67 research outputs found
SLR tracking of GPS-35
An experiment was designed to launch a corner cube retroreflector array on one of the Global Positioning Satellites (GPS). The launch on Aug. 31, 1993 ushered in the era of SLR tracking of GPS spacecraft. Once the space operations group finished the check-out procedures for the new satellite, the agreed upon SLR sites were allowed to track it. The first site to acquire GPS-35 was the Russian system at Maidanak and closely after the MLRS system at McDonald Observatory, Texas. The laser tracking network is currently tracking the GPS spacecraft known as GPS-35 or PRN 5 with great success. From the NASA side there are five stations that contribute data regularly and nearly as many from the international partners. Upcoming modifications to the ground receivers will allow for a further increase in the tracking capabilities of several additional sites and add some desperately needed southern hemisphere tracking. We are analyzing the data and are comparing SLR-derived orbits to those determined on the basis of GPS radiometric data
The impact of tidal errors on the determination of the Lense-Thirring effect from satellite laser ranging
The general relativistic Lense-Thirring effect can be detected by means of a
suitable combination of orbital residuals of the laser-ranged LAGEOS and LAGEOS
II satellites. While this observable is not affected by the orbital
perturbation induced by the zonal Earth solid and ocean tides, it is sensitive
to those generated by the tesseral and sectorial tides. The assessment of their
influence on the measurement of the parameter mu, with which the
gravitomagnetic effect is accounted for, is the goal of this paper. After
simulating the combined residual curve by calculating accurately the
mismodeling of the more effective tidal perturbations, it has been found that,
while the solid tides affect the recovery of mu at a level always well below
1%, for the ocean tides and the other long-period signals Delta mu depends
strongly on the observational period and the noise level: Delta mu(tides)
amounts to almost 2% after 7 years. The aliasing effect of K1 l=3 p=1 tide and
SRP(4241) solar radiation pressure harmonic, with periods longer than 4 years,
on the perigee of LAGEOS II yield to a maximum systematic uncertainty on
\m_{LT} of less than 4% over different observational periods. The zonal
18.6-year tide does not affect the combined residuals.Comment: 24 pages, 4 tables, 6 figures, submitted to Int. Journal of Mod.
Phys. D. Changes in auctorship, references and conten
The Global Geodetic Observing System: Space Geodesy Networks for the Future
Ground-based networks of co-located space geodetic techniques (VLBI, SLR, GNSS. and DORIS) are the basis for the development and maintenance of the International Terrestrial Reference frame (ITRF), which is our metric of reference for measurements of global change, The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) has established a task to develop a strategy to design, integrate and maintain the fundamental geodetic network and supporting infrastructure in a sustainable way to satisfy the long-term requirements for the reference frame. The GGOS goal is an origin definition at 1 mm or better and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale and orientation components. These goals are based on scientific requirements to address sea level rise with confidence, but other applications are not far behind. Recent studies including one by the US National Research Council has strongly stated the need and the urgency for the fundamental space geodesy network. Simulations are underway to examining accuracies for origin, scale and orientation of the resulting ITRF based on various network designs and system performance to determine the optimal global network to achieve this goal. To date these simulations indicate that 24 - 32 co-located stations are adequate to define the reference frame and a more dense GNSS and DORIS network will be required to distribute the reference frame to users anywhere on Earth. Stations in the new global network will require geologically stable sites with good weather, established infrastructure, and local support and personnel. GGOS wil seek groups that are interested in participation. GGOS intends to issues a Call for Participation of groups that would like to contribute in the network implementation and operation. Some examples of integrated stations currently in operation or under development will be presented. We will examine necessary conditions and challenges in designing a co-location station
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
A new laser-ranged satellite for General Relativity and space geodesy: I. An introduction to the LARES2 space experiment
We introduce the LARES 2 space experiment recently approved by the Italian Space Agency (ASI). The LARES 2 satellite is planned for launch in 2019 with the new VEGA C launch vehicle of ASI, ESA and ELV. The orbital analysis of LARES 2 experiment will be carried out by our international science team of experts in General Relativity, theoretical physics, space geodesy and aerospace engineering. The main objectives of the LARES 2 experiment are gravitational and fundamental physics, including accurate measurements of General Relativity, in particular a test of frame-dragging aimed at achieving an accuracy of a few parts in a thousand, i.e., aimed at improving by about an order of magnitude the present state-of-the-art and forthcoming tests of this general relativistic phenomenon. LARES 2 will also achieve determinations in space geodesy. LARES 2 is an improved version of the LAGEOS 3 experiment, proposed in 1984 to measure frame-dragging and analyzed in 1989 by a joint ASI and NASA study
A Test of General Relativity Using the LARES and LAGEOS Satellites and a GRACE Earth's Gravity Model
We present a test of General Relativity, the measurement of the Earth's
dragging of inertial frames. Our result is obtained using about 3.5 years of
laser-ranged observations of the LARES, LAGEOS and LAGEOS 2 laser-ranged
satellites together with the Earth's gravity field model GGM05S produced by the
space geodesy mission GRACE. We measure ,
where is the Earth's dragging of inertial frames normalized to its
General Relativity value, 0.002 is the 1-sigma formal error and 0.05 is the
estimated systematic error mainly due to the uncertainties in the Earth's
gravity model GGM05S. Our result is in agreement with the prediction of General
Relativity.Comment: 13 pages, 4 figures, published on EPJ
LARES Satellite Thermal Forces and a Test of General Relativity
We summarize a laser-ranged satellite test of frame-dragging, a prediction of
General Relativity, and then concentrate on the estimate of thermal thrust, an
important perturbation affecting the accuracy of the test. The frame dragging
study analysed 3.5 years of data from the LARES satellite and a longer period
of time for the two LAGEOS satellites. Using the gravity field GGM05S obtained
via the Grace mission, which measures the Earth's gravitational field, the
prediction of General Relativity is confirmed with a 1- formal error of
0.002, and a systematic error of 0.05. The result for the value of the frame
dragging around the Earth is = 0.994, compared to = 1 predicted by
General Relativity. The thermal force model assumes heat flow from the sun
(visual) and from Earth (IR) to the satellite core and to the fused silica
reflectors on the satellite, and reradiation into space. For a roughly current
epoch (days 1460 - 1580 after launch) we calculate an average along-track drag
of -0.50 .Comment: 6 pages, multiple figures in Proceedings of Metrology for Aerospace
(MetroAeroSpace), 2016 IEE
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