By Girish Linganna
The unveiling of the B-21 ‘Raider’ at the Air Force Plant 42 in Palmdale, California marked a significant milestone in the ongoing battle between stealth and counter-stealth technologies. Developed as part of the US Air Force’s Long-Range Strike Bomber Program, this strategic stealth bomber represents a major leap forward in aviation technology, aimed at countering the A2AD strategy adopted by rival nations.
Designed with ‘sixth-generation’ characteristics, the B-21 boasts a sophisticated stealth technology that enables it to evade detection and penetrate hostile airspace. However, the introduction of this advanced technology also presents a challenge for rival nations to enhance their counter-stealth capabilities, further escalating the global competition in this domain.
Several programs for the development of Sixth Generation Fighter Aircraft (SGFA) are currently underway, encompassing a range of advanced stealth military aircraft. The term SGFA/FGFA is used for convenience to refer to these initiatives.
Various nations are actively engaged in the pursuit of advanced Sixth Generation Fighter Aircraft (SGFA) programs. Here are some notable examples:
1. The USAF is focusing on the Next Generation Air Dominance Program, which includes the development of the F-X SGFA as a successor to the F-22 Raptor. Additionally, they are working on the Penetrating Counter Air (PCA) fighter-escort aircraft to operate alongside their stealth bombers. The US Navy is dedicated to its Fighter/Attack F/A-XX Program, aiming to replace the F/A-18E/F Super Hornet and complement the F-35C Lightning-II.
2. Germany, France, and Spain have joined forces in the development of the New Generation Fighter (NGF) under the Europe’s Future Air Combat System (FCAS) Program. This collaborative effort aims to replace the F/A-18E/F, Dassault Rafale, and Eurofighter Typhoon currently in service with these countries.
3. The UK, Sweden, and Italy are invested in the development of BAE Systems Tempest, a future SGFA slated to replace the Eurofighter Typhoon. It is expected to enter service in the next decade.
4. Russia is actively working on the ‘MiG-41’ SGFA Interceptor as a successor to the MiG-31.
5. China, following the successful induction of the J-20 Fifth Generation Fighter Aircraft (FGFA), has plans to complete the development of its own SGFA by the mid-2030s.
6. India is scheduled to begin production of the Advanced Medium Combat Aircraft (AMCA) Mark-I FGFA in 2028. The Mark-II variant of the AMCA is expected to incorporate Sixth-Generation characteristics.
The latest FGFA programs like the US F-35/F-22, Chinese J-20/J-31, and Russian SU-57/Su-75 exhibit true stealth capability, distinguishing them from their predecessors. Their stealth design includes visual camouflage, low-reflectivity composite materials, flush fuselage, internal weapon bays, minimal external projections, non-perpendicular faceted surfaces, optimized exhaust for reduced acoustic/heat signature, and passive sensors to minimize EM emissions. These features enable stealth across all detection mediums.’
As a key component of sixth-generation technology, SGFA stealth incorporates FGFA stealth technologies while also implementing additional measures to mitigate detection across various mediums.
Some of these measures may include:
1. The Stealthy Fuselage and Inlets SGFA incorporates a sharply chiseled nose and angular airframe design to minimize reflection and location detection errors. It utilizes Divertiess Supersonic Inlets (DSI) and conformal engine nacelles to improve stealth by eliminating the need to divert air from the intake. The DSI’s bumped surface shields the engine from radar exposure. Stealth is maintained when bomb bays/landing gear open through trapezoidal/serrated or sliding doors. The aircraft follows a flying wing planform design, eliminating surfaces that reflect radar waves. Explorations include integrating control surfaces into the wing to reduce radar cross-section (RCS).
2. The SGFA utilizes a high durability radar-absorbent composite material. It features electrically conductive radar-absorbent polymers and ablative aircraft paint embedded with metal spheres or carbon nano-fibers, coating the airframe’s leading edges. The canopy is coated with a transparent conductor coating to increase radar transparency. These coatings require minimal maintenance between missions, reducing operational turnaround time. The aircraft’s radar operates in a narrow frequency band, and a band-pass radar coating transparent only to desired frequencies further enhances stealth. The use of a “Fibre Mat” coating, similar to the F-35, adds depth and prevents degradation of radar cross-section (RCS).
3. The SGFA incorporates airborne Next-Generation (NG) jammers, spoofers, and low-power emitters. These NG jammers aim to degrade ground-based emitters and infiltrate networks to introduce inaccuracies. Spoofing technology, inspired by the B-21, allows the SGFA to disguise itself by emitting targeted radar signals or modulating ambient emissions. Metasurface coatings enhance low-observability by controlling the propagation of electromagnetic waves. Plasma-stealth technique employs ionized gas plumes to create a plasma cloud that deflects or absorbs radar waves. Low-probability-intercept radars, passive IR sensors, and low-light TV serve as onboard sensors, reducing electromagnetic emissions. Unmanned wingmen, controlled by the stealth platform, act as sensors and relay information, minimizing the need for aircraft emissions.
4. The SGFA incorporates IR obscurators to reduce the body temperature caused by engine exhaust and air friction. These features include ceramic tile-coated exhausts, modified tail-pipe shapes, and exhaust vents to dissipate the exhaust plume. The exhaust gases are pre-mixed with cold intake air to lower the temperature, and thermal conductor coatings and vapor vents conduct heat away and disperse it in various directions. The use of wing-mounted or embedded engines with over-wing exhausts, such as those seen in aircraft like the B-2/B-21, effectively conceals the engines and exhaust from ground-level observation. The fuel circuits are routed in a way that allows the fuel tanks to absorb and dissipate a portion of the exhaust heat.
Era of CST
In the era of stealth combat aircraft dominance, an effective counter-stealth system is crucial for a nation’s Defensive Counter-Air Operations. It serves as an integral component of the “kill-chain” process, which involves detecting, identifying, targeting, and assessing post-strike damage against adversary stealth aircraft. This system is essential for protecting own combat air power and countering the use of stealth by adversaries in various operational domains.
Traditionally, counter-stealth technologies have followed developments in stealth capabilities. However, the race between stealth and counter-stealth is now closer than ever. Nations like Russia and China are focusing on Anti-Access/Area Denial (A2AD) strategies to protect and deny airspace, maritime areas, and overland spaces to potential adversaries. This heightened sensitivity to stealth-aided incursions necessitates the advancement of counter-stealth capabilities.
Radar As The Foundation
Stealth aircraft are primarily designed to minimize their Radar Cross Section (RCS) in the X-Band frequency range, which is suitable for high-accuracy weapon lock-on. However, as the radar wavelength increases towards higher bands such as Ku and L, the effectiveness of the stealth shape diminishes, compromising stealth capabilities. Higher wavelengths also result in lower accuracy for weapon-grade tracking and require larger radar emitters.
To address this challenge, the use of multiple high-power emitters with separate receivers, known as bi/multistatic radars, can detect stealth aircraft by leveraging different viewing angles and radar frequencies. By utilizing multi-sensor data fusion (MSDF), these radars can detect aspects of the aircraft that exhibit a larger RCS and achieve detection.
Multi-static radars can also exploit an aircraft’s jamming frequency to determine its location. For example, the Russian 55Zh6M Nebo-M radar system, integrated with the S-400 Triumf Integrated Air Defense System, utilizes a multi-static array of VHF Active Electronically Scanned Array (AESA) radar systems. These radars can detect aircraft and hypersonic vectors at ranges up to 600km, even against stealth targets.
The Nebo-M system includes the Nebo SVU in the VHF-band, the Protivnik-G in the L-band, and the Gamma-S1 array in the S/X-bands. This multi-band approach enables the detection, tracking, and targeting of stealth aircraft during various stages of their approach.
In response to systems like Nebo-M, China has developed the JY-27A VHF AESA long-range air surveillance and guidance radar. Although with lower accuracy, it claims to detect aircraft such as the F-22 and F-35, with a maximum range of 500km.
These developments highlight the importance of countering stealth aircraft using multi-static radar systems, leveraging different frequencies and angles to detect and track stealth platforms across various bands and wavelengths.
Eyes on Beijing?
Satellite imagery reveals the installation of a MIMO Synthetic Impulse and Aperture Radar (SIAR) on Subi Reef in the South China Sea. This radar array consists of three concentric rings of emitter/receiver antennae operating in the VHF Band. Utilizing impulse synthesis and aperture synthesis techniques, the radar system can generate a 3D track of stealth aircraft, overcoming the limitations of a single VHF receiver to provide a weapons-grade track.
Wavelength Maneuver refers to a technique employed in multi-static radar technology that enables the detection and tracking of stealth aircraft by utilizing lower frequency radars. This information is then used to cue an AESA radar, which emits multiple UHF beams over a narrow field-of-view to penetrate the aircraft’s stealth and generate target-engagement data.
Over-The-Horizon Radars (OTHR) employ HF radar waves to detect and track aerial targets beyond line-of-sight. Skywave OTHR uses ionospheric reflection, allowing detection at ranges up to 4,000km. Surface Wave OTHR uses reflection from the ocean surface, enabling detection at ranges up to 300km. While OTHR may lack engagement accuracy, they provide early warning and can cue other radars. The French Nostradamus, for example, is a Skywave OTHR system capable of detecting a B-2 at over 3000km with low accuracy, necessitating the coupling with weapons track capable radars for effective counter-stealth operations.
Passive Anti-Stealth (PAS) radars, which fall under Electronic Support Measures (ESM) systems, compute accurate aircraft locations by analyzing the time difference of the received emitted signals. These systems, such as the Czechoslovak Tamara KRTP-91 Trash-Can and Thales Ground Alerter-100 Multistatic Passive Radar, operate without actively transmitting EM waves, making them difficult to neutralize.
LIDAR technology utilizes directed LASER beams in the near-IR spectrum to generate weapons-grade track once a stealth target is detected and its inbound track localized. It can be integrated within multi-static radar arrays or deployed in multiple airborne platforms to create a LASER “mesh” for detecting stealth aircraft ingress. Atmospheric attenuation remains a challenge that needs to be addressed. A private US vendor reportedly demonstrated successful detection of an F-35 using air-to-air/ground-to-air LIDAR at a distance/altitude of 5 kilometers/15,000 feet.
CELLDAR, an emerging PAS technology, involves detecting reflected cellular/radio/TV signals off an inbound stealth aircraft using cellular radars. Multiple sensors, including acoustic detectors, may be deployed to detect the aircraft’s aural signature. By collating and fusing these inputs, an inbound track of a stealth aircraft can be obtained to cue other EM emitters for weapons-grade track and engagement. This technology is being developed in collaboration with BAE Systems in the UK.
China claims to have developed a quantum-based multi-purpose anti-stealth radar capable of IRST detection of stealth aircraft at 100 km (ground-based) and 300 km (aircraft-based). The system incorporates LIDAR technology with high-sensitivity receivers capable of single-photon detection, enabling the detection of even minute reflections of LASER light. China has also announced the development of “ghost-imaging satellite-based detectors” using quantum entanglement principles to produce images of stealth aircraft. These claims, however, require corroboration.
The author is Aerospace & Defence Analyst.
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