Carrier Tracking System

This invention relates to an infrared carrier tracking, and more particularly to a system for tracking the carrier through clutter.

In the past guidance techniques, such as those disclosed in U.S. patent application, Ser. No. 896,087, filed Apr. 13, 1978 for a "Missile Detecting and Tracking Unit", have provided some clutter immunity as follows. During the early portion of the carrier flight, the carrier engine, if it has one and if not a beacon, is the brightest object in the detector field of view; all clutter objects have less intense images. The size and location of the clutter is stored so that it will not become confused with the beacon during the latter portion of flight when the carrier engine image is dim. In addition, a two dimension track gate is placed about the carrier to gate out any clutter. The gate is made just large enough to contain the portion of space into which the carrier is moving; as the carrier moves away, the gate is narrowed to eliminate widely scattered clutter. Nevertheless, when a moving carrier is tracked, new clutter is brought into the field view. Further, aspect angles of the clutter during the flight can change and clutter location can change due to operator jitter.

Accordingly, it is an object of this invention to provide for reliable, effective tracking of a carrier through clutter.

Another object of the invention is to provide a tracking system having a heat source whose intensity is controllable at short range to avoid blooming and to effect smoke penetration at long range.

Still another object of the invention is to provide a tracking system having clutter cancellation while tracking the carrier.

Yet another object of the invention is to provide a tracking system whose sub-system aboard the carrier is highly efficient and reliable, yet economical to produce using mass production techniques.

Briefly stated the invention comprises a tracking system which includes a beacon sub-system mounted upon a carrier, and a beacon control sub-system located remotely to the carrier. When a clutter ambiguity enters the field, the control sub-system sends a beacon interrupt signal to the beacon sub-system to interrupt the beacon. The resulting video frame is stored for comparison with a subsequent video frame taken with the beacon emitting energy. The subsequent frame is compared with the previous frame and the comparison reviewed to determine the location of the beacon. Any clutter present will be in both frames; however, the beacon will be present in only one frame. By this technique the clutter is differentiated from the carrier.

The novel features characteristic of the embodiments of the invention may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings wherein;

FIG. 1 depicts the utilization of a combined infrared sight and tracker unit;

FIG. 2 is an isometric view of the carrier including the beacon shutter system;

FIG. 3 is an isometric view of the beacon shutter system;

FIG. 4 is an isometric view of the shutter drive having a portion of the housing broken away to show more clearly the shutter drive mechanism;

FIG. 5 is a fragmentary cross sectional view of the thermal beacon taken along line A--A of FIG. 3;

FIG. 6 is a schematic view of the shutter-signal separation circuit and power driver of the shutter electronics;

FIG. 7 is a schematic of the beacon/carrier interface; and

FIG. 8 is a simplified flow diagram of the infrared sight and tracker unit.

For purposes of description and not by way of limitation the invention shall be described in connection with a guided missile used as the carrier. Such a guided missile is shown in FIG. 1 in which an infrared sight and tracker unit 10 comprises a missile 12 which has been launched from launcher 14 toward its destination or target 16. The target is shown as a tank viewed through the visual sight. It could also have been viewed through the infrared sight at the gunner's option. A beacon 18 is attached to the aft end of the missile 12. The beacon 18 is a part of the beacon system described hereinafter. A sighting means 20 which may be, for example, a thermal night sight such as that manufactured by Texas Instruments Incorporated under the designation AN/TAS4 Night Sight, is attached to the launcher 14 for viewing and tracking the carrier 12. The night sight is a forward looking infrared receiver and imaging device which includes a linear array of infrared detectors for scanning a field of view to detect the thermal energy emitted from the carrier's beacon. The night sight is modified, as hereinafter described, to accommodate a beacon control sub-system.

Each detector of the sighting means together with its preamplifier constitutes a channel (not shown) connected to an electronics package 22. A controller 24 controls the launching of the missile, activation of the night sight infrared receiver and activation of the beacon tracker unit. The electronics package 22 includes a microprocessor, which is preferably a Texas Instruments Incorporated SBP9900 microprocessor, controlled by the controller 24.

The carrier missile 12 (FIG. 2) includes a beacon system 26, a housing 28, an electronics pod 30 attached to the housing, an umbilical connector 32, and ballast 34 attached to the faring 36. The housing 28 has an aft end to which the beacon system is attached and a body portion to which the electronics pod 30 is attached. The electronics pod 30 contains the electronics for the beacon system. The umbilical connector 32 connects the electronics pod 30 to the beacon system 26. The ballast 34 attached to the faring 36 is to maintain the center of gravity or balance of the carrier owing to the weight of the beacon system.

Referring now to FIG. 3, the beacon system comprises a housing 38, a pyrotechnic igniter 40, a squib hammer 42, a shutter actuator 44, shutter drive linkage 46, a shutter return spring 48, installation hooks 50, and an installation bracket 52. The housing 38 is attached to the missile housing 28 (FIG. 2) by the bracket 52 and hooks 50. The housing 38 includes a case 54 FIG. 5 having an open end covered by a frangible glass cover 56. The case 54 may be, for example, a cast carbon type case. The frangible glass cover is shattered for removal by the squib hammer 42 (FIG. 3). A layer of non-combustible insulation material 58 (FIG. 5) covers the bottom of the case. A pyrotechnic heater 60 is hermetically sealed in foil 62 for protection during storage. The pyrotechnic heater may be selected from the group of intermetallic reaction pyrotechnic materials consisting of titanium boride, titanium boride plus titanium carbide, titanium carbide, zirconium boride, and zirconium carbide. The foil 62 is a heat meltable foil which melts when the pyrotechnic heater is ignited thereby enhancing the thermal path to an emitter 64. The emitter 64 is, for example, a carbon type emitter capable of withstanding the high temperature (3800.degree. C.) effects.

An apertured base plate 66 covers the emitter 64. An apertured sheet 68 is slidably mounted in base plate guides between the apertured base plate 66 and an apertured honeycomb optics 70. The aperture sheet 68 acts as a shutter for obscuring the apertures of the base plate 66 and honeycomb optics 70, which are in alignment, when displaced by about 1/2 the hole spacing. The apertured sheet or shutter 68 has two flexures 48 and 74 at opposite ends (FIG. 4). Flexure 48 acts as a return spring to hold the shutter 68 open, i.e. the aperture sheet holes are aligned with those of the base plate and honeycomb optics. Flexure 74 acts as a transfer lever to the drive linkage 46.

The drive linkage 46 includes a rod 76 having, for example, ball shaped ends. The ball shaped ends of rod 76 extend, respectively, through slots in flexure 74 and one arm of a slotted flexure-pivoted bell crank 78. The other arm of the flexure-pivoted bell crank is attached to the core 79 of a linear solenoid comprising the shutter actuator 44. Thus, with the return spring 48 pulling the aperture sheet and the linear solenoid pulling the shutter drive linkage to close it the system always acts in tension thereby utilizing the tensile strength of the member to substantially reduce the size of the members.

The shutter electronics 30 (FIG. 2) comprises a shutter-signal separation circuit and power driver packaged separately from the beacon to fit the available space and reduce mass unbalance in the missile. A power source such as, for example, the existing missile battery 80 (FIG. 6) provides power to a dc regulator 82 and power driver 84. The dc regulator provides selected dc voltages to a buffer amplifier 86, 2-pole low pass filter 88 and threshold detector 90. The buffer amplifier 86 reestablishes the values of the guidance and beacon actuator signals received by the missile. The two-pole, low pass filter, with a preselected corner frequency rejects the missile steering commands and passes the shutter actuating dc pulse. The dc shutter pulse signal triggers a threshold detector 90 which drives the power driver output stage 84. The power driver contact is connected to the shutter actuator 44 solenoid (FIGS. 3 & 4). The command pulse duration is selected to keep the shutter closed for an interval equal to one time frame of the night sight.

The beacon/missile interface electronics (FIG. 7) comprises the power source 80 which is connected to the junction of the shutter drive electronics pod 30, fusible link 92 of a pyrotechnic initiator branch circuit, and switch 94 of a squib hammer branch circuit. The pyrotechnic initiator branch circuit, in addition to the fusible link 92 includes a pyrotechnic initiator 96, which is, for example, an electrically fired heat match. The squib hammer branch circuit includes, in addition to the switch 94, a fusible link 98 connected to the switch 94 and to a squib 100. The fusible links 92 and 98 are included in the heater ignition and cover removal circuits to protect the battery from potential overloading.

At start up, the squib of the squib hammer circuit is fired electrically and the gas generated drives the hammer 102 which is a low brisance pyrotechnic hammer. The cover 56 being a chemically tempered glass having a thickness of about 0.050 to 0.060 inch and a modulus of rupture of about 40,000 psi. is fragmented and removed by the hammer within about 10 milliseconds. Also at start up the beacon or heater is fired. The heater pyrotechnic has a propogation velocity such that the time for the reaction to spread to the entire source is comparable to the missile's flight time. Thus, the emitter 64 (FIG. 5) first meets the need for lower intensity early in flight and is gradually raised throughout the flight to meet the higher intensity need during the later stages of flight.

As previously described the shutter drive electronics 30 (FIG. 2) controls the actuation of the shutter actuator 44 solenoid (FIG. 3). Standby power for the shutter electronics 30 is low (about 1 watt). When shutter operation is commanded, each cycle draws up to about 10 watt-seconds.

Shutter operation, if it occurs at all, will happen near the end of the flight. The microprocessor of the electronics package 22 (FIG. 1) is programmed (FIG. 8) so that upon receipt of a start up signal 104 tracker conditioning 106 is effected by starting the clock, timing sequence and determining pre-fire conditions. A time decision 108 is then made. If the time is less than a preselected time, a decision 110 is made whether the tracker is in handoff. Handoff results when the tracker looses the missile. If the answer is no the computer commands the missile to fly a standard track link 112, and the computer returns 114 to start 104. If the tracker is in handoff, a decision 116 is made whether the missile is in the field of view of the forward looking infrared (FLIR) sight. If not, a command 118 is given for the missile to fly a preprogrammed flight profile. Next a command 120 is given to activate a GLI tracker for missile acquisition and the computer returns 122 to start 104. If the missile is in the field of view a command 124 is given to compute the centroid area of the last field and based thereon to compute a position estimate. The computer then returns 126 to start.

When the decision 108 is that the preselected time has been reached, commands 128 and 130 are given to establish, respectively, scene stabilization and a peak set. Next a command 132 is given to establish a clutter map reference from the stabilized scene. Then a command 134 is given to reject peaks in the clutter maps by comparing the established peaks with the clutter map reference. Next a command 136 is given to update the clutter map. Then a decision 138 is made whether any peak remains. If no peak remains a command 140 is given for the tracker to coast and then return 142 to start 104. If yes, a decision 144 is made whether more than one peak exists within a reasonable radius of the previous missile track. If only one peak exists, a command 146 is given to compute the centroid area which is converted to guidance signals. Then the computer returns 148 to start. If more than one peak exists, a command 150 is given to actuate the beacon shutter system, and the beacon shutter 68 is closed for one video frame. All peaks appearing in the map during this frame are known to be clutter and are entered in the clutter map. The beacon is then turned on again and the computer returned 152 to the start.

Although only a single embodiment of this invention has been described herein, it will be apparent to one skilled in the art that various modifications to the details of construction shown and described such as for example, substituting a laser (CO2 laser) for the pyrotechnic, may be made without departing from the scope of the invention.