Optical Design for the Laser Astrometric Test of Relativity

TL;DR

The LATOR mission aims to perform highly precise measurements of gravitational effects near the Sun to test and refine theories of relativity and gravity with unprecedented accuracy.

Contribution

This paper introduces the optical design and mission concept of LATOR, a novel experiment to measure relativistic gravity effects with significantly improved precision.

Findings

Projected measurement of the Eddington parameter γ to 1 part in 10^9

First measurement of gravity's non-linear light effects at 0.01% accuracy

Direct measurement of solar quadrupole moment J2 and frame-dragging effects

Abstract

This paper discusses the Laser Astrometric Test Of Relativity (LATOR) mission. 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 the interplanetary scales (to a precision respectively better than $10^{-13}$ radians and 1 cm), LATOR will significantly improve our knowledge of relativistic gravity. The primary mission objective is to i) measure the key post-Newtonian Eddington parameter $\gamma$ with accuracy of a part in 10$^9$. $(1-\gamma)$ 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 $\sim$0.01% accuracy; including both the traditional Eddington $\beta$ parameter and also the spatial metric's 2nd order potential contribution (never been 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; iv) direct measurement of the ``frame-dragging'' effect on light by the Sun's rotational gravitomagnetic field to one percent 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. 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 of this proposed experiment.