VFM instrument: The VFM (fluxgate type) is based on the fluxgate transducer using a ringcore with amorphous magnetic material, which has a very low noise (10-20 pT rms). It has an extremely high stability < 0.05 nT/year. VFM consists of a CSC (Compact Spherical Coil) sensor, non redundant, mounted on the deployable boom, an internally redundant data processing unit (DPU) and the connecting harness. The spherical coils that create a homogeneous vector field inside the sphere are mounted on an isotropic and extremely stable mechanical support. In feedback conditions the sensor is used as a nulling device and the coils define uniquely the magnetic axes of the sensor. The VFM exhibits high linearity (< 1ppm), a component accuracy of 0.5 nT and precision of 50 pT rms.