WO1999030105A1

WO1999030105A1 - Method and device for trajectory correction of aerodynamic projectiles

Info

Publication number: WO1999030105A1
Application number: PCT/SE1998/002047
Authority: WO
Inventors: Kjell Albrektsson
Original assignee: Bofors Weapon Systems AB; Bofors AB
Current assignee: Saab Bofors AB; BAE Systems Bofors AB
Priority date: 1997-12-08
Filing date: 1998-11-13
Publication date: 1999-06-17
Anticipated expiration: 2000-06-08
Also published as: SE9704558D0; SE9704558L; SE513646C2

Abstract

The present design relates to a method and a device for correcting the trajectory (16) of a projectile (1, 13) which is travelling in a balistic trajectory. In accordance with the invention, impulse devices (6, 7) are used to give the projectile (1, 13) when so required a transverse correction to a new projectile trajectory (21) while when necessary the projectile trajectory is corrected in longitude by means of an active retardation of the projectile which shortens the original somewhat overlong projectile trajectory taken. In accordance with a further development of the invention several co-functioning impulse devices (6, 7) arranged on each side of the projectile (1, 13) centre of gravity are used for each trajectory correction in transverse.

Description

METHOD AND DEVICE FOR TRAJECTORY CORRECTION OF AERODYNAMIC PROJECTILES

The present invention relates to a method and a device for correcting the trajectory of a projectile travelling in a ballistic trajectory.

Projectiles which travel in ballistic trajectories such as artillery projectiles and rockets are subjected to a number of different external factors which influence their trajectories. A number of these factors are of such character that they cannot be completely calculated in advance. It has therefore been the practice previously to fire one or more adjustment rounds and to use the impact points of these rounds to correct subsequent rounds. Increased firing ranges for artillery have meant that it was no longer possible to use this method as the time between firing these range-finding rounds and firing the effect rounds became too long and gave long warning times. The method was then changed to measuring the range-firing round in trajectory and making corrections for the subsequent rounds using these measurement values as the basis.

Modern artillery-locating radar makes it possible, however, to localise very quickly an artillery gun which has opened fire. Artillery tactics of the present and future therefore demand that effect firing shall be carried out directly and within a very short time period whereupon the gun must be moved before counterfire is started.

In order to obtain the desired hit pattern, artillery projectiles of the future will require to have their own ballistic trajectories corrected while they are on the way to the target.

The technology required for measuring a projectile position in trajectory and for calculation of the trajectory correction required for the desired hit in target is already in existence. It has also been suggested that for example, artillery grounds can be fitted with so-called impulse devices which on command, give the round an impulse at right angles to the trajectory which results in the round being moved to a new trajectory which depending on the direction of the impulse, can mean a transverse or longitudinal correction. The impulse should be applied at or very close to the projectile centre of gravity as otherwise the result can be undesirable projectile oscillation. In order to attain the necessary trajectory changes, several impulse devices have always been required. As the impulse devices have so far required a relatively large amount of space and furthermore have blocked the most central and spacious parts of the round, this has caused certain problems especially with rounds which shall function as carriers of several submunitions intended to be spread over a pre-determined target area.

The impulse devices have so far consisted of small rocket motors with short burning times and with nozzles collected to form a unit distributed round the projectile periphery near the centre of gravity. A proposal has already been made, however, to use the impulse device which has given the desired impulse force by ejecting heavy metal rods or suchlike from the projectile surface. This type of impulse device must also give the desired impulse close to the projectile centre of gravity.

For all types of impulse control, the projectile rotation position must be checked very carefully using a gyroscope or other device, at the same time as the projectile must have either a fully autonomous guidance function which determines the deviations from the planned ballistic trajectory and gives the necessary commands for activating the impulse device at the correct time, or have a receiver which can receive guidance commands from a ground station from where the necessary trajectory measurements and correction calculations have been carried out.

The total deviation between a calculated ballistic trajectory and the actual trajectory consists of the sum of a number of different error sources with different causes and sizes. The sum of the longitudinal errors and the sum of the transverse errors are roughly the same size even if the relative size of the errors can vary from occasion to occasion. It is therefore necessary to be able to correct both error types to the same degree and, with the technology available up to this point, it has been necessary to ensure the availability of a sufficient number of powerful impulse devices in order to make these corrections.

In accordance with the present invention, a limitation of the use of the projectile impulse device to only transverse corrections is now proposed while the corrections necessary in the flight trajectory longitudinal direction are made by a retardation of the projectile which in its turn, means that the projectile trajectory must always be calculated so that in reality, it is never too short. The retardation of the projectile in question necessary for the method proposed in accordance with the present invention, can then be achieved with considerably less bulky devices than the impulse devices used for transverse correction of the projectile trajectory. In order to retard a projectile flying through the atmosphere in a ballistic trajectory, it can be sufficient to remove a major or minor part of the projectile aerodynamically designed retardation devices. A further advantage is that these retardation devices do not necessarily need to be close to the centre of gravity of the projectile.

In accordance with the present invention, it is therefore possible to save in principle almost half the space for the impulse devices compared with the case in which the devices are also used for the necessary correction in longitude as the devices for longitudinal correction are now located in the projectile nose section.

In accordance with one version of the invention, it is also proposed that for trajectory correction using impulse devices, instead of using one impulse device which gives an active trajectory correction impulse close to the^centre of gravity of the projectile, that at least two impulse devices are used, one of which is located in front of the centre of gravity in the direction of flight, and one of which is located to the rear of the centre of gravity, and also that these devices are activated simultaneously, upon which the impulse devices selected, which can be of rocket or solid (projectile) type, are so adjusted regarding the distance to the projectile centre of gravity and also so directed, that they together give the projectile an impulse the effect of which is close to the centre of gravity, and thereby provides a new projectile trajectory without oscillation. Should a trajectory correction be necessary which is greater than can be obtained using such a pair of impulse devices or charges, several correction steps can be used in accordance with previous technology in which a gyro or other roll position checking device which is available, is used in order to give these trajectory corrections in the correct direction.

By dividing the impulse devices necessary for projectile trajectory correction into two groups which are placed at a distance from the projectile centre of gravity and allowing these to function together for trajectory corrections, it is possible to release the centre section of the projectile which is also usually the section with the greatest diameter, for an active pay load such as submunitions.

The proposal that the projectile trajectory correction in transverse is carried out by means of impulse charges, and in longitude by possible retardation, requires only that the projectile trajectory shall never by too short but can, on the other hand, initially provide a range which is too long.

The said invention is defined in the subsequent patent claims and is now further described in connection with the enclosed figures of which

Figure 1 shows a schematic longitudinal section through an artillery round Figure 2 shows a cross-section along II: II in Figure 1 and Figure 3 shows a schematic plan of a trajectory correction in accordance with the invention.

The artillery round shown in Figure 1 has a centre section 2 for active payload, for example submunitions, a front section 3 with gyro for control of the shell instantaneous roll angle receiver for correction orders and devices for carrying out the orders, while the rear section 4 has a location for a base-bleed device and is fitted with deployable fins 5. The fins 5 are essential in this context as it is considerably easier to correct the projectile trajectory using impulse motors for a fin-stabilised ballistic projectile than for a roll-stabilised projectile. A front and a rear group of impulse devices 6 and 7, are also included. The figure also shows a separation charge 8 for the active payload in the projectile centre section 2. The front section of the projectile has a removable ring-formed section 9. If this is removed, the projectile's ldrag is increased considerably and this has a retardation effect on the projectile resulting in a shortening of its ballistic trajectory. Part 9 can also be replaced by deployable brake flaps of various designs.

As shown in Figure 2, the impulse devices 6 and 7 include a number of radially directed impulse charges 10 together with a centrally located part 11 in which the ignition functions for the various impulse charges are expected to be located. The radial positioning of the impulse charges provides space for a large number of small but sufficient impulse charges within a small projectile volume.

The sequence which is initiated by the method in accordance with the invention is also illustrated in Figure 3. An artillery gun positioned at 12 fires a round 13 which corresponds to round 1 in Figure 1. It would be desirable for this round to follow accurately the dashed trajectory 14 towards the target 15 which is assumed to consist of a bridge. Various error sources which cannot be entirely predicted have the result, however, that the round follows the partially dashed and partially fully drawn trajectory 16 towards the impact site 17. As shown in the figure, this is a transverse error and is beyond the target. From the measurement unit 18, measurement of the projectile 13 trajectory is carried out and the incorrect trajectory can be confirmed by calculation. At point 19, the round then receives the order to initiate an impulse charge in one and each of the groups of impulse motors 6 and 7. This results in the schematically marked trajectory change marked with the arrow 20. Following the trajectory change, the projectile 13 therefore follows the new trajectory 21 which is partially fully drawn and partially ring-dashed. This new trajectory 21, would if completed result in impact at point 22, that is correct in transverse but too long. A retardation is therefore initiated at point 23 which provides a projectile trajectory 21 modification 24 which, as the figure shows, would result in a hit in the target.

Claims

PATENT CLAIMSWe hereby claim and desire to secure by Letters Patent the following.

1. A method for correcting the projectile trajectory (16) on route to a pre-determined target (15) of a projectile (1, 13) in a ballistic trajectory fitted with impulse devices for trajectory correction with consideration to the measurement of errors confirmed in the trajectory w h e re i n measurement of errors in transverse confirmed in the trajectory are corrected by the activation of the requisite number of impulse devices (6, 7) while the projectile (1, 13) trajectory in longitude is initially corrected so that irrespective of unforeseeable errors the trajectory is never too short and the calculated longitudinal error at the time of the measurement is corrected by retardation of the projectile achieved by an increase of the projectile drag.

2. A method as claimed in Claim 1 w h e r e i n instantaneously initiated impulse devices (6, 7) positioned both in front of and to the rear of the projectile centre of gravity are used for the correction of the projectile (1, 13) trajectory in transverse.

3. A method as claimed in Claim 1 or 2 w h e r e i n the impulse forces of each impulse device (6, 7) are adapted to their distances to the projectile centre of gravity so that the projectile is not caused to oscillate when it is transferred to its new trajectory (21).

4. A method as claimed in Claim 3 w h e r e i n the projectile trajectory is limited in longitude by the removal of a larger or smaller part preferably of the aerodynamically formed nose section (9) on command at a time which is calculated on the basis of the measurement of the error confirmed in the trajectory.

5. Device for in accordance with the method in Claims 1-4 correction of the projectile trajectory of a projectile (1, 13) which is of the type fitted with impulse devices (6, 7) fired into a ballistic trajectory for correction of the projectile trajectory (16) with consideration to the trajectory errors (21) confirmed by measurement in the trajectory h e r e i n the projectile besides the impulse devices (6, 7) designed so as to correct the projectile trajectory in transverse when activated also includes devices with which the projectile dragcan be increased in order to shorten the projectile trajectory in longitude.

6. A device as claimed in Claim 5 wh e rei n on each side of its own centre of gravity the projectile has a group of impulse devices (6, 7) one of which from each group can be instantaneously initiated on command in order to give the projectile the required transverse trajectory correction.

7. A device as claimed in Claims 5 to 7 w h e r e in the retardation (9) of the projectile is activated by the removal of parts of the aerodynamically formed front section or by means of deployable flaps or devices with the same function.

AMENDED CLAIMS

[received by the International Bureau on 5 May 1999 (05.05.99); original claims 1 and 5-7 amended; remaining claims unchanged (2 page)]

We hereby claim and desire to secure by Letters Patent the following.

1. A method for correcting the projectile trajectory (16) on route to a pre-determined target (15) of a projectile (1, 13) in a ballistic trajectory fitted with impulse devices for trajectory correction with consideration to the measurement of errors corifirmed in the trajectory w h e r e i n measurement of errors in transverse confirmed in the trajectory are corrected by the activation of the requisite number of impulse devices (6, 7) while the projectile (1, 13) trajectory in longitude is initially corrected never to be too short and that the calculated longitudinal error at the time of the measurement is corrected by retardation of the projectile achieved by an increase of the projectile drag.

2. A method as claimed in Claim 1 h e r e i n instantaneously initiated impulse devices (6, 7) positioned both in front of and to the rear of the projectile centre of gravity are used for the correction of the proj ectile ( 1 , 13) traj ectory in transverse.

3. A method as claimed in Claim 1 or 2 h e r e i n the impulse forces of each impulse device (6, 7) are adapted to their distances to the projectile centre of gravity so that the projectile is not caused to oscillate when it is transferred to its new trajectory (21).

4. A method as claimed in Claim 3 h e r e i n the projectile trajectory is limited in longitude by the removal of a larger or smaller part preferably of the aerodynamically formed nose section (9) on command at a time which is calculated on the basis of the measurement of the error confirmed in the trajectory.

5. An artillery projectile (1, 13) of the type provided with impulse devices (6, 7) for the correction of its ballistic trajectory (16), said impulse devices being intended to be fired for correction of said trajectory with consideration of the trajectory errors (21) confirmed by measurement in said trajectory h e r e i n the projectile besides the impulse devices (6, 7) designed so as to correct the projectile trajectory in transverse when activated also includes devices with which the projectile drag can be increased in order to shorten the projectile trajectory in longitude in accordance with the measurement.

6. An artillery projectile as claimed in Claim 5 w h e r e i n on each side of its own centre of gravity the projectile has a group of impulse devices (6, 7) one of which from each group can be instantaneously initiated on command in order to give the projectile the required transverse trajectory correction.

7. An artillery projectile as claimed in Claims 5 to 7 h e r e i n the retardation (9) of the projectile is activated by the removal of parts of the aerodynamically formed front section or by means of deployable flaps or devices with the same function.