Night Sight for a Missile Launcher Comprising an Image Intensifier Tube, a Reticle, and an Objective Lens

1. Field of the Invention

The present invention relates to a missile launcher sight, and more particularly to a sight having an image intensifier providing night vision capability for use with hand held missile launchers.

2. Description of the Prior Art

The STINGER Man Portable Air Defense System (MANPADS) is a shoulder launched anti-aircraft missile which has been produced in large quantities by several manufacturers. The STINGER launcher utilizes an open sight similar to the "iron sights" on a rifle in daylight conditions (day sight) for "acquiring" aircraft targets, i.e., aiming the launcher to enable the missile's guidance system to sense and track ("lock on to") a target. The day sight, like a standard rifle sight, has a rear aperture or "peep sight" and a front aperture. To acquire a target, the front and rear apertures are aligned with the target and the missile's heat seeking guidance system is activated. Once the target is acquired and locked on to, the front sight has further alignment features which the gunner uses to elevate the launch tube and adjust for proper lead angle prior to launching the missile. The lead angle is the angular displacement of the launcher from a position of pointing at the target to a position of pointing forward of the target in its direction of movement. The object of aiming forward of the target is to allow the missile to meet the target using the shortest trajectory possible. The sight assembly described above is also used for estimating the range to an aircraft target to assist in making a launch decision and to avoid launching when the target is out of range.

The STINGER is very effective during daylight hours against both fixed wing and rotary wing targets, and has even been used successfully by third world "freedom fighters" with limited formal training in the operation and use of the system. Presently, the STINGER missile system does not have a night vision optical sight for acquisition and identification of aircraft targets. Utilization of the missile system is therefore severely restricted during the night time because of the need to positively identify targets before launch, particularly when friendly aircraft are also in the area. At night, even when no friendly aircraft are present, the gunner can only use his ears and the missile infrared sensor in a usually futile attempt to "lock-on" to an aircraft, which would typically be moving at a high rate of speed. This results in greatly reduced capability for the STINGER system during hours of darkness.

The U.S. military employs a number of fielded night vision weapon sights, such as, the AN/PVS-4 Individual Served Weaponsight for aiming rifles and other projectile weapons. The problem with the AN/PVS-4 sight is that it has insufficient field of view to implement the STINGER firing sequence with the required elevation and lead angle. The, AN/PVS-4 has a 14 degree circular field of view, whereas a minimum of about 22 degrees is required for a sight designed for the STINGER. The small field of view also inhibits the search for aircraft targets, requiring a longer period of time to search a given search area.

The problems and disadvantages associated with the conventional techniques and devices utilized to aim hand-held missile launchers are overcome by the present invention which includes a night sight for a missile launcher having an objective lens with a field of view of at least 22 degrees. A light intensifier tube positioned with respect to the objective lens to receive as input the output image of the objective lens intensifies the image. An eyepiece is used for viewing the output of the light intensifier tube. A reticle is disposed between the light intensifier and the eyepiece for use in aiming the launcher.

For a better understanding of the present invention, reference is made to the following detailed description of an exemplary embodiment considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of a missile sight in accordance with a preferred embodiment of the present invention.

FIG. 2 is a view in elevation of a reticle which is utilized in a preferred embodiment of the present invention.

FIG. 3 is an exploded perspective view of a reticle assembly and associated image intensifier.

Referring to FIG. 1 there is shown a night sight 10 for aiming a man-portable missile launcher in accordance with a preferred embodiment of the present invention. The sight 10 may be removably connected to a missile launching tube (not shown) by a commercially available mounting bracket 12. A thumbscrew 14 secures the sight 10 to the mounting bracket 12. A flip-up lens cover assembly 18 is affixed to an objective lens assembly 20 to protect it from contamination and mechanical damage. The objective lens assembly 20 has a 60 mm focal length objective lens with 25 mm diameter format and an F/number of F/1.2. The image produced by the objective lens assembly forms the input to an image intensifier tube 22 (see FIG. 3) housed within housing section 22a which also houses batteries for powering the tube. The image intensifier tube of the exemplary embodiment is an inverting, 25 mm format, GEN III+I device. A GEN II intensifier, such as, one in accordance with military standard MX-9644, could also be used, however. An eyepiece assembly 24 is affixed to the image intensifier tube 22 for viewing the output of the tube and has mounted thereon an elastomeric eyeguard 26 to absorb shocks generated by missile launching. The gunner's left eye is shielded from missile blast gases, particulate matter and any other ejecta, by a clear polycarbonate blast shield 28 which is attached to the eyepiece assembly 24 by means of a clamp ring and locking screw. The blast shield 28 is attached to the clamp ring via a flexible neoprene rubber mount to provide a flexible mounting for the shield 28. A reticle assembly 30, as shall be described at length below, is disposed between the output end of the image intensifier tube 22 and the eyepiece assembly 24. A sight in accordance with the present invention has a wide 23.5 degree field of view and an illuminated reticle which duplicates the operation of the day sight reticle pattern familiar to daytime gunners. The illumination of the reticle pattern and the gain of the image intensifier are variable and are adjusted by external control knobs 32 and 34, respectively, for optimum target contrast under varying night sky conditions.

Referring now to FIG. 2, a reticle lens 36 in accordance with an exemplary embodiment of the present invention is there shown. The reticle lens 36 is essentially a clear, flat substrate through which the output of the image intensifier passes without distortion. It is preferably formed from optical crown glass type 523-586 as per military specification G-174, Grade B, Annealed. A reticle pattern 38 is etched on one surface of the reticle lens 36 and filled with Titanium Dioxide. The line width of the pattern 38 should be about 0.10 mm. Both the front and back surfaces of the reticle lens should be polished, the outer peripheral edge 40 being fine ground. The surface of the lens 36 opposite to the pattern 38 is preferably anti-reflective coated as per military specification MIL C-675. A pair of flats 42 are formed on the outer peripheral edge 40 of the reticle lens 36 to receive light from LED's positioned within the interior of the reticle assembly. Although flats are shown as the preferred indentation shape in the otherwise circular periphery, grooves or any other shape indentation could be used. The outer peripheral edge 40 of the reticle lens 36 is painted with a reflective coating, such as, white paint, to enhance the reflection of light emitted by the LED's back into the reticle lens 36. The flats 42 are not painted as they are the entry point of the light emitted by the LED's. Light from the LED's is trapped within the lens by the polished front and back surfaces and by the reflective coating on the periphery 40 of the lens 36 and thus escapes only from the etched and filled reticle pattern 38.

FIG. 3 shows the preferred apparatus for holding the reticle lens 36 in association with an image intensifier tube assembly 22. The tube assembly 22 is essentially common to the industry, however, it is adapted to be used with the present invention by the addition of two wire leads 44 which affix internally within the tube assembly 22 to a voltage source which provides power to the LED's 46 used to illuminate the reticle pattern 38. The reticle lens 36 is received in a mating recess or depression 48 formed by a retainer lip around the periphery of the central light conducting aperture of a reticle holder 50. The LED's 46 are positioned in suitable cavities 52 ground into, or otherwise formed in the reticle holder 50 at about a 90 degree separation. The use of two LED's 46 and a 90 degree separation insures uniform illumination across the reticle lens 36. The reticle lens 36 is secured to the reticle holder 50 with a light shield ring 54 having an adhesive backing. Besides mechanically holding the reticle lens 36 in the recess 48, the ring 54 prevents light emitted by the LED's 46 from radiating in a direction parallel to the axis of the tube 22 and into the viewer's eyes e.g., through the space between the reticle lens 36 and the reticle holder 50. The LED's 46 are electrically connected to the voltage supply wires 44 by means of a printed circuit board 56 in the shape of a partial ring to which the wires 44 and LED's 46 are soldered. The printed circuit board 56 also functions as a retainer ring because it is received under rim 58 and captures the ring 54 and lens 36 within the recess 48. The reticle holder 50 is affixed to the end of the intensifier tube assembly 22 by double sided tape dots 60 or other conventional means. An RTV sealant is used to secure the LED's 46 and the board 56 in position.

In operation, the reticle pattern 38 appears as a black line against the green phosphor screen when the LED's 46 are off. When power is applied to the LED's 46, the reticle pattern 38 will glow with the LED 46 color, typically red, which contrasts with the green phosphor of the tube.

The sight 10 may be stored in a shipping/mounting case with the mounting bracket 12 attached. When it is necessary to use the STINGER launcher, the gunner may then remove the sight 10 from its case and install it onto a STINGER launcher tube. The gunner installs two standard "AA" batteries in the sight 10 for power, turns on the sight 10 and the reticle 30. The sight 10 is then ready for target acquisition by the gunner. When the target is acquired, the gunner uses the special reticle design to estimate ranges and attempts to visually identify the target. If the target is identified as "hostile", the gunner activates the missile infrared seeker and listens for an audible tone which indicates that the missile has locked on to the target. The gunner then uses the reticle pattern to elevate the launch tube and adjust the lead angle prior to missile launch. Once the missile is launched, the gunner can quickly remove the sight from the used launcher and install it on the next launcher to engage additional targets.

It should be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention as defined in the appended claims.