  Gravitational physics of VLBI experiment conducted on September 8, 2002 and
dedicated to measure the speed of gravity (a fundamental constant in the
Einstein equations) is treated in the first post-Newtonian approximation.
Explicit speed-of-gravity parameterization is introduced to the Einstein
equations to single out the retardation effect caused by the finite speed of
gravity in the relativistic time delay of light, passing through the variable
gravitational field of the solar system. The speed-of-gravity 1.5
post-Newtonian correction to the Shapiro time delay is derived and compared
with our previous result obtained by making use of the post-Minkowskian
approximation. We confirm that the 1.5 post-Newtonian correction to the Shapiro
delay depends on the speed of gravity $c_g$ that is a directly measurable
parameter in the VLBI experiment.
