Course-correction system for course-correctable objects

Abstract: The invention relates to a course-correction system provided with a transmitting and control device 1 for wireless correction of the course of a launched object provided with a receiving device 2 by transmitting a course-correction signal containing course-correction information C q and identification codes I q for individual or collective correction of objects arranged into fixed or variable groups. The receiving device 2 of each object is thereto provided with identification parameter P k for selecting an identification code I q=m from the course correction signal, for which I q=m = P k . A fixed group is obtained by identical identification parameters P k for the objects within the group, while variable group is obtained with different identification parameters P k but identical course-corrrection information C q for the objects within the group. The identification parameter P k of a launched object has a known relation with the trajectory data, such as e.g. the time of lauching the object.

Description: The invention relates to a course-correction system for wireless correction of the course of launched projectiles, provided with at least one transmitting and control device which, supplied with course data of the launched projectiles, is suitable for generating and transmitting course-correction signals (I m , C m ) (m = 1, 2, ...), I m being an identification code and C m being course-correction information, for correction of the course of the launched projectiles; a receiving device fitted in each projectile k (k = 1, 2, 3, ...) for receiving the course-correction signals to be supplied to the course-correction means for the purpose of executing the course correction, the receiving device of each projectile k being provided with a selection unit, containing an identification parameter P k , the selection unit selecting an identification code I m from the course-correction signals, for which I m = P k , and supplies the corresponding course-correction information C m to the course-correction means to execute the course correction. The invention furthermore relates to a projectile using such a course-corrrection system. A course correction system of this type is known from US-A 3,594,500. More specific the known system is used to correct missiles in-flight. As usually only a few missiles are in-flight simultaneously, these missiles are addressed individually. The purpose of the present invention is to correct gun fire in-flight. In this situation many projectiles are in-flight simultaneously and it is not necessary to address them individually. This would make the computer load of the control device and the data rate of course-correction signals unnecessary high. The invention therefore is characterised in that the selection units of groups of r (r = 2, 3, ...) successively launched projectiles respectively comprise the same identification parameter. The selection unit of a receiving device can be provided with an identification parameter P k in various ways and at different times. The selection unit may be provided with identification parameters through radio or wire communication, at a time before or after launching. The projectiles may be provided with identification parameters, either at the site of the weapon system or during production, in which case the identification parameters are to be read by the transmitting and control device. In a first embodiment of the system according to the invention the identification parameters are transmitted to the launched projectiles by means of a read-out unit mounted on the launching device and that the launched projectiles are provided with a read-in unit to read the parameters transmitted by the read-out unit. The assignment of the same identification parameter P k = I₀ to several projectiles can be realised by repeating this identification parameter at a particular repetition frequency, whether or not at certain intervals. In case of an identification parameter which is coded as a signal having a particular frequency, this can be realised by generating this signal during a certain period of time. In a second embodiment of the system according to the invention an identification parameter is derived from an elapsed time of flight of an projectile. An embodiment suitable for this purpose is characterised in that the selection unit of an projectile k comprises a timer and a launching detector where the launching detector is suitable for initiating the timer at the moment a predetermined time interval after launching of projectile k has elapsed for the purpose of generating a time-dependent identification parameter P k . The projectiles can now be identified on the basis of the time of flight elapsed since the instant of launching. A course-correction signal should then be provided with an identification code representing the time of flight of the projectile for which the correction is intended. The invention will now be explained with reference to the accompanying figures, of which Fig. 1 contains schematic examples of individual and collective control of launched projectiles; Fig. 2 shows an elementary setup of a course-correction system comprising a transmitting and control device and a receiving device; Fig. 3 shows an embodiment of a course-correction system comprising a transmitting and control device and a receiving device applied in a weapon system; Fig. 4 shows an embodiment of a control unit of the transmitting and control device of Fig. 3. Fig. 1 illustrates a transmitting and control device 1 and a number of launched correctable projectiles, which projectiles are each provided with a receiving device 2. The transmitting and control device 1 transmits course-correction signals (I q , C q ) containing course-correction information C q with q ε {1,2,3} and an identification code I q with q ε {1,2,3}. Each receiving device 2 is provided with an identification parameter P k with k ε {1,2,3,4}. Receiving device 2 with identification parameter P k selects from the received course-correction signals (I q , C q ) the course-correction information C q for which the corresponding identification code I q equals the identification parameter P k (I₁ = P₁, I₂ = P₂, I₃ = P₃, I₄ = P₄). Fig. 1a illustrates an example in which the projectiles each have different identication parameters P k and execute individual course corrections (individual control). Fig. 1b illustrates an example in which a number of projectiles have identical identification parameters P k and execute a collective course correction (collective control with fixed groups). Fig. 1c illustrates an example of projectiles each with different identification parameters executing a collective course correction (collective control with variable groups). Fig. 2 contains the most elementary elements of a course-correction system according to the invention. The transmitting and control device 1 generates and transmits signals (C q ,I q ) f containing course-correction information C q and an identification code I q for the purpose of course correction of at least one course-correctable projectile (q = 1, 2, m, ...), which projectile is fitted with receiving device 2. The transmitting and control device 1 is provided with a control unit 3 and a transmitting unit 4. On the basis of trajectory data D p supplied to control unit 3, which data relate to the correctable projectile, and signals D T initiating course corrections, control unit 3 generates course correction information C q for one or more actual or imaginary projectiles launched around a particular firing time TF. In the case of r independent corrections, q may vary from m to m+r. On the basis of firing time TF, transmitting unit 4 subsequently generates an identification code I q and transmits an rf-signal (C q ,I q ) f having a carrier-wave frequency f and containing by means of modulation this course-correction information and identification code. The transmitted correction signal (C q ,I q ) f is received by a receiver 5, tuned to frequency f. By means of demodulation, the information (C q ,I q ) is subsequently derived from the course-correction signal and supplied to a data processing unit 6. This unit 6, by means of identification parameter P k generated by an identification generator 7, selects from the supplied information (C q ,I q ) the correction information C q=m with corresponding identification code I q=m = P k . This correction information C q=m is subsequently supplied to well-known course-correction means 8 with which a course correction of the projectile can be carried out. The said trajectory data D p relating to the trajectory of the projectile may have been obtained by measurement, by calculation, or by means of a combination of both. In the case of a measurement, a sensor is required which determines the position of the projectile. In the case of calculation, a computer is required, such as a fire control computer for a gun system, where the fire control computer predicts, on the basis of ballistic constants, the trajectory of a non-selfpropelling projectile for the purpose of, for instance, a calculation of the gun aiming point. The trajectory data D p need not comprise a comprehensive description of the trajectory; control unit 3 may, in a particular embodiment, generate additional trajectory data on the basis of the limited trajectory data. Signals D T may comprise information relating to a desired change of the end of the trajectory of the projectiles in flight, necessitating a course correction; for instance in case of long-distance artillery fire with an observer who can see the target. Signals D T may also contain information on the position of a moving target measured by a target sensor. The identification generator 7 can have different embodiments and can in various ways be provided with an identification parameter P k . For instance, identification parameter P k may be supplied to identification generator 7 before or after launching of the projectile. In this case, identification generator 7 should be interpreted as a memory, which at a later point in time regenerates by means of reproduction the identification parameter P k supplied earlier. In a particular embodiment, the identification generator 7 is capable of generating an identification parameter P k itself, whether or not after an externally supplied signal. If the projectile has already been provided with an identification parameter P k in order to determine the relation between the parameter and the trajectory data, this parameter should be read out when the projectile has a known trajectory position at a known point in time, e.g. the launching instant and the launching position. If the projectile has not yet been provided with an identification parameter P k , it should be supplied when the projectile has a known trajectory position at a known point in time. In this embodiment, the relation between the identification parameter P k and the trajectory data is known at least to the transmitting and control device 1, so that the course-correction information C q can be determined on the basis of a particular trajectory position at a particular point in time. As a result of this relation, at least the transmitting and control device 1 is familiar with the identification parameter P k of an projectile which happens to be in the vicinity of the particular trajectory position at the particular point in time. By providing the correction information C q=m with an identification code I q=m = P k first, at a later stage the correction signal C q=m is selected by the projectile by means of the identification parameter P k . The identification parameter P k generated by identification generator 7 may be a constant time-independent parameter but also a parameter continuously varying with time, provided that its relation with the trajectory data is known. In the first case, identification generator 7 comprises a memory and in the second case it consists e.g. in a clock generating a signal which is proportional to the time of flight. In case of spin-stabilised projectiles, the spin velocity decrease of which is a known function of time, a signal proportional to this spin velocity may also function as an identification parameter. Fig. 3 illustrates an embodiment of a course-correction system according to the invention which is applied in a weapon system. The illustrated embodiment of a weapon system is suitable for tracking two targets simultaneously and for that purpose provided with two target tracking sensors 9 and 10, two guns 11 and 12 and a fire control computer 13 with two common weapon interfaces 14 and 15. The weapon system therefore comprises two fire control channels, where a fire control channel is characterised by a particular sensor-weapon combination. The target tracking sensors 9 and 10 can either be a radar tracking apparatus or an electro-optical sensor such as IR or TV camera. Target tracking sensors 9 and 10 continuously supply target signals D T , relating to a current target position of a target tracked by the relevant target tracking sensor, to the fire control computer 13. Fire control computer 13 continuously generates in the customary way signals comprising information on trajectory data D p of the projectiles 16 to be fired at a target by guns 11 and 12. These trajectory data comprise predicted hitting points PHP, projectile times of flight TS and corresponding time validity moments TVM. Moreover, fire control computer 13 continuously calculates in the customary way gun control values for the purpose of aiming the guns 11 and 12. Furthermore, fire control computer 13 generates signals D p1 , comprising information on the weapon system platform (if applicable), meteorological conditions and projectile characteristics. The embodiment of the course-correction system according to the invention illustrated in Fig. 3 is provided with transmitting and control device 1 and several identical receiving devices 2 fitted to projectiles 16. Transmitting and control device 1 is provided with two identical and independently operating control units 3 and 17. Each control unit is separately provided with signals relating to one of the fire control channels by means of fire control computer 13 via weapon interfaces 14 and 15. The signals supplied to control units 3 and 17 comprise target signals D T , signals concerning the trajectory data D p of projectiles 16 and signals relating to platform data D p1 . If required, it is also possible to include signals from the guns 11 or 12 via weapon interfaces 14 and 15, or to supply signals from transmitting and control device 1 to these guns. This weapon system does not comprise means for tracking the launched projectiles 16. The projectile trajectory data D p are obtained by calculation of the fire control computer 13. However, if position information of a projectile 16 measured by a sensor is available, this information may of course be used to check or even replace the calculated trajectory data D p . Control units 3 and 17 supply course-correction information C q for one or more projectiles launched around the same firing time TF and the corresponding firing time TF to the tranmitting unit 4 for the purpose of generating identification codes I q and transmission of course-correction signals (C q ,I q ) f , comprising this course-correction information and identification code, at an r.f. carrier-wave frequency f. In this embodiment, transmitting unit 4 also generates and transmits identification parameter signals (P k ) f comprising identification parameters P k for the purpose of supplying these parameters to receiving units 2. Furthermore, transmitting unit 4 in this embodiment also generates and transmits the orientation reference signals RR, on the basis of which projectiles 16 can determine an orientation with respect to a reference coordinate system. The transmitting and control device 1 is further provided with adjusting means 18 for the purpose of supplying information g identifying guns 11 and 12 and information f identifying fire control computer 13 to transmitting unit 4 as well as to receiving device 2. The identification parameter P k , generated by control units 3 and 17, is subsequently provided with information g with which the gun is identified. Fire control computer 13 is identified by the adjusted carrier-wave frequency f at which the correction signals are transmitted. Transmitting unit 4 can be adjusted to a number of different frequencies. Besides the said receiver 5, receiving device 2 is provided with a launching detector 19 in the form of an acceleration detector, a clock 20, identification generator 7 in the form of an identification memory, data processing unit 6, orientation determination means 21, and course-correction means 8 to execute course corrections. Acceleration detector 19 generates, at a certain point in time after the occurrence of a particular acceleration as a result of the launching of the projectile, a trigger signal S g for clock 20. The time elapsed after that point in time, recorded by clock 20, practically corresponds with an elapsed time of flight of the relevant projectile. When this time of flight has exceeded a certain value, identification generator 7 is enabled, by means of signals originating from clock 20, to store the identification parameter P k=m , represented by the next signal (P k=m ) f , from the identification parameter signals (P k ) f (k=1,2,3,...m..), continuously received by receiver 5. Once identification memory 7 has been provided with identification parameter P k=m , the next identification parameters P k are generated. Before launching, data processing unit 6 in receiving device 2 has already been provided, by means of adjusting means 18, with gun and fire control computer identification information f and g. On the basis of the identification parameter P k , stored in identification memory 7, data processing unit 6 selects from the received course-correction signals (C q ,I q ), the course-correction information C q=m which is coupled to identification code I q=m = P k . The course-correction information C q=m is subsequently supplied to correction means 8 with which course-corrections can be executed. This can be realised in the customary way by means of small thrusters mounted on the periphery of the projectile, or by changing the orientation of the adjustable control fins fitted to the projectile. In order to determine the proper time of correction, correction means 8 are provided with signals representing the orientation of the projectile to be corrected. These signals are generated by the orientation determination unit 21 on the basis of orientation reference signals RR transmitted by transmitting unit 4 and received by receiver 5. In the embodiment described, the projectiles rotate about their longitudinal axis, where course corrections are executed by means of small thrusters. The orientation in this case applies to an angular spin position of the correctable projectile about the longitudinal axis of the projectile. The angular spin position determination may be carried out in the customary way as described in patent specification EP-A 0.239.156. The stabilised omni-antenna for transmission of orientation reference signals RR is in this embodiment also used as an antenna for transmitting the correction and identification assignment signals. Correction means 8 are furthermore supplied with the signal, generated by clock 20, representing the elapsed time of flight. The correction-information C q=m supplied to correction means 8 comprises a course correction direction C, the number of thrusters to be detonated NC, and a first point in time TC for executing the corrrection. On the basis of these signals and information supplied to correction means 8, the correction means calculate for each available thruster the point in time at which the thruster reaches the optimal angular spin position for the required course correction The thruster for which this point in time most approximates the first point in time TC is selected and detonated when a thruster has reached the correct angular spin position, taking into account reaction times for data processing and detonation. The embodiment of a course-correction system as illustrated in Fig. 3 can be added to an existing weapon system without requiring drastic changes to the weapon system. In the case of an integrated design of a fire control computer and a course-correction system according to the invention, the fire control computer may of course comprise one or more parts of the couse-correction system. Fig. 4 illustrates an embodiment of control unit 3 which is suitable for use in the transmitting and control device 1 of Fig. 3. Via weapon interface 4 indicated in Fig. 3, control unit 3 is provided with target information D T , trajectory data D p and platform information D p1 . Target position filter 22 filters position data R T comprised in D T and supplies this data, together with information comprising the target velocity V T , target acceleration A T , and target and target trajectory parameters, to a course-correction generator 23, where these data are used in the compilation of any course correction information C q . The platform data D p1 and projectile trajectory data D p are supplied to a trajectory generator 24. This trajectory generator 24 supplies the information relating to a projectile trajectory, which is required for the generation of course corrections by correction generator 23. Since fire control computer 13 in this application already generates trajectory data D p in the form of end points (PHP, TS) and starting points (platform position and speed), trajectory generator 24 may carry out a simpler calculation than the one carried out by the fire control computer. Trajectory generator 24 calculates a projectile position R p and a projectile velocity V p corresponding with an imaginative firing time TF. For that purpose, the platform data comprise the platform's own velocity and own course information. For subsequent generation of these firing times TF, a clock 25 is fitted which, on the basis of supplied time validity information TVM concerning the trajectory data D p , synchronises the calculations of the trajectory generator 24 with these time validity moments TVM. The time validity moments TVM may then be interpreted as imaginary firing times TF at which imaginary projectiles are fired and for which course corrections are calculated if applicable. At a later stage, transmitting unit 4 (Fig. 3) supplies an identification parameter P k , based on the imaginary projectile trajectory corresponding with a certain firing time TF, to all projectiles actually fired during a particular time slot around that firing time TF. This imaginary projectile trajectory is characterised by the projectile velocity V p , the projectile position R p , the hitting point PHP and the time of flight TS corresponding with this firing time TF. The data relating to the projectile trajectory R p , V p , PHP and TS, together with the firing time TF, are supplied to course-correction generator 23, which compiles the course-correction information C q . The signals representing the firing times TF, generated by clock 25, are supplied to transmitting unit 4 (Fig. 3) together with course-correction information C q generated by the course-correction generator 23.

Claims: Course-correction system for wireless correction of the course of launched projectiles, provided with at least one transmitting and control device which, supplied with course data of the launched projectiles, is suitable for generating and transmitting course-correction signals (I m , C m ) (m = 1, 2, ...), I m being an identification code and C m being course-correction information, for correction of the course of the launched projectiles; a receiving device fitted in each projectile k (k = 1, 2, 3, ...) for receiving the course-correction signals to be supplied to the course-correction means for the purpose of executing the course correction, the receiving device of each projectile k being provided with a selection unit, containing an identification parameter P k , the selection unit selecting an identification code I m from the course-correction signals, for which I m = P k , and supplies the corresponding course-correction information C m to the course-correction means to execute the course correction, characterised in that the selection units of groups of r successively launched projectiles respectively comprise the same identification parameter, where r is an integer greater than or equal to 2. Course-correction system as claimed in claim 1, characterised in that the identification parameters are fixed after launching. Course-correction system as claimed in claim 2, characterised in that the identification parameters are transmitted to the launched projectiles by means of a read-out unit mounted on the launching device and that the launched projectiles are provided with a read-in unit to read the parameters transmitted by the read-out unit. Course-correction system as claimed in claim 3, characterised in that the receiving device comprises the read-in unit and the transmitting device comprises the read-out unit. Course-correction system as claimed in claim 3, characterised in that the selection unit of a projectile k is provided with a launching detector and a timer, where the launching detector is suitable for initiating the timer after launching. Course-correction system as claimed in claim 3 or 5, characterised in that projectiles launched during a certain time slot form a group. Projectile using the course-correction system as described in one of the above claims.

Inventors: HAVERDINGS HENDRIK, WOLFF HENDRIKUS JOHANNES GERHA, ZWART HENDRIK JAN, HAVERDINGS, HENDRIK, WOLFF, HENDRIKUS JOHANNES GERHARDUS, ZWART, HENDRIK JAN
Applicants: HOLLANDSE SIGNAALAPPARATEN BV, HOLLANDSE SIGNAALAPPARATEN B.V.
Application year: 1989
Main classification: F41G7
IPC codes: G05D1, F41G7