Laser Astrometric Test Of Relativity Research Articles

The second post-Newtonian light propagation and its astrometric measurement in the solar system

The relativistic theories of light propagation are generalized by introducing two new parameters ς and η in the second post-Newtonian (2PN) order, in addition to the parametrized post-Newtonian (PPN) parameters γ and β. This new 2PN parametrized (2PPN) formalism includes the nonstationary gravitational fields and the influences of all kinds of relativistic effects. The multipolar components of gravitating bodies are taken into account as well at the first post-Newtonian (1PN) order. The equations of motion and their solutions of this 2PPN light propagation problem are obtained. Started from the definition of a measurable quantity, a gauge-invariant angle between the directions of two incoming photons for a differential measurement in astrometric observation is discussed and its formula is derived. For a precision level of a few microarcsecond (μas) for space astrometry missions in the near future, we further consider a model of angular measurement, the Laser Astrometric Test of Relativity (LATOR)-like missions. In this case, all terms with aimed at the accuracy of ~1μas are estimated.

Advancing fundamental physics with the Laser Astrometric Test of Relativity

The Laser Astrometric Test of Relativity (LATOR) is an experiment designed to test the metric nature of gravitation—a fundamental postulate of the Einstein’s general theory of relativity. The key element of LATOR is a geometric redundancy provided by the long-baseline optical interferometry and interplanetary laser ranging. By using a combination of independent time-series of gravitational deflection of light in the immediate proximity to the Sun, along with measurements of the Shapiro time delay on interplanetary scales (to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will significantly improve our knowledge of relativistic gravity and cosmology. The primary mission objective is i) to measure the key post-Newtonian Eddington parameter γ with accuracy of a part in 109. $\frac{1}{2}(1-\gamma)$ is a direct measure for presence of a new interaction in gravitational theory, and, in its search, LATOR goes a factor 30,000 beyond the present best result, Cassini’s 2003 test. Other mission objectives include: ii) first measurement of gravity’s non-linear effects on light to ∼0.01% accuracy; including both the traditional Eddington β parameter and also the spatial metric’s 2nd order potential contribution (never measured before); iii) direct measurement of the solar quadrupole moment J 2 (currently unavailable) to accuracy of a part in 200 of its expected size of ≃ 10 − 7; iv) direct measurement of the “frame-dragging” effect on light due to the Sun’s rotational gravitomagnetic field, to 0.1% accuracy. LATOR’s primary measurement pushes to unprecedented accuracy the search for cosmologically relevant scalar-tensor theories of gravity by looking for a remnant scalar field in today’s solar system. We discuss the science objectives of the mission, its technology, mission and optical designs, as well as expected performance of this experiment. LATOR will lead to very robust advances in the tests of fundamental physics: this mission could discover a violation or extension of general relativity and/or reveal the presence of an additional long range interaction in the physical law. There are no analogs to LATOR; it is unique and is a natural culmination of solar system gravity experiments.

LASER ASTROMETRIC TEST OF RELATIVITY: SCIENCE, TECHNOLOGY AND MISSION DESIGN

The Laser Astrometric Test of Relativity (LATOR) experiment is designed to explore the general theory of relativity in close proximity to the Sun — the most intense gravitational environment in the solar system. Using independent time series of highly accurate measurements of the Shapiro time delay (interplanetary laser ranging accurate to 3 mm at ~2 AU) and interferometric astrometry (accurate to 0.01 picoradian), LATOR will measure gravitational deflection of light by the solar gravity with an accuracy of one part in a billion — a factor of ~30,000 better than what is currently available. LATOR will perform a series of highly accurate tests in its search for cosmological remnants of the scalar field in the solar system. We present the science, technology and mission design for the LATOR mission.

Light deflection in the second post-Newtonian approximation of scalar-tensor theory of gravity

AbstractIn this paper, we use the metric coefficients and the equation of motion in the 2nd post-Newtonian approximation in scalar-tensor theory including intermediate range gravity to derive the deflection of light and compare it with previous works. These results will be useful for precision astrometry missions like Gaia, SIM, and LATOR (Laser Astrometric Test Of Relativity) which aim at astrometry with micro-arcsecond and nano-arcsecond accuracies and a need for the 2nd post-Newtonian framework and ephemeris to determine the stellar and spacecraft positions.

LATOR covariance analysis

We present results from a covariance study for the proposed laser astrometric test of relativity (LATOR) mission. This mission would send two laser-transmitter spacecraft behind the Sun and measure the relative gravitational light bending of their signals using a hundred-metre-baseline optical interferometer to be constructed on the International Space Station. We assume that each spacecraft is equipped with a <1.9 × 10−13 m s−2 Hz−1/2 drag-free system and assume approximately 1 year of data. We conclude that the observations allow a simultaneous determination of the orbit parameters of the spacecraft and of the parametrized post-Newtonian (PPN) parameter γ with an uncertainty of 2.7 × 10−9. We also find a 5 × 10−9 determination of the solar quadrupole moment, J2, as well as the first measurement of the second-order post-PPN parameter δ to an accuracy of about 10−3.

Mission design for the laser astrometric test of relativity

This paper focuses on the mission design for the laser astrometric test of relativity (LATOR). This mission uses laser interferometry between two micro-spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (100 m) multi-channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. Such a design enables LATOR to improve the value of the parameterized post-Newtonian (PPN) parameter γ to unprecedented levels of accuracy of 1 part in 10 8; the misson will also measure effects of the next post-Newtonian order (∝ G 2) of light deflection resulting from gravity’s intrinsic non-linearity. The solar quadrupole moment parameter, J 2, will be measured with high precision, as well as a variety of other relativistic effects including Lense-Thirring precession. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law.

EXPERIMENTAL DESIGN FOR THE LATOR MISSION

This paper discusses experimental design for the Laser Astrometric Test Of Relativity (LATOR) mission. LATOR is designed to reach unprecedented accuracy of 1 part in 108 in measuring the curvature of the solar gravitational field as given by the value of the key Eddington post-Newtonian parameter γ. This mission will demonstrate the accuracy needed to measure effects of the next post-Newtonian order (∝G2) of light deflection resulting from gravity's intrinsic non-linearity. LATOR will provide the first precise measurement of the solar quadrupole moment parameter, J2, and will improve determination of a variety of relativistic effects including Lense–Thirring precession. The mission will benefit from the recent progress in the optical communication technologies — the immediate and natural step above the standard radio-metric techniques. The key element of LATOR is a geometric redundancy provided by the laser ranging and long-baseline optical interferometry. We discuss the mission and optical designs, as well as the expected performance of this proposed mission. LATOR will lead to very robust advances in the tests of fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.

The Laser Astrometric Test of Relativity Mission

This paper discusses new fundamental physics experiment to test relativistic gravity at the accuracy better than the effects of the 2nd order in the gravitational field strength, ∝ G 2 . The Laser Astrometric Test Of Relativity (LATOR) mission uses laser interferometry between two micro-spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (100 m) multi-channel stellar optical interferometer placed on the International Space Station (ISS). The interferometer is used for measuring the angles between the two spacecraft. In Euclidean geometry, determination of a triangle's three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR will not only improve the value of the parameterized post-Newtonian (PPN) parameter γ to unprecedented levels of accuracy of 10 − 8 , it will also reach ability to measure effects of the next post-Newtonian order ( c − 4 ) of light deflection resulting from gravity's intrinsic non-linearity. The solar quadrupole moment parameter, J 2, will be measured with high precision, as well as a variety of other relativistic effects including Lense-Thirring precession. LATOR will lead to very robust advances in the tests of fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.

The laser astrometric test of relativity mission

This paper discusses the motivation and general design elements of a new fundamental physics experiment that will test relativistic gravity at the accuracy better than the effects of the second order in the gravitational field strength, ∝G2. The laser astrometric test of relativity (LATOR) mission uses laser interferometry between two micro-spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (100 m) multi-channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. In Euclidean geometry, determination of a triangle's three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy.LATOR will not only improve the value of the parametrized post-Newtonian (PPN) parameter γ to unprecedented levels of accuracy of 1 part in 108, it will also reach the ability to measure effects of the next post-Newtonian order (∝G2) of light deflection resulting from gravity's intrinsic nonlinearity. The solar quadrupole moment parameter, J2, will be measured with high precision, as well as a variety of other relativistic effects including Lense–Thirring precession. LATOR will lead to very robust advances in the tests of fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogues to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.