  A feasible design for a magnetic diagnostics subsystem for eLISA will be
based on that of its precursor mission, LISA Pathfinder. Previous experience
indicates that magnetic field estimation at the positions of the test masses
has certain complications. This is due to two reasons. The first one is that
magnetometers usually back-act due to their measurement principles (i.e., they
also create their own magnetic fields), while the second is that the sensors
selected for LISA Pathfinder have a large size, which conflicts with space
resolution and with the possibility of having a sufficient number of them to
properly map the magnetic field around the test masses. However,
high-sensitivity and small-size sensors that significantly mitigate the two
aforementioned limitations exist, and have been proposed to overcome these
problems. Thus, these sensors will be likely selected for the magnetic
diagnostics subsystem of eLISA. Here we perform a quantitative analysis of the
new magnetic subsystem, as it is currently conceived, and assess the
feasibility of selecting these sensors in the final configuration of the
magnetic diagnostic subsystem.
