A process to control the trajectory of a spinning projectile. The projectile's accelerations are measured by means of an inertial unit in three axes within a reference linked to the projectile so as to prepare the piloting commands for the projectile's trajectory. The velocity vector V components (V.sub.X, V.sub.Y, V.sub.Z) of the projectile are measured using a global positioning system (GPS) along three axes and within a land reference (G.sub.X, G.sub.Y, G.sub.Z). Based on these measurements, the components (.GAMMA..sub.X,.GAMMA..sub.Y,.GAMMA..sub.Z) of the acceleration vector .GAMMA. are evaluated in the same land reference (GX, GY, GZ). At each of these measurements and periodical evaluations by the GPS, the Euler angles of the projectile are recalculated by combining the resultants of the velocity (V) and acceleration (.GAMMA.) measurements given by the GPS and those of the acceleration given by the inertial unit.