Process to control the trajectory of a spinning projectile

1. A process used in a computation device of a spinning projectile to control the trajectory of the spinning projectile and an inertial unit in the spinning projectile measures the projectile's accelerations in three axes within a reference linked to the projectile so as to prepare the piloting commands for the projectile's trajectory, wherein:

measuring the velocity vector V components (V X , V Y , V Z ) of the projectile using a global positioning system (GPS) along three axes and within a land reference (G X , G Y , G Z )

evaluating based on the velocity vector component measurements, the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the same land reference (GX, GY, GZ); and

recalculating, at each of the measurements and periodic evaluations by the GPS, the Euler angles of the projectile by combining the resultants of the velocity (V) and acceleration (Γ) measurements given by the GPS and those of the acceleration given by the inertial unit in order to adjust a piloting device of the spinning projectile.

2. The process according to claim 1 , wherein for the calculations of the Euler angles used for piloting, instead of the acceleration values measured by the inertial unit, so-called corrected acceleration values are used:

γ CX =γ X Γ/γ; γ CY =γ Y Γ/γ; γ CZ =γ Z Γ/γ

expressions in which Γ=√{square root over ((Γ X 2 +Γ Y 2 +Γ Z 2 ))} is the norm of the projectile's acceleration vector in the land reference such as evaluation thanks to the positioning system and γ=√{square root over ((γ X 2 +γ Y 2 +γ Z 2 ))} is the norm of the projectile's acceleration vector in the reference linked to the projectile such as measured by the inertial unit.

3. The process according to claim 2 having a canard type architecture, wherein the evaluation of the Euler angles is carried out by the computation device during the piloted flight phase using a calculation of the constant of the incidence time

Λ

=

-

Ps

-

Δ

′

Γ

2

,

expression in which P S is the scalar product of the velocity vector V and the acceleration vector Γ measured or calculated from the GPS (P S ={right arrow over (V)}.{right arrow over (Γ)}), and Δ′ is a reduced discriminant

Δ

′

=

(

Γ

2

⁢

V

2

-

P

S

2

)

⁢

γ

CX

2

γ

CT

2

,

expression in which γ CT is a corrected value of the transversal acceleration of the projectile (γ CT =√{square root over ((γ CY 2 +γ CZ 2 ))}).

4. The process according to claim 3 , wherein, when the projectile is in the piloted flight phase:

the Euler angles of the projectile are evaluated by the following formulae:

pitch angle θ (between −π/2 and +π/2):

θ

=

arcsin

⁡

(

V

Z

+

ΛΓ

Z

U

+

Λγ

CX

)

yaw angle ψ (between −π and +π):

cos

⁢

⁢

ψ

=

V

X

+

ΛΓ

X

(

U

+

Λγ

CX

)

⁢

cos

⁢

⁢

θ

sin

⁢

⁢

ψ

=

V

Y

+

ΛΓ

Y

(

U

+

Λγ

CX

)

⁢

cos

⁢

⁢

θ

roll angle φ:

cos

⁢

⁢

φ

=

γ

z0

⁢

γ

cz

+

γ

Y0

⁢

γ

cy

γ

cy

2

+

γ

cz

2

sin

⁢

⁢

φ

=

γ

z0

⁢

γ

cy

+

γ

y0

⁢

γ

cz

γ

cy

2

+

γ

cz

2

expressions in which:

γ Y0 =( V X sin ψ− V Y cos ψ)/Λ,

γ Z0 =( U sin θ− V Z )/Λcos θ and

U 2 =V 2 −Λ 2 Γ cT 2 .

5. The process according to claim 4 , wherein the evaluation of the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the land reference (G X , G Y , G Z ) will be carried out from N periodical measurements made by the GPS of components (V X , V Y , V Z ) of the velocity vector V of the projectile in the same land reference and with a sampling interval Δt, measurements to which a KALMAN filter will be applied.

6. The process according to claim 3 , wherein, when the projectile is in the ballistic flight phase, the value of the incidence time constant Λ will be rounded up to zero and the projectile's Euler angles will be calculated by the computation device using the following formulae:

the pitch θ and yaw ψ angles are equal to:

θ=arcsin( V Z /V ); ψ=arcsin( V Y /V cos θ)

the roll angle φ being defined by:

cos

⁢

⁢

φ

=

q

q

2

+

r

2

⁢

⁢

sin

⁢

⁢

φ

=

-

r

q

2

+

r

2

expressions in which q and r are respectively the angular pitch and yaw velocities of the projectile in a reference linked to the projectile, velocities measured by the inertial unit.

7. The process according to claim 3 , wherein the evaluation of the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the land reference (G X , G Y , G Z ) will be carried out from N periodical measurements made by the GPS of components (V X , V Y , V Z ) of the velocity vector V of the projectile in the same land reference and with a sampling interval Δt, measurements to which a KALMAN filter will be applied.

8. The process according to claim 2 , wherein, when the projectile is in the ballistic flight phase, the value of the incidence time constant Λ will be rounded up to zero and the projectile's Euler angles will be calculated by the computation device using the following formulae:

the pitch θ and yaw ψ angles are equal to:

θ=arcsin( V Z /V ); ψ=arcsin( V Y /V cos θ)

the roll angle φ being defined by:

cos

⁢

⁢

φ

=

q

q

2

+

r

2

⁢

⁢

sin

⁢

⁢

φ

=

-

r

q

2

+

r

2

expressions in which q and r are respectively the angular pitch and yaw velocities of the projectile in a reference linked to the projectile, velocities measured by the inertial unit.

9. The process according to claim 8 , wherein the evaluation of the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the land reference (G X , G Y , G Z ) will be carried out from N periodical measurements made by the GPS of components (V X , V Y , V Z ) of the velocity vector V of the projectile in the same land reference and with a sampling interval Δt, measurements to which a KALMAN filter will be applied.

10. The process according to claim 2 , wherein the evaluation of the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the land reference (G X , G Y , G Z ) will be carried out from N periodical measurements made by the GPS of components (V X , V Y , V Z ) of the velocity vector V of the projectile in the same land reference and with a sampling interval Δt, measurements to which a KALMAN filter will be applied.

11. The process according to claim 1 , wherein the evaluation of the components (Γ X ,Γ Y ,Γ Z ) of the acceleration vector Γ in the land reference (G X , G Y , G Z ) will be carried out from N periodical measurements made by the GPS of components (V X , V Y , V Z ) of the velocity vector V of the projectile in the same land reference and with a sampling interval Δt, measurements to which a KALMAN filter will be applied.