  LISA Pathfinder is a science and technology demonstrator of the European
Space Agency within the framework of its LISA mission, the latter aiming to be
the first space-borne gravitational wave observatory. The payload of LISA
Pathfinder is the so-called LISA Technology Package, which is designed to
measure relative accelerations between two test masses in nominal free fall.
The diagnostics subsystem consists of several modules, one of which is the
magnetic diagnostics unit. Its main function is the assessment of the
differential acceleration noise between the test masses due to magnetic
effects. This subsystem is composed of two onboard coils intended to produce
controlled magnetic fields at the location of the test masses. These magnetic
fields couple with the remanent magnetic moment and susceptibility and produce
forces and torques on the test masses. These, in turn, produce kinematic
excursions of the test masses which are sensed by the onboard interferometer.
We prove that adequately processing these excursions, the magnetic properties
of the test masses can be estimated using classical multi-parameter estimation
techniques. Moreover, we show that special processing procedures to minimize
the effect of the multi channel cross-talks are needed. Finally, we demonstrate
that the quality of our estimates is frequency dependent. We also suggest that
using a multiple frequency experiment the global estimate can be obtained in
such a way that the results of the magnetic experiment are more reliable.
Finally, using our procedure we compute the the contribution of the magnetic
noise to the total proof-mass acceleration noise.
