
of gravitation. We use data spanning 1008 days from two satellites of Galileo, Europe’s global satellite
navigation system, which were launched in 2014, but accidentally delivered on elliptic rather than circular
orbits. The resulting modulation of the gravitational redshift of the onboard atomic clocks allows the
redshift determination with high accuracy. Additionally, specific laser ranging campaigns to the two
satellites have enabled a good estimation of systematic effects related to orbit uncertainties. Together with a
careful conservative modelling and control of other systematic effects we measure the fractional deviation of
the gravitational redshift from the prediction by general relativity to be ð0.19 2.48Þ × 10−5 at 1 sigma,
improving the best previous test by a factor 5.6. To our knowledge, this represents the first reported
improvement on one of the longest standing results in experimental gravitation, the Gravity Probe A
hydrogen maser rocket experiment back in 1976