SYSTEM FOR GUIDING A PROJECTILE

Abstract: The invention relates to a system for guiding at least one projectile provided with a roll position stabilization. By means of a laser, a raster is written in a solid angle surrounding a target. An inventive timing of the raster enables the projectile to independently determine its position in the solid angle and to make in-flight corrections.

Description: System for guiding a projectile System for guiding, from a reference system by means of an electromagnetic radiation beam, at least one projectile to a target, comprising: means for determining a rotational position of the projectile relative to the reference system; a beam generator incorporated in the reference system for generating the beam and a deflection arrangement for deflecting the beam in azimuth and elevation according to a preselected pattern; a receiving device incorporated in the projectile for receiving the beam, a processing unit and guidance means for guiding the projectile on the basis of information derived from the beam. A system of this type can be used for target engagement on the basis of small, inexpensive projectiles that are not equipped with sensors to independently detect the targets. These projectiles will receive the necessary directives from the reference system, for instance a ship. It is of importance to code the directives such that the processing within the projectile can be reduced to a minimum and that moreover a compact system is obtained which is difficult to jam. The present invention realizes a system of this type and is characterized in that the deflection arrangement is designed to cause the beam to execute a raster scan, the processing unit being designed to generate control signals for the guidance means on the basis of successive points in time on which the beam is received by the receiving device. A favourable embodiment of the invention has the advantage that aside from the known rotational position and the information implied in the scan itself, no further information is required and is characterized in that the deflection arrangement is designed to alternately perform, in a fixed time sequence, scans of a first type, in which parallel line scans are executed in a first direction, and scans of a second type, in which parallel line scans are executed in a second direction, such that the first direction and the second direction are at least substantially opposed and a line is scanned consecutively in both directions. In a further advantageous embodiment, the line scans are spaced at least substantially equidistantly. A still further advantageous embodiment of the invention in which the processing can be reduced to a minimum, is characterized in that the processing unit is designed to determine a shortest interval between the successive reception of the beam in order to guide the projectile in a direction of a line scan, the processing unit being designed to determine a longest interval between the successive reception of the beam for guiding the projectile in a direction perpendicular to the line scan. A still further advantageous embodiment of the invention that realizes a compact system which is difficult to jam is characterized in that the beam generator comprises a laser, which may be of the CW type. A further advantageous embodiment of the invention in which an even greater suppression of possible interference sources is realized, is characterized in that the receiver comprises a detector which is at least substantially suitable for the detection of light emitted by the laser. The invention will now be explained in further detail with reference to the following figures, of which: Fig. 1 represents a block diagram of the system according to the invention; Fig. 2A represents a possible scan of the first type and two projectiles; Fig. 2B represents a possible scan of the second type and two projectiles; Fig. 3A indicates the points in time on which the first projectile is illuminated; Fig. 3B indicates the points in time on which the second projectile is illuminated. Fig. 1 represents a block diagram of the system according to the invention in which a reference system l, for instance a ship, transmits an electromagnetic radiation beam 2 in the direction of a projectile 3 for guiding the projectile to a target not shown here. Projectile 3 is provided with prior art means 4 for determining its rotational position relative to reference system 1, or for keeping the rotational position constant. Reference system 1 is provided with a beam generator 5, for instance a laser, and with a deflection arrangement 6, for instance a prior art system of mechanically adjustable mirrors or a system of acousto-optical deflectors on the basis of which beam 2 executes a raster scan in such a manner that the target is always located at least substantially in the raster centre. To this end use is made of positional data pertaining to the target which have been obtained by means of additional means not shown here, for instance a radar installation. Beam 2 is received by projectile 3 by means of a receiving device 7, for instance a detector, suitable for the wavelength of the electromagnetic radiation emitted by beam generator 5, and is processed in a processing unit 8, which may be a digital computer. Processing unit 8 generates, possibly in association with the means 4 for the determination of the rotational position, control signals for guidance means 9 in such a manner that the projectile 3 is guided towards the target. If a traditional raster scan is performed, for instance similar to the build-up of a TV image, the projectile 3 will, each raster period, be briefly illuminated by beam 2. A modified raster scan as presented in Fig. 2A and Fig. 2B is required in order to guide projectile 3. Fig. 2A shows a line being scanned consecutively in two directions. A projectile 10 situated on the left of the scan centre will then be illuminated twice with a time difference roughly corresponding to two line times, i.e. twice the duration of one line time. A projectile 11 situated on the right-hand side of the scan centre will be illuminated twice with a considerably smaller time difference. More precisely, the time difference is proportional to the horizontal position of the projectile and the time difference for a projectile which is exactly on course is precisely one line time. Fig. 2B shows that a similar effect can also be obtained by scanning the raster from bottom to top. Also here, the time difference is proportional to the horizontal position of the projectile. If the raster presented in Fig. 2A and Fig. 2B is written consecutively, projectile 10 will be illuminated four times, twice after approximately two line times and twice at an interval of approximately two raster times as the projectile is situated at the top of the raster. Since projectile 11 is situated at the bottom of the raster, it will be illuminated twice at an interval of a fraction of one line time and subsequently twice after a fraction of one raster time. By way of illustration, Fig. 3A shows the illumination of projectile 10 as a function of time. It is assumed here that firstly a raster according to Fig. 2A is written in 2.5 msec, followed by a raster according to Fig. 2B after which no emissions are made during a period of 5 msec in order to prevent ambiguity. It can be seen that the projectile is illuminated twice in quick succession with a time difference of approximately two line times. Subsequently, a waiting period of almost two raster times is required, after which two illuminations are received again. Fig 3B shows a similar situation for projectile 11, but as projectile 11 is in a right-hand downward position, the intervals between the illuminations occurring in rapid succession and the intervals between the illuminations resulting from the two successive rasters are both shorter. Processing unit 8 may be of a relatively uncomplicated design. It determines the shortest interval between successive illuminations. If this interval is shorter than one line time, it controls guidance means 9 such that projectile 3 will shift leftwards. If the interval is longer, projectile 3 is guided rightwards. It also determines the longest interval between two successive illuminations. If that interval is shorter than one raster time, projectile 3 is guided upwards. If the interval is longer, projectile 3 is guided downwards. In this context it is assumed that additional means, for instance a radar installation, are available for generating positional data pertaining to the target so that the raster is written in such a way that the target is situated in the raster centre. Should, however, projectile 3 be far smaller than the target, reference system 1 can be provided with additional detection means for receiving the target's light reflection on the moment that the target is illuminated by beam 2. This makes it possible to readjust the raster such that the target is kept in the raster centre, thus obviating the need for incorporating additional means. The explanations to Fig 2 and Fig 3 are based on the assumption that projectile 3 has a stabilized roll position which gives a meaning to concepts such as top and bottom. If this is not the case and the only known factor is the roll position relative to reference system 1, the same arguments apply in fact, although then the roll position needs to be compensated for in accordance with procedures known in the art.

Claims: Claims 1. System for guiding, from a reference system by means of an electromagnetic radiation beam, at least one projectile to a target, comprising: means for determining a rotational position of the projectile relative to the reference system; a beam generator incorporated in the reference system for generating the beam and a deflection arrangement for deflecting the beam in azimuth and elevation according to a preselected pattern; a receiving device incorporated in the projectile for receiving the beam, a processing unit and guidance means for guiding the projectile on the basis of information derived from the beam; characterized in that the deflection arrangement is designed to cause the beam to execute a raster scan, the processing unit being designed to generate control signals for the guidance means on the basis of successive points in time on which the beam is received by the receiving device. 2. System as claimed in claim 1, characterized in that the deflection arrangement is designed to alternately perform, in a fixed time sequence, scans of a first type in which parallel line scans are executed in a first direction, and scans of a second type in which parallel line scans are executed in a second direction, such that the first direction and the second direction are at least substantially opposed and a line is scanned consecutively in both directions. 3. System as claimed in claim 2, characterized in that the deflection arrangement is designed for spacing the line scans at least substantially equidistantly. 4. System as claimed in claim 3, characterized in that the processing unit is designed to determine a shortest interval between the successive receptions of the beam in order to guide the projectile in a direction of a line scan. 5. System as claimed in claim 3, characterized in that the processing unit is designed to determine a longest interval between the successive receptions of the beam for guiding the projectile in a direction perpendicular to a line scan. 6. System as claimed in any of the preceding claims, characterized in that the beam generator comprises a laser. 7. System as claimed in claim 6, characterized in that the laser is a CW type of laser. 8. System as claimed in claim 6, characterized in that the deflection arrangement comprises a system of mechanically adjustable mirrors. 9. System as claimed in claim 6, characterized in that the deflection arrangement comprises a system of acousto- optical deflectors. 10. System as claimed in any of the claims 6 through 9, characterized in that the receiving device comprises a detector which is at least substantially suitable for the detection of light emitted by the laser.

Inventors: OLBERTZ ANTONIUS HENDRICUS MAR, SCHOLZ JOHN ARTHUR, OLBERTZ, ANTONIUS, HENDRICUS, MARIA, SCHOLZ, JOHN, ARTHUR
Applicants: HOLLANDSE SIGNAALAPPARATEN BV, OLBERTZ ANTONIUS HENDRICUS MAR, SCHOLZ JOHN ARTHUR, HOLLANDSE SIGNAALAPPARATEN B.V., OLBERTZ, ANTONIUS, HENDRICUS, MARIA, SCHOLZ, JOHN, ARTHUR
Application year: 1997
Main classification: F41G7
IPC codes: F41G7