48 research outputs found
General Relativity with the two Galileo satellites DORESA and MILENA
No full textG4S_2.0 is a new project funded by the Italian Space Agency which aims to perform measurements in the field of Fundamental Physics with two satellites, DORESA and MILENA, of the Galileo-FOC constellation.
These satellites are characterized by the high eccentricity of their orbits and the accuracy of their atomic clocks. For these characteristics, they have recently been used to improve a previous measurement of gravitational redshift (GRS) by Gravity Probe-A in 1980 ([1]). GRS, which is a local position-invariance test, is only one of the predictions of General Relativity (GR) that can be tested with the Galileo constellation. In particular, the G4S_2.0 project aims to provide a new measurement of GRS and to measure relativistic precessions of the elliptical orbits. These results will place new constraints on possible alternative theories of gravitation, both metric and non-metric in their structure. Furthermore, constraints on the presence of Dark Matter in our Galaxy can be placed by analyzing the data of the constellation's atomic clocks.
In this framework a fundamental point is obtaining a satellite orbit solution precise as far as possible. For this purpose, we focus firstly on the precise orbit determination and on a dynamic model for the non-conservative forces acting on these satellites. In particular, the model manages the perturbing effects produced by the direct solar radiation pressure (the major perturbation), the Earth's infrared radiation and the Earth-albedo.
The results of G4S_2.0 project will extend the number of tests of Einstein's Theory of GR that can be achieved with Galileo satellites.
[1] Vessot R.F.C. et al., (1980) Test of relativistic gravitation with a spaceborne hydrogen maser. Phys Rev Lett 45(26):2081–2084. https://doi. org/ 10. 1103/ Phys. Rev. Lett. 45. 2081
Fundamental physics with the Galileo FOC satellites and the G4S_2.0 project
No full textThis Thesis has been developed within the Galileo for Science Project (G4S_2.0) since its beginning in 2021. The G4S_2.0 is an ongoing project developed under the auspices of the Italian Space Agency (ASI) in collaboration with the National Institute for Astrophysics (INAF) and Politecnico di Torino. The project has several goals in the field of Fundamental Physics by exploiting the Global Navigation Satellite System (GNSS) Galileo, in particular the Full Operational Capability (FOC) Constellation. The relatively high eccentricity (≃ 0.16) of the two FOC in elliptical orbits, GSAT0201 and GSAT0202, and the accuracy of their atomic clocks allow to measure the gravitational redshift and the relativistic precessions of the orbits. Furthermore, the analysis of the atomic clock data of the entire Galileo FOC constellation also allows us to probe the presence of DomainWall (DW) Dark matter in the Milky Way and to place severe constraints on their interaction with ordinary matter.
This work outlines the state of the art of the G4S_2.0 activities necessary for the gravitational redshift and the relativistic precessions measurements and for Dark Matter constraints. For all these measurements, a fundamental point is to obtain a suitable satellite orbit solution by performing an accurate Precise Orbit Determination (POD) with a reliable estimate of the clock-bias of the onboard atomic clocks. This work presents the efforts to achieve this, starting with the development of a dynamical model to account for the complex effects of the non-gravitational
perturbations, in particular those related to the direct solar radiation pressure, and performing dedicated PODs to test our results. Based on the PODs results, we requested a dedicated Satellite Laser Ranging campaign to the International Laser Ranging Service to improve the available number of laser observations, given their importance for some of the G4S_2.0 measurements.
Regarding Dark Matter constraints, this work describes the strategy adopted to analyse the on-board atomic clock data, stressing the original statistical approach: a physical simulation pipeline is developed to simulate the interaction between a set of Galileo FOC satellites and a DW, allowing the study of the detection efficiency of the considered clock-network.
Finally, we present our reflections and prospects for the future
The Galileo for science (G4S_2.0) project: fundamental physics experiments with the Galileo satellites Doresa and Milena
No full textG4S_2.0 is a new project funded by the Italian Space Agency which aims to perform measurements in the field of Fundamental Physics with the two satellites DORESA and MILENA of the Galileo-FOC constellation. These satellites are characterized by the high eccentricity of their orbits and the accuracy of their atomic clocks. An accurate orbit determination will allow to carry out a series of measurements in the fields of gravitation and cosmology, and the implementation of an inverse relativistic positioning system. After a general introduction to the main objectives of G4S_2.0, the activities developed at IAPS-INAF in Rome will be presented
The Galileo satellites Doresa and Milena and their goals in the field of fundamental physics within the Galileo for science (G4S_2.0) project
No full textThe G4S_2.0 (Galileo for Science) project is a new proposal funded by the Italian Space Agency (ASI) and aims to perform a set of measurements in the field of Fundamental Physics with the two Galileo satellites DORESA and MILENA. Indeed, the accurate analysis of the orbits of these satellites — characterized by a relatively high eccentricity of about 0.16 — and of their clocks — the most accurate orbiting the Earth — allows to test relativistic gravity by comparing the predictions of Einstein's theory of General Relativity with those of other theories of gravitation. After a general introduction to the project objectives, we will present the preliminary activities of G4S_2.0 which are being developed by IAPS-INAF in Rome. The results of G4S_2.0 will be particularly useful for the applications of the Galileo FOC satellites in the fields of space geodesy and geophysics as some of these activities will concern the improvement of the precise orbit determination of the satellites through an enhancement of the dynamic model of their orbits, analyzing, in particular, the modelling of non-conservative forces
The SaToR-G experiment: testing metric and non-metric theories of gravity in the Earth’s field via laser tracking to geodetic satellites
No full textSatellite Tests of Relativistic Gravity (SaToR-G) is a new experiment in fundamental physics of the National
Scientific Committee 2 (CSN2) of the Italian National Institute for Nuclear Physics (INFN).
The experiment aims at testing gravitation beyond the predictions of Einstein’s Theory of General Relativity
in its weak-field and slow-motion limit, searching for effects foreseen by alternative theories of gravitation
and possibly connected with ‘’new physics’’. The predictions of General Relativity on the orbits of geodetic
satellites, which play the role of test masses, will be compared with those of alternative theories of gravity
both metric and non-metric in their essence. This will allow to test, in addition to other aspects of gravita tion, the field equation of gravity. The natural theoretical framework to test gravitation will be that of the Parameterized Post-Newtonian (PPN) formalism. However, we will also try to apply, as far as possible, the approach suggested by R. H. Dicke more than 50 years ago, usually referred to as the Dicke framework. This is a fairly general framework that allows us to conceive experiments not connected, a priori, with a given physical theory and also provides a way to analyze the results of an experiment under primary hypotheses.
The activities of the experiment related to the development of perturbative models to better determine the dynamics of the orbits of the considered satellites will be presented together with preliminary results on possible
new constraints to alternative theories of gravitation
Fundamental physics measurements with Galileo FOC satellites and the Galileo for science project. I. A 3D-CAD and a box wing for modeling the effects of nonconservative forces
No full textThis paper introduces the main problems related to the modeling of the effects of nongravitational perturbations on satellites of the Galileo FOC constellation. The problem is addressed from the point of view of the scientific objectives of the Galileo for Science (G4S_2.0) project. These objectives are reflected in a set of fundamental physics measurements that will exploit the orbits and atomic clocks aboard the Galileo satellites, in particular the GSAT-0201 and GSAT-0202 satellites characterized by elliptical orbits, and not by almost circular orbits such as in the case of the remaining satellites of the constellation. The main focus is on the modeling of the direct solar radiation pressure, the largest nongravitational perturbation on GNSS satellites. After an in-depth presentation of the main nongravitational perturbations of interest, and of the models currently in use in the literature for their consideration, the work focuses on the amplitudes of the different effects and, with particular attention, on their intrinsic knowledge. Finally, two different models are introduced for the structure of the Galileo satellite specially developed for the objectives of G4S_2.0. The first is a simple model of the box-wing type, developed on the basis of the information currently available on the characteristics of the satellite. The second is a 3D model of the Galileo spacecraft, somewhat sophisticated due to the richness of the details on the structure and the various elements that make up the surfaces of the satellite. The activities carried out and in progress with these models and those planned with their subsequent updated versions are described
The G4S\_2.0 Project: state of the art and SLR Campaign.
No full textGalileo for Science (G4S_2.0), funded by ASI, has several goals in the fields of Fundamental Physics and Cosmology: i) new measurement of gravitational redshift, ii) measurement of relativistic precessions on the two Galileo FOC satellites in eccentric orbit, iii) constraints on Dark Matter in the Milky Way, iv) Relativistic Positioning System, v) development of new models for non-gravitational forces and vi) development of a new accelerometer concept for a next generation of Galileo satellites. The state of the art of the project will be presented in terms of development of perturbation models, orbit determination and clock-bias analysis in relation to dark matter constraints. Finally, the characteristics of the SLR observation campaign agreed with the ILRS will be highlighted
The Galileo for science (G4S 2.0) project. Measurement of the gravitational redshift with the Galileo satellites DORESA and MILENA
No full textThe G4S 2.0 project represents an important opportunity to perform fundamental physics measurements with the two Galileo-FOC satellites DORESA and MILENA in elliptic orbits. In this paper, we discuss the possibility to improve the current constraints on local position invariance via a new measurement of the gravitational redshift, taking into account both a new model of the satellites and more in-depth considerations on non-gravitational perturbations
Modeling of non-conservative forces for the Galileo-FOC spacecraft
No full textSuboptimal modeling of direct Solar Radiation Pressure (SRP) is currently the main source of error in determining the orbit of any type of spacecraft of the Global Navigation Satellite System (GNSS). The complex shape of these satellites (bus and wings) combined with their particular attitude law – which requires the face of the satellite that collects the different antennas to continuously point to the nadir and deep space the face near which the atomic clocks are located, while at the same time the array of solar panels must continuously point towards the Sun for energy reasons – make the modeling of this perturbation and its optimal insertion into the Precise Orbit Determination (POD) process a non-trivial issue. We will present the results for the perturbative accelerations produced by solar and terrestrial (albedo and infrared) radiation in the case of a Box-Wing model built using the ESA Galileo metadata. The Yaw Steering law for the spacecraft attitude was also include in our model. The Box-Wing model and a 3D model of the satellite were also incorporated into the s/w COMSOL for a preliminary activity on the use of the Ray-tracing technique. Our final aim is, in fact, to build a Finite Element Model of the satellite and apply an ad hoc Ray-tracing for the calculation of the different perturbations related to the radiation pressure, also considering umbra and penumbra effects and multiple reflections. This activity is part of those of the Galileo for Science project (G4S 2.0) funded by ASI. The main objectives of G4S 2.0 are in the field of Fundamental Physics and a POD of the Galileo satellites based on a reliable dynamic model, in particular for Doresa and Milena, the two satellites in elliptical orbit, is of primary importance
Measurement in the field of gravitation of the Galileo for science project
No full textThe Galileo for Science (G4S 2.0) project, funded by the Italian Space Agency (ASI), aims to perform a set of gravitational measurements with the two Galileo satellites GSAT-0201 (Doresa) and GSAT-0202 (Milena) exploiting the relatively high eccentricity of their orbits with respect to that of the other satellites of the Full Operational Capability (FOC) constellation. These two satellites have been already used in 2018 by both ZARM and SYRTE for a new measurement of the gravitational redshift (GRS) that has improved the 1976 measurement of Gravity Probe A by a factor between 4 and 6 respectively. In fact, from an accurate analysis of the orbits and clocks of these two Galileo satellites, a set of relativistic tests can be performed with the objectives of comparing the predictions of Einstein’s theory of General Relativity with those of other gravitational theories concerning, mainly, the motion of a test particle along a geodesic of space-time and the time dilation of the on-board clocks. Three Italian research institutes are involved in G4S 2.0: Center for Space Geodesy (ASI-CGS) in Matera, Istituto di Astrofisica e Planetologia Spaziali (IAPS-INAF) in Roma and Politecnico (POLITO) in Torino. We will present some of the ongoing activities at IAPS-INAF in the field of tests and measurements of gravitational interaction. Among these, the possibility of measuring the relativistic precessions of the orbits of the satellites, the constraints on a possible long-range force at a scale comparable to the semi-major axis of the satellite orbit and, consequently, on the validity of the Newtonian inverse square law and, finally, on the validity of the Local Position Invariance (i.e., a measurement of the GRS), that is one of the three ingredients that constitute, in its modern conception, Einstein’s Principle of Equivalence. A key aspect, to perform such measurements in the field of fundamental physics, is to improve the dynamic model for the non-conservative forces acting on the Galileo FOC satellites, starting from that of the solar radiation pressure, the largest non-gravitational perturbation on navigation satellite
