EP0455531B1 - Method for selfguidance of missile towards a supersonic target - Google Patents

Description

The present invention relates to a method for homing tactical missiles to a supersonic aim.

Traditionally, the guided organ of guided missiles is a sensor sensitive to the electromagnetic or infrared radiation of the target. This sensor is, in general, carried on a mobile pointing system slaved to the goal called seeker. Gyros mounted on the seeker measure the absolute angular speed of the line of sight which is, to the accuracy of the servo, the missile-target line. The sensor can also be linked to the missile. In this case the absolute angular speed of the missile-target line is obtained by combining the direction of the target relative to the missile, measured by the sensor, and the absolute orientation of the missile measured by an inertial unit. The electromagnetic sensor is active or passive, depending on whether or not it emits radiation illuminating the target. The law of guidance transforms the absolute angular speed of the line of sight into an order with the missile. It requires knowledge of the target missile radial speed which is either measured or estimated.

• . Coût très élevé,
• . Sensibilité au leurrage,
• . point visé sur la cible mal connu et fluctuant, pouvant sortir du contour apparent,
• . accrochage sur la cible délicat, qu'il soit réalisé avant ou après le départ du missile,
• . portée limitée.

The seeker has the following disadvantages:

• . Very high cost,
• . Sensitivity to decoy,
• . target point on the poorly known and fluctuating target, which may leave the apparent contour,
• . attachment to the delicate target, whether carried out before or after the missile's departure,
• . limited range.

The method according to the invention overcomes the above drawbacks because it is based on the control of the missile to the shock wave attached to the target by means of sensitive organs yes are simple pressure sensors. It therefore only concerns supersonic targets. The term shock wave is used here to define the pressure wave induced over a long distance by a supersonic target, comparable to a thin sheet of revolution, propagating according to the laws of acoustics. The term "acoustic wave" could be used in an equivalent manner.

We know (DE-A-3334758) the use of acoustic sensors to detect subsonic targets and also (DE-A-3528075) the application of such sensors, positioned on the ground, to measure the trajectory of a mobile supersonic. In this prior technique, there is no question of controlling the trajectory of a supersonic missile to the shock wave of a supersonic target in order to obtain the advantages and technical effects mentioned above.

• en détectant ladite onde de choc par des premiers capteurs de pression installés à bord du missile,
• en estimant la trajectoire de la cible à partir des positions et attitudes du missile aux instants datés auxquels lesdits capteurs de pression traversent l'onde de choc de la cible, au moyen d'algorithme approprié,
• en commandant au missile une trajectoire quasi sinusoïdale de part et d'autre de l'onde assurant l'excitation périodique des capteurs de pression et les mesures subséquentes et,
• en asservissant la trajectoire relative moyenne du missile à la génératrice de l'onde de choc conique de la cible.

The subject of the invention is therefore a method of guiding a supersonic anti-aircraft missile towards a supersonic target using pressure sensors, characterized in that the trajectory of the missile is subject to the shock wave induced by the target:

• by detecting said shock wave by first pressure sensors installed on board the missile,
• by estimating the trajectory of the target from the positions and attitudes of the missile at the dated instants at which said pressure sensors cross the shock wave of the target, by means of an appropriate algorithm,
• by commanding the missile a quasi-sinusoidal trajectory on either side of the wave ensuring the periodic excitation of the pressure sensors and the subsequent measurements and,
• by slaving the average relative trajectory of the missile to the generator of the target's conical shock wave.

The missile is provided with a rustic inertial unit providing at all times a measurement of its position M, of its speed vector V _M , of its acceleration Γ _M and of its reference trihedron T _M in an initial trihedron of reference T _o .

The sensitive guidance member, replacing the seeker, consists of one or more pressure sensors placed on board the missile. These sensors may consist of one or more orifices distributed over the missile connected to as many pressure detectors, or to a single detector for all of the orifices. These are simple microphone type detectors. These sensors detect and date, thanks to an internal clock, their passage through the shock wave of the target. Taking into account the stiffness of the front of the shock wave of the target, these passages are dated with very great precision. The bandwidth of the sensors is chosen accordingly. Figure 1 shows possible locations of sensors 1, 2, 3 installed on board missile 4.

a étant la célérité du son.The shock wave of the target is assimilated to a conical sheet of origin a point B of the target, of axis the speed of the target V _B and of angle at the top

a being the speed of the sound.

In principle, the guidance order produces a trajectory of the missile, which, relative to the goal has the appearance of a sinusoid of low amplitude located alternately inside and outside the conical sheet by following a generator of this tablecloth. The measurements contributing to the development of the order are carried out at each crossing of the conical sheet. Interception takes place when the missile arrives at the top of the cone which obviously requires that its speed be higher than that of the target.

FIG. 2 shows the target 5, the absolute trajectory 6 of the target, the missile 4, the conical shock wave 7 of the target 5, the average relative trajectory 8 of the missile 5 which is a generator of the cone, the absolute trajectory average 9 of the missile leading to the interception point 10.

In its embodiment according to the invention, the guidance law comprises two functional modules programmed on the missile computer. The first, called an estimator, determines the speed of the missile relatively to the conical tablecloth at each crossing of it. The second, called the controller, develops the missile command based on the estimated relative speed.

. Ces positions sont déduites de la position à t

du missile élaborée par la centrale inertielle et de la disposition des capteurs dans le missile. L'estimateur non linéaire utilise un algorithme du gradient conjugué ou d'un autre type. Il est initialisé avec les informations éventuelles sur la trajectoire du but communiquées au missile avant tir. En l'absence de telles informations, la convergence est acquise après un nombre n de traversées dépendant du nombre k de capteurs installés dans le missile, tel que nk=6. Il est possible, lorsque le transitoire de recalage est amorti, d'estimer l'accélération du but Γ_B . La grande précision des mesures l'autorise.The estimator estimates the trajectory of the target defined by its position B and its speed vector V _B , that is to say in all six parameters, from the successive positions of the pressure sensors M _C (k, i) at the crossing of the wave shock (k the number of the sensor, i number of the crossing), occurring at time T

. These positions are deduced from the position at t

the missile developed by the inertial unit and the arrangement of the sensors in the missile. The nonlinear estimator uses a conjugate gradient or other type algorithm. It is initialized with any information on the trajectory of the goal communicated to the missile before firing. In the absence of such information, convergence is acquired after a number n of crossings depending on the number k of sensors installed in the missile, such as nk = 6. It is possible, when the registration transient is damped, to estimate the acceleration of the goal Γ _B. The high accuracy of the measurements allows it.

, V̂_B

obtenue quand ce capteur effectue la traversée n°i au point M

, on détermine en ce point le trièdre instantané du guidage T_C constitué par la génératrice du cône x_c , la normale intérieure z_c, la tangente au cercle directeur y_c . On calcule en outre les composantes de la vitesse relative du missile au but suivant z_c et y_c , notées ė_z et ė_y .One chooses a particular sensor (in the case where it is unique it is obviously this one) as point of the missile whose trajectory will be controlled. From the estimated goal B̂

, V̂ _B

obtained when this sensor crosses n ° i at point M

, we determine at this point the instantaneous trihedron of the guidance T _C constituted by the generator of the cone x _c , the interior normal z _c , the tangent to the directing circle y _c . We also calculate the components of the relative speed of the missile at the goal following z _c and y _c , denoted ė _z and ė _y .

The controller prepares the orders ordered with the missile. The missile to which the invention applies can have any organization. It can be stabilized in roll or in natural autorotation. Its lateral movement can be produced by aerodynamic and / or pyrotechnic forces. The taking of incidence can be caused by an aerodynamic actuator (rudder), pyrotechnic (impeller, transverse jet) or other. The actuator can operate along two transverse maneuvering axes (yaw, pitch) or only one (if the missile is directly in autorotation). The command ordered can be addressed directly to the actuator (s) or to an autopilot, if it exists. It can be an autopilot under acceleration or transverse angular velocity. The following presentation is made by assuming a missile stabilized in roll and equipped with an autopilot in acceleration.

, k= gain. Une fonction de transfert plus élaborée pourrait être substituée au gain suivant la dynamique du missile. La seconde composante Γ_zc , dirigée suivant la normale au cône z_c a pour but d'entretenir une trajectoire périodique perpendiculaire à l'onde de choc assurant les traversées nécessaires à l'excitation des capteurs de pression et aux mesures subséquentes. Elle est produite par une loi non linéaire de la forme ${\text{Γ}}_{\text{zc}}{\text{= Γ}}_{\text{max}}$

signe (f(e)). La fonction f est choisie, en liaison avec l'amplitude Γ_max de la commande et la dynamique du missile, pour régler comme il convient l'amplitude et la fréquence du cycle limite. La distance de passage est de l'ordre de l'amplitude de ce cycle.The accelerated missile orders are first calculated in the frame x _c , y _c , z _c . They have two components. The first component Γ _yc directed along y _c , has the effect of controlling the projection of the missile on the plane tangent to the cone x _c y _c , to follow the generator of the cone x _c , or even to control the projection of the speed of the missile on the plane tangent to the cone to be parallel to the generator. It is linear, of the form ${\text{Γ}}_{\text{yc}}\text{= -k}\dot{\text{e}}\text{y}$

, k = gain. A more sophisticated transfer function could be substituted for the gain depending on the dynamics of the missile. The second component Γ _zc , directed along the normal to the cone z _c aims to maintain a periodic trajectory perpendicular to the shock wave ensuring the crossings necessary for the excitation of the pressure sensors and for subsequent measurements. It is produced by a nonlinear law of the form ${\text{Γ}}_{\text{zc}}{\text{= Γ}}_{\text{max}}$

sign (f (e)). The function f is chosen, in conjunction with the amplitude Γ _max of the command and the dynamics of the missile, to adjust the amplitude and the frequency of the limit cycle as appropriate. The passage distance is of the order of the amplitude of this cycle.

The acceleration orders are then calculated in the missile coordinate system x _m y _m , z _m (measured by the inertial unit), on the condition that their projections on y _c and z _c are respectively equal to Γ _yc and Γ _zc .

FIG. 3 constitutes a simplified functional diagram of the method according to the invention showing the functions exercised by the sensor (s) (function A), the inertial unit (function B), the estimator (functions C) and the controller (functions D).

FIG. 4 shows the relative trajectory 8 ′ of the missile around the cone generator 8 contained in the plane defined by this generator 8 and the normal 11.

a étant la célérité du son. La détermination de cette trajectoire suppose que le poste de tir ait des informations sur la trajectoire du but (une telle information peut être simplement la détection du passage de l'onde de choc de la cible par le poste de tir). Si aucune information n'est disponible le missile peut être tiré au jugé et la trajectoire de ralliement est rectiligne. Il en résulte que, dans la plupart des cas, la condition cinématique d'interception ne sera pas réalisée à la première traversée, mais après un transitoire résorbé au bout d'une à deux traversées supplémentaires, au delà duquel le cycle limite asservissant le missile à l'onde de choc sera effectivement enclenché. Les ordres Γ_yc,Γ_zc calculés aux premières traversées tiennent compte de cette circonstance et aussi du temps de réponse de l'algorythme de l'estimateur. La figure 6 montre une trajectoire relative complète d'interception pour un poste de tir situé à l'intérieur de la nappe conique, ce qui pourrait être le cas d'un tir air-air. On y voit la cible 5, son onde de choc 7, la trajectoire relative de ralliement 16 et la trajectoire relative d'interception 17.The missile is launched from a firing station. The invention applies to a land, naval or air firing station. The launching direction can be arbitrary under the conditions that the missile rallies the shock wave of the target and has sufficient kinematic capacities to enslave itself there and catch up with the target. During the initial phase between launch and the first crossing of the shock wave of the target, the missile is slaved to a precalculated rallying trajectory under the criterion that the speed of the missile relative to the goal at the first crossing of the The shock wave has a direction as close as possible to that of the generator of the conical sheet, that is to say that the kinematic condition of interception indicated in FIG. 5 is fulfilled. In this figure we see the absolute speed 12 of the goal, that 13 of the missile, the relative speed 14 of this missile. The angle

a being the speed of the sound. The determination of this trajectory supposes that the shooting station has information on the trajectory of the goal (such information can be simply the detection of the passage of the shock wave of the target by the shooting station). If no information is available, the missile can be fired on trial and the rallying trajectory is straight. It follows that, in most cases, the kinematic condition of interception will not be achieved on the first crossing, but after a transient resorbed after one to two additional crossings, beyond which the limit cycle enslaving the missile the shock wave will actually be triggered. The orders Γ _yc , Γ _zc calculated on the first crossings take into account this circumstance and also the response time of the estimator's algorithm. FIG. 6 shows a complete relative trajectory of interception for a shooting station located inside the conical sheet, which could be the case of an air-air shooting. We see the target 5, its shock wave 7, the relative rallying trajectory 16 and the relative interception trajectory 17.

Claims (3)

1. Method of guiding a supersonic anti-aircraft missile onto a supersonic target using pressure sensors, characterized in that the trajectory (9) of the missile (4) is locked to the shockwave (7) created by the target (5):

   - by detecting said shockwave by first pressure sensors (1, 2, 3) installed on the missile (4),

   - by estimating the trajectory (6) of the target from positions and attitudes of the missile (4) at the dated instants at which said pressure sensors pass through the shockwave (7) of the target, by appropriate algorithm,

   - by instructing to the missile (4) a quasi-sinusoidal trajectory on either side of the wave assuring the periodic excitation of the pressure sensors and the subsequent measurements and,

   - by locking the mean relative trajectory (8) of the missile (4) to the generatrix of the conical shockwave (7) of the target.
2. Method of guiding according to Claim 1, characterized in that it consists, in an initial phase, of launching the missile equipped with said first pressure sensors in a direction calculated by an automatic firing station equipped with second pressure sensors.
3. Method of guiding according to Claim 1, characterized in that it is applied to a missile equipped with an electromagnetic or infrared homing device.

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