Guidance method and system

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.