ALQ-144

The AN/ALQ-144, AN/ALQ-147, and AN/ALQ-157 are US infra-red guided missile countermeasure devices (IRCM). They were developed by Sanders Associates in the 1970s to counter the threat of infra-red guided surface to air missiles like the 9K32 Strela-2. While decoy flares were effective at jamming first generation infra-red guided missiles, each flare was only effective for a short period. If an aircraft needed to loiter over a high risk area or was flying slowly (as helicopters do), it would require a large number of flares to decoy any missile fired at it. The IRCM provided constant protection against infra-red guided missiles.

The ALQ-144 and ALQ-147 were first delivered to the US military in 1981. Currently there are over 3,500 in use with the US military, and a total of 6,000 in use by nineteen countries globally. Seven hundred ALQ-157 systems are currently in service.

Both systems consist of a heated silicon carbide block that radiates a large amount of infra-red energy. It is surrounded by a large cylindrical mechanical shutter that modulates the infra-red output, producing a pulsing pattern. Early infrared guided missiles used a rotating reticle. When a target was not on the sensor's centerline, it would produce a pulse as the reticle swept over the target. When the target was on the sensor's centerline, the sensor would produce a constant signal. This constant signal was required by the early missiles to produce a "lock on" that would allow a launch.

The ALQ-144 and 147 IRCM produced a pattern of pulses that was approximately synchronized with the rotation rate of these reticles. Before launch this would prevent the missile actually locking onto the target, preventing the operator from firing the missile. After launch this would cause the missile to think that the target was off to one side and cause the missile to steer away from the aircraft carrying the IRCM.

The introduction of rosette and "staring" scanning techniques in second generation missiles reduced the effectiveness of the ALQ-144 and 147; later upgrades restored the effectiveness of the jammers.

The ALQ-144A was rushed into US service in time for the 1991 Gulf War, as Iraq had stocks of 9K34 Strela-3 and 9K38 missiles, against which the ALQ-144 was only partially effective. By the time the war started, two-thirds of the AH-64 Apaches in the persian Gulf had been upgraded to ALQ-144A standard. The only AH-64 Apache lost to an infra-red guided missile was hit by a 9K34 Strela-3 missile; the helicopter in question was one of the few that had not been upgraded.

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Wikipedia