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IRST has a spotty history. F-4s and F-106s were equipped with primitive units and Russia included IRST on the MiG-29 and Su-27 families. The U.S. Navy developed IRST for the F-14D Super Tomcat, mainly as a counter to the formidable jamming system on the Tu-22M Backfire. The same hardware was slated for F-22 but discarded in an early budget scrub. In the West, that left Typhoon (Selex) and Rafale (Thales, built into the front sector optronics unlt) as the standard-bearers. More recently, the U.S. Navy has started working on IRST for the Super Hornet, initially with optical hardware from the F-14D days, and Aggressor F-16s have been seen with IRST pods. Selex and others have developed surface-to-air IRSTs.
Early systems had limited range. This had less to do with basic physics and IR technology than with false alarm rates: the IR world is a noisy one, and if the system gain is turned up too high it will detect birds, the sun reflecting off clouds, ground vehicles and everything else. Faster processing and the ability to record and analyze a great deal of IRST data has gradually whittled away at the problem -- and progress in the last few years (according to Eurofighter and other sources) has been rapid.
Hiding from IRST is difficult for anything flying much above 300 knots. There have been isolated reports that the F-22 uses an active cooling system to deal with hot-spots at high speed, but that raises problems -- the heat has to go somewhere.
Like Russia's work on advanced VHF radars, IRST does not mean that stealth is dead. However, it does raise the bar for stealth, particularly in an air-to-air engagement. It makes it more difficult for a low-RCS fighter to engage its adversary without being detected itself -- if both are using IRST, detection may be mutual. (At the same time, the much better electronic warfare systems on modern flighters have redefined "low probability of detection" for a stealth attacker's radar.)
The F-35's electro-optical targeting system (EOTS) is described as having an IRST function. However, like other air-to-ground targeting sensors, it operates in the IR mid-wave band; IRST uses long-wave IR, which is better at long range. Neither is it optimised for the kind of very rapid "step-stare" scanning that an IRST uses to cover a wide area.
http://aviationweek.com/blog/quite-special-and-not-all-boring
Later systems
IRST systems re-appeared on more modern designs starting in the 1980s with the introduction of 2-D sensors, which cued both horizontal and vertical angle. Sensitivities were also greatly improved, leading to better resolution and range. In more recent years, new systems have entered the market. In 2015, Northrop Grumman introduced its OpenPod(TM) IRST pod, which uses a sensor by Selex ES.
Optronique secteur frontal (IRST) of the Dassault Rafale, below the cockpit and to the side of the refueling boom. On the left, the main IR sensor (100 km range), on the right a TV/IR identification sensor with laser rangefinder (40 km range)
Eurofighter Typhoon with PIRATE IRST
The best known users of modern IRST systems are:
MiG-29 nose showing radome and S-31E2 KOLS IRST
With infrared homing or fire-and-forget missiles, the aircraft may be able to fire upon the targets without having to turn their radar sets on at all. Otherwise, they can turn the radar on and achieve a lock immediately before firing if desired. They could also close to within cannon range and engage that way.
Whether or not they use their radar, the IRST system can still allow them to launch a surprise attack.
An IRST system may also have a regular magnified optical sight slaved to it, to help the IRST-equipped aircraft identify the target at long range. As opposed to an ordinary forward looking infrared system, an IRST system will actually scan the space around the aircraft similarly to the way in which mechanically (or even electronically) steered radars work. The exception to the scanning technique is the F-35 JSF's DAS, which stares in all directions simultaneously, and automatically detects and declares aircraft and missiles in all directions, without a limit to the number of targets simultaneously tracked.
When they find one or more potential targets they will alert the pilot(s) and display the location of each target relative to the aircraft on a screen, much like a radar. Again similarly to the way a radar works, the operator can tell the IRST to track a particular target of interest, once it has been identified, or scan in a particular direction if a target is believed to be there (for example, because of an advisory from AWACS or another aircraft).
IRST systems can incorporate laser rangefinders in order to provide full fire-control solutions for cannon fire or launching missiles (Optronique secteur frontal). The combination of an atmospheric propagation model, the apparent surface of the target, and target motion analysis (TMA) IRST can calculate the range.
Performance
Detection range varies with
At high altitudes, temperatures range from −30 to −50 °C - which provide better contrast between aircraft temperature and background temperature.
The Eurofighter Typhoon's PIRATE IRST can detect subsonic fighters from 50 km from front and 90 km from rear - the larger value being the consequence of directly observing the engine exhaust, with an even greater increase being possible if the target uses afterburners.
The range at which a target can be sufficiently confidently identified to decide on weapon release is significantly inferior to the detection range - manufacturers have claimed it is about 65% of detection range.
https://en.wikipedia.org/wiki/Infra-red_search_and_track
Early systems had limited range. This had less to do with basic physics and IR technology than with false alarm rates: the IR world is a noisy one, and if the system gain is turned up too high it will detect birds, the sun reflecting off clouds, ground vehicles and everything else. Faster processing and the ability to record and analyze a great deal of IRST data has gradually whittled away at the problem -- and progress in the last few years (according to Eurofighter and other sources) has been rapid.
Hiding from IRST is difficult for anything flying much above 300 knots. There have been isolated reports that the F-22 uses an active cooling system to deal with hot-spots at high speed, but that raises problems -- the heat has to go somewhere.
Like Russia's work on advanced VHF radars, IRST does not mean that stealth is dead. However, it does raise the bar for stealth, particularly in an air-to-air engagement. It makes it more difficult for a low-RCS fighter to engage its adversary without being detected itself -- if both are using IRST, detection may be mutual. (At the same time, the much better electronic warfare systems on modern flighters have redefined "low probability of detection" for a stealth attacker's radar.)
The F-35's electro-optical targeting system (EOTS) is described as having an IRST function. However, like other air-to-ground targeting sensors, it operates in the IR mid-wave band; IRST uses long-wave IR, which is better at long range. Neither is it optimised for the kind of very rapid "step-stare" scanning that an IRST uses to cover a wide area.
http://aviationweek.com/blog/quite-special-and-not-all-boring
Later systems
IRST systems re-appeared on more modern designs starting in the 1980s with the introduction of 2-D sensors, which cued both horizontal and vertical angle. Sensitivities were also greatly improved, leading to better resolution and range. In more recent years, new systems have entered the market. In 2015, Northrop Grumman introduced its OpenPod(TM) IRST pod, which uses a sensor by Selex ES.
Optronique secteur frontal (IRST) of the Dassault Rafale, below the cockpit and to the side of the refueling boom. On the left, the main IR sensor (100 km range), on the right a TV/IR identification sensor with laser rangefinder (40 km range)
Eurofighter Typhoon with PIRATE IRST
The best known users of modern IRST systems are:
- Russia
- Su-27/30/35 Flanker (OLS-27/30/35)
- Mikoyan MiG-29 (OLS-29)
- Sukhoi PAK FA (101KS-V)
- China
- Chengdu J-10B
- Shenyang J-11/15/16
- Chengdu J-20 (EORD-31)
- United States
- Grumman F-14 Tomcat (AN/AAS-42 IRST)
- Lockheed Martin F-16 E/F Block 60/62 (AN/AAQ-32 IFTS)
- Boeing F/A-18E/F Super Hornet (Block III)
- Lockheed Martin F-35 Lightning II AN/AAQ-37 electro-optical Distributed Aperture System (DAS) with a 360 degree IRST, missile detection/warning, and day/night vision capabilities, designed and produced by Northrop Grumman Electronic Systems.
- Saab JAS 39 Gripen E/F (Selex ES Skyward-G)
- United Kingdom / Germany / Italy / Spain
- Eurofighter Typhoon (Selex ES PIRATE)
- France
MiG-29 nose showing radome and S-31E2 KOLS IRST
With infrared homing or fire-and-forget missiles, the aircraft may be able to fire upon the targets without having to turn their radar sets on at all. Otherwise, they can turn the radar on and achieve a lock immediately before firing if desired. They could also close to within cannon range and engage that way.
Whether or not they use their radar, the IRST system can still allow them to launch a surprise attack.
An IRST system may also have a regular magnified optical sight slaved to it, to help the IRST-equipped aircraft identify the target at long range. As opposed to an ordinary forward looking infrared system, an IRST system will actually scan the space around the aircraft similarly to the way in which mechanically (or even electronically) steered radars work. The exception to the scanning technique is the F-35 JSF's DAS, which stares in all directions simultaneously, and automatically detects and declares aircraft and missiles in all directions, without a limit to the number of targets simultaneously tracked.
When they find one or more potential targets they will alert the pilot(s) and display the location of each target relative to the aircraft on a screen, much like a radar. Again similarly to the way a radar works, the operator can tell the IRST to track a particular target of interest, once it has been identified, or scan in a particular direction if a target is believed to be there (for example, because of an advisory from AWACS or another aircraft).
IRST systems can incorporate laser rangefinders in order to provide full fire-control solutions for cannon fire or launching missiles (Optronique secteur frontal). The combination of an atmospheric propagation model, the apparent surface of the target, and target motion analysis (TMA) IRST can calculate the range.
Performance
Detection range varies with
- clouds
- altitude
- air temperature
- target's attitude
- target's speed
At high altitudes, temperatures range from −30 to −50 °C - which provide better contrast between aircraft temperature and background temperature.
The Eurofighter Typhoon's PIRATE IRST can detect subsonic fighters from 50 km from front and 90 km from rear - the larger value being the consequence of directly observing the engine exhaust, with an even greater increase being possible if the target uses afterburners.
The range at which a target can be sufficiently confidently identified to decide on weapon release is significantly inferior to the detection range - manufacturers have claimed it is about 65% of detection range.
https://en.wikipedia.org/wiki/Infra-red_search_and_track
