287 research outputs found
LARES succesfully launched in orbit: satellite and mission description
On February 13th 2012, the LARES satellite of the Italian Space Agency (ASI)
was launched into orbit with the qualification flight of the new VEGA launcher
of the European Space Agency (ESA). The payload was released very accurately in
the nominal orbit. The name LARES means LAser RElativity Satellite and
summarises the objective of the mission and some characteristics of the
satellite. It is, in fact, a mission designed to test Einstein's General
Relativity Theory (specifically 'frame dragging' and Lense-Thirring effect).
The satellite is passive and covered with optical retroreflectors that send
back laser pulses to the emitting ground station. This allows accurate
positioning of the satellite, which is important for measuring the very small
deviations from Galilei-Newton's laws. In 2008, ASI selected the prime
industrial contractor for the LARES system with a heavy involvement of the
universities in all phases of the programme, from the design to the
construction and testing of the satellite and separation system. The data
exploitation phase started immediately after the launch under a new contract
between ASI and those universities. Tracking of the satellite is provided by
the International Laser Ranging Service. Due to its particular design, LARES is
the orbiting object with the highest known mean density in the solar system. In
this paper, it is shown that this peculiarity makes it the best proof particle
ever manufactured. Design aspects, mission objectives and preliminary data
analysis will be also presented.Comment: To appear in Acta Astronautica 201
LARES-lab: a thermovacuum facility for research and e-learning. Tests of LARES satellite components and small payloads for e-learning
LARES, an Italian Space Agency satellite, has been launched successfully in 2012. A small thermovacuum facility has been designed and built specifically for performing tests on the optical components of the satellite. Due to the extremely demanding performances of the optical cube corner reflectors, the space conditions have been simulated using the most up-to-date technology available. In particular Sun, Earth and deep space can be simulated in a ultra high vacuum. It is planned to automate the facility so that it can be operated remotely over the internet. The students during the lectures and the researchers from home will be able to perform thermal tests on specimens by exposing them, for specified amount of time, toward Earth, Sun or deep space. They will collect pressures and temperatures and will input additional thermal power through resistive heaters. The paper will first describe the facility and its capabilities showing the tests performed on LARES satellite components but will focus mainly to the planned upgrades that improve its remote use both for research and e-learning
The LARES mission: an opportunity to teach general relativity. Frame dragging and Lense-Thirring effect
LARES is an Italian Space Agency mission devoted to test frame-dragging, a prediction of general relativity.
On February 2012 the satellite has been successfully put in orbit with the qualification flight of VEGA, the new European Space Agency launcher. Basic concepts of general relativity are becoming more and more familiar because of the part they play in science fiction movies. But frame-dragging (more formally known as the Lense-Thirring effect), is so peculiar that it is a relatively unknown effect. The idea of this paper is to start from the description of the experiment and then to push some parameters of the experiment to extreme values in order to magnify the effects of relativity. This approach will provide not only the students and general people but also professionals not strictly specialized in general relativity, with increased interest in
gravitational theories
LARES a new satellite specifically designed for testing general relativity
It is estimated that today several hundred operational satellites are orbiting Earth while many more either already re-entered the atmosphere or are no longer operational. On the 13th of February 2012 one more satellite of the Italian Space Agency has been successfully launched. The main difference with respect to all other satellites is its extremely high density that makes LARES (LAser RElativity Satellite) not only the densest satellite but even the densest known orbiting object in the solar system. That implies the non-gravitational perturbations on its surface will have the smallest effects on its orbit with respect to all other artificial orbiting objects. Those design characteristics are required to perform an accurate test of frame dragging and specifically a test of Lense-Thirring effect, predicted by General Relativity. LARES satellite is passive and covered with 92 retroreflectors. Laser pulses, sent from several ground stations, allow an accurate orbit determination. Along with this last aspect and the mentioned special design one has to take into account the effects of the Earth gravitational perturbations due to the deviation from the spherical symmetry of the gravitational potential. To this aim the latest determinations of the Earth gravitational field, produced using gravitational data from several dedicated space missions including GRACE, and the combination of data from three laser ranged satellites is used in the LARES experiment. In spite of its simplicity LARES was a real engineering challenge both in term of manufacturing and testing. The launch was performed with the VEGA qualification flight provided by the European Space Agency. Data acquisition and processing is in progress. The paper will describe the scientific objectives, the status of the experiment, the special feature of the satellite and separation system including some manufacturing issues, and the special tests performed on its retroreflectors
An improved mathematical prediction of the time evolution of the Covid-19 pandemic in Italy, with a Monte Carlo simulation and error analyses
We present an improved mathematical analysis of the time evolution of the Covid-19 pandemic in Italy and a statistical error analyses of its evolution, including a Monte Carlo simulation with a very large number of runs to evaluate the uncertainties in its evolution. A previous analysis was based on the assumption that the number of nasopharyngeal swabs would be constant. However, the number of daily swabs is now more than five times what it was when we did our previous analysis. Therefore, here we consider the time evolution of the ratio of the new daily cases to number of swabs, which is more representative of the evolution of the pandemic when the number of swabs is increasing or changing in time. We consider a number of possible distributions representing the evolution of the pandemic in Italy, and we test their prediction capability over a period of up to 6 weeks. The results show that a distribution of the type of Planck black body radiation law provides very good forecasting. The use of different distributions provides an independent possible estimate of the uncertainty. We then consider five possible trajectories for the number of daily swabs and we estimate the potential dates of a substantial reduction in the number of new daily cases. We then estimate the spread in a substantial reduction, below a certain threshold, of the daily cases per swab among the Italian regions. We finally perform a Monte Carlo simulation with 25,000 runs to evaluate a random uncertainty in the prediction of the date of a substantial reduction in the number of diagnosed daily cases per swab
Preliminary study for the measurement of the Lense-Thirring effect with the Galileo satellites
The precession of the orbital node of a particle orbiting a rotating mass is
known as Lense-Thirring effect (LTE) and is a manifestation of the general
relativistic phenomenon of dragging of inertial frames or frame-dragging. The
LTE has already been measured by using the node drifts of the LAGEOS satellites
and GRACE-based Earth gravity field models with an accuracy of about 10% and
will be improved down to a few percent with the recent LARES experiment. The
Galileo system will provide 27 new node observables for the LTE estimation and
their combination with the LAGEOS and LARES satellites can potentially reduce
even more the error due to the mismodeling in Earth's gravity field. However,
the accurate determination of the Galileo orbits requires the estimation of
many different parameters, which can absorb the LTE on the orbital nodes.
Moreover, the accuracy of the Galileo orbits and hence, of their node drifts,
is mainly limited by the mismodeling in the Solar Radiation Pressure (SRP).
Using simulated data we analyze the effects of the mismodeling in the SRP on
the Galileo nodes and propose optimal orbit parameterizations for the
measurement of the LTE from the future Galileo observations
Testing General Relativity and gravitational physics using the LARES satellite
The discovery of the accelerating expansion of the Universe, thought to be
driven by a mysterious form of `dark energy' constituting most of the Universe,
has further revived the interest in testing Einstein's theory of General
Relativity. At the very foundation of Einstein's theory is the geodesic motion
of a small, structureless test-particle. Depending on the physical context, a
star, planet or satellite can behave very nearly like a test-particle, so
geodesic motion is used to calculate the advance of the perihelion of a
planet's orbit, the dynamics of a binary pulsar system and of an Earth orbiting
satellite. Verifying geodesic motion is then a test of paramount importance to
General Relativity and other theories of fundamental physics. On the basis of
the first few months of observations of the recently launched satellite LARES,
its orbit shows the best agreement of any satellite with the test-particle
motion predicted by General Relativity. That is, after modelling its known
non-gravitational perturbations, the LARES orbit shows the smallest deviations
from geodesic motion of any artificial satellite. LARES-type satellites can
thus be used for accurate measurements and for tests of gravitational and
fundamental physics. Already with only a few months of observation, LARES
provides smaller scatter in the determination of several low-degree
geopotential coefficients (Earth gravitational deviations from sphericity) than
available from observations of any other satellite or combination of
satellites
Fundamental Physics and General Relativity with the LARES and LAGEOS satellites
Current observations of the universe have strengthened the interest to
further test General Relativity and other theories of fundamental physics.
After an introduction to the phenomenon of frame-dragging predicted by
Einstein's theory of General Relativity, with fundamental astrophysical
applications to rotating black holes, we describe the past measurements of
frame-dragging obtained by the LAGEOS satellites and by the dedicated Gravity
Probe B space mission. We also discuss a test of String Theories of
Chern-Simons type that has been carried out using the results of the LAGEOS
satellites. We then describe the LARES space experiment. LARES was successfully
launched in February 2012 to improve the accuracy of the tests of
frame-dragging, it can also improve the test of String Theories. We present the
results of the first few months of observations of LARES, its orbital analyses
show that it has the best agreement of any other satellite with the
test-particle motion predicted by General Relativity. We finally briefly report
the accurate studies and the extensive simulations of the LARES space
experiment, confirming an accuracy of a few percent in the forthcoming
measurement of frame-dragging.Comment: To be publihed in Nuclear Physics. arXiv admin note: substantial text
overlap with arXiv:1306.1826, arXiv:1211.137
- …