A better knowledge of the nuclear cross sections is becoming essential for the Hadrontherapy improvement and for the astronauts radio-protection. For this purpose the experiment FOOT ( FragmentatiOn Of Target ) has been envisaged. The direct and inverse kinematic approach will be used to measure the cross sections respectively after the Bragg peak and in the proton entrance channel. For this purpose a key element in FOOT is the magnetic spectrometer based on the monolithic active pixel sensor. The pixel tracker is composed by three main elements: the Vertex detector, the bending permanent magnet and a larger acceptance two layer inner tracker. Both the four layer Vertex and the downstream tracker will use the MIMOSA28 pixel sensors developed by the Strasbourg PICSEL group.
An overview of the detector with its main simulated characteristics will be described and some details on main implementation problems will also be underlined.