The laser astrometric test of relativity mission

Abstract

Abstract. 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, ∝ 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 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 parameterized post-Newtonian (PPN) parameter γ to unprecedented levels of accuracy of 1 part in 10 8 , it will also reach ability to 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. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments. The LATOR mission 2

Signals for Lorentz violation in post-Newtonian gravity

“…Current measurements of the deflection of light by the Sun have attained the 10 ÿ4 level [72], which suggests sensitivities to Lorentz violation at this level might already be attainable with a complete data analysis. Future missions such as GAIA [82] and LATOR [83] may achieve sensitivities to coefficients for Lorentz violation at the level of 10 ÿ6 and 10 ÿ8 , respectively.…”

Experimental Tests of General Relativity

“…In many cases, such tests would require reaching the accuracy needed to measure effects of the next post-Newtonian order (∝ G 2 ) [3,47], promissing important outcomes for the 21st century fundamental physics.…”

General Theory of Relativity: Will It Survive the Next Decade?

“…The recently proposed Laser Astrometric Test Of Relativity (LATOR) [121,233,234,235] is an experiment designed to test the metric nature of gravitation -a fundamental postulate of Einstein's theory of general relativity. By using a combination of independent time-series of highly accurate 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 10 −13 radians and 1 cm), LATOR will significantly improve our knowledge of relativistic gravity.…”