At first I intended to write on the balance of air power in the South Asia but feeling later that it would need a much detailed article, I switched to the topic of air to air missiles (AAMs) and restricted to India and Pakistan. Additionally AAMs carried by combat helicopters are not included here.
Air superiority over the battlefield or over a theater of war is primarily established through fighter aircrafts using air to air missiles and associated sensors and systems. Ground-based air defence systems on the other hand are designed to deny the use of airspace to the opponent. They can't establish air superiority by themselves.
What many people do not realize is that Indian Air Force today has more variety of air to air missiles than any other country on the planet. The Surface to Air missiles (SAMs) types are also varied. These missiles have been purchased from Russia, Israel, France and United Kingdom. The indigenous air to air missile program is an additional category. Variety poses its own problems for a defender. The onboard jammers (called self-protection jammers) carried by fighter jets give best results if optimised against certain threat types.
AAMs have traditionally been categorized as Within Visual Range (WVR) and Beyond Visual Range (BVR). In simple terms, WVR missiles are short-range guided weapons and BVR missiles are medium to long-range missiles.
The WVR AAMs present in the South Asia are a mix of cold war technology and modern (post-Cold War era). These missiles include AIM-9P/L/M (Pakistan), Vympel R-73 (or AA-10), ASRAAM (Advanced Short Range Air to Air Missile), MICA-IR (ordered by India) and possibly Python-4. India has a clear edge in possessing modern WVR AAMs. A few important features of these missiles are discussed here.
1- Imaging Infra-Red (IIR)
2- Thrust-Vectoring Control
3- Helmet-Mounted Cueing System
4- Smart Proximity Fuse
5- Directional Warhead
6- All Weather Performance
7- Lock-On After Launch (LOAL) feature
8- Altitude Envelope
Imaging Infra Red (IIR)
Using easy examples, there are two types of heat-seeking missiles. One that "smell" or "feel" the aircraft and others that "see" an aircraft. The former are ordinary IR seeker missiles and latter are Imaging Infra Red seeker missiles.
Imaging IR seekers are those that actually "see" the thermal image of the aircraft. For early heat-seekers, aircraft was a dot in the sky. The Infra Red seekers are identified by their transparent glass domes at the nose. AIM-9, ASRAAM, IRIS-T, MICA-IR all have transparent glass nose sections.
The seeker of FIM-92B Stinger MANPADS (Man Portable Air Defence System) used a dual-band seeker using both Infra-Red and Ultra-Violet bands, almost 30 years ago. FIM-92C was a reprogrammable microprocessor equipped (software) Stinger. As the flares are mostly in Infra-Red spectrum, they are useless against a seeker who also seeks ultra-violet radiation. In addition, Block-II Advanced Stinger uses an Imaging Infra-Red seeker. Almost all the Imaging IR seekers use image-processing techniques and thus microprocessors and thus software for it. Developping or getting this software is extremely important. As the imaging seeker sees the whole aircraft, it can be programed to hit the hottest engine part or less hotter fuselage, according to the tactics developed by the air force.
Thrust Vector Control (TVC)
Thrust-Vector Control (TVC) is another feature of the new missiles. ASRAAM, Python-4 and Python-5 are not using TVC. Pythons use complex aerodynamic controls for achieving good turn rates but ASRAAM is neither using complex aerodynamic surfaces nor TVC (except the P3I version), casting doubts on its maneuverability (turning performance). MICA, IRIS-T, R-73 use TVC.
IRIS-T is said to pull 60g, MICA 50g and Python-4 is siad to pull 70g. But I think that the measure of turning performance (both aircraft and missiles) is not so simple. Its not just pulling so much gs. Minimum turn radius is also not sufficient.
Important thing is time, tightest turn in shortest time is what we need to look. If an aircraft or missile makes a more tight turn but takes longer than his opponent, who pulls a less tight turn more quickly, then there is no use of this tightest turn. Tighest and fastest turn is what is required. Thats why we talk of corner speed, the speed at which turning performance is maximum.
Now comes the solid rocket motor. In early missiles, the rocket motor burn times were short and the missile would fly unpowered towards its target at max range and become energy-less, easy to dodge. Now the energy of rocket-motor is better managed to give it more energy at "end game". This is achieved through dual-thrust rocket motors, meaning that thrust of rocket is not the same during the flight, the thrust is increased slowly as the missile nears the target and then drops off.
Helmet-Mounted Cueing System
Short-Range Air-to-Air missiles typically have two phases of pursuing or following a target, first cueing of the missile's gimballed seeker in the general direction of the target and then using other sensors for locking on it. A lock means that missile's movements are now relative to the target for intercepting it. For missiles with gimballed seekers, cueing can be provided by many systems, i.e., Helmet-Mounted Sight (HMS), fighter aircraft radar, Infra-Red Search and Track (IRST) system and possibly Air to Air Laser etc.
Proximity Fuse
All missiles have impact fuses and now its important to see what other fuses are installed. For air to air, the proximity fuse is most important after the impact fuse because either the missile shall hit the target or it shall miss it by a small margin. Therefore it is necessary to initiate the warhead on hitting the target and when its nearly missing the target. Fuse is the thing that explodes the warhead.
AIM-9L (Nine Lima) has laser-proximity fuse, which should be jam resistant. Python-5 and ASRAAM also use laser proximity fuse, which is plus point. MICA uses RF (radio frequency) proximity fuse, which is apparently a disadvantage. However, one can demand to install a laser- or a tailor-made proximity fuse from the manufacturer as it should not be difficult. All proximity fuses have their lethal ranges within which they shall trigger the warhead. If proximity fuse is somehow jammed, the effectiveness of the missile would be greatly impacted.
Directional Warhead
Warhead of MICA seems to be the most advanced one, using "Focused Splinters". When an ordinary warhead explodes, it distributes its explosive energy (destructive power or blast power) equally in all directions. This is not desired. We want the explosive energy to be directed towards the target.
MICA's warhead seems to be doing it. If MICA misses the target by a little margin to the right side, the proximity fuse shall initiate the warhead and it shall explode, sending its splinters towards the aircraft (left side of the missile). This is directed-energy warhead technology. I think this was first used in anti-tank missiles, with top-attack anti-armour warheads. The warhead concentrates most of its energy in direct downward direction to damage the tank or other armoured vehicle to the maximum, without diving on it.
All-Weather Performance
A factor that affects the performance of heat-seeking or IR missiles is atmospheric elements like Clouds, fog, mist, sandstorms etc, and this effect must be seen before acquiring a new short range Air to Air missile.
Mist, clouds and rain mask heat signatures and so prevent effective use of infra red guidance. Earlier models of Sidewinder could easily be fooled by the Sun, clouds, flares, or even rain.
The atmosphere basically affects IR energy in three different ways - absorption, scattering and scintillation. Missile is said to lose "sight" of the target....clouds absorb and scatter the IR radiation and some a bit less important like sandstorms too scatter the IR radiation. Sandstorms may become important over Rajihstan area of Sindh and clouds/Mist is a special consideration over all of Pakistan especially in Winter.
If the water vapour concentration increases, scattering becomes noticeable. Scattering occurs when the wavelength of the IR is comparable in size with the scattering particles. Clouds and fog contain droplets around 1 micrometre in size - this results in extremely low transmission throughout most of the IR band.
On the other hand, rain droplets are much larger, with the seemingly surprising result that IR transmission through rain is substantially better. Rain is liable to degrade the systems performance, but still allow it to function. It is claimed that ASRAAM counters the target obscurity in clouds. Given the weather over UK and Europe, this seems to be an advantage. Heat seeking missiles can't be true all-weather weapons.….and although the later Sidewinder models are good as compared to earlier, ……it seems true that if an intruder gets into cloud cover, the range of Sidewinder shall decrease…. For the missiles used in the region, it would be interesting to know that exactly how much the acquisition range is affected by a specific type of clouds.
Lock-On After Launch (LOAL)
Lock-On After Launch (LOAL) is important for those fighters that carry missiles internally like F-22 or F-35. The seeker of missile is not out in the air to feel the heat or IR radiation. LOAL is useful also for submarines carrying such missiles. Also LOAL is required for backward firing of missiles i.e., firing it straight and then the missile turns 180 degree to the rear and achieves a lock upon seeing the target.
IAF is planning to arm Jaguars with ASRAAM because Jaguars do low-level flying and need a missile that can engage high flying fighters. Lock-On-After-Launch (LOAL) feature enables ASRAAM to climb towards target without lock-on until target is within the seeker range.
In 1980s, IAF acquired Mirage-2000s for deep penetration strikes at low-level because they were armed with Super 530D which could engage targets with a large altitude difference. But as Jaguar-IS and Mig-27 do not carry airborne (nose) radars, they needed an IR missile with good vertical range.
Modern air to air IR missiles featuring LOAL are ASRAAM, AIM-9X, IRIS-T, Python-5 and MICA-IR. The baseline R-73 used by IAF is a good dogfight missile but reportedly lacks LOAL feature.
Altitude Envelope
As discussed earlier, whenever short-range IR missiles are discussed, mostly horizontal ranges with head-on and tail-on configurations are mentioned. Sometimes the effects of launch altitude and launch speed on missile range and maneuvering capacity are also mentioned. But what normally lacks is the ability of missiles to engage targets with a large difference in altitude. For the early heat-seekers, we know that the launching aircraft had to be in at the tail of target (aspect) and almost at the same altitude as target with almost no off-boresight angle. Technology has not changed all that. Engagements at large off-boresight angles and altitude différences are now possible.
Lets say that the tail-on range of a Sidewinder is 10 miles. Its evident that this 10 miles is not a vertical range because a Sidewinder can't be expected to kill or lock onto a target which is 10 miles high either due to the missile seeker's inability to acquire target at such altitude or because the rocket motor burns out quickly in such a climb.
While it is true that with large altitude difference, mostly radar-guided BVR missiles are used, still for a surprise kill, IR missiles can be employed. It can also happen that radar-guided BVR missiles are used up. One possibility of surprise interception is that IR missile be launched without radar lock with range estimated from air-to-air laser range finder / IRST/ AWACS input etc. For such a surprise shot, it is important to know the engagement envelope of one's missile especially the vertical range from low altitude upwards and inversely. As a Stinger MANPADS can engage targets upto a maximum theoretical altitude of 11,000 feet, it can be guessed that IR-missiles without Lock-On-After-Launch feature can't engage target if altitude difference is around 15-20,000 feet.
Lets consider a scenario. An aircraft is flying at 30,000 feet altitude and is one mile behind a target which is flying at 100 feet. Can this aircraft fire AIM-9L/R-60/R-73/Magic-2/R-27T on target from that altitude without diving for it? Perhaps Not. The other question is whether low-flying aircraft at 100 feet can engage the high-flying aircraft at 30,000 feet with above IR missiles? seems negative.
For a downwards shot, the rocket motor range may not be a problem but the seeker still may not acquire the target due to large altitude difference. For an upwards shot, the rocket motor range will also be important in addition to the acquistion range of the seeker itself.
Still many things remain like arming of the warhead, navigation techniques used, ranges, minimum launch speed restrictions (all heat-seeking missiles can't be fired from helicopters because of minimum launch speed restrictions), further filters for ECCM, maximum speed and its effect, inter-operatability with Sidewinder rails, seeker cooling systems, range of Proximity Fuse and its effect??? etc etc.
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