  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 $\gamma$ to unprecedented levels of accuracy of
1 part in 10$^{8}$; the misison will also measure effects of the next
post-Newtonian order ($\propto G^2$) 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.
