FIELD OF THE INVENTION 0001 This invention relates to tracking systems for aiborne missiles, and more particularly, to tracking devices that have a wider field-of-regard to prior art devices and yet do not significantly affect the aerodynamic performance of the missile.

BACKGROUND OF THE INVENTION 0002 Airborne missiles are provided with seeker and tracker heads for locating and homing on targets such heads comprise a detector or detectors, of any type known in the art such as optical or radar detectors; a scanning mechanism, which actuates the detectors with a scanning motion; a shield or shields to protect the detectors from the environment; and electronic processing means for processing the information received from the detectors and guiding the missile accordingly. 0003 At each moment and in each position, each detector has an instantaneous field-of-view, which depends on its structure, and can be defined as the solid angle that includes all the directions that are seen, viz. from which a signal can reach the detector and be sensed by it. This will be called hereinafter briefly the field-of-view. As the detector is scanned, the field-of-view changes. The sum of all possible fields-of-view, or, in other words, the solid angle that includes all the directions that can be seen by the detector in its scanning, will be called herein the field-of-regard. The field-of-regard does not depend only on the structure of the detector, but depends also on the scanning mechanism and on the other parts of missile that may limit the width of the scanning and/or obstruct in certain positions the detector's field-of-view. Clearly, the seeker and tracker device is unable to detect a target that is outside its field-of-regard, and is unable to keep track of detected targets, if they move to outside its field-of-regard. 0004 Obviously, a seeker and tracker device placed in front of the tip of the missile will have a wider field-of-regard, but it will cause air drag, particularly in high speed cruising, and damage the aerodynamic performance of the missile. Further, it will be greatly exposed to aerodynamic attrition and consequent overheating. 0005 The prior art has not found any way to provide a wide field-of-view without creating aerodynamic and/or thermal drawbacks. Thus, U.S. Pat. No. 3,974,985 discloses a tracker comprising a rotatable lens barrel mounted on a turret mounted in a tubular section of a missile located aft of the missile tip. Such a tracker causes a limited air drag, but has a limited field-of-regard. 0006 Israeli patent application discloses a missile having a homing head arranged in an intermediate position of the missile, which homing head is at a slant to the missile axis and views the environment through a lateral window. Such a device does not damage the aerodynamic performance of the missile, but has a poor field-of-regard. 0007 UK patent application GB 2 284 465 A discloses a seeker head movable between two positions: a first position in which it extends forwardly of the missile tip and a second position in which it is retracted aft of said tip. In the first position it has a wide field-of-regard and can search for a target, while in the second position it has a very narrow field-of-regard which is intended to permit it to track a detected target. Such a seeker head, however, not only involves a mechanical complication and serious overheating problems when in said first position, but is able to track a detected target, in said second position, only if the target's movement is not quick or sharply angled. While said application states that, if an infrared detector is used, a cooling system may be used for cooling the interior of the seeker head, no cooling system is shown or described. 0008 It is therefore a purpose of this invention to provide a seeker and tracker system for missiles, which is free of the drawbacks of the prior art. 0009 It is another purpose to provide such a system that has a wide field-of-regard, and yet has no significant influence on the aerodynamic performance of the missile. 0010 It is a further purpose to provide such a system that is capable of tracking a detected target no matter how it moves. 0011 It is a still further purpose to provide such a system that is not affected by heat developed from air attrition. 0012 It is a still further purpose to provide such a system that does not involve any mechanical complication. 0013 It is a still further purpose to provide such a system that achieves concurrently all the objects and advantages achieved separately by prior art systems, and further, objects and advantages tat are not achieved by them.

SUMMARY OF THE INVENTION 0014 The seeker and tracker device according to the invention comprises; 0015 Iat least an optical sensing unit (briefly, hereinafter, sensing unit), comprising a lens barrel or sensor barrel, which preferably has an axis in a transverse plane of the missile; 0016 IIa dome, projecting from the side of the missile and covering the sensor barrel, said barrel extending into said dome beyond the side surface of the missile; 0017 IIIa detector, preferably coaxial with the missile; 0018 IIIdrive means for rotating the sensor barrel about two perpendicular axis; and 0019 IVa processor for processing the signals produced by the detector and guiding the missile accordingly. 0020 Of the aforesaid two perpendicular axis, one (that can be called the inner one) is connected to the sensor barrel while the other (that can be called the outer one) is connected to the first. Said two axes together constitute a gimbal suspension. 0021 The sensing unit comprises a lens (objective lens) barrel, extending into the dome beyond the side surface of the missile and having a field-of-view that depends on the optical characteristics of its components, first drive means comprising a first (pitch) motor and an inner joint for imparting to said barrel a pitching motion about a first axis, second drive means comprising a second (roll) motor and an outer joint for imparting to said barrel a rolling motion about a second axis, and optical deviating means, generally comprising mirrors or prisms, for transmitting the optical signals sensed by the objective lens to the detector, which receives them through an ocular lens. It should be understood that the expressions ocular lens or objective lens include the case in which one or the other or both of the lenses is an optical sensor comprising more than one optical component, e.g. more than one lens or a combination of lenses and other optical components. Such optical sensors are well known to skilled persons and need no further description. Therefore the lens barrel will be synonymously called the sensor barrel. 0022 The rotation of the sensor barrel about its axis will be called herein roll or rolling motion. By pitch or pitching motion is meant herein rotation about an axis perpendicular to the axis of the sensor barrel. When no pitching motion has occured, said axis is in its average position, viz. it lies on a plane perpendicular to the missile axis. The pitching swings it fore and aft of the average position. The combination of the pitching and the rolling motions generates a practically hemispherical, or 180360, field-of-regard for the optical sensor. 0023 The sensing unit is located in an intermediate portion of the missile. A radar antenna dish or conformal antenna strips can be housed in the portion of the missile forward of the sensing unit. 0024 The device of the invention is periscopic and transmits the picture as it is without additional mechanical motion. The pitching motion becomes a rolling motion of the picture. This motion can be computed and it is possible to neutralize said rolling motion or at least to take it into account at the time of signal processing and of calculation of the tracking error. 0025 In a preferred embodiment of the invention, cooling means are provided for the sensing unit, which comprise a cooling fluid reservoir, a cowling for directing a flow of coolant fluid released from the tank to the rear surface of the dome, and motor and transmission means for rotating the dome about its axis, whereby every portion of its surface in turn will come into contact with the coolant. The cooling fluid may be, for example, a gas such as nitrogen or argon under a pressure of e.g. 2000 psi, or ethylene glycol under low pressure. 0026 In another preferred embodiment of the invention, at least two sensing units are provided, angularly spaced about the periphery of the missile, and preferably coaxial and on opposite sides of the missile, whereby it can be said that they are the specular image one of the other. Optical means, such as an optical coupler, is also provided, selectively to render one or the other of the sensing units operative, by directing to the detector only the optical signals originating from said operative unit. Shutter means are preferably provided for preventing optical signals, received by the sensing unit that is not operative at the moment, from interfering with the optical signals transmitted by the operative sensing unit. The optical coupler and the shutters are controlled by the processor. When a target, that is being tracked by a sensing unit, moves out of the field-of-regard of that unit, and therefore the signals concerning it cease to be transmitted to the detector and from it to the processor, this latter deactivates said unit and activates the other unit. 0027 When two sensing units are provided, each has a field-of-regard that is approximately emispheric, viz approaches 180360. Therefore, together, the two sensing units have complementary fields-of-regard which practically cover the entire space around the missile. 0028 This invention therefore comprises a method of tracking targets from missiles, which comprises providing in the missile two optical sensors having complementary and symmetrical fields-of-regard; tracking a target by means of an operative optical sensor while maintaining the other sensor inoperative; and when a targets moves out of the field-of-regard of said operative optical sensor, deactivating it and activating the other optical sensor to continue tracking the target.

BRIEF DESCRIPTION OF THE DRAWINGS 0029 In the drawings: 0030 FIG. 1 is a schematic axial cross-section of the fore portion of a missile having a sensing unit and a detector mounted thereon; 0031 FIG. 2 is a like cross-section at a larger scale showing two sensing units, a portion of the missile being broken off; 0032 FIG. 3 is a cross-section similar to FIG. 1, but additionally showing cooling means; 0033 FIG. 4 is a view from the outside of the cooling means; 0034 FIG. 5 is a cross-section similar to FIG. 1, but additionally showing a radar antenna dish; 0035 FIG. 6 is a cross-section similar to FIG. 2, but additionally showing conformed antenna strips.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 0036 In FIG. 1, the fore portion of a missile is schematically indicated at 10. Numeral 11 generally designates a sensing unit, which extends from a outer surface of the missile and is protected by a dome 14 of optical material. 12 is a detector axially mounted in the missile. Sensing unit 11 comprises a sensor barrel 13 which is actuated for pitching motion by a motor 15 and is supported by bearing 16. An outer axis 17 is provided for permitting a rolling motion, actuated by rolling motor 20 supported on bearings 21. Sensor barrel 13 has an opening 18 through which the optical signals pass. They impinge on a succession of mirrors 19 and on a central mirror 23, placed so as to reflect the optical signals to detector 12 provided with an ocular lens 22. 0037 FIG. 2 shows a similar missile 10 in which two sensing units 11 and 11 are mounted opposite to each other and on the same axis, so that unit 11 is the specular image of unit 11. Each sensing unit is identical to sensing unit 11 of FIG. 1, and therefore its components are the same and need not be described once more. Detector 12, with ocular lens 22, is equal or equivalent to detector 12 of FIG. 1. Additionally, an optical coupler 25 is provided in place of central mirror 23 of FIG. 1, to reflect the optical signals from either sensing unit 11 or 11 into the detector. Shutters 26 and shutter actuators 27 are also provided. 0038 FIGS. 3 and 4 illustrate a cooling system for a single sensing unit, as that of FIG. 1, but it is clear that the same cooling system can be used for both sensing units, when two are present as in FIG. 2. The missile and the sensing unit are indicated by the same numerals as in FIG. 1. Additionally, a motor 30 and a gearing 31 are provided for rotating dome 14 on supports 32. A cowling 33 leads a cooling fluid from a reservoir, not shown, to the dome. The cooling fluid is discharged as indicated by the arrows 34. Because the dome rotates, all its surface is successively exposed to the cooling gas and cooled. 0039 FIG. 5 shows the same apparatus as in FIG. 1, with the addition of a radar antenna dish 40 mounted on a pedestal 41. 0040 FIG. 6 shows the same apparatus as in FIG. 1, with the addition of conformed antenna strips 42. Obviously, such antennae could be mounted in missiles provided with two sensing units, as in FIG. 2. 0041 While embodiments of the invention have been described for purposes of illustration, they are not limitative and skilled persons may carry out the invention with many adaptations, modifications and variations.