GB2177213A - Determining the ballistic trajectory of a projectile - Google Patents

Abstract

A method for determining the ballistic flight path (23) of a projectile 21 that is to be fired from a weapon barrel 22 and which changes in a self-controlled manner from a ballistic firing flight path with linking flat flight path into an end-phase homing flight path removes the need for error-prone firing-data inputs into the projectile. For this, measurements are made on board the projectile of the muzzle velocity v1 of the projectile and of the time from firing (t1) up to passage through the apogee (t2). Additionally, by measuring the apogee, the build-up of a positional reference for the flight path control is made possible. Acceleration sensor 45, apogee detector 49 and exit sensors 41,42 provide signals t1, t2, t41 and t42 to a time measuring circuit 43, the measurements from which are translated into measurements of firing elevation angle w1 and propellant charge number # and fed to the store 38 for a navigation computer. <IMAGE>

Description

1 GB2177213A 1 SPECIFICATION pellantcharge number, or to put-in directly

the range, calculable from these parameters and A method for determining the ballistic tra- the preset linearly-flat flight path, to the theo jectory of a projectile as well as devices for retical path end point. However, this is com carrying out the method 70 plicated and, particularly under combat condi tions, is extremely fraught with error.

The invention concerns improvements in or re- Therefore there arises a problem of ascer lating to determining the ballistic trajectory of taining on board the missile, without the need a projectile, as well as a device for carrying for a manual data input regarding the firing out the method. 75 factors, the ballistic trajectory or the actual It is known to provide means for the end- initial flight path of the fired projectile.

phase steering of artillery projectiles (see the In order to solve this problem, there is pro article by Peter J. Geogre in---WEI-IRTECHNIK- vided in accordance with the invention, a 3/79, pages 19, 22, 24,27) which are fired in method of determining characteristic data of a a caseless manner and without self-propulsion 80 ballistic firing flight path of a projectile, such so that projectiles initially describe a purely as an artillery projectile which self-controls its ballistic trajectory which is afforded by the flight end phase, characterised in that on propellant-charge number (e.g. the launching board the projectile, during and after the firing speed) and the weapon barrel elevation. thereof from a weapon barrel, the muzzle This Application is divided from our Applica85 velocity and the timespan between firing and tion No. 2134632A which discloses a method apogee passage of the projectile are mea for the target homing of a projectile such as sured, which, in relation to preset ballistic an artillery projectile which is self-controlling in characteristic values of the projectile, repre its flight end phase along a flat flight path, sent a measure of the firing propellant-charge such as a range extending glide path at a 90 number and the firing elevation angle, and small angle of inclination, from which a target thus a determination the ballistic firing flight search and target homing is effected, charac- path of the projectile. There is further pro terised in that after detection of the target vided a device for the input of the character object that is to be homed in on initially the istic values of a ballistic firing flight into the flat flight path is still maintained, before upon 95 store of a navigation computer on board a further distance shortening with regard to the projectile which is self- steering along a flat target object a pitch-angle control for transi- end-phase flight path, such qs for carrying out tion from the flat flight path into a steeper the method of the invention, characterised in target approach path is effected; and further that provided on board the projectile is a time discloses a device for steering a projectile, 100 measuring circuit for measuring the timespan such as an artillery projectile, which self-con(t41 t42) which elapses between the exit of trols in a program me-controlled manner its two sensors, offset relative to one another by flight end phase and which is equipped with a a specific distance along the projectile, from target search mechanism, with regulating and the muzzle of a firing weapon barrel, and con control mechanisms and with control surfaces 105 nected to which circuit, for determining the for the transition from a ballistic firing flight apogee timespan (tl/t41 t2), is an apogee path into a flat range extending flight path and detector, so that items of information which then for steering into a target approach path, are dependent upon these time spans are for example for carrying out said method; transmitted as the ballistic firing characteristic characterised in that a navigation computer is 110 values into the store.

connected subsequent to a store for charac- This solution stems from the realisation that teristic data of the ballistic firing flight path the purely ballistic trajectory or flight path, can and for the transition, ensuing therefrom, into be determined not solely from the firing barrel the flat flight path, the navigation computer elevation and propellantcharge number, i.e.

having a flight-path extrapolation computing 115 from data specific to the gun, but can also be mechanism to which also the target search determined specifically from the muzzle velo mechanism is connected and which detercity and apogee instant, in other words from mines a pitch-angle change point in time for a actual flight derived data. This flight derived pitch angle change for steering of the projec- data can be ascertained on board the projec tile control surfaces to give a steeper target 120 tile itself, from which data therefore the approach path, the pitch-angle change point in sought flight-path information can be made time being delayed as compared with a target available on board the projectile, without hav acquisition point in time and delivered into a ing to in-put manually information specific to flight-cycle time control circuit so that the flat the gun.

flight path is maintained until the pitch angle 125 An embodiment of the invention is de change point in time is reached. scribed, by way of example, with reference to It is known to in-put manually on the projecthe accompanying simplified diagrammatic tile that is to be fired (prior to introduction drawings, wherein:

thereof into the weapon barrel) characteristic FIGURE 1 shows the entire flight path of a values regarding the barrel elevation and proprojectile over the path covered above ground; 2 GB2177213A 2 FIGURE 2 shows, in a detail representation enlarged as compared with FIGURE 1, the flight end phase beginning with onset of the target search phase; FIGURE 3 shows a block schematic diagram 70 of essential functional elements for control of the projectile during in the flight end phase represented with FIGURE 2; and FIGURE 4 shows a block schematic diagram of a device of the invention for an on-board ascertainment of the ballistic firing flight path of the projectile for obtaining information for control of the end-phase represented in with FIGURE 2.

The projectile 21 sketched in FIGURE 1 represents a caseless artillery shell which is equipped with control circuits and control means for an end-phase steering and with a built-in target search mechanism for increasing the accuracy of fire.

The projectile 21 is fired from a weapon barrel 22. A purely ballistic firing flight path 23 and therewith the orientation of the projec tile 21 relative to the horizontal results from the elevation wi of the weapon barrel 22 at the firing point zl, taking into account factors such as the flow geometry of the projectile 21 and the control fins being swung out, as shown, immediately after the firing; and from the firing or muzzle velocity vl of the projec- 95 tile 21. The latter in turn is determined by the number # (in other words the quantity) of the firing propellant charge s which are arranged and ignited, for the initial acceleration of the projectile 21, behind the projectile in the wea- 100 pon barrel 22. For a purely ballistic flight path 23 there would thus emerge a ballistic point of impact z3.

To achieve a greater combat range, the pro- jectile 21 is steered into a non-ballistic range 105 extending 'linearly- flat flight path 25. For this, after flying through the apogee 26 of the height h2 above the location z2, flight stabilisation and control measures are initiated in a programme-controlled manner by means of the 110 control surfaces 24, and lift wings 27 (see FIGURE 2) are run out (deployed). From the stored advance data for the automatic control along the flat flight path 25 and the firing derived ballistic flight data there would result an advanced point of impact z 11 of the projectile 21 in a correspondingly further remote target zone.

The projectile is steered out of the ballistic flight path 23 so that the inclination w25 (FIGURE 2) of the approximately linear flight path 25 amounts typically to 20' relative to the horizontal. From this, in the advanced target point of impact z11 1 an impact path angle wil of the order of magnitude of also 20' would result, which would however represent an un favourable attack effective angle with respect to the combat charge in the projectile 21.

Therefore there is effected an approach the target object 28 to be combatted in the actual130 target point M with a target approach path 29, made steeper relative to the flat flight path 25, at an actual target path angle w8 which is at least twice as large as the impact path angle wil in the case of the uninfluenced flat flight path 25, and preferably lies in the order of magnitude of 45', whereby to greatly improve the effectiveness of the combat charge in the projectile 21 upon the target object 28 to be attacked.

The so-called flight end-phase begins with the failing below of a preprogrammed target search height h4, which is preset in accordance with the target search and target track- ing mechanism 30 incorporated into the projectile 21 and in the case of a millimetre-wave radar target search mechanism 30 the height is for example of the order of 650 m to 700 m, whereupon the target search mechanism 30 (FIGURE 3) is switched on. Because constructional reasons restrict the angle of pitch relative to the flight angle of the projectile 21, and because of the, somewhat steeper, inclination of the flat flight path 25 downwards, there results a target-acquisition limiting angle w6 of, for example, 35' (FIGURE 2); which is why from the position of the search start location z4 only target objects 28 can be acquired which lie beyond the nearest acquisition point z6. Potential target objects beyond the advanced point of impact zl 1 of the flat flight path 25 cannot as a rule be attacked from this, because that would require a reversal of direction (decrease in inclination) of the flight path angle w25, which would as a rule be impermissible because it would apply high accelerative forces to the projectile which could affect the mechanical stability of the projectile 21 and the mechanisms incorporated therein.

If the intended target object 28 were to be attacked directly, upon being acquired by the target search mechanism 30, by target tracking homing of the projectile, a target tracking path 31 would occur which would indeed deviate downwards from the flat flight path 25, but would still yield a too small and therefore unfavourable impact path angle w31 for effective attack.

In the present embodiment, provision is made to control the projectile 21, even after acquisition of the intended target object 28, in such a way that, whilst its yaw direction is immediately changed at the target acquisition point z5 towards the direction of the target object 28, the projectile continues to follow the actual flat flight path 25 so that its inclination is maintained.

A delayed point in time t7, for a change of angle of pitch for the derivation from the flat flight path 25, is ascertained in accordance with the proximity to the target object 28, taking into account the theoretical end flight time as far as the linearly advanced point of impact A of the flat flight path 25 and the target approach path 29 striven for, on board i 3 GB2177213A 3 c 10 t c the projectile 21 as a delay or residual flight timespan t5 to t7. At the point in time 0 then initially the target tracking and the regulation for the previous maintenance of the pro5 jectile path inclination w25 are transiently interruptd and a non-controlled change to a steeper angle of pitch undertaken; whereupon the flight attitude regulation is again put into operation in accordance with this more steeply preset path impact angle w8, in conjunction with target tracking, switched on again, by means of the target search mechanism 30.

For these flight phases, shown in FIGURE 2 as height/path diagrams, for attacking the tar- get object 28 at an optimum target-path impact angle w8, provided on board the projectile 21 is a time control circuit 32 (FIGURE 3). (in FIGURES 3 and 4 lines are denoted by the reference characters accorded to the specific information referred to hereinafter, for the sake of brevity.j The circuit 32 determines the function of the time t and thus, from the known data of the ballistic and the flat flight paths 23 to 25, the point in time t4, so that, as the limiting height h4 for the commencement of the target search is fallen below, the target search mechanism 30 is thus put into operation. Upon target acquisition at the point in time t5, the target search mechanism 30 provides follow-up control information regarding the horizontal target displacement 33 and the vertical target displacement 34, in each case related to the instantaneous spatial orientation of the projectile 21 in its situation rela- tive to the flat flight path 25. The horizontal target displacement information 33 serves immediately as control information for a yaw target follow-up regulator 35. A simple flightpath extrapolation calculating mechanism 36, determines the point-in-time t7 for the initiation of the pitch maneouvre from the flat flight path 25, which maneouvre, as mentioned, is intended to be left for the transition into the steeper target approach path 29.

After receipt of the point-in-time information t7 from the mechanism 36, the time control circuit 32 supplies, upon occurrence of the point in time t7, to pitch regulation mechanism 37 an item of information to cause the pitch control system to be initially interrupted for the change into the steeper target approach path 29, and, after renewed achievement of a stable flight state, to put the regulation mechanism 37 into operation again, but now taking into account the new path-direction desired value w8 and the follow-up control by the target search mechanism 30 which is likewise interrupted or switched off and on again. By appropriate control of the adjusting members for the control surfaces 24 from the yaw target follow-up regulator 35 and the pitch regulation mechanism 37 there is effected an end-phase steering in accordance with the target approach path 29 up to impact at the target point z8.

For the characteristic values of the actual data regarding the initially ballistic flight path 23 and the following flat flight path 25, for determining the point in time t7 of the pitch angle change, as well as for the determining, derived from the path data, of the point in time t4 for the beginning of the flight endphase target search, a store 38 is provided. Into this there are in-put prior to the firing point in time t1 (FIGURE 1)-or immediately afterwards and at any rate prior to the transition into the flat flight path 25 after reaching of the apogee point in time t2-the firing data which determine the ballistic flight path 23 of the projectile 21 and which correspond to the elevation angle wl and the muzzle velocity v1 of the projectile 21. Together with projectiletypical characteristic values preset in the store 38 there can thus be determined by a naviga- tion computer 54 the height/time flight path picture (as is shown in FIGURE 1 and FIGURE 2 (taking into account the time coordinates t over the location z), after which the described search and control procedures can be trig- gered by the time control circuit 32.

The actual elevation and velocity data wl, v 1, or the range z 1 to z 11 calculable therefrom, are set customarily by means of externally accessible adjusting elements on the pro- jectile 21, that is to be fired, prior to loading thereof into the weapon barrel 22 in accordance with the inclination wl thereof and in accordance with the propellant charges that are to be supplied. This handling is, however, very prone to non-reproducible false settings or inputs, particularly under combat factors.

In this embodiment of the invention, provision is made for determining this initial data, decisive for the flight paths 23 to 25, and thus for the time course of the control interventions from the time control circuit 32, without the need for a manual setting, immediately after the firing of the projectile 21, on board the projectile 21 and for feeding the data into the store 38.

In the projectile walling 40 are two exit sensors 41, 42 which respond to the leaving of the weapon barrel 22 through the muzzle thereof, to ascertain the muzzle or exit velo- city v1. The sensors 41, 42 are offset mutually by a specific extent 39 in the direction of the velocity vector and thus in the longitudinal direction of the projectile 21. The sensors 41, 42 may be opto-electronic pick-ups which re- spond to the jump in the ambient brightness upon exit from the weapon barrel 22, or preferably simply coil arrangements which supply exit signals t4l, t42 as a result of the field change at the weapon barrel muzzle.

Upon or in consequence of firing of the projectile 21 in the weapon barrel 22, a power source 44 is activated, for example by control from an acceleration sensor 45. The power source 44 can, for example, be an activatable battery, the electrochemical components of 4 GB2177213A 4 which are now brought into action with one another, or be a thermoelectrical or pizoelectri cal generator which, by reason of the temper ature difference behind and in front of the rearward end of the projectile 21 or respec tively the initial acceleration thereof, supplies electrical power into the signal processing cir cuit (in accordance with FIGURE 3 and FIGURE 4). What is crucial is the fact that upon exit from the weapon barrel 22 in any event al ready the electrical power is available to meet the needs a time measuring circuit 43 (for example a counting circuit for equidistant or regular timing impulses) in order to ascertain the timespan t41 to t42. Since the installation distance 39 is preset constructively, in other words is known, it is sufficient, for the ascer tainment of the firing velocity v11 from that timespan t41 to t42, to provide, instead of a computer, a table- or reference correlation or decoding store 47. Connected subsequent to this there could be an appropriate translation matrix 48 by means of which the velocity in formation would be expressed as propellant charge number, as is more customary, in the case of artillery, than the numerical value re garding the firing velocity v1 of the projectile 21.

A time-dependent or path-dependent deter mination of the ballistic flight path 23, can be made from the necessary knowledge of the muzzle velocity A together with knowledge of the firing elevation wl; and the latter would indeed be determinable by measuring tech niques from the actual factors pertaining upon the firing of the gun, but this information is needed on board the fired projectile 21 in or der, as described in connection with FIGURE 3, to determine the end point 11 and to de rive therefrom the point in time for the control procedures for a delayed and thereby steeper target approach path 29. It is proposed herein to make a determination of the purely ballistic flight path 23 from the muzzle velocity A of the projectile 21 in combination with the point in time t2 of the passage thereof through the apogee 26, by means of an apogee detector 49 provided on board the projectile 2 1. The apogee detector may comprise a pressure sensor 50 which supplies a signal regarding the derivative trend in pressure with respect to time during the first time period derived from the flight path height h; or/and of an acceleration sensor 51 which supplies, as out put signal, directly an item of acceleration information or else the second temporal deriva tion of the height course of the ballistic flight path 23. Connected subsequent to these sen sors 50 or/and 51 is at least one zero indica tor 52 which supplies a signal (t2) to the time measuring circuit 43 when the ballistic flight path 23 (FIGURE 1) passes in the apogee 26 through its height maximum over the time t or respectively over the path z.

The timespan tl (respectively with sufficient 130 accuracy t4l or t42) to t2 thus represents the second necessary characteristic value for determining the theoretical course of the purely ballistic flight path 23. Together with the al- ready ascertained velocity information in corresponding the actual propellant-charge number #, thus by way of a further reference table or decoding matrix 53 on board the projectile 21 the associated value of the firing elevation wl can be ascertained, or the matrix input information can be evaluated directly for the path determination.

These items of information (vl, t2) (which correspond to the decisive characteristic data (wl, Q for the describing of the ballistic flight path 23) are, as explained in connection with FIGURE 3, stored immediately in the store 38, in order to determine therefrom, by way of a navigation computer 54, the theoretical impact point-in-time or instant t1 1 of the projectile 21 in the advanced path end point z1 1. From this impact instant t1 1, occurring only upon absence of the target acquisition, then by means of the calculating mechanism 36, on board the projectile 21, as explained in connection with FIGURE 2 and FIGURE 3, it is extrapolated what delay timespan t5 to t7 after target acquisition (t5 over z5) up to the delayed pitch angle change is to be preset in order then to initiate the target approach path 29 (which provides the considerably improved steeper impact path angle w8) from the control circuit 32.

These point-in-time ascertainments and flight path transitions are ensurable, with comparatively slight cost, in an exceedingly exact and reproducible manner on board the projectile 21, as an apogee detector 49 (FIGURE 4) is present on board the projectile 21 for the combination of the flight paths 23 and 25. This is because the apogee 26 of the ballistic firing flight path (which the projectile leaves only after the apogee) extends transiently horizontally; and because the flight attitude of the projectile 21 upon passage through the apogee 26 is practically horizontal or in any event divergent only by a slight (and in this respect preset, or known) flight angle-of-incidence relative to the horizontal. Therefore, the apo- gee instant t2, the instantaneous orientation of the projectile 21 in space can be accepted as a horizontal reference position for the function of the pitch regulation mechanism 37 (for control of the projectile along the paths 25 and 29), for example by resetting or zeroing a gyroscopically-stabilised position reference system and of a pitch speed integrator, as taken into account symbolically in FIGURE 3 by a pitchposition reference transmitter 55. The end-phase steering control, crucial for the accuracy of fire, along the flat path 25 is thus effected in an exceedingly precise manner, because previously, namely immediately prior to leaving the ballistic firing path 23, the pitch reference value, crucial for the path angle GB2177213A 5 # 10 t v 45 c w25/1 1, has been obtained from the actual flight factors of the projectile 21 itself.

The invention generally provides methods and means to produce a more favourably ef fective target approach path 29 and for re moving the need for error-prone firing-date in puts into the driveless projectile 21 that is to be fired from a weapon barrel 22 and which changes in a self-controlled manner from a ballistic firing flight path with linking flat flight 75 path 25 into an end-phase flight path from which a located target object 28 is homed in on. For this, a change point in time t7 for a pitch angle change out of the flat end phase flight path 25 is delayed relative to the target 80 acquisition point in time 65, whilst the projec tile 21 is still moving in accordance with the preset flat flight path 25, so that only upon the change point in time is the projectile turned to the more steeply extending target approach path 29. To detemine the optimised change point in time 9 in relation to the ap proach to the located target object 28, a theoretical impact point in time z '11 of the flat flight path 25, taking into account the ballistic firing flight path 23, is computed on board the projectile 21; for this the actual ballistic firing flight path 23 is ascertained from the times- pans t41... t42, from the exit velocity vi of the projectile 21 from the weapon barrel 22 and from the time tl/t41... t/2 up to passage through the apogee 26 which are measured on board the projectile. Additionally, by mea suring the apogee, the build-up of a positional reference for the path control is made pos sible.

Claims (12)

1. A method of determining characteristic data of a ballistic firing flight path of a projec tile, such as of an artillery projectile which self-controls its flight end phase, characterised in that on board the projectile during and after the firing thereof from a weapon barrel the muzzle velocity and the timespan between fir ing and apogee passage of the projectile are measured, which, in relation to preset ballistic haracteristic values of the projectile represent a measure of the i ring prope llant-charge number and the fi ring e levation angle, and us a determination of the ballistic firing flight path of the ojectile.

2. A method as claimed in Claim 1 charac terised in that to determine the launching velo city of the projectile a timespan is measured 120 etween the instants at which two points, at a specific distance from ne another along the projectile, emerge from the barrel as the pro jectile leaves the weapon barrel.

3. A method as claimed in Claim 1 or 2, characterised in that, to obtain information regarding the ballistic flight path, on board the proj ectile upon or a fter Isunching thereof an evaluation of acceleration measuring signals is undertaken.

4. A method as claimed in Claim 1, 2 or 3, characterised in that the timespan is measured which elapses between an instant of the propulsion of the projectile in the weapon barrel and the instant when the ballistic flight path of the projectile passes through its height maxiMUM.

5. A method as claimed in Claim 1, characterised in that, to determine the muzzle velocity, and thus the propellant-charge number, a timespan is measured which lies between the points in time of exit of two points given at a specific spacing along the projectile when the fired projectile leaves the weapon barrel; whilst to determine the firing elevation, in addition to the thus ascertained muzzle velocity, the timespan is measured which elapses between a point in time of the progression of the projectile in the weapon barrel and the point in time when the ballitic firing flight path of the projectile passes through its height maximum.

6. A device, for providing characteristic values of a ballistic launching flight path for a store of a navigation computer on board a projectile which is selfsteering along a flat end-phase flight path, characterised in that the device is provided, on board the projectile, with a time measuring circuit for measuring a timespan (t41... t42) which elapses between the emergence of two sensors, mutually offset by a defined distance along the projectile, from the muzzle of a launching weapon barrel, which circuit is connected to a measuring cir- cuit, for determining the apogee timespan (t 1 /t41... t2), to provide information dependent upon these timespans which information provides the ballistic launching path characteristic values. 105

7. A device as claimed in Claim 6, characterised in that to the device is arranged to receive an input from an acceleration sensor of the projectile.

8. A device as claimed in Claim 6 or 7, characterised in that a pitch-position reference transmitter is provided, which upon apogee passage provides an item of horizontal reference information for a pitch regulating mechanism.

9. A projectile incorporating a control sys- tem which is constructed or arranged to perform the method claimed in any one of Claims 1 to 5.

10. A projectile incorporating a device as claimed in Claim 6, 7 or 8.

11. A projectile comprising means to detect or ascertain measurements of the velocity of the projectile at the moment of discharge of the projectile from a weapon barrel and the actual height of apogee or moment at which the missile reaches apogee; means to store information relating to the ballistic or aerodynamic characteristics of the projectile; and means to derive from said measurements and information a determination of the flight of the 6 GB2177213A 6 projectile to apogee.

12. A device or a projectile incorporating a device arranged, substantially as hereinbefore described with reference to FIGURE 1 or FIGURE 4, of the accompanying drawings, to ascertain characteristic values of a ballistic flight path of a or the projectile from firing to apogee.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1987, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.