  The closest ever fly-by of the Martian moon Phobos, performed by the European
Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen
and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE)
technique in the interest of studying planet - satellite systems. The aim of
this work is to demonstrate a technique of providing high precision positional
and Doppler measurements of planetary spacecraft using the Mars Express
spacecraft. The technique will be used in the framework of Planetary Radio
Interferometry and Doppler Experiments in various planetary missions, in
particular in fly-by mode. We advanced a novel approach to spacecraft data
processing using the techniques of Doppler and phase-referenced very long
baseline interferometry spacecraft tracking. We achieved, on average, mHz
precision (30 {\mu}m/s at a 10 seconds integration time) for radial three-way
Doppler estimates and sub-nanoradian precision for lateral position
measurements, which in a linear measure (at a distance of 1.4 AU) corresponds
to ~50 m.

Instrumentation and Methods for Astrophysics