EP0939881A1

EP0939881A1 - Method for correcting the trajectory of a projectile of a gun, a mortar or a rocket launcher or the like

Info

Publication number: EP0939881A1
Application number: EP97927216A
Authority: EP
Inventors: Pekka Pylkkänen
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-06-19
Filing date: 1997-06-19
Publication date: 1999-09-08
Anticipated expiration: 2017-06-19
Also published as: DE69717488D1; FI98957B; WO1997048963A1; DE69717488T2; FI98957C; EP0939881B1; FI962545A0

Abstract

The invention relates to a method for correcting the trajectory of a projectile (5) of a gun, a mortar or a rocket launcher or the like firearm. The method comprises a step of determining the site coordinates of a firing position (2) and a scouted target (4) on a map and of using e.g. a compass for determining the bearing from the firing position (2) to the target (4) at the accuracy of a few degrees. The direction of fire of a firearm (1) is aimed at a desired strike point (P1) and an indicator projectile (5) corresponding to a live explosive projectile in terms of its flying characteristics is fired at such an elevation that with standard atmosphere, i.e. without disturbance factors, the strike is obtained at the distance of the desired strike point (P1). A receiver included in an electronic unit (8) incorporated in or released from the indicator projectile (5) is used to receive a spotting signal transmitted by an external spotting system, e.g. a GPS-system (6), for determining a real strike point (P2). A transmitter included in the electronic unit is used to transmit the site coordinates of the strike (P2) to a receiving unit (3) in the firing position and the elevation and bearing of the firearm (1) are corrected on the basis of a difference between the hypothetical (P1) and real (P2) sites of the indicator projectile or the electronic unit released therefrom.

Description

Method for correcting the trajectory of a projectile of a gun, a mortar or a rocket launcher or the like

The present invention relates to a method for correcting the trajectory of a projectile of a gun, a mortar or a rocket launcher or the like firearm, said method compris¬ ing a step of determining the site coordinates of a firing position and a recognized target on a map, and of using a compass, an azimuth gyro or some other method for deter- mining the bearing from the firing position to the target at the accuracy of a few degrees. More specifically, the invention is about the speedy adjustment of bearing and elevation of the barrel of a gun for high-precision firing .

When firing a gun, a mortar and a rocket launcher or the like firearm to far-away targets, the projectile will reach a very high altitude at the highest point of its trajectory, even an altitude of up to 5 - 15 km. Thus, the climatic disturbances have a major effect on target-hit- ting precision. The force and direction of wind may vary at various altitudes. Also the air density and atmospheric humidity may vary substantially at various altitudes. In order to correct the displacement and elevation of the barrel of a gun so as to account for the climatic distur¬ bance factors, it is prior known to provide a weathei data by means of a weather probe which, upon ascending to upper atmospheric layers, transmits information about wind direction and atmospheric pressure. This information is then utilized for calculating a corrected trajectory by means of a so-called layer formula, wherein the trajectory is calculated in increments in various atmospheric layers. This provides an improvement in target-hitting precision, but such prior known method involves several drawbacks . The ascent of a weather sonde to a sufficient altitude may take up to 40 minutes and, thus, the method is slow and not suitable for modern high-speed warfare. In addition,

RECTIFIED SHEET <RULE91) the method involves two inaccuracy factors. First of all, the weather probe is exposed to winds and, hence, during the ascent, it may drift even far away from the location of the projectile trajectory. Secondly, the calculation effected with the layer formula only provides an approxi¬ mation for the required correction. Attempts have been made to correct the positional inaccuracy by dropping the weather probe from an aircraft. This possibility is not always available. Furthermore, the determination of eleva- tion also requires a temperature correction of gunpowder, since the rate of combustion of gunpowder and the muzzle velocity of a projectile are dependent on the temperature of gunpowder. Taking all the corrections into consider¬ ation requires a substantial calculating power and accord- ingly expensive equipment, if the calculation is to be performed within a reasonable time frame.

The previously common search firing, in which the fire controllers monitor strikes and supply correction coordi- nates to the firing position, is no longer widely used since, by such search firing, the firing position reveals its location to the enemy and possibly makes itself a target prior to hitting anything. This is due to the fact that there is modern equipment available which is capable of rapidly clearing the launching site of an approaching projectile on the basis of its trajectory.

An object of the invention is to provide an improved method for determining the required correction for dis- placement and elevation of the barrel or tube of a gun, a mortar or a rocket launcher by simultaneously accounting for all firing-related disturbance factors so as to achieve a target-hitting precision better than before. Another object of the invention is to speed up the calcu- lation of required correction and the transfer to a new firing position. These objects are achieved by the invention on the basis of the characterizing features set forth in the annexed claim 1. The non-mdependent claims disclose preferred embodiments for the invention.

The invention will now be described m more detail with reference made to the accompanying drawing, in which

fig. 1 is a schematic overhead view of the operating principle for a method of the invention, and

figs. 2a and 2b show alternative embodiments for details associated with one stage in a method of the invention.

In the depicted case, a gun 1 has been driven to a firing position 2 which has fixed its position accurately e.g. by means of spotting signals received thereby from a GPS- system 6, 7. The reconnaissance has cleared the site coordinates of a target 4 on the map at an accuracy which is sufficient for a projectile finding said coordinates to destroy the target 4.

A compass utilizing the magnetic field of the earth (e.g. a flux gate compass), an azimuth gyro or some other method is used for determining the bearing from the firing posi¬ tion 2 to the target 4 at an accuracy of a few degrees . An indicator projectile 5 is fired intentionally a few degrees off the target 4 and the elevation is determined such that with standard atmosphere a strike is made at a point P the same distance away as the target 4. If the wind action is e.g. from the direction of an arrow A, the bearing and flying distance of an indicator pro_jectile differ from hypothetical values based on standard atmo- sphere in such a manner that the indicator projectile falls on the point P. The flying characteristics of the indicator projectile 5, such as weight, shape, and rota- tive moments relative to various axes, correspond to those of a real explosive projectile.

The indicator projectile 5 is fitted with an electronic package 8, which contains a receiver for picking up positioning signals from an external spotting system, e.g. a GPS-system 6, 7 conventional electronic elements for fixing a position on the basis of received signals - a transmitter for sending the site coordinates with a properly ciphered digital radio signal to a receiver unit 3 in the firing position.

When the receiver unit 3 in the firing position receives the site coordinates of an indicator projectile, the corrections for elevation and bearing can be made easily on the basis of a difference between the coordinates of a hypothetical location P₁ and a real location P₂ of the indicator projectile.

Although the indicator projectile 5 is fired sufficiently off the target 4 not to be observed in the target area, the indicator projectile must nevertheless travel in substantially the same weather conditions over substan- tially the same distance as the actual live projectile to the target 4. Thus, all firing-related disturbance factors can be taken into consideration at the same time. This applies also to the temperature of gunpowder, which will be automatically accounted for as the indicator projectile corresponding to the actual explosive projectile in terms of its dimensions and weight is stored at the same temper¬ ature as live ammunition.

The spotting system may be a spotting system based on fixed ground stations or a GPS-system or a differential

GPS-system, wherein the inaccuracy intentionally added in satellite spotting 6 is eliminated by means of a ground

RECTIFIED SHEET (RULE SI) station 7. These spotting systems are well known and in general use and thus not discussed further in this con¬ text .

If the indicator projectile 5 has its spotting based on a conventional (not differential) GPS-system, the spotting accuracy can be increased according to the invention in such a manner that, in the receiving unit 3 of a firing position, whose site coordinates are precisely known, the spotting is performed simultaneously with the spotting of an indicator projectile by receiving a spotting signal of the GPS-satellites 6 and by comparing the spotting result with the precisely known site coordinates of the firing position 2, 3. This comparison results in the discovery of a position error caused by the fading of system coordi¬ nates, whereby a correction equal to said error can be made in the site coordinates received from the indicator projectile 5.

Fig. 2a illustrates how the electronic unit 8 containing a transmitter and a receiver can be launched or e jected from the indicator projectile 5 rearwards to a substantially stationary position before tne indicator projectile 5 hits the ground. Technology for discovering the proper instant is used e.g. in mid-air exploding ammunition.

Alternatively, the indicator projectile 5 or the electron¬ ic unit 8 released therefrom can be decelerated with a parachute 9 prior to hitting the ground, as shown in fig. 2b.

The arrangements shown in figs. 2a and 2b are used to make sure that the electronic unit 8 does not sink too deep in the ground or disintegrate in case the indicator projec- tile 5 hits a rock or a stone. The release of the electronic unit 8 from the projectile can also be effected on the basis of flying time, in other words the electronic unit has its clock activated during the muzzle acceleration of a projectile and the electronic unit is released after a preset time.

The electronic unit 8 can be incorporated also in explod¬ ing projectiles so as to receive coordinates from all strikes .

The information supplied by the electronic unit 8 may also include a measured flying time, which can be utilized in fire control calculations.

The information provided by the electronic unit 8 can also be utilized, such that the received information is used for calculating the corrections necessitated by weather, Coriolis effect, change of gravity (according to lati¬ tude), gunpowder temperature and muzzle velocity for conventional fire control calculation.

The electronic unit 8 can be made self-destructive after it has transmitted site coordinates for its own location. The purpose of this is to avoid revelation of the applied technology.

Claims

Cl a ims

1. A method for correcting the trajectory of a projectile (5) of a gun, a mortar or a rocket launcher or the like firearm, said method comprising a step of determining the site coordinates of a firing position (2) and a recognized target (4) on a map, and of using a compass, an azimuth gyro or some other method for determining the bearing from the firing position (2) to the target (4) at the accuracy of a few degrees, and of aiming the direction of fire of a firearm (1 ) at a desired strike point (P-_]), c h a r ¬ a c t e r i z e d in that an indicator projectile (5) corresponding to a live explosive projectile in terms of its flying characteristics is fired at such an elevation that with standard atmosphere, i.e. without disturbance factors, the strike of the indicator projectile (5) or an electronic unit (8) released therefrom is obtained sub¬ stantially at the distance of the desired strike point (P_i), a receiver included in the electronic unit (8) m- corporated in the indicator projectile (5) or released from the indicator projectile is used to receive a posi¬ tioning signal transmitted by an external positioning system, e.g. a GPS-system (6) for determining the site of the indicator projectile (5) or- electronic unit, a trans- mitter included in the electronic unit (8) is used to transmit site coordinates (P₂) of the indicator projectile (5) or the electronic unit (8) to a receiving unit (3) in the firing position and the elevation and bearing of the firearm (1 ) are corrected on the basis of a difference between the hypothetical (P<) and real (P-, ) sites of the indicator projectile or electronic unit.

2. A method as set forth in claim 1 , c h a r a c t e r ¬ i z e d in that a clock included in the electronic unit (8) activates during the muzzle acceleration of the pro¬ jectile (5) and the electronic unit (8) is released from the projectile after a preset time lapse. O 97/48963 PO7FI97/00397

3. A method as set forth m claim 1 , c h a r a c t e r ¬ i z e d in that the information transmitted by the elec¬ tronic unit (8) includes a measured flying time, which is utilized in fire control calculations.

4. A method as set forth in any of claims 1-3, c h a r ¬ a c t e r i z e d in that, in the receiving unit (3) of a firing position, whose site coordinates are precisely known, the spotting is performed simultaneously with the spotting of the electronic unit (8) by receiving a spot¬ ting signal of said external spotting system (6), the spotting result is compared with said precisely known site coordinates of the firing position (2, 3) and the spotting result received from the electronic unit (8) is corrected on the basis of a discovered difference.

5. A method as set forth in any of claims 1-4, c h a r ¬ a c t e r i z e d in that the electronic package (8) containing a transmitter and a receiver is launched or ejected from the indicator projectile (5) rearwards to a substantially stationary position before the indicator projectile hits the ground.

6. A method as set forth in any of claims 1-5, c h a r - a c t e r i z e d in that the indicator projectile (5) or the electronic package (8) released therefrom, which includes a transmitter and a receiver, is decelerated with a parachute (9) prior to hitting the ground.

7. A method as set forth m any of claims 1-6, c h a r ¬ a c t e r i z e d in that the indicator projectile (5) corresponds to an actual explosive projectile in terms of its design and weight and that the indicator projectile (5) is stored at the same temperature as live projectiles. O 97/48963 PC 17FI97/00397

8. A method as set forth in any of claims 1-7, c h a r ¬ a c t e r i z e d in that the indicator projectile com¬ prises a conventional explosive projectile.