GB2056927A - Guiding moving objects - Google Patents

Abstract

A method of guiding a flying or moving object (e.g. a shell) in which the object is provided with a rocket or jet motor 14, and in which magnetic or electrostatic deflection (C1, C2) is applied to the efflux from the motor to control the emergence angle of the efflux relative to the direction of flight or motion. <IMAGE>

Description

SPECIFICATION Guidance system This invention relates primarily to a method of guiding flying or moving objects such as projectiles, aircraft, torpedoes, or spacecraft. The invention is however also capable of wider application.

Known methods used for in-flight control of guided missiles, for example, include the provision of movable fiight surfaces and/or the deflection of a propellant gas stream byeitherswivellingthejet nozzle or actuating a deflector plate within the efflux.

All such methods involve complex electromechanical control systems and motive power units which take up valuable space and weight. Such systems, being mechanical, have a finite operating speed which limits the inflight response of the missile. It also prevents the application of such systems to projectiles, such as rifle bullets, which are spin stabilised, unless the rotational speed is sufficiently low. With high rotational speeds, the inherent lag between application of a corrective signal and the response of the mechanical element applying the corrective force is too great for accurate control.

Furthermore the electro-mechanical systems represent a considerable proportion of the total missile cost both regarding development, production and maintenance.

The present invention provides a vector control system utilising the efflux of a rocket or jet motor, the system having no moving parts such that it is intrinsically reliable, operating at a much higher speed than that of conventional electro-mechanical systems, and being cheap to manufacture and maintain. Moreover, the system is applicable to any type of projectile, including small spin stabilised projectiles such as rifle bullets.

In accordance with one aspect of the present invention a method of guiding a flying or moving object comprises: providing the object with a rocket or jet motor, and applying magnetic or electrostatic deflection to the efflux from the motor to control the emergence angle of the efflux relative to the direction of flight or motion.

The invention is thus based firstly on the appreciation that the hot gases of the motor efflux will contain a proportion of ionised molecules and, secondly, on the realisation that these molecules will respond to an applied electrostatic or magnetic field.

The deflected efflux will impart a vector force to the flying object in exactly the same manner as it does in conventional electro-mechanical systems where the efflux is deflected by means of swivelling jet nozzles or actuable deflector plates. However, the speed of response will be of a different order, there will be no moving parts, and the system is ideally suited for application not only to missiles but to artillery shells as well as to small spin stabilised projectiles such as rifle bullets.

The invention may be used in a conventional ter minal guidance system where the projectile is launched toward a target illuminated with a beam of radiation such as a laser. In this case, the projectile will include two or more sensors for deriving an error signal representing the deviation of the projectile from the path defined by the reflected beam, and the magnetic or electrostatic field will be varied in accordance with the error signal such that the resulting applied vector turns the projectile about its centre of mass toward the target.

By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawings in which: Fig. 1. is a diagrammatic sectional view of an artillery shell embodying the present invention, Fig. 2. is a circuit diagram of a guidance control circuit for use in the shell of Fig. 1., and Fig. 3 is a graphical representation to illustrate the operation of the circuit of Fig. 2.

In the drawings, Fig. 1 shows a terminally guided, gyroscopically stabilised artillery shell which is guided onto a target 10 illuminated by a laser 16.

The nose ofthe shell includes conventional proximity or contact fuses 13, and the body 12 of the shell includes a cavity filied with an explosive charge 11.

The rear section of the shell is provided with a small rocket motor which essentially consists of a charge of solid propellant 14 located in a second cavity of the shell, the cavity communicating with the open tail end of the shell through a venturi 15. When the shell is fired, the propellant charge 14 is ignited by the propellant gases in the breach of the firing weapon, and the resulting jet efflux passes through the venturi 1 to emerge from the tail end of the shell. The amount of charge 14 and its burn rate are selected to provide a sufficient burn time for the particular guidance required.

The guidance control circuit for the shell is extremely simple and is illustrated in Fig. 2. It includes a pair of sensing elements A1, A2 located in the nose ofthe shell as shown in Fig. 1., and also a pair of parallel conductive plates C1,C2 located in the tail of the shell as shown in Fig. 1.

The control circuit can be sub-divided into three main sections. The first section A includes the sensing elements A1 and A2. The second section B consists essentially of a differential amplifier, and the third section C includes the control (deflector) plates C1 and C2.

The target 10 (Fig. 1) is illuminated by a narrow beam of radiation, such as a laser, and the sensing elements A" A2 respond to the radiation energy reflected from the illuminated target. The elements may, for example, comprise sensing diodes.

Assuming both sensing elements produce positive signals when responding to the reflected energy, the differential amplifier B will amplify an input signal e from sensor A1 such that e0 = - R2ej where R2 represents the R1 amplification factor.

Plate C2 is therefore charged negatively, and plate C1 positively, up to the voltage Vcc.

Since the shell is spin stabilised, and is therefore rotating about its longitudinal axis, the sensing ele ment A, will pick up the reflected radiation from the target during only a small proportion of each revolu tion of the shell. In practice, unless the nose of the shell is pointing directly at the target so that both the sensing elements are continuously illuminated by the radiation, one of the sensing elements will pro vide an output for an interval during the first 1800 of rotation in each revolution while the second element will provide an outputforan interval during the remaining 1800 of rotation.

When the sensing element A2 responds to the reflected energy, the output voltage e0 of the diffe rential amplifier will be given by ego = R1 + R2 e R1 where R1 + R2 equals the amplification factor.

R1 The output voltage swing is therefore positive, charging C2 positively, and C1 negatively, up to the voltage Vcc.

The effect of charging the plates Cl ,C2 will be to draw the ionised molecules of the jet efflux toward the positively charged plate. The proportion of ionised molecules in the exhaust gases increases with temperature, and is also dependant on the composition of the propellant. If necessary, the proportion could be further increased by conventional ionization techniques. The overall effect of the charged plates will therefore be to swing the efflux through an angle e as shown in Fig. 1, e being proportional to the quantity of charge on the plates.

It will be appreciated that, although in the above case the plates Cl and C2 are alternately charged positively, the two plates will have interchanged their positions around the longitudinal axis of the shell so that, throughout the sheli's rotation, the deflection of the jet efflux will always be such that the resultant applied vector turns the shell about its centre of mass M towards the target.

The above-described system provides on/off control by intermittently applying a corrective force to the shell. The magnitude of the force is however fixed. In particular it is independent of the magnitude of the error signal eO. The effluxwill be deflected through a fixed angle to one side or the other of the longitudinal axis depending on the polarity of the error signal. The operation ofthe system is graphically illustrated in Fig. 3. The three graphs are based on experimental results. In graph (a), the output ei from sensing element A, peaks when the shell has rotated 90 , while the corresponding output e from A2 peaks after 270 of rotation. The peak voltage in each case is less than 1 C mV.At each peak, the plates C1,C2 become oppositely charged to the max imum value of + or - Vcc regardless of the mag nitude of the peaks. This is shown by graph (b). The value of Vcc is in the region of 500 volts, and this voltage is derived in any convenient manner from an internal battery. The final graph (c) shows that the efflux will be turned through something like 200 each time the plates become charged.

The circuit could be easily adapted to provide proportional control in which the quantity of the charge on the plates is varied in accordance with the magnitude of the error signal. In this case o would also vary in accordance with the error signal.

When e A1 = ej A2 there is no output e0 due to the common rejection ratio of the amplifier B. Accordingly, the efflux is not deflected and the shell will continue to travel along a straight path toward the target.

It will be apparent that the invention can be readily integrated with more advanced electronic guidance command/control systems and that it may be used not only in shells but in any type of projectile from small rifle bullets to large missiles.

Where the projectile being controlled is not continuously rotating, or is not rotating at a sufficiently high speed, it would be necessary to include at least two mutually perpendicular pairs of opposing plates in orderto provide directional control in more than one plane.

Instead of charging plates C1,C2 electrostatically, it would be possible to substitute the poles of an electro-magnet for the plates and modify the circuit to provide magnetic instead of electrostatic deflection.

The invention is also capable of wider application.

It might for example be used with a retro-rocket in the nose of practice shells to keep the shell stable as it is brought to a halt at the end of a firing range. In this case a pair of conductive plates located either side of the efflux from the retro-rocket would be selectively charged in accordance with signals derived from a detection system responsive to the orientation of the shell. If the shell deviated from, say, a level position, a correcting force would be applied by deflecting the efflux from the retro-rocket.

The detection system might comprise, for example, a simple gyroscopic positional error detector.

Another possible application would be in the control ofjumpjet aircraft. The very fast response of a system embodying the invention means that it is ideally suited for replacing mechanical bleed systems in the efflux of jet motors which are difficu It to control because of the inevitable lag between application of the electrical signal and the response of the mechanical actuating element.

The invention may have even wider application to any field in which it is desired to control a mass or stream of hot gas since it may be used to form the mass or stream of gas into a predetermined shape or to deflect it through a predetermined angle. It could be used, therefore, to vary the point at which a flame or hot gas stream impinges on a given surface area as, for example, in plasma arc-cutting.

Claims (10)

1. A method of guiding a flying or moving object comprising: providing the object with a rocket or jet motor, and applying magnetic or electrostatic deflection to the efflux from the motor to control the emergence angle of the efflux relative to the direction of flight or motion.

2. A method according to Claim 1 in which the object comprises a projectile and in which the deflection is applied selectively in response to an error signal representing deviation of the projectile from a fixed path.

3. A method according to Claim 2 in which the path is defined by a beam of electromagnetic radiation reflected from a target, and the deflection is applied such that the resulting applied vector turns the projectile about its centre of mass toward the target.

4. A method according to Claim 3 in which the source of the radiation is a laser.

5. A projectile provided with a rocket or jet motor and further comprising means for selectively applying magnetic or electrostatic deflection to the efflux from the motor to control the emergence angle of the efflux.

6. A projectile according to Claim 5 in which said electrostatic deflection applying means comprises at least one pair of conductive plates disposed on opposite sides of said efflux, means for selectively connecting said plates across a source of electric potential, and means for reversing the polarity of said potential.

7. A projectile according to Claim 6 in which each of the plates extend longitudinally in a direction parallel to the direction in which the efflux initially emerges from the motor.

8. A projectile according to Claim 5 in which the projectile includes a nose section containing a pair of sensing elements and a tail section containing the rocket or jet motor, the sensing elements being positioned opposite one another on either side of a longitudinal axis of the projectile and each being responsive to electro-magnetic radiation within a predetermined frequency range impinging on said nose section on respective sides of said axis, the said deflection applying means being responsive to the respective outputs from the sensing elements such that the efflux is deflected in one direction in response to an output from a first of the elements and in the opposite direction in response to an output from the other element.

9. A rocket or jet powered object comprising a rocket or jet motor and means for applying magnetic or electrostatic deflection to the efflux from the motor to control the emergence angle of the efflux relative to the direction of flight or motion.

10. A method of heating selected areas of an object comprising directing a stream of hot gas toward the object and applying selective magnetic or electrostatic deflection to the stream to control the point at which the stream impinges on the surface of the object.