The Laser Astrometric Test Of Relativity (LATOR) is a European-U.S. Michelson-Morley-type experiment designed to test the tensor metric nature of gravitation - the fundamental postulate of Einstein's theory of general relativity. By using a combination of independent timeseries 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 7 with accuracy of a part in 10⁹. (1 - γ) 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 been measured before); iii) direct measurement of the solar quadrupole moment J₂ (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. LATOR is envisaged as a partnership between European and US institutions and with clear areas of responsibility between the space agencies: NASA provides the deep space mission components, while optical infrastructure on the ISS is an ESA contribution. We discuss the mission and optical designs of this proposed experiment.