Processes and devices to guide and/or steer a projectile

1. A terminal guidance and/or steering process for a projectile towards a target, process in which the orientation of a velocity vector {right arrow over (Vp)} is determined then a guidance law is applied and finally a steering algorithm enabling the projectile to be reoriented towards a target, process wherein the measurements of the three components of the terrestrial magnetic field {right arrow over (H)} are measured in a projectile-linked reference marker (Ox m Y m Z m ) and said measurements are used in the guidance law and/or steering algorithm as a fixed reference marker enabling the orientation at least partially of said projectile-linked reference marker with respect to the terrestrial reference marker.

2. A guidance and/or steering process according to claim 1 , wherein a target detector is implemented that enables said target to be detected in a projectile-linked reference marker, and the coordinates of a line of sight vector {right arrow over (Los)} to be deduced between said target and said projectile, process wherein, to ensure steering:

in said projectile-linked reference marker, the projection {right arrow over (N)} of the terrestrial magnetic field {right arrow over (H)} is determined in a guidance plane defined by the line of sight {right arrow over (Los)} of said projectile and velocity {right arrow over (Vp)} vectors,

a guidance law proportional to the variation with respect to time {dot over (λ)}=dλ/dt of angle λ between this projection {right arrow over (N)} of the magnetic field and said line of sight vector {right arrow over (Los)}.

3. A guidance and/or steering process according to claim 2 , wherein the guidance law is expressed in the following way: {right arrow over (γ)} cmd =K{dot over (λ)}{right arrow over (u)}, expression in which {right arrow over (γ)} cmd represents the correction set point acceleration vector, {dot over (λ)} represents the variation with respect to time (dλ/dt) of angle λ between the projection {right arrow over (N)} of the magnetic field and said line of sight vector {right arrow over (Los)} and {right arrow over (u)} represents a unitary vector perpendicular to said velocity vector {right arrow over (Vp)} of said projectile and located in said guidance plane.

4. A guidance and/or steering process according to claim 3 , wherein to determine the orientation of said projectile's velocity vector in said projectile-linked reference marker, one can consider that said vector is collinear to the axis OX m of said projectile-linked reference marker.

5. A guidance and/or steering process according to claim 3 , wherein to determine the orientation of said projectile's velocity vector in said projectile-linked reference marker, one can use the signals supplied by at least two accelerometers oriented respectively along the axes of measurement in pitch (OY m ) and yaw (OZ m ) of said projectile.

6. A guidance and/or steering process according to claim 1 , wherein to ensure the servo control steering of the yaw and/or pitch positioning of the fins of said projectile:

the projection of the magnetic field vector is determined in one of the yaw (X m OY m ) or pitch (X m OZ m ) planes of said projectile,

a servo-control chain is used in yaw and/or pitch in place of the yaw and/or pitch spin rate, the derivative with respect to time of an angle made by the projection thus made with one of the axes of the plane in question.

7. A guidance and/or steering process according to claim 6 , wherein to servo control the yaw positioning of said fins, one:

determine the projection of the magnetic field vector on said projectile's yaw plane (X m OY m ),

compute the variation with respect to time (r mes =dρ 2 /dt) of angle ρ 2 made by this projection with the roll axis (OX m ),

in a yaw servo control chain, use value r mes thus computed (pseudo-gyrometric feedback) in place of the yaw spin rate measurement r.

8. A guidance and/or steering process according to claim 6 , wherein to servo control the pitch positioning of said fins, one:

determine the projection of the magnetic field vector on said projectile's pitch plane (X m OZ m ),

compute the variation with respect to time (q mes =dρ 2 /dt) of angle ρ 1 made by this projection with the yaw axis (OZ m ),

in a pitch servo control chain, use value q mes thus computed (pseudo-gyrometric feedback) in place of the pitch spin rate measurement q.

9. A guidance and/or steering process according to claim 1 , wherein to servo control the roll positioning of said fins, one:

determine the projection of the magnetic field vector on said projectile's roll plane (Z m OY m ),

measure the angle ρ 3 made by this projection with one of the axes of said plane (for example the pitch spin axis (OY m )),

in a roll servo control chain, use value ρ 3 thus computed in place of roll angle Φ.

10. A guidance process according to claim 6 , wherein to ensure the guidance of said projectile a tracking law is implemented.

11. A guidance and/or steering device for a projectile towards a target that implements a terminal guidance and/or steering process for a projectile towards a target, process in which the orientation of a velocity vector {right arrow over (Vp)} is determined then a guidance law is applied and finally a steering algorithm enabling said projectile to be reoriented towards a target, such device wherein it associates a target detector or deviation finder, a computer incorporating a projectile guidance and/or steering algorithm, projectile steering means, at least two accelerometers oriented along the projectile's pitch acceleration (OZ m ) and yaw acceleration (OY m ) measurement axes and one or several magnetic sensors arranged so as to measure the three components of the terrestrial magnetic field vector {right arrow over (H)} in a projectile-linked reference marker, the guidance and/or steering algorithm using components of the terrestrial magnetic field vector {right arrow over (H)} as a fixed reference marker enabling the projectile-linked reference marker to be at least partially oriented with respect to a terrestrial reference marker.