IL153781A - Laser directional infrared countermeasures (dircm) system for protecting aircraft with a large thermal signature against missiles - Google Patents

Description

LASER DIRECTIONAL INFRARED COUNTERMEASURES (DIRCM) SYSTEM FOR PROTECTING AIRCRAFTS WITH A LARGE THERMAL SIGNATURE AGAINST MISSILES 153781/2 1 LASER DIRECTIONAL INFRARED COUNTERMEASURES SYSTEM (DIRCM) FOR PROTECTING ATRCRAFTS WITH A LARGE THERMAL SIGNATURE AGAINST MISSILES FIELD AND BACKGROUND OF THE INVENTION The present invention relates to an improved directional infrared countermeasures (DIRCM) system, and more specifically to a method and a system that effectively defeats infrared guided missile threats, especially to aircrafts with a large thermal signature.

Since the Second World War one of the primary threats to aircraft has been infrared "heat-seeking" guided missiles. Indeed, more than 80% of downed aircraft have been shot down by infrared guided missiles, whether surface-launched (SAM) or air- launched (AAM). In an effort to neutralize this threat, the launching of heat-emitting decoys ("flares") has been widely used. Flares have three primary disadvantages. First, all but the most primitive heat-seeking missiles are unaffected by flares. Second, the time required after missile-launch detection for flare launch and lighting is relatively long when compared to the total time of a typical aircraft/missile engagement. Third, the number of flares a given platform carries at one time is very limited.

In order to defeat the threat of infrared missiles, directional infrared countermeasures (DIRCM) have been developed. In Figure 1 , the use of early prior-art types of DIRCM, such as the AN/ALQ-204 by Lockheed-Martin (Owego, New York, USA) is depicted. When a threat is anticipated, the operator of the DIRCM in a small aircraft 10 activates a lamp 12, illurninating a broad swathe, of a beam 14 having an angle spread of roughly 40°, in a direction from which a threat 18 is expected. The 153781/2 2 illumination of an infrared seeker 16 of threat 18 by beam 14 causes seeker 16 to be jammed or destroyed, causing threat 18 to miss small aircraft 10. However, the energy density of beams such as beam 14 has proven to be insufficient to neutralize the infrared seekers of newer missiles.

A system such as the AN/AAQ-24 (V) NEMESIS by Northrop-Grumman Defensive Systems Division (Rolling Meadows, Illinois, USA) is a significant improvement over earlier DIRCM systems. The operation of such a system is depicted in Figure 2. An MWS (Missile Warning System), such as the AAR-54 (V) by Northrop-Grumman ES3 (Baltimore, Maryland, USA), having a plurality of detectors 20 and an MWS control system 22 mounted on small aircraft 10 detects a missile launch, tracks the launched missile and identifies the missile as threat 18 to small aircraft 10. MWS control system 22 transfers or "hands-off ' the trajectory of threat 18 to a DIRCM control system 24. DIRCM control system 24 then uses a dedicated missile-tracking system 26 to track threat 18, and direct a light beam 28 (with a width down to about an angle of 4°) produced by a gimbaled light source 30 to illuminate threat 18.

An improved DIRCM system similar to that described above and in Figure 2 replaces or supplements gimbaled light source 30 with an ultraviolet laser. Ultraviolet laser DIRCM systems include the AN/AAQ-24 (V) / Viper by Northrop Grumman Defensive Systems Division (Rolling Meadows, Illinois, USA) or the AN/ALQ-212 (ATIRCM) by BAE Systems (Nashua, New Hampshire, USA). In such a DIRCM system, depicted in Figure 3, an ultraviolet laser 32 is used to illuminate threat 18. Due to the narrowness of a laser beam 34 produced by ultraviolet laser 32 (having an angle of less than 3 microradians or 1.7 x 10"4 degrees), dedicated missile-tracking system 26 must be highly accurate in order to identify, pinpoint, and irradiate infrared seeker 16 of 153781/2 3 threat 18. The intensity of laser beam 34 allows for a highly-effective, albeit expensive and not robust, DIRCM system. It is important to note that some laser-based DIRCM systems are hybrid systems in which a lamp and a coaxial laser are used to illuminate the threat. Although significantly more expensive, such hybrid configurations are often necessary to overcome the likelihood that, in real-time engagements, the laser cannot be aimed properly for threat neutralization.

An alternative approach is found in the Aero-Gem (Electro-Optical Self-Protection Suite) of Rafael (Israel) which uses a gimbaled wide beam-divergence light source 36 (having a beam divergence of between an angle of 4° and 10°) to illuminate threat 18, as depicted in Figure 4. Different from the DIRCM systems depicted in Figures 2 and 3, the Aero-Gem lacks a dedicated missile-tracking system. Once MWS control system 22 identifies threat 18, the threat trajectory calculated by MWS control system 22 is used to direct gimbaled light source 36 to illuminate threat 18 with beam 28. The Aero-Gem system is significantly better than other prior-art systems in that no hand-off time is required. The longer illumination time gained by eliminating the hand-off time as well as the increased chance for seeker illumination gained by width of beam 28 when compared to laser beam 34 (Figure 3) compensates for the lesser intensity of beam 28, allowing for effective threat neutralization. Further, since the reaction time to a detected threat is low (less than 100 ms), aircraft survivability is increased. In addition, the removal of a dedicated missile-tracking system allows for a significantly less expensive and more robust system.

Depicted in Figures 5, 6 A, and 6B are two embodiments of an additional DIRCM system developed by Rafael (Israel) and fully described in co-pending Israeli patent application Nr. 145730. 153781/2 4 In Figure 5, small aircraft 10 is provided with an MWS including detectors 20 and MWS control system 22. Further, small aircraft 10 is provided with a DIRCM system including DIRCM control system 24, dedicated missile-tracking system 26, and a narrow-beam broad-band light source 38 {e.g. Xenon lamp). When MWS detectors 20 detect a missile launch, MWS control system 22 evaluates if the launched missile is a threat 18. If the missile is a threat, MWS control system 22 hands-off the trajectory of threat 18 to DIRCM control system 24, which aims light source 38 at threat 18 to illuminate threat 18 with narrow light-beam 40. Dedicated missile-tracking system 26 tracks threat 18, and ensures that threat 18 remains illuminated by beam 40 by directing light source 38, until threat 18 is no longer a threat to small aircraft 10. Beam 40 produced by light source 38 is relatively narrow, being no more than an angle of approximately 4°, and preferably much narrower, e.g. 0.5°, as depicted in Figure 5.

Figures 6A and 6B illustrate a second embodiment of the DIRCM system described in co-pending Israeli patent application Nr. 145730, included by reference as if fully set forth herein. In Figures 6A and 6B, small aircraft 10 is provided with an MWS including detectors 20 and MWS control system 22. Further, small aircraft 10 is provided with a DIRCM system including DIRCM control system 24, dedicated missile-tracking system 26, and a variable-width-beam broad-band light source 42. When detectors 20 detect a missile launch, MWS control system 22 evaluates if the launched missile is a threat 18. When threat 18 is detected, DIRCM control system 24 reacts immediately, commanding light source 42 to illuminate threat 18 using the threat trajectory determined by MWS control system 22, Figure 6 A. The width of a light beam 44a used to illuminate threat 18 is selected such that threat 18 is effectively illuminated despite the relatively inaccurate trajectory determined by MWS control system 22. Thus, 153781/2 the width of beam 44a is relatively broad, e.g. an angle of 4° or more. If the accuracy of the threat trajectory determined by the MWS is sufficient, the beam width can be reduced. Simultaneously, with the engagement of threat 18 by beam 44a, MWS control system 22 hands-off the trajectory of threat 18 to DIRCM control system 24 that activates dedicated missile-tracking system 26. Once dedicated missile-tracking system 26 acquires threat 18, DIRCM control system 24 causes light source 42 to produce a narrower light beam 44b, for example, having an angle of no more than approximately Γ wide, or even less than 0.25°, as depicted in Figure 6B. Since dedicated missile-tracking system 26 can identify the trajectory of threat 18 much more accurately then MWS control system 22, light beam 44b is much narrower than light beam 44a to increase the energy density illuminating threat 18, and consequently the neutralization efficiency.

The DIRCM systems known in the art, especially those produced by Rafael, are highly effective in defending certain types of aircraft. Aircrafts with a small thermal signature or fast and agile aircrafts equipped with the prior-art DIRCM systems have a relatively-high survivability when challenged by an infrared-guided threat.

In recent years, the need to defend other aircraft, especially large civilian or military passenger transports, has increased. Relatively cheap shoulder-fired missiles are becoming increasingly available to militants who may target a passenger aircraft to further political ends. Unfortunately, prior-art lamp-based DIRCM systems are insufficient to defend large passenger-transport aircrafts from such missiles. Passenger aircrafts are slow and virtually non-maneuverable, especially during the take-off and landing stages of flight. In addition, as these are multi-engine aircrafts designed for efficient peacetime flight, the thermal signature of such aircrafts is very large. The 153781/2 6 illumination power deployed and engagement time available for prior-art lamp-based DIRCM systems to neutralize a thermal-guided threat is insufficient to effectively protect this type of aircraft. Sufficiently-powerful suitable lamps are unavailable. The illumination power available to laser-based DIRCM systems may suffice but laser-based DIRCM systems are generally expensive and not robust as the dedicated missile-tracking system must be exceptionally accurate and mechanical components of the gimbal mount need to have an exceptionally-high tolerance and tracking accuracy. An innovative and highly-effective solution has been formulated using a plurality of lamps and is described in co-pending Israeli patent application Nr. 151672, included by reference as if fully set forth herein. Despite this, it would be advantageous to be able to harness lasers for use in DIRCM systems.

There is a need for a laser-based DIRCM device that is cheaper to manufacture than existing laser-based DIRCM devices.

SUMMARY OF THE INVENTION This and other aims are achieved by the DIRCM device of the present invention. Further, embodiments of the device of the present invention are easily attached to existing aircraft with little modification when the aircraft must fly in high-risk airspace and easily detachable when the aircraft is to fly in low-risk airspace in order to lower fuel costs and increase cargo capacity. Embodiments of the device are simple to operate with even minimal training.

There is provided, according to the teachings of the present invention, a device for defeating a threat posed by a guided missile to a platform comprising a) at least one laser light source; and b) a DIRCM control system, configured to aim at least one beam 153781/2 7 produced by the at least one laser light source at the missile based on a trajectory of the missile.

According to a feature of the present invention the at least one laser light source is selected the group of laser light sources consisting of pulsed, continuous, multi-spectral, chemical, fiber optic, solid state and diode lasers.

According to a further feature of the device of the present invention also comprises c) a beam expander functionally associated with at least one of said at least one laser light sources. The beam expander is configured to broaden a beam of light produced by a laser light source with which it is associated to an angular width of greater than 0.001°, or greater than 0.0 , or greater than 0.Γ, or greater than 0.25°, or even greater than 0.5°.

According to a still further feature of the present invention the beam expander is a variable beam expander, allowing an operator of the device to select the extent of beam broadening, for example, dependent on conditions and the nature of a threat. Preferably the DIRCM control system of the device of the present invention is configured to control the extent by which the variable beam expander expands a beam produced by an associated laser light source.

There is also provided according to the teachings of the present invention a method for neutralizing the threat posed by a guided missile comprising: a) detecting the guided missile; b) detecting a trajectory of the guided missile; and c) illuminating the guided missile with a beam emitted by a device of the present invention. 153781/2 8 BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, where: Figure 1 (prior art) is a schematic depiction of a permanently-lit wide- illumination DIRCM system; Figure 2 (prior art) is a schematic depiction of a DIRCM system using a gimbal- mounted lamp and a dedicated missile-tracking system; Figure 3 (prior art) is a schematic depiction of a DIRCM system using a gimbal- mounted laser and a dedicated missile-tracking system; Figure 4 (prior art) is a schematic depiction of a DIRCM system using a gimbal- mounted lamp and an MWS to direct the light beam; Figure 5 (prior art) is a schematic depiction of a DIRCM system using a gimbal- mounted narrow-beam lamp and a dedicated missile-tracking system; Figures 6A and 6B (prior art) are schematic depictions of a DIRCM system using a gimbal-mounted variable-width beam and a dedicated missile-tracking system, and Figures 7 A and 7B are schematic depictions of a DIRCM system using a laser- based DIRCM system with a laser beam wavelength outside the UV region, according to preferred embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of a DIRCM system that is effective in neutralizing an infrared-guided threat to a non-agile and high thermal-signature aircraft, such as a commercial passenger aircraft. The DIRCM system of the present invention illuminates 153781/3 9 a threat with at least one laser light source so that the illumination power density is sufficient to neutralize the threat.

The principles and operation of a DIRCM system according to the present invention may be better understood with reference to the accompanying description. In general, the methods and devices of the present invention work analogously to the devices and methods taught in IL 151672, with differences which are obvious to one skilled in the art upon reading the disclosure herein.

The basic principle of the present invention is to provide a method and a device to illuminate the seeker of a threat using a laser to neutralize the threat, but overcoming the disadvantages of the prior art. The approach to solving this problem is by implementing one or more of the aspects of the present invention.

Figures 7A and 7B are schematic depictions of a DIRCM system using a laser-based DIRCM system with a laser-beam wavelength outside the UV region, according to preferred embodiments of the present invention. A first aspect of the present invention for a large thermal-signature aircraft 46, shown in Figure 7A, is superficially similar to other laser-based DIRCM systems. However, unlike the ultraviolet lasers, a laser 48 includes the use of other lasers including pulsed, continuous, multi-spectral, chemical, fiber-optic, solid-state, and diode lasers. Each of these lasers gives unexpected advantages. For example, the use of multi-spectral lasers increases the chance of neutralizing seeker 16 of threat 18 by a laser beam 50. Further, many of these lasers are significantly cheaper to make and operate than ultraviolet lasers used in prior-art DIRCM systems.

A second aspect of the present invention, shown in Figure 7B, involves using a beam expander 52 together with a laser 54, including lasers used in prior-art DIRCM 153781/2 systems and the lasers recited hereinabove for use according to the present invention.

Beam expander 52 is a device, usually comprising a plurality of lenses (not shown), that expands the width and/or the angular width of a laser beam 56, yet retains a desired level of collimation. Such a plurality of lenses, functionally associated with laser 54 in such a way as to expand laser beam 56.

For example, close to the point wherefrom laser beam 56 emerges from laser 54, a double concave lens (not shown) is disposed as part of beam expander 52. By passing through the double concave lens, laser beam 56 is expanded significantly and emerges from the far side of the double concave lens with an increased angular width. Following the double concave lens is a collimating lens (not shown) as part of beam expander 52 that reduces the angular width of a now broader collimated laser beam 58.

Since laser beam 58 is significantly broader than a laser beam of a prior-art laser- based DIRCM system, it is easy to direct and successfully engage seeker 16 of threat 18.

The tolerance and accuracy of detection and direction are significantly lower, allowing a much more robust yet cheaper DIRCM system.

In another embodiment of beam expander 52, there is no post-expansion collimation. Rather, the angular width of the beam is broadened to a desired extent using one lens.

Depending on the details of the DIRCM device of the present invention, the extent of broadening and the angular beam widths of the laser beam according to the present invention as well as the method of use of the DIRCM device itself are determined.

Production of a beam expander for a laser is well-known to one skilled in the art.

Upon reading the disclosure herein, one skilled in the art can expand a laser beam 153781/2 11 having an angular width of, for example, 3 microradians to an angular width of greater than 0.001°, greater than 0.01°, greater than 0.1°, greater than 0.25°, or even greater than 0.5°. Further fashioning a variable-beam expander, which is a beam expander that can vary the extent of beam expansion on command, is within the ability of one skilled in the art.

The purpose of the DIRCM device of the present invention is to defend large passenger aircrafts from thermal-guided threats. Clearly the lion's share of such aircrafts do not need to be defended from thermal-guided threats, making it undesirable that the DIRCM device of the present invention be fully integrated into the aircraft during production. Thus, it is exceptionally preferable that the DIRCM device of the present invention be easily attachable and detachable to an aircraft. Further, since the DIRCM device is not a permanent fixture of an aircraft, the DIRCM device of the present invention is preferably operable without necessitating extensive pilot training.

The convenient attachment of peripheral, auxiliary, or extra equipment to an aircraft by the use of nacelles or pods attached to the wings or hulls of aircrafts is well- known in the art. Such nacelles or pods are used to equip an airplane with, amongst others, fuel, armaments, flares, and electronic warfare equipment. Most modern aircrafts are constructed with strong points at appropriate places for the attachment of nacelles or pods. For example, most large transport aircrafts are equipped with at least one strong point on each wing for the purpose of attaching an extra motor. These points are suitable for the attachment of DIRCM pods or nacelles of the present invention, such as a DIRCM pod 60 shown in Figures 7 A and 7B.

As is clear to one skilled in the art, the specific details of any nacelle or pod deploying the DIRCM system or components of the system of the present invention are determined by the parameters of the aircraft to be protected. For explanatory purposes, a plurality of non-limiting embodiments of a DIRCM device of the present invention are described in IL 151672.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. For example, although described as being useful against infrared-guided missiles, with appropriate modification, the DIRCM system of the present invention can be used against threats guided by radiation at other frequencies (e.g. UV/VIS).

It is important to note that the teachings of IL 151672 are in many cases directly adaptable to the present invention and are considered a part thereof. Specifically, the external mounting, attachable pods, remote control, ease of control of a DIRCM system, the combination of a plurality of light sources to make a single effective light source, and other teachings are all considered part of the present invention and preferred embodiments thereof.

It is clear to one skilled in the art that the system of the present invention can be used to neutralize munitions that are a threat to an entity that is not the platform on which the device of the present invention is deployed. For example, a DIRCM device of the present invention may be located at a ground station for example at the periphery of a threatened airfield. A special DIRCM aircraft (e.g. manned aircraft, unmanned aircraft, blimp, and zeppelin) equipped with the DIRCM device of the present invention may be deployed in the vicinity of a high-risk airfield. This is useful to allow large supply aircrafts to land at the airfield even before the airfield is completely secured, for example, in the framework of a rapid deployment force. Thus, it is understood that the 153781/2 13 specification and examples are illustrative and do not limit the present invention. Other embodiments and variations not explicitly described herein understood to be within the scope and spirit of the invention.

Claims (10)

153781/3

1. A device for defeating a threat posed by a guided missile to a platform comprising: a) at least one laser light source; b) a DIRCM control system, configured to aim at least one beam produced by said at least one laser light source at the missile based on a trajectory of the missile; and c) a beam expander functionally associated with at least one of said at least one laser light source.

2. The device of claim 1 wherein said at least one laser light source is selected from a group of laser light sources consisting of pulsed, continuous, multispectral, chemical, fiber optic, solid state and diode.

3. The device of claim 1 wherein said beam expander is configured to broaden a beam of light produced by said at least one laser light source to an angular width of greater than 0.001°.

4. The device of claim 1 wherein said beam expander is configured to broaden a beam of light produced by said at least one laser light source to an angular width of greater than 0.01°.

5. The device of claim 1 wherein said beam expander is configured to broaden a beam of light produced by said at least one laser light source to an angular width of greater than 0.1°. 153781/J 15

6. The device of claim 1 wherein said beam expander is configured to broaden a beam of light produced by said at least one laser light source to an angular width of greater than 0.25°.

7. The device of claim 1 wherein said beam expander is configured to broaden a beam of light produced by said at least one laser light source to an angular width of greater than 0.5°.

8. The device of claim 1 wherein said beam expander is a variable beam expander.

9. The device of claim 8 wherein said DIRCM control system is further configured to control an extent by which said variable beam expander expands a said beam produced by said at least one laser light source.

10. A method for neutralizing the threat posed by a guided missile comprising: a) detecting the guided missile; b) detecting a trajectory of the guided missile; and c) illuminating the guided missile with at least one beam emitted by a device including: i) at least one laser light source; ii) a DIRCM control system, configured to aim at least one beam produced by said at least one laser light source at the missile based on a trajectory of the missile; and 15378^3 16 iii) a beam expander functionally associated with at least one of said at least one laser light source.