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Fundamental physics with the Galileo FOC satellites and the G4S_2.0 project
Get PDFThis 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
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
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
Get PDFThis 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
First results in testing gravity theories with SatoR-G
No full textThe main goal of the SaToR-G (Satellite Test of Relativistic Gravity) experiment is to test and verify gravity beyond the predictions of General Relativity (GR) by focusing on possible effects connected with "new physics" and foreseen by different alternative theories of gravitation. These theories may be both metric and non-metric in their consequences. This objective can be achieved by means of a Precise Orbit Determination of the two LAGEOS and LARES satellites based on an improved dynamical model of their orbits. This implies to consider these passive geodetic satellites as "quasi-ideal" proof masses and measuring the deviation of their trajectory from the pure geodesic motion predicted by GR. A very interesting aspect is represented by the possible existence of a new long-range interaction. This kind of effect in gravitation has some importance since it cannot be interpreted within the standard Parametrized Post-Newtonian formalism currently used in the weak-field and slow-motion limit of GR. Indeed, deviations of the gravitational potential from the Newtonian law would lead to new weak interactions between macroscopic objects that are predicted by several theories of gravity. For these theories, a Yukawa-like parameterization seems general at the lowest order of the interaction and in the non-relativistic limit, independently of the nature of the new field that contributes to mediate the gravitational interaction, that is, of a possible scalar, vector or tensor field. We first introduce the constraint on a Yukawa-like long-range force obtained in the case of LAGEOS II from a precise and accurate analysis of the long-term behavior of its orbit. We then show the possible constraints to alternative theories of gravitation that can be further deduced from this result
The Galileo for science (G4S 2.0) project: the measurement of the gravitational redshift 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 (E18) and MILENA (E14) of the Galileo-FOC constellation. Indeed, the orbits of these satellites are characterized by a relatively high eccentricity of about 0.16. After a general introduction to the main objectives of G4S 2.0, the preliminary activities developed at IAPS-INAF in Rome for the measurement of the gravitational redshift, based on the time bias analysis of accurate onboard atomic clocks, will be presented. This measurement will be a test for the validity of the local position invariance, one of the ingredients of Einstein’s principle of equivalence
The Galileo for science (G4S_2.0) project: precise orbit determination for fundamental physics and space geodesy
No full textG4S_2.0 is a project funded by the Italian Space Agency aiming to perform a set of Fundamental Physics measurements using the two Galileo FOC satellites GSAT0201 (Doresa) and GSAT0202 (Milena). Indeed, the orbits of these satellites are characterized by a relatively high eccentricity, about 0.16, which represents a good prerequisite for a series of tests and measurements concerning the predictions of different theories of gravitation, as compared with the General Relativity (GR) ones. The main objectives include a new measurement of the gravitational redshift effect of the on-board atomic clocks --- thanks to its modulation with the orbital period due to the high eccentricity of the orbits --- and the measurement of the main precessions of relativistic origin, primarily the Schwarzschild one.
To achieve these significant results, and possibly improve the current constraints of several theories of gravitation with respect to GR, it is of fundamental importance to take a step forward --- compared to the state of the art --- in the reliability of the dynamic model used for the orbits of the satellites and, as a direct consequence of this, in their precise orbit determination (POD). In this context, non-gravitational perturbations (NGPs) are the most subtle and difficult to model because of the complex shape of the Galileo satellites and their attitude law. In this regard, the main challenge is represented by a more refined and reliable model for the direct solar radiation pressure (SRP), the largest NGP on Galileo satellites, as well as on every satellite of every GNSS constellation.
Our final goal is to build a finite element model (FEM) of the Galileo FOC spacecraft, as refined as possible, and apply a dedicated raytracing technique to it to compute the perturbing accelerations due to radiation pressure. In view of this, we have already developed a 3D-CAD model of the spacecraft. As an intermediate step, we have built a Box-Wing (BW) model based on the relatively poor information presently available on the geometrical and physical properties of the spacecraft. This BW model has been used to compute the perturbing accelerations due to the direct SRP and to the Earth's albedo and infrared radiation. The results obtained for the accelerations, to be included in the POD process, will be presented in various cases. Then, by computing the residuals in the orbital elements, it will be possible to verify the goodness of the POD results and observe the expected progressive improvement starting from the BW model towards the FEM one. The present analyses were made using the nominal attitude law of the Galileo FOC spacecraft; the application of this law will be discussed in the case of satellites in elliptical orbit. We finally highlight that the results of G4S_2.0 in terms of POD improvements are particularly useful for all applications of the Galileo FOC satellites in the fields of space Geodesy and Geophysics
Fundamental physics measurements with Galileo FOC satellites and the Galileo for science project. II. A box wing for modeling direct solar radiation pressure and preliminaries orbit determinations
Get PDFThis paper concerns the development of a first simplified model to take into account the perturbations produced by the nongravitational forces acting on the satellites of the Galileo FOC constellation and the corresponding first orbital determinations within the G4S_2.0 project. G4S_2.0 has a series of objectives in verifying the gravitational interaction in the weak field limit of the theory of general relativity, exploiting in particular the eccentricity of the orbits of some Galileo FOC satellites and the precise measurements that can be derived from the atomic clocks on board these satellites. The study focused on the model for the acceleration produced by direct solar radiation pressure on the satellites. This is the largest of all nongravitational perturbations. It is therefore necessary to build a sufficiently accurate model for it before being able to seriously consider smaller perturbation effects, such as those related to terrestrial radiation and thermal thrust effects. The work presents new aspects in the literature of navigation satellites. One of these is the determination of the effects in the Keplerian elements produced by the direct solar acceleration obtained from a box -wing model of the satellite. A second aspect is the comparison of these predictions in the orbital elements with the corresponding orbital residuals achieved from an orbit determination of the satellite. The study therefore highlights even more the importance of being able to improve the model of the perturbation originating from solar radiation in the field of global navigation satellite systems. This is very important if one wants to extract gravitational measurements from the orbit and clock -bias measurements of these satellites to verify the predictions of general relativity and compare them with those of alternative theories of gravitation
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