Abstract: A temporary locking device for a rotor of an inertia wheel, sustained, with respect to a stator, by magnetic means and associated with two emergency bearings having a conical bearing surface for each said emergency bearing. A complementary conical bearing surface is provided for each of said conical bearing surfaces, one of the two conical bearing surfaces being able to come into mechanical contact with said complementary bearing surface, and one of said complementary bearing surfaces being rendered axially movable. Thus the rotor can be immobilized against three degrees of freedom, two radially and one axially, after placing said bearing surfaces in mechanical contact, said rotor remaining free to rotate. The device is particularly useful for satellites.