  We study the impact of relativistic gravitational deflection of light on the
accuracy of future Space Interferometry Mission (SIM). We estimate the
deflection angles caused by the monopole, quadrupole and octupole components of
gravitational fields for a number of celestial bodies in the solar system. We
observe that, in many cases, the magnitude of the corresponding effects is
significantly larger than the 1 uas accuracy expected from SIM. This fact
argues for the development of a relativistic observational model for the
mission that would account for the influence of both static and time-varying
effects of gravity on light propagation. Results presented here are different
from the ones obtained elsewhere by the fact that we specifically account for
the differential nature of the future SIM astrometric measurements. We also
obtain an estimate for the accuracy of possible determination of the
Eddington's parameter \gamma via SIM global astrometric campaign; we conclude
that accuracy of ~7 x 10^{-6} is achievable via measurements of deflection of
light by solar gravity.
