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A breakdown of Lorentz Invariance is predicted by some theories as a result of quantum physics applied to gravity or for the presence of vector/tensor fields, beside the metric tensor of General Relativity, mediating the gravitational interaction. A violation of Lorentz Invariance would manifest itself, in the gravitational sector, mainly through a non-zero value of the post-Newtonian parameter $\alpha_1$, that is null in General Relativity. In this paper we describe a test of Local Lorentz Invariance considering the effect of a possible preferred frame, that of the cosmic microwave background, on the orbit of the LAGEOS II satellite tracked by the Satellite Laser Ranging technique. We constrain this parameter down to the level of $3\times10^{-5}$, improving a previous limit obtained through the Lunar Laser Ranging technique., Comment: 6 pages, 4 figures. Under review in Physical Review Letters

The Italian Spring Accelerometer (ISA) is a three axis mass-spring accelerometer, one of the payloads of the BepiColombo joint space mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). At launch in October 2018, BepiColombo started its seven-year cruise as a stack of three different modules, overall named Mercury Composite Spacecraft (MCS). The spacecraft will provide BepiColombo the necessary Delta V to reach Mercury with its electric thrusters and along with one, two and six gravity assists, respectively with Earth, Venus and Mercury. The accelerometer is accommodated on the Mercury Planetary Orbiter (MPO) module and, jointly with the Ka-band Transponder (KaT) tracking data, will primarily serve the BepiColombo Radio Science Experiment (BC-RSE). During the second Venus swing-by, strong tidal effect and external perturbations was expected to act on the spacecraft and to become detectable by ISA. The swing-by had a closest approach of about 550 km and the gravity gradient expected on the IDA sensing elements was perfectly measured. Hence, in this paper, the first direct Gravity Gradient effect detection generated by an extraterrestrial body is shown. Nevertheless, around the closest approach, the measurements evidenced a spurious acceleration event lasting for several minutes. This work, exploiting information on the Attitude and Orbit Control System (AOCS) commanded torques, focuses and analyses this ISA acceleration signal, ascribing it to a net force really acting on the MCS spacecraft. Furthermore, using an estimation method, the application point of the force is confined to an area close to the MPO radiator., Comment: 14 pages, 12 figures

We present a new measurement of the Lense-Thirring effect on the orbits of the geodetic satellites LAGEOS, LAGEOS II and LARES. This secular precession is a general relativity effect produced by the gravitomagnetic field of the Earth generated by its rotation. The effect is a manifestation of spacetime curvature generated by mass-currents, a peculiarity of Einstein's theory of gravitation. This measurement stands out, compared to previous measurements in the same context, for its precision ($\simeq7.4\times10^{-3}$) and accuracy ($\simeq16\times10^{-3}$), i.e. for a reliable and robust evaluation of the systematic sources of error due to both gravitational and non-gravitational perturbations. For this new measurement, we have largely exploited the results of GRACE mission to significantly improve the description of the gravitational field of the Earth, by also modeling its time dependence. In this way, we strongly reduced the systematic errors due to the uncertainty in the knowledge of the Earth even zonal harmonics and, at the same time, avoided a possible bias of the final result and, consequently, of the precision of the measurement, linked to a non-reliable handling of the unmodeled and mismodeled periodic effects.

The paper presents the results of an ambient vibration monitoring campaign conducted on so-called Clock Tower (Torre delle Ore), one the best known and most visited monuments in the historic centre of Lucca. The vibrations of the tower were continuously monitored from November 2017 to March 2018 using high-sensitivity instrumentation. In particular, four seismic stations provided by the Istituto Nazionale di Geofisica e Vulcanologia and two three-axial accelerometers developed by AGI S.r.l., spin-off of the Istituto Nazionale di Astrofisica, were installed on the tower. The measured vibration level was generally very low, since the structure lies in the middle of a limited traffic area. Nevertheless, the availability of two different types of highly sensitive and accurate instruments allowed the authors to follow the dynamic behaviour of the tower during the entire monitoring period and has moreover provided cross-validation of the results.

Recent results of the LARASE research program in terms of models improvements and relativistic measurements are presented. In particular, the results regarding the development of new models for the non-gravitational perturbations that affect the orbit of the LAGEOS and LARES satellites are described and discussed. These are subtle and complex effects that need a deep knowledge of the structure of the satellite and of its physical characteristics in order to be correctly accounted for. In the field of gravitational measurements, we introduce a new and precise measurement of the relativistic Lense-Thirring precession. The role of the errors related to the knowledge of the gravitational field of the Earth in this kind of measurements is also discussed. Finally, the main results in relativistic measurements and constraints obtained during the last few years by means of the laser tracking of passive satellites are summarized. The key role of the Satellite Laser Ranging technique in these activities is highlighted, together with the sinergy it produces between space geodesy and fundamental physics measurements.

The two LAGEOS and LARES are laser-ranged satellites tracked with the best accuracy ever achieved. Using their range measurements many geophysical parameters were calculated and some General Relativity effects were directly observed. To obtain precise and refined measurements of the effects due to the predictions of General Relativity on the orbit of these satellites, it is mandatory to model with high precision and accuracy all other forces, reducing the free parameters introduced in the orbit determination. A main category of non-gravitational forces to be considered are those of thermal origin, whose fine modeling strongly depends on the knowledge of the evolution of the spin vector. We present a complete model, named LASSOS, to describe the evolution of the spin of the LAGEOS and LARES satellites. In particular, we solved Euler equations of motion considering not-averaged torques. This is the most general case, and the predictions of the model well fit the available observations of the satellites spin. We also present the predictions of our model in the fast-spin limit, based on the application of averaged equations. The results are in good agreement with those already published, but with our approach we have been able to highlight small errors within these previous works. LASSOS was developed within the LARASE research program. LARASE aims to improve the dynamical model of the two LAGEOS and LARES satellites to provide very precise and accurate measurements of relativistic effects on their orbit, and also to bring benefits to geophysics and space geodesy.

We examine quantum corrections of time delay arising in the gravitational field of a spinning oblate source. Low-energy quantum effects occurring in Kerr geometry are derived within a framework where general relativity is fully seen as an effective field theory. By employing such a pattern, gravitational radiative modifications of Kerr metric are derived from the energy-momentum tensor of the source, which at lowest order in the fields is modelled as a point mass. Therefore, in order to describe a quantum corrected version of time delay in the case in which the source body has a finite extension, we introduce a hybrid scheme where quantum fluctuations affect only the monopole term occurring in the multipole expansion of the Newtonian potential. The predicted quantum deviation from the corresponding classical value turns out to be too small to be detected in the next future, showing that new models should be examined in order to test low-energy quantum gravity within the solar system., Comment: 12 pages, 1 figure

The use of four Lagrange points of the Sun/Earth system for fundamental physics experiments in space is presented. L1, L2, L4 and L5 rotating rigidly together with the Earth form a natural reference frame at the scale of the inner solar system. The idea which is discussed in the paper considers the possibility of locating four spacecraft in the four cited Lagrange points and exchanging electromagnetic pulses among them. Including stations on earth, various closed paths for the pulses are possible. Time of flight measurements would be performed. The time of flight difference between right- and left-handed circuits is proportional to the angular momentum of the Sun and the detection of the effect would reach accuracies better than 1% depending on the accuracy of the clock. The four points could also be used as "artificial pulsars" for a relativistic positioning system at the scale of the solar system. Additional interesting possibilities include detection of a galactic gravito-magnetic field and also, using a global configuration as a zero area Sagnac contour, detection of gravitational waves. More opportunities are also mentioned., Comment: 28 pages, 2 figures

The laser-ranged satellite LARES is expected to provide new refined measurements of relativistic physics, as well as significant contributions to space geodesy and geophysics. The very low area-to-mass ratio of this passive and dense satellite was chosen to reduce as much as possible the disturbing effects of non-gravitational perturbations. However, because of its height, about 1450 km compared with about 5800-5900 km for the two LAGEOS satellites, LARES is exposed to a much stronger drag due to neutral atmosphere. From a precise orbit determination, analyzing the laser ranging normal points of LARES over a time span of about 3.7 years, it was found an average semi-major axis decay rate of -0.999 m per year, corresponding to a non-conservative net force with a mean along-track acceleration of -1.444 x 10^-11 m/s^2. By means of a modified version of the SATRAP (ISTI/CNR) code, the neutral drag perturbation acting on LARES was evaluated over the same time span, taking into account the real evolution of solar and geomagnetic activities, with five thermospheric density models. All of them were able to model most of the observed semi-major axis decay, with differences among the average drag coefficients smaller than 10%. A further independent check carried out analyzing the orbital decay of a passive spherical satellite (Ajisai) just 40 km higher than LARES, it was then concluded that some of the currently best models developed for neutral atmosphere, within their uncertainties and range of applicability, were able to account for most (about 98.6%) of the observed semi-major axis decay of LARES. Finally, after modeling the neutral atmosphere drag, a residual semi-major axis decay, corresponding to an average along-track acceleration of about -2 x 10^-13 m/s^2 (i.e. about 1/72 of neutral drag), was detected as well.

In the course of the selection of the scientific themes for the second and third L-class missions of the Cosmic Vision 2015-2025 program of the European Space Agency, the exploration of the ice giant planets Uranus and Neptune was defined "a timely milestone, fully appropriate for an L class mission". Among the proposed scientific themes, we presented the scientific case of exploring both planets and their satellites in the framework of a single L-class mission and proposed a mission scenario that could allow to achieve this result. In this work we present an updated and more complete discussion of the scientific rationale and of the mission concept for a comparative exploration of the ice giant planets Uranus and Neptune and of their satellite systems with twin spacecraft. The first goal of comparatively studying these two similar yet extremely different systems is to shed new light on the ancient past of the Solar System and on the processes that shaped its formation and evolution. This, in turn, would reveal whether the Solar System and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation. A space mission to the ice giants would also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy. Finally, such a mission would allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and on the behaviour of the solar wind and the interplanetary magnetic field., Comment: 29 pages, 4 figures; accepted for publication on the special issue "The outer Solar System X" of the journal Planetary and Space Science. This article presents an updated and expanded discussion of the white paper "The ODINUS Mission Concept" (arXiv:1402.2472) submitted in response to the ESA call for ideas for the scientific themes of the future L2 and L3 space missions

The purpose of this document is to discuss the scientific case of a space mission to the ice giants Uranus and Neptune and their satellite systems and its relevance to advance our understanding of the ancient past of the Solar System and, more generally, of how planetary systems form and evolve. As a consequence, the leading theme of this proposal will be the first scientific theme of the Cosmic Vision 2015-2025 program: What are the conditions for planetary formation and the emergence of life? In pursuing its goals, the present proposal will also address the second and third scientific theme of the Cosmic Vision 2015-2025 program, i.e.: How does the Solar System work? What are the fundamental physical laws of the Universe? The mission concept we will illustrate in the following will be referred to through the acronym ODINUS, this acronym being derived from its main fields of scientific investigation: Origins, Dynamics and Interiors of Neptunian and Uranian Systems. As the name suggests, the ODINUS mission is based on the use of two twin spacecraft to perform the exploration of the ice giants and their regular and irregular satellites with the same set of instruments. This will allow to perform a comparative study of these two systems so similar and yet so different and to unveil their histories and that of the Solar System., Comment: White paper submitted in response to the ESA's call for scientific themes for the L2 and L3 missions. The white paper is also available on the ESA's website (http://sci.esa.int/jump.cfm?oid=52030) and on the ODINUS website (http://odinus.iaps.inaf.it)

The pericenter shift of a binary system represents a suitable observable to test for possible deviations from the Newtonian inverse-square law in favor of new weak interactions between macroscopic objects. We analyzed 13 years of tracking data of the LAGEOS satellites with GEODYN II software but with no models for general relativity. From the fit of LAGEOS II pericenter residuals we have been able to obtain a 99.8% agreement with the predictions of Einstein's theory. This result may be considered as a 99.8% measurement in the field of the Earth of the combination of the {\gamma} and {\beta} parameters of general relativity, and it may be used to constrain possible deviations from the inverse-square law in favor of new weak interactions parametrized by a Yukawa-like potential with strength {\alpha} and range {\lambda}. We obtained |{\alpha}|\lesssim1\times10-11, a huge improvement at a range of about 1 Earth radius.

In this paper we analyze quantitatively the concept of LAGEOS--type satellites in critical supplementary orbit configuration (CSOC) which has proven capable of yielding various observables for many tests of General Relativity in the terrestrial gravitational field, with particular emphasis on the measurement of the Lense--Thirring effect., Comment: LaTex2e, 20 pages, 7 Tables, 6 Figures. Changes in Introduction, Conclusions, reference added, accepted for publication in Classical and Quantum Gravity

A new proposal for the implementation of LARES mission is presented. In particular, a new observable is proposed and alternative scenarios are discussed., Comment: Latex2e, 20 pages, 6 figures, 5 tables. To appear on Classical and Quantum Gravity