The main objective of the project RotaNut is to significantly improve of the model for the orientation of the spin axis to just the sub-centimetre, which has never previously been achieved and which is the aim of all existing decadal surveys in geodesy. This will be extremely helpful to European and international satellite missions and GNSS (Global Navigation Satellite System, such as GPS or its European equivalent Galileo) positioning. At the same time, it will allow scientists to learn much more about the interior of the Earth such as the predominant coupling mechanisms at the core boundaries (inner core boundary and core-mantle boundary) at nutation timescale and the amplitude of the magnetic field at these boundaries, which are not directly observable from the Earth surface (as only a part of the field is observable above the insulating mantle).