REACTION CONTROL SYSTEM

Abstract: A projectile reaction control system (10) includes a nozzle assembly (18) in which the efflux exhausted thereby may be controlled in a continuously variable fashion. In one example control is by means of a slidable piston (24) so that the thrust developed by the nozzle assembly (18) is substantially linearly dependent on the displacement of the piston (24), whereby the reaction control system may be controlled by an autopilot with little or no modification.

Description: This invention relates to a reaction control system for a projectile, for example a missile or a mortar round and to projectiles including such systems. Directional control of missiles in flight may be achieved either aerodynamically using movable control surfaces, e.g., fins, or by using a reaction control system in which control thrusts are generated by emitting a reaction gas transversely of the missile. In the known examples of the latter method of control it is usual to employ single shot squibs or pulsed units. This is believed to limit the degree and accuracy of control and requires the missile autopilot to be specifically designed to deal with this method of control. In these systems the magnitude of the thrust remains generally the same; the only control available is control of the length of the impulse. Studies conducted by the applicants show that there is a need for a reaction control system which produces a thrust whose magnitude may be varied continuously. Furthermore, there is a need for such a system in which the relationship between the movement of the member controlling the reaction control system and the thrust thereby is generally compatible with that of a fin assembly so that the reaction system may be controlled by an existing autopilot without major modification. EP-A-244971 discloses a missile flight control system in which a common actuator controls both a fin and a gas thruster valve. According to this invention, there is provided a reaction control system for a projectile, including a nozzle assembly which comprises a housing defining a nozzle outlet means and a bore adjacent said outlet means, a piston means located in said bore and movable to open or to close said nozzle outlet means, and drive means for moving said piston means, wherein said piston means includes passage means extending therethrough whereby the pressure at one end of said piston means is transmitted to the other end thereof. The invention also extends to a projectile including the reaction control system as defined above. In a further aspect of this invention, there is provided a projectile including a reaction control system as defined above capable of effecting control in each of the control senses of the projectile, aerodynamic control surface means movable for effecting control in each of the control senses of the projectile, and autopilot means for effecting control simultaneously via said reaction control system and said aerodynamic control surface means. A preferred embodiment of the system is particularly useful where a projectile requires the control function exerted by the aerodynamic fins either to be augmented by the reaction control system, e.g. to execute a terminal manoeuvre, or to be replaced thereby when the projectile is travelling too slowly for the aerodynamic fins to be effective, e.g. at launch. The invention will now be described by way of non-limiting example, reference being made to the accompanying drawings, in which:- Figures 1 and 2 are section views of a control thruster assembly in accordance with the invention, in the open and closed positions respectively; Figure 3 shows schematically an example of a control thruster assembly configured in a servo loop. Figure 4 is a schematic rear view of an actuator assembly of an example of reaction control system according to this invention; Figure 5 is a section view of the actuator assembly of Figure 5 taken on lines V-V; Figure 6 is a diagrammatic view of an example of a missile incorporating a reaction control system and a fin assembly; and Figure 7 is a block diagram of the control system of the missile of Figure 6. Referring to the Figures, the illustrated embodiment of a missile reaction control system is intended to be operated in conjunction with a fin assembly by an autopilot. The reaction control system may however also be used in missiles which do not incorporate a fin assembly. Figures 1 to 3 are intended to provide a control thruster assembly in which the force or torque required to move the control element is greatly reduced, so that the assembly is suitable for use in flight vehicles such as guided missiles. Figures 1 and 2 illustrate an embodiment of control thruster assembly in the fully open and fully closed positions respectively. The assembly comprises a housing 50 defining an outlet throat 52 and a fluid supply manifold 54, and a plunger 56 which is slidably located in a pair of spaced bores 58,60 each of which includes a gas seal 62. The bore 60 at the rear of the plunger 56 is closed to define a variable volume chamber 63, together with the rear end of the plunger 56. A pressure balance bore 64 interconnects the two axial end faces of the plunger 56 to tend to equalise the pressure forces acting on the plunger 56. A pressure transducer 66 may be provided to sense the pressure in the variable volume chamber 63, the sensed pressure being a measure of the pressure of the fluid in the outlet throat 52 and also of the displacement of the plunger 56. Intermediate the bores 58 and 60, the housing 50 is relieved and receives for limited axial movement an actuating lever 68 secured to the plunger 56. The actuating lever 68 includes a rack portion 70 which engages the pinion 72 of a drive motor (not shown) for driving the plunger between the positions shown in Figures 1 and 2. A plunger position sensor linkage 74 may be connected to the actuating lever 68 for determining the position of the plunger. In this arrangement, the thrust can be switched "on" or "off" or modulated by movement of the plunger 56. For a proportional thrust system the drive may be in the form of a servo motor/gear box, whilst for a bang-bang system a stepping motor drive connected directly to the plunger may be used. The important part of the assembly of Figures 1 and 2, is the pressure balance bore 64, which allows the pressure at the outlet throat to be sampled. The magnitude of !he sampled pressure will be a function of the plunger displacement. With this system only a modestly powered servo actuator drive will be required for the plunger as the resultant pressure force acting on the plunger will be low. In the "off" position, ambient pressure will act on both ends of the plunger. Plunger position data may be determined from a position sensor connected to the position sensor linkage 74 or it may be derived from a pressure transducer 66 which samples the pressure at the outlet throat via the pressure balance bore 64. For high gas temperature operation, refractory or ceramic materials may be used in the assembly. The gas supply to the thruster assembly may be taken from the main propulsion rocket motor system or from a dedicated hot or cool propellant gas supply. The number of thrusters will be a function of the particular control system required. Figure 3 is a schematic illustration of a thruster assembly of the type illustrated in Figures 1 and 2 configured in a servo-control loop. Many of the component parts are similar and will not be described in detail again. In this arrangement the plunger 56 has an integral rack portion 70 which meshes with a pinion 72 connected via a gear train to an electric motor 80. A potentiometer 81 associated with the electric motor 80 provides a position feedback signal which is supplied to one input of a differential amplifier 82 which controls the motor 80. It will readily be seen that the arrangement of Figures 1 and 2 may be incorporated into the proportional control systems illustrated in Figure 3. Alternatively, it may be incorporated in a bang-bang system. The position servo can control a single unit as shown with a pressure balance bore 64 to reduce actuation forces, or two units arranged back-to-back. In the examples of Figures 1 to 3, the use of torque motors or gear motors to actuate the pistons may allow transmission of larger forces which might damage cam-type arrangements. It will be understood that the reaction control systems described herein may be coupled to operate in tandem with the fin control system or they may operate independently of any fin control system. Figures 4 and 5 illustrate an actuator assembly 10 for a reaction control system. The assembly 10 comprises a casing 12 which houses a gas generator 14 and which includes an outer flange 16. The outer flange carries four thruster units 18 equispaced around the periphery of the missile. Each thruster unit 18 comprises a pair of aligned thruster assemblies 20 connected by conduits 22 to the gas generator 14 and each arranged to exhaust in opposite directions. The flow of gas from gas generator 14 through each nozzle 20 is continuously controllable. The thruster units 18 are controlled by a cam member 30 rotatably secured to the flange 16 and attached to an operating lever 32. Rotation of the cam member causes inverse operation of the thruster assemblies of a unit. The four thruster units 18 are equispaced around the periphery of the missile so that two units (the upper and lower assemblies as viewed in Figure 4) lie in spaced planes parallel to the yaw plane and two units (the left hand and right hand assemblies as viewed in Figure 4) lie in spaced planes parallel to the pitch plane. In use, as illustrated in Figure 6, the actuator assembly illustrated in Figures 4 and 5 is mounted forwardly of the centre of gravity 40 of the missile. Hence, when used in unison, the upper and lower assemblies effect control in the yaw sense and the left and right hand assemblies effect control in the pitch sense. If the upper and lower assemblies are not operated to generate the same magnitude of thrust in parallel directions, then a component of roll torque is generated. If the thrust generated by the upper and lower assemblies is equal and opposite then a simple roll torque will be generated. Similar considerations apply to operation of the left and right hand assemblies. The gas generator may be of any suitable form; in the illustrated embodiment, it takes the form of a hot gas generator which is ignited by means of an igniter 36. A burster disc assembly 38 is provided for safety purposes. Figure 6 illustrates a missile with a reaction control assembly 10 located forwardly of the centre of gravity 40 of the missile and an aft fin assembly 42 comprising four movable fins 44 arranged at the aft of a missile. The fins are oriented around the missile body so that operation of one set of diametrically opposed fins in unison effects control in the yaw sense whilst operation of the other set of diametrically opposed fins in unison effects control in the pitch sense. Differential operation of either set of fins effects control in the roll sense. Figure 7 illustrates a navigation system for the missile of Figure 6. An autopilot 46 calculates the control movements required for the desired course corrections and controls a servomotor assembly 48 which controls movement of the fins 44 and also movement of the actuating members of the associated thruster assembly. It will be understood that each of the thruster assemblies is operable to impart a control moment which is similar to that imparted by rotation of a fin member when the missile is in normal flight. Thus the control function exerted by thruster assembly 18′ is analogous to that exerted by movable fin 44′ etc. Thus, by linking the actuating members to a normal fin servo system, the thruster control system may provide a thrust which is proportional to the fin deflections, so enhancing the control effectiveness of the fins. This is particularly useful when the missile is travelling too slowly for the fins to be effective e.g. at launch, or where an extra mount of control is desired e.g. for a terminal manoeuvre. Because of the similarity between the movement/thrust characteristics of the fins and reaction control system this method of control augmentation may be added to a missile with little or no change to the autopilot. In the arrangements of Figures 4 to 7, since the magnitude of the thrust developed can be adjusted across a large continuous, range of values, the missile "weave" associated with squibs or pulsed thrusters can be avoided. The reaction gas may be a cold or hot gas and the storage reservoir or gas generator may be integrated with the nozzle units to provide a compact control package. The reaction gas may be bled off the main missile rocket motor; indeed a plurality of thruster assemblies may be inclined rearwards to provide not only lateral control but also the main source of rocket propulsion.

Claims: A reaction control system for a projectile, including a nozzle assembly which comprises a housing (50) defining a nozzle outlet means (52) and a bore (58,60) adjacent said outlet means (52), a piston means (56) located in said bore (58,60) and movable to open or to close said nozzle outlet means, and drive means (68,70,72) for moving said piston means (56), characterised in that said piston means (56) includes passage means (64) extending therethrough whereby the pressure at one end of said piston means (58) is transmitted to the other end thereof. A reaction control system according to Claim 1, wherein said drive means comprises a continuously variable servo drive system (80,81,82). A reaction control system according to Claim 1 or 2, wherein position sensor means (81) is associated with said piston means (56) for sensing the position thereof. A reaction control system according to any preceding claim, wherein pressure transducer means (66) is associated with said piston means (56) for providing a pressure signal representative of the position of said piston means (56). A reaction control system as claimed in any of the preceding claims, comprising two oppositely directed nozzle assemblies arranged such that, in use, the thrust generated by one nozzle assembly increases as the thrust generated by the other nozzle assembly decreases. A reaction control system as claimed in any preceding claim, which includes four pairs of nozzle assemblies equispaced about the projectile, said reaction control system being operable to impart at least one of pitch, yaw or roll control to the projectile. A projectile including a reaction control system as claimed in any of the preceding claims. A projectile as claimed in Claim 7, further including aerodynamic control surface means (44) for effecting control in at least one of the roll, pitch or yaw senses, and an autopilot (46) including an actuator (48) operable to effect movement of said aerodynamic control surface means (44) to impart control in a given sense and at the same time to effect adjustment of the magnitude of the thrust developed in use at the nozzle outlet means (52) to impart control in the same sense.

Inventors: FOULSHAM, PETER G., MACHELL, ANTHONY
Applicants: BRITISH AEROSPACE PUBLIC LIMITED COMPANY
Application year: 1989
Main classification: F42B10
IPC codes: F02K9