131 research outputs found
Test of general relativity: 1995-2002 measurement of frame-dragging
After an introduction on phenomena due to spin and mass-energy currents on
clocks and photons, we review the 1995-2001 measurements of the gravitomagnetic
field of Earth and Lense-Thirring effect obtained by analyzing the orbits of
the two laser-ranged satellites LAGEOS and LAGEOS II; this method has provided
a direct measurement of Earth's gravitomagnetism with accuracy of the order of
20 %. A future accurate measurement of the Lense-Thirring effect, at the level
of 1 % accuracy, may include the LARES experiment that will also provide other
basic tests of general relativity and gravitation. Finally, we report the
latest measurement of the Lense-Thirring effect, obtained in 2002 with the
LAGEOS satellites over nearly 8 years of data. This 2002 result fully confirms
and improves our previous measurements of the Earth frame-dragging: the
Lense-Thirring effect exists and its experimental value is within ~ 20 % of
what is predicted by Einstein's theory of general relativity.Comment: 12 pages, 2 figure
On the orbit of the LARES satellite
This paper is motivated by the recent possibility to find an inexpensive
launching vehicle for the LARES satellite, however at an altitude much lower
than originally planned for the LAGEOS III/LARES satellite.
We present here a preliminary error analysis corresponding to a lower,
quasi-polar, orbit, in particular we analyze the effect on the LARES node of
the Earth's static gravitational field, and in particular of the Earth's even
zonal harmonics, the effect of the time dependent Earth's gravitational field,
and in particular of the K1 tide, and the effect of particle drag
LAGEOS 3 and the gravitomagnetic field
The importance of the gravitomagnetic field is discussed. A never-measured field of nature, the foundations of inertia in Einstein General Relativity, and a key role in theories of quasars and active galactic nuclei are important aspects of this field and are discussed. In high energy astrophysics, some theories of energy storage, power generation, jet formation and jet alignment of quasars and active galactic nuclei are based on the existence of the gravitomagnetic field of a supermassive black hole (Thorne et al. 1986). LAGEOS 3 is discussed in terms of laser ranged satellites to detect the gravitomagnetic field and supplementary inclination satellites to avoid gravity field uncertainties. Many experiments have been proposed to measure the gravitomagnetic field. The GPB experiment intends to measure the Lense-Thirring-Schiff precession of gyroscopes orbiting the earth. Polar satellites have been proposed to measure the Lense-Thirring precession of the orbital plane (an enormous gyroscope and two guided, drag-free, counter-rotating, polar satellites have been suggested to avoid orbital inclination errors.) The new idea to measure the gravitomagnetic drag of the nodes of two nonpolar, supplementary inclination, satellites is summarized
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
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
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
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
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