(NEAR). The objective of many of these flybys is to obtain data from the planets as they flyby them and to take advantage of the energy transfer obtained during the flyby [@Transfer].

Apart from the obvious contribution to planetary science, these missions have provided an excellent framework to perform tests of General Relativity and to improve the accuracy of trajectory determination systems. As soon as 1976, the Viking mission allowed for the verification of Shapiro’s echo delay prediction of an increase in a time taken for a round-trip’s light signal to travel between the Earth and Mars as a consequence of the curvature of space-time by the Sun [@VikingExp]. More recently, Everitt et al. [@Everitt] have tested the geodetic and frame-dragging effects. Also, the analysis of the data from the Messenger mission to Mercury is now used for improving the accuracy of ephemeris as they also put a stringent test on the parameters in the post-newtonian formalism [@Messenger1; @Messenger2]. With such an ongoing interest in fundamental aspects of spacecraft dynamics and gravity it is, perhaps, not surprising that some anomalies have showed up in the years passed since the beginning of the space age. Among them, the so-called Pioneer anomaly 