Guidance method and system

1 . A method for guiding a weapon to a target, the method comprising:

obtaining, using at least one processor of an electronic device, a required impact vector for the weapon at the target;

obtaining, using the at least one processor, a line of sight (LOS) vector from the weapon to the target;

determining a velocity vector of the weapon;

defining a guidance plane, the guidance plane being a plane in which both the impact vector and the LOS vector lie;

calculating an optimum flight path angle in a vertical plane;

determining a flight path at the optimum flight path angle which lies in the guidance plane with a velocity perpendicular to a guidance plane of zero; and

generating guidance commands for the weapon causing the velocity vector of the weapon to become the determined flight path.

2 . The method of claim 1 , wherein the optimum flight path angle maximises gliding range.

3 . The method of claim 1 , wherein the optimum flight path angle maintains dynamic pressure of the weapon at an optimum value.

4 . The method of claim 1 , further comprising:

using a proportional navigation guidance law in the guidance plane to guide the weapon to the target.

5 . The method of claim 4 , wherein the proportional navigation guidance law:

determines a rate of change of angle of the LOS vector; and

uses the determined rate of change to determine a required rate of change of angle of a velocity component parallel to the guidance plane of the velocity vector;

and the method further comprises:

determining a velocity component perpendicular to the guidance plane of the velocity vector;

wherein the generating the guidance commands comprises generating guidance commands to change the angle of the velocity component parallel to the guidance plane of the velocity vector at the determined required rate of change and to reduce the velocity component perpendicular to the guidance plane of the velocity vector to zero.

6 . The method of claim 1 , wherein the method is iteratively repeated.

7 . The method of claim 1 , wherein the weapon is a glide weapon.

8 . A weapon configured to carry out the method according to claim 1 .

9 . A controller coupled to a weapon configured to carry out the method according to claim 1 .

10 . A non-transitory computer-readable medium comprising instructions which, when executed by a computer cause the computer to carry out the method of claim 1 .

11 . A method for guiding a weapon to a target, the method comprising:

i) obtaining, using at least one processor of an electronic device, a required impact vector for the weapon at the target;

ii) obtaining, using the at least one processor, a line of sight (LOS) vector from the weapon to the target;

iii) determining a velocity vector of the weapon;

iv) defining a guidance plane, the guidance plane being a plane in which both the impact vector and the LOS vector lie;

v) determining whether the weapon is capable of impacting the target with the required impact vector by following a proportional navigation guidance law with a navigation gain having a value within a predetermined range having a maximum navigation gain value and a minimum navigation gain value; and

if it is determined that the weapon is not capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range because achieving the required impact vector would require a lower navigation gain value than the minimum navigation gain value:

vi) calculating an optimum flight path angle in a vertical plane;

vii) determining a flight path at the optimum flight path angle which lies in the guidance plane with a velocity perpendicular to the guidance plane of zero; and

viii) generating guidance commands for the weapon to make the velocity vector of the weapon the determined flight path; and

ix) returning to i);

if it is determined that the weapon is capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range;

x) obtaining, using the at least one processor, a line of sight (LOS) vector from the weapon to the target;

xi) determining a velocity vector of the weapon;

xii) defining a guidance plane, the guidance plane being a plane in which both the impact vector and the LOS vector lie;

xiii) determining a navigation gain value required to impact the target with the required impact vector by following the proportional navigation guidance law in the guidance plane with that navigation gain value;

xiv) using a proportional navigation guidance law in the guidance plane to guide the weapon to the target, wherein the proportional navigation guidance law:

determines a rate of change of angle of the LOS vector; and

uses the determined rate of change and the determined navigation gain value to determine a required rate of change of angle of a velocity component parallel to the guidance plane of the velocity vector; and

the method further comprising:

xv) determining a velocity component perpendicular to the guidance plane of the velocity vector; and

xvi) generating guidance commands to change the angle of the velocity component parallel to the guidance plane of the velocity vector at the determined required rate of change and to reduce the velocity component perpendicular to the guidance plane of the velocity vector to zero; and

repeating from x) until the weapon reaches the target.

12 . The method of claim 11 , further comprising:

if it is determined that the weapon is not capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range because achieving the required impact vector would require a higher navigation gain value than the maximum navigation gain value;

xvii) calculating a flight path angle in the vertical plane which corresponds to application of a constant downward acceleration to the weapon;

xviii) determining a flight path at the flight path angle which lies in the guidance plane with a velocity perpendicular to the guidance plane of zero; and

xix) generating guidance commands for the weapon to make the velocity vector of the weapon the determined flight path; and

xx) returning to i).

13 . The method of claim 11 , further comprising:

if it is determined that the weapon is not capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range because achieving the required impact vector would require a higher navigation gain value than the maximum navigation gain value;

xxi) calculating a flight path angle in the vertical plane which corresponds to application of a constant downward acceleration to the weapon;

xxii) generating guidance commands for the weapon to make the velocity vector of the weapon have the determined flight path angle; and

xxii) returning to i).

14 . The method of claim 11 , wherein the optimum flight path angle maximises gliding range.

15 . The method of claim 14 , wherein the optimum flight path angle maintains dynamic pressure of the weapon at an optimum value.

16 . The method of claim 11 , wherein the weapon is a glide weapon.

17 . The method of claim 11 , wherein v) comprises:

determining a first impact angle for the weapon by following a proportional navigation guidance law with the maximum navigation gain value;

determining a second impact angle for the weapon by following a proportional navigation guidance law with the minimum navigation gain value; and

comparing the determined first and second impact angles to the required impact vector.

18 . The method of claim 17 , wherein it is determined that the weapon is capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range if the required impact vector is between or equal to the first and second impact angles.

19 . The method of claim 17 , wherein it is determined that the weapon is not capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range because achieving the required impact vector would require a higher navigation gain value than the maximum navigation gain value if the impact vector is outside the first and second impact angles, and the first impact angle is located between the second impact angle and the impact vector.

20 . The method of claim 17 , wherein it is determined that the weapon is not capable of impacting the target with the required impact vector by following the proportional navigation guidance law with a navigation gain having a value within the predetermined range because achieving the required impact vector would require a lower navigation gain value than the maximum navigation gain value if the impact vector is outside the first and second impact angles, and the second impact angle is located between the first impact angle and the impact vector.