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 comprising 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 determining 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-hitting 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 disturbance factors, it is prior known to provide a weather 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, 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 approximation 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 elevation 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 consideration requires a substantial calculating power and accordingly 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 coordinates 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 displacement 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 calculation 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-independent claims disclose preferred embodiments for the invention.
The invention will now be described in more detail with reference made to the accompanying drawing, in which
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 position 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 projectile differ from hypothetical values based on standard atmosphere 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 rotative 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
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 substantially 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 temperature 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 station 7. These spotting systems are well known and in general use and thus not discussed further in this context.
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 coordinates, 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 ejected from the indicator projectile 5 rearwards to a substantially stationary position before the 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 electronic 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 projectile 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 exploding 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 latitude), 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.