Since MESSENGER passed deep within the Sun's gravity well during the Mercury flyby, relativistic effects due to Einstein's general theory of relativity were included in the KinetX trajectory calculations.
KinetX also applies corrections due to Einstein's special and general theories of relativity in order to estimate the trajectory from radio metric tracking data supplied by NASA's Deep Space Network.
KinetX uses the MIRAGE software set developed at NASA/JPL that includes the formulation for these effects developed by Theodore D. Moyer.
Properly including these effects were part of the overall precision trajectory estimation and planning effort that the KinetX team used to deliver the MESSENGER spacecraft to a very precise planetary flyby.
KinetX Flight Director and then MESSENGER Navigation Team Chief, Anthony Taylor, answered specific questions about the KinetX team's use of relativity corrections sent in by Emily Stewart Lakdawalla of the Planetary Society which can be seen on the Planetary Society blog.
Mr. Taylor was also contacted by Dr. Stefan Scherer of the Johann Wolfgang Goethe Institute for Theoretical Physics at Max-von-Laue-Strasse University, Frankfurt, Germany.
Dr. Scherer produced a blog speculating on the effect General Relativity might have on the MESSENGER flyby before he contacted Mr. Taylor.
The resulting dialog between Dr. Scherer and Mr. Taylor clarified what was done by the KinetX Navigation Team to account for relativity at Mercury flyby 1.