India should address the serious issue of stealth aircraft detection
Gp Capt. Gopal Sharma
In the coming decade, the Indian Air Force (IAF) will confront the problem of detection of stealth aircraft. Our Northern neighbour has developed a fifth generation air dominance fighter J-20 with stealth characteristics.
The J-20, a midair-refuelable, missile-capable jet designed to fly far beyond China’s borders, was for years kept in top-secret development by the Chinese. It was first showcased to the world with a test flight during US defence secretary, Robert M. Gate’s visit of China in January 2011. It has been operationalised since then and 20 plus are in service. After solving the engine related issue, the Chinese are expected to undertake the serial production of the aircraft. The Chinese are known to be engaged in developing stealth long-range bomber (H-20) which, too, could materialise soon from their stable. Analysts forecast the H-20’s first flight in the early 2020s, with production possibly beginning around 2025.
An intruding aircraft can be detected by its radar, infrared (IR) and acoustic signatures. For radar detection, reflected radio waves from the aircraft are also picked up by the source radar (airborne or ground) which leads to its radar detection. The range depends on the transmitted power, height of the aircraft, the radar horizon of the ground radar, and effect of extraneous clutter/ interference.
The IR signatures, too, can lead to detection of the airborne/ground targets. This mode of detection is normally employed by the aircraft. Aircraft generate heat from their engines as well through frictional heating with the air. The nose and leading edges become hot, more so when flying supersonically. This can make detection easier. Therefore, stealth planes stay subsonic even if they can fly supersonically or have super-cruise capability without switching reheat. For example, Forward Looking Infrared (FLIR) is available in most combat aircraft for forward-looking to all-round situation awareness. Such systems use a passive thermographic camera, so that they do not give out any radiation of their own, unlike radar. As the IR attenuates in the atmosphere, the range of detection by this means is not very large.
Relevant literature suggests that acoustic signatures, too, can be processed to detect the aircraft. This is possible as all aircraft emit specific acoustic signatures. This is a passive system; hence, it would not be prone to the threats of anti-radiation missiles But, acoustic detection has not developed to an extent that this can be universally used to detect the combat aircraft. In the US, however, customs and border protection record excursions at low level across the northern borders for illegal activities like smuggling of drugs/criminal transit / human trafficking etc. The sound emitted by the low flying aircraft is picked up by the Acoustic Seismic Detection System (ASDS) which consists of several nodes. The single node detects the presence of the aircraft by more than one giveaway direction. The detection by more than one node helps in determining the bearing and localisation. Logically it is not suited for detecting the fighter aircraft unless these are approaching at low level.
Stealth aircraft have been designed to reduce the radar, IR signatures to avoid detections. A look at stealth fighter like F-22 reveals its designs adhere to the shaping principles of a stealthy design to reduce the radar cross-section. The leading and trailing edges of the wing and tail have identical sweep angles (a design technique called plan form alignment). The fuselage and canopy have sloping sides. The canopy seam, bay doors, and other surface interfaces are saw-toothed. The vertical tails are canted. The engine face is deeply hidden by a serpentine inlet duct and weapons are carried internally. The result is that for the size of the aircraft its radar cross-section, which for the size of the aircraft should be more that 3-4 metres, is just reduced to from certain angle -40dB sm equivalent to the reflection from a size of a steel marble. F22 is known to be an example of perfect stealth. This has raised its cost to astronomical level which even America has found it unaffordable and therefore, has developed F-35, a fewer stealth aircraft but a cheaper version. Likewise, the Northrop B-2 Spirit, also known as the Stealth Bomber, is an American heavy penetration strategic bomber, featuring stealth technology designed for penetrating dense anti-aircraft defences. Other aircraft under development such as Chinese J 20, J 31 and Russian SU 57(Pak-FA) may not be as stealth as F-22 but, these aircraft still would be difficult to detect and even if detected, the ranges would be so low to enable credible response by the air defence. Russia and China are also developing stealth bombers, the details are classified. The US company, the Northrop, is developing a new and more capable B-21 Raider, a long strategic bomber, capable of delivering conventional and thermo-nuclear weapons. Few details are known but claim to survive enemy air defences while operating from all heights unlike B-2 which flies at high altitude at subsonic speeds. The stealth and height of operation shield B-2 from detection as well as from the destructive ranges of air defence weapons.
Some Drawbacks of Stealth
For stealth features the aircraft must pay penalty too. Some of these are explained below:
- The stealth aircraft is poorly suited for combat manoeuvring, as its shape results in low speed and manoeuvrability
- The stealth plane can be seen and identified visually and with high-frequency radar. Conventional pulse radar, too, can detect a stealth aircraft when its radar cross section increases while executing hard turns or when its bomb bay is opened for deploying weapon arsenal allowing it to be easily targeted.
- Stealth aircraft are very expensive. As a reference, the B-2 bomber is the most expensive aircraft in aviation history, costing USD1.157 billion.
- A fully stealth aircraft carries all its fuel and armament internally, this naturally limits the capacity of total payload. For example, US retired F-117 in 2008 could carry only two laser- or GPS-guided bombs, while a non-stealth attack aircraft can carry several times more.
In view of these drawbacks, the countries may not opt for full stealth aircraft in their inventory.
Impact of Stealth Aircraft in Operations
The US alone has used stealth aircraft in operation simply because no other country earlier possessed stealth aircraft. Now apart from the US which has three operational stealth aircraft i.e. F22, F35 and B2 spirit, Russia and China, too, have developed and tested their indigenous designed stealth aircraft in 2010 (Pak FA) and 2011 (J-20) respectively. The US is developing more accomplished stealth bomber B-21 Raider which will eventually replace the B-2 bomber.
The US has used F117, the Night hawk, the first stealth aircraft and stealth B2 Spirit bombers in several operations with great success. Till date only one F117 has been the battle causality which was shot by the Pechora surface to air missile over Yugoslavia. This, too, was claimed due to the pilot’s manoeuvring error. After its first use in Operation Just Cause in Panama in almost all operations thereafter these have been used by the US achieving spectacular successes. In Iraq, the US has generally employed them mainly against heavily fortified targets in Operation Desert Storm. The success rate can be gauged from the fact that F-117s flew 1,300 sorties and had scored direct hits on 1,600 high-value targets without any loss of aircraft.
While stealth aircraft formed only 2.5 per cent of the American aircraft in Iraq, they struck 40 per cent of the strategic targets, dropping 2,000 tonnes of precision-guided munitions and striking their targets with an 80 per cent success rate. Stealth aircraft has been used with advantage in Libya and Afghanistan as well. Even to eliminate Osama bin Laden the helicopter used to transport the Seal commandos to the compound of bin Laden in Abbottabad had stealth features. This was probably the reason that it could not be detected by Pakistani air defences.
Stealth aircraft successes in operation point out their continued use despite their high price and relatively lower weapon load capacity is due to their own safety during operations obtained by stealth features of the aircraft. In time to come, development of anti-stealth weaponry is expected to decrease the value of stealth.
Detection of the Stealth Aircraft Threat
Stealth Aircraft Detection by Radars: Presently, the detection of stealth aircraft poses a problem. Stealth, however, does not make the aircraft invisible, rather the technology simply delays detection due to the reduced cross section on certain radar frequencies which hampers the activation of defence mechanism. Radar absorbent material coatings which have carbon black particles or tiny iron spheres on every surface of the stealth fighter can further help conceal the aircraft by absorbing the radar energy with minimal reflection. There are certain types of radar techniques and/ frequencies which despite aircraft stealth design will detect these aircraft with some inherent limitations.
Use of Low Frequency Radars (LFRs): These radars will certainly detect the stealth aircraft. Low frequencies can detect that the absorbing material applied attenuates higher frequencies in the centimetre band and above, the absorbent coating is not thick enough to absorb the low frequencies in the metric band and below, so target aircraft reflects such radio frequency despite its stealth features. However, the reflected signal displayed has poor azimuth discrimination due to large beam width and poor range resolution of the detected pick up. Thus, VHF and UHF band radars cannot be used for aircraft tracking but, these can provide good early warning for activation of air defence weapons. Our northern neighbour’s J-20 fighter is not even fully stealth, it could thus be detected by one of the several UHF/VHF radars which India too possesses. But, these radars, due to the design limitations, do not offer long detection ranges and cannot thus be used to detect deep inside the territory of the adversary. Since J-20 is not a truly stealth aircraft, therefore, assertion by the IAF that airborne radar of SU 30MKI did track J-20 flight may be right. This affirms the belief that unlike the US’ F-22 and F-35 stealth jets, the J-20 doesn’t have all aspect stealth. A US expert, however, believes that it is possible that the Chinese are flying the J-20 with radar reflectors attached to enlarge and conceal its true radar cross section during peacetime operations — just as the USAF routinely does with the F-22 and F-35.Hence, challenge of J-20 cannot be brushed aside and countermeasures surely are needed to tackle the threat.
Over the Horizon Radars: Essentially, these radars operate on HF band or below, working on sky wave/ ground wave technology. These have detection ranges of thousands of km and allow surveillance of very large territories. These radars, too, can provide early warning of the threat but, are not suited for tracking aircraft threats. These require large powerful transmitters and huge antenna (antenna dimension is in miles) and are very expensive. The HF frequency used in this radar returns to the earth after bouncing from the ionosphere. The stealth aircraft are optimised for defeating much higher-frequency radar from front-on/below rather than low-frequency radars from above and are detected. The US and Canada have deployed these radars. Even Australia and China have deployed one radar each.
Passive (Multi-static/Bi-static) Radars: These are known to better in detecting the stealth aircraft than the mono-static radars. Such a system typically uses either low frequency broadcast TV and FM radio signals at which frequencies controlling the aircraft’s signature is more difficult.
Quantum Radars: Quantum radar might eventually provide a capable means of detecting stealth fighters and bypassing electronic warfare capabilities of the adversary’s aircraft. A quantum radar functions by using a crystal to split a photon into two entangled photons. The radar beams one half of the entangled pair outwards and monitors the corresponding effects on their entangled partners. If the beamed particles hit say a stealth fighter, the effect on the beamed photon would be visible on the un-beamed partner photon as well. Then the photons which register a ‘ping’ are sorted out from the unaffected photons to form a sort of radar image. Quantum radars will make the stealth technology ineffective. The Quantum technology is still at the laboratory level even though many countries are engaged in the research.
IR detection has application in the airborne sensors rather than ground-based sensors. Infra-Red Search and Track systems (IRSTs) fighter aircraft can be used against stealth aircraft as well, because any aircraft surface heats up due to air friction and with two-channel IRST, detection is possible by comparing the difference between the low and high channel. Such facility is fitted to the MiG-29 and Su-27 aircraft. The French Rafale, the British/German/Italian/Spanish Euro fighter and the Swedish Gripen also make extensive use of IRST. This is not to say that IRST can be used to detect the adversary’s aircraft at the ab-initio stage, but it would be used during engagements to know about the adversary, aircraft position to take advantage of the tactical situation. In air combat, the optronic suite allows:
- Detection of non-afterburning targets at 45-kilometre and more
- Identification of those targets at 8-to-10-kilometre
For ground targets, the suite allows:
- A tank-effective detection range is up to 15 kilometres, and aircraft carrier detection at 60 to 80 kilometres
- Identification of the tank type on the 8-to-10-kilometre, and of an aircraft carrier at 40 to 60 kilometres
- Estimates of other ground target range of up to 20 kilometres
The acoustic detection could be employed for Low Flying Aircraft (LFA). The sound radiated by LFA was used for their detection, tracking and classification by the developed Acoustic Seismic Air Detection (ASAD) system which determines the direction by correlating the detection from more than one detector of the system. The US uses this system on the northern border to check the entry of the smugglers/ drug/ human trafficking. The system can also be used as the early warning system and can replace the visual detection by the operators who are also in some places deployed along the border to fill in the gaps in the radar system. The acoustic library of the system can help in distinguishing the type i.e. whether transport/ helicopter/ fighter aircraft.
The introduction of stealth aircraft in India’s neighbourhood will surely pose a challenge for the IAF in detection and engagement of the threat. On the other hand, its use will give a manifold advantage to the potential adversary which needs to be addressed. We need to procure detection systems which can detect stealth aircraft. India is also procuring S-400 Triumf from Russia which claims capability to engage and destroy the stealth aircraft. India needs to be future ready and install at least one OTH radar to warn of stealth aircraft and ballistic missile launches by our adversary. India is also working on its fifth generation fighter aircraft programme FGFA based on Russian plane PAK-FA 50 and Advanced Multirole Combat Aircraft (AMCA) which is claimed to be better than Chinese counterpart. The most important is to fix the deadlines for procurement and meet these punctiliously.