Gravity Assist as a Test of Relativistic Gravity

We consider the gravity assist maneuver, that is, a correction of spacecraft motion at its passing near a planet, as a tool for evaluating the Eddington post-Newtonian parameters beta and gamma, characterizing vacuum spherically symmetric gravitation fields in metric theories of gravity. We estimate the effect of variation in beta and gamma on a particular trajectory of a probe launched from the Earth's orbit and passing closely near Venus, where relativistic corrections slightly change the impact parameter of probe scattering in Venus's gravitational field. It is shown, in particular, that a change of 10(-4) in beta or gamma leads to a shift of about 50 km in the probe's aphelion position.