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Electrothermal-chemical technology

Electrothermal-chemical (ETC) technology is an attempt to increase accuracy and muzzle energy of future tank, artillery, and close-in weapon system guns by improving the predictability and rate of expansion of propellants inside the barrel.

An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy to trigger the process. ETC increases the performance of conventional solid propellants, reduces the effect of temperature on propellant expansion and allows for more advanced, higher density propellants to be used.

The technology has been under development since the mid-1980s and in 1993 was actively being researched in the United States by the Army Research Laboratory, Sandia National Laboratories and defense industry contractors, including FMC Corporation, General Dynamics Land Systems, Olin Ordnance, and Soreq Nuclear Research Center. It is possible that electrothermal-chemical gun propulsion will be an integral part of US Army's future combat system and those of other countries such as Germany and the United Kingdom. Electrothermal-chemical technology is part of a broad research and development program that encompasses all electric gun technology, such as railguns and coil guns.

Background

The constant battle between armour and armor-piercing round has led to continuous development of the main battle tank design. The evolution of American anti-tank weapons can be traced back to requirements to combat Soviet tanks. In the late 1980s, it was thought that the protection level of the Future Soviet Tank (FST) could exceed 700 mm of rolled homogeneous armour equivalence at its maximum thickness, which was effectively immune against the contemporary M829 armour piercing fin stabilized discarding sabot. In the 1980s the most immediate method available to NATO to counter Soviet advances in armour technology was the adoption of a 140 mm main gun, but this required a redesigned turret that could incorporate the larger breech and ammunition, and it also required some sort of automatic loader. Although the 140 mm gun was considered a real interim solution, it was decided after the fall of the Soviet Union that the increase in muzzle energy it provided was not worth the increase in weight. Resources were therefore spent on research into other programs that could provide the needed muzzle energy. One of the most successful alternative technologies remains electrothermal-chemical ignition.

Most proposed advances in gun technology are based on the assumption that the solid propellant as a stand-alone propulsion system is no longer capable of delivering the required muzzle energy. This requirement has been underscored by the appearance of the Russian T-90 main battle tank. The elongation of current gun tubes, such as the new German 120 mm L/55, which was introduced by Rheinmetall is considered only an interim solution as it does not offer the required increase in muzzle velocity. Even advanced kinetic energy ammunition such as the United States' M829A3 is considered only an interim solution against future threats. To that extent the solid propellant is considered to have reached the end of its usefulness, although it will remain the principal propulsion method for at least the next decade until newer technologies mature. To improve on the capabilities of a solid propellant weapon the electrothermal-chemical gun may see production as early as 2016.

ETC technology offers a medium-risk upgrade and is developed to the point that further improvements are so minor that it can be considered mature. The lightweight American 120 mm XM291 came close to achieving 17 MJ of muzzle energy, which is the lower-end muzzle energy spectrum for a 140 mm gun. However, the success of the XM291 does not imply the success of ETC technology as there are key parts of the propulsion system that are not yet understood or fully developed, such as the plasma ignition process. Nevertheless, there is substantial existing evidence that ETC technology is viable and worth the money to continue development. Furthermore, it can be integrated into current gun systems.

Operational Principle

An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy as a catalyst to begin the process. Originally researched by Dr. Jon Parmentola for the U.S. Army, it has grown into a very plausible successor to a standard solid propellant tank gun. Since the beginning of research the United States has funded the XM291 gun project with USD 4,000,000, basic research with USD 300,000, and applied research with USD 600,000. Since then it has been proven to work, although efficiency to the level required has not yet been accomplished. ETC increases the performance of conventional solid propellants, reduces the effect of temperature on propellant expansion and allows for more advanced, higher density propellants to be used. It will also reduce pressure placed on the barrel in comparison to alternative technologies that offer the same muzzle energy given the fact that it helps spread the propellant's gas much more smoothly during ignition. Currently, there are two principal methods of plasma initiation: the flashboard large area emitter (FLARE) and the triple coaxial plasma igniter (TCPI).

Flashboard large area emitter
Flashboards run in several parallel strings to provide a large area of plasma or ultraviolet radiation and uses the breakdown and vaporization of gaps of diamonds to produce the required plasma. These parallel strings are mounted in tubes and oriented to have their gaps azimuthal to the tube's axis. It discharges by using high pressure air to move air out of the way. FLARE initiators can ignite propellants through the release of plasma, or even through the use of ultraviolet heat radiation. The absorption length of a solid propellant is sufficient to be ignited by radiation from a plasma source. However, FLARE has most likely not reached optimal design requirements and further understanding of FLARE and how it works is completely necessary to ensure the evolution of the technology. If FLARE provided the XM291 gun project with the sufficient radiative heat to ignite the propellant to achieve a muzzle energy of 17 MJ one could only imagine the possibilities with a fully developed FLARE plasma igniter. Current areas of study include how plasma will affect the propellant through radiation, the deliverance of mechanical energy and heat directly and by driving gas flow. Despite these daunting tasks FLARE has been seen as the most plausible igniter for future application on ETC guns.

Triple coaxial plasma igniter
A coaxial igniter consists of a fully insulated conductor, covered by four strips of aluminium foil. All of this is further insulated in a tube about 1.6 cm in diameter that is perforated with small holes. The idea is to use an electrical flow through the conductor and then exploding the flow into vapour and then breaking it down into plasma. Consequently, the plasma escapes through the constant perforations throughout the insulating tube and initiates the surrounding propellant. A TCPI igniter is fitted in individual propellant cases for each round of ammunition. However, TCPI is no longer considered a viable method of propellant ignition because it may damage the fins and does not deliver energy as efficiently as a FLARE igniter.

Feasibility

The XM291 is the best existing example of a working electrothermal-chemical gun. It was an alternative technology to the heavier caliber 140 mm gun by using the dual-caliber approach. It uses a breech that is large enough to accept 140 mm ammunition and be mounted with both a 120 mm barrel and a 135 mm or 140 mm barrel. The XM291 also mounts a larger gun tube and a larger ignition chamber than the existing M256 L/44 main gun. Through the application of electrothermal-chemical technology the XM291 has been able to achieve muzzle energy outputs that equate that to a low-level 140 mm gun, while achieving muzzle velocities greater than those of the larger 140 mm gun. Although the XM291 does not mean that ETC technology is viable it does offer an example that it is possible.

ETC is also a more viable option than other alternatives by definition. ETC requires much less energy input from outside sources, like a battery, than a railgun or a coilgun would. Tests have shown that energy output by the propellant is higher than energy input from outside sources on ETC guns. In comparison, a railgun currently cannot achieve a higher muzzle velocity than the amount of energy input. Even at 50% efficiency a rail gun launching a projectile with a kinetic energy of 20 MJ would require an energy input into the rails of 40 MJ, and 50% efficiency has not yet been achieved. To put this into perspective, a rail gun launching at 9 MJ of energy would need roughly 32 MJ worth of energy from capacitors. Current advances in energy storage allow for energy densities as high as 2.5 MJ/dm³, which means that a battery delivering 32 MJ of energy would require a volume of 12.8 dm³ per shot; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. There has even been discussion about eliminating the necessity for an outside electrical source in ETC ignition by initiating the plasma cartridge through a small explosive force.

Furthermore, ETC technology is not only applicable to solid propellants. To increase muzzle velocity even further electrothermal-chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. ETC technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. Understandably, recoil of a gun firing a projectile at 17 MJ or more will increase directly with the increase in muzzle energy in accordance to Newton's third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an ETC powered gun in an existing vehicle design. For example, OTO Melara's new lightweight 120 mm L/45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism (550 mm) and a pepperpot muzzle brake. Reduction in recoil can also be achieved through mass attenuation of the thermal sleeve. The ability of ETC technology to be applied to existing gun designs means that for future gun upgrades there's no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel.

Several countries have already determined that ETC technology is viable for the future and have funded indigenous projects considerably. These include the United States, Germany and the United Kingdom, amongst others. The United States' XM360, which was planned to equip the Future Combat Systems Mounted Combat System light tank and may be the M1 Abrams' next gun upgrade, is reportedly based on the XM291 and may include ETC technology, or portions of ETC technology. Tests of this gun have been performed using "precision ignition" technology, which may refer to ETC ignition.

title: Electrothermal-chemical technology


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Boeing E-3 Sentry

The Boeing E-3 Sentry is an American airborne early warning and control (AEW&C) aircraft developed by Boeing. E-3s are commonly known as AWACS (Airborne Warning and Control System). Derived from the Boeing 707 airliner, it provides all-weather surveillance, command, control, and communications, and is used by the United States Air Force, NATO, French Air and Space Force, Royal Saudi Air Force and Chilean Air Force. The E-3 has a distinctive rotating radar dome (rotodome) above the fuselage. Production ended in 1992 after 68 aircraft had been built.

In the mid-1960s, the U.S. Air Force (USAF) was seeking an aircraft to replace its piston-engined Lockheed EC-121 Warning Star, which had been in service for over a decade. After issuing preliminary development contracts to three companies, the USAF picked Boeing to construct two airframes to test Westinghouse Electric's and Hughes's competing radars. Both radars used pulse-Doppler technology, with Westinghouse's design emerging as the contract winner. Testing on the first production E-3 began in October 1975.

The first USAF E-3 was delivered in March 1977, and during the next seven years, a total of 34 aircraft were manufactured. E-3s were also purchased by NATO (18), the United Kingdom (7), France (4) and Saudi Arabia (5). In 1991, when the last aircraft had been delivered, E-3s participated in the Persian Gulf War, playing a crucial role of directing coalition aircraft against Iraqi forces.

The aircraft was also the last of the Boeing 707 derivatives after 34 years of continuous production. The aircraft's capabilities have been maintained and enhanced through numerous upgrades. In 1996, Westinghouse Electric's Defense & Electronic Systems division was acquired by Northrop Corporation, before being renamed Northrop Grumman Mission Systems, which currently supports the E-3's radar. In April 2022, the U.S. Air Force announced that the Boeing E-7 is to replace the E-3 beginning in 2027.

Background
In 1963, the USAF asked for proposals for an Airborne Warning and Control System (AWACS) to replace its EC-121 Warning Stars, which had served in the airborne early warning role for over a decade. The new aircraft would take advantage of improvements in radar technology and computer-aided radar data analysis and data reduction. These developments allowed airborne radars to "look down", i.e. to detect the movement of low-flying aircraft, and discriminate, even over land, target aircraft's movements; previously this had been impossible due to the inability to discriminate an aircraft's track from ground clutter. Contracts were issued to Boeing, Douglas, and Lockheed, the latter being eliminated in July 1966. In 1967, a parallel program was put into place to develop the radar, with Westinghouse Electric Corporation and Hughes Aircraft being asked to compete in producing the radar system. In 1968, it was referred to as Overland Radar Technology (ORT) during development tests on the modified EC-121Q. The Westinghouse radar antenna was going to be used by whichever company won the radar competition since Westinghouse had pioneered the design of high-power radio frequency (RF) phase-shifters, which are used to both focus the RF into a pencil beam and scan electronically for altitude determination.

Boeing initially proposed a purpose-built aircraft, but tests indicated it would not outperform the already-operational 707, so the latter was chosen instead. To increase endurance, this design was to be powered by eight General Electric TF34s. It would carry its radar in a rotating dome mounted at the top of a forward-swept tail, above the fuselage. Boeing was selected ahead of McDonnell Douglas's DC-8-based proposal in July 1970. Initial orders were placed for two aircraft, designated EC-137D, as test beds to evaluate the two competing radars. As the test beds did not need the same 14-hour endurance demanded of the production aircraft, the EC-137s retained the Pratt & Whitney JT3D commercial engines, and a later reduction in the endurance requirement led to retention of the JT3D engines in production.

The first EC-137 made its maiden flight on 9 February 1972, with the fly-off between the two radars taking place from March to July of that year. Favorable test results led to the selection of Westinghouse's radar for the production aircraft. Hughes' radar was initially thought to be a certain winner due to its related development of the APG-63 radar for the new F-15 Eagle. The Westinghouse radar used a pipelined fast Fourier transform (FFT) to digitally resolve 128 Doppler frequencies, while Hughes's radars used analog filters based on the design for the F-15. Westinghouse's engineering team won this competition by using a programmable 18-bit computer whose software could be modified before each mission. This computer was the AN/AYK-8 design from the B-57G program, and designated AYK-8-EP1 for its much expanded memory. This radar also multiplexed a beyond-the-horizon (BTH) pulse mode that could complement the pulse-Doppler radar mode. This proved to be beneficial especially when the BTH mode is used to detect ships at sea when the radar beam is directed below the horizon.

Full-scale development
Approval was given on 26 January 1973 for the full-scale development of the AWACS system. To allow further development of the aircraft's systems, orders were placed for three preproduction aircraft, the first of which performed its maiden flight in February 1975. IBM and Hazeltine were selected to develop the mission computer and display system. The IBM computer was designated 4PI, and the software was written in JOVIAL. A Semi-Automatic Ground Environment (SAGE) or back-up interceptor control (BUIC) operator would immediately be at home with the track displays and tabular displays, but differences in symbology would create compatibility problems in tactical ground radar systems in Iceland, mainland Europe, and South Korea over Link-11 (TADIL-A). In 1977, Iran placed an order for ten E-3s, however this order was cancelled following the Iranian Revolution.

Engineering, test and evaluation began on the first E-3 Sentry in October 1975. Between 1977 and 1992, a total of 68 E-3s were built.

Future status
Because the Boeing 707 is no longer in production, the E-3 mission package has been fitted into the Boeing E-767 for the Japan Air Self Defense Forces. The E-10 MC2A was intended to replace USAF E-3s—along with the RC-135 and the E-8 Joint STARS, but the program was canceled by the Department of Defense.

NATO intends to extend the operational status of its AWACS until 2035 when it is due to be replaced by the Alliance Future Surveillance and Control (AFSC) program. The Royal Air Force (RAF) chose to limit investment in its E-3D fleet in the early 2000s, diverting Sentry upgrade funds to a replacement program. On 22 March 2019, the UK Defence Secretary announced a $1.98 billion (~$ in ) contract to purchase five E-7 Wedgetails. The U.S. Air Force intends to retire 15 of its 31 E-3s and acquire the E-7.

On 31 March 2023, the USAF retired an E-3 from service for the first time.

Overview

The E-3 Sentry's airframe is a modified Boeing 707-320B Advanced model. Modifications include a rotating radar dome (rotodome), uprated hydraulics from 241 to 345 bar (3500–5000 PSI) to drive the rotodome, single-point ground refueling, air refueling, and a bail-out tunnel or chute. A second bail-out chute was deleted to cut mounting costs.

USAF and NATO E-3s have an unrefueled range of 7400 km or 8 hours of flying. The newer E-3 versions bought by France, Saudi Arabia, and the UK are equipped with newer CFM56-2 turbofan engines, and these can fly for about 11 hours or more than 9250 km. The Sentry's range and on-station time can be increased through air-to-air refueling and the crews can work in shifts by the use of an on-board crew rest and meals area. The aircraft are equipped with one toilet in the rear, and a urinal behind the cockpit. Saudi E-3s were delivered with an additional toilet in the rear.

When deployed, the E-3 monitors an assigned area of the battlefield and provides information for commanders of air operations to gain and maintain control of the battle; while as an air defense asset, E-3s can detect, identify, and track airborne enemy forces far from the boundaries of the U.S. or NATO countries and can direct interceptor aircraft to these targets. In support of air-to-ground operations, the E-3 can provide direct information needed for interdiction, reconnaissance, airlift, and close-air support for friendly ground forces.

Avionics
The unpressurized rotodome is 30 feet in diameter, 6 feet thick at the center, and is held 11 feet above the fuselage by 2 struts. It is tilted down at the front to reduce its aerodynamic drag, which lessens its detrimental effect on take-offs and endurance. This tilt is corrected electronically by both the radar and secondary surveillance radar antenna phase shifters. The rotodome uses bleed air, outside cooling doors, and fluorocarbon-based cold plate cooling to maintain the electronic and mechanical equipment temperatures. The hydraulically rotated antenna system permits the and AN/APY-2 passive electronically scanned array radar system to provide surveillance from the Earth's surface up into the stratosphere, over land or water.

Other major subsystems in the E-3 Sentry are navigation, communications, and computers. 14 consoles display computer-processed data in graphic and tabular format on screens. Its operators perform surveillance, identification, weapons control, battle management and communications functions. Data may be forwarded in real-time to any major command and control center in rear areas or aboard ships. In times of crisis, data may also be forwarded to the National Command Authority in the U.S. via RC-135 or aircraft carrier task forces.

Electrical generators mounted in each of the E-3's four engines provide 1 megawatt of electrical power required by the aircraft's radars and electronics. Its pulse-Doppler radar has a range of more than 250 mi (400 km) for low-flying targets at its operating altitude, and the pulse (BTH) radar has a range of approximately 400 mi (650 km) for aircraft flying at medium to high altitudes. The radar, combined with a secondary surveillance radar (SSR) and electronic support measures (ESM), provides a look down capability, to detect, identify, and track low-flying aircraft, while eliminating ground clutter returns.

Upgrades

Between 1987 and 2001, USAF E-3s were upgraded under the "Block 30/35 Modification Program". Enhancements included:
 * The installation of ESM and an electronic surveillance capability, for both active and passive means of detection.
 * Installation of the Class 2H Joint Tactical Information Distribution System (JTIDS), which provides rapid and secure communication for transmitting information, including target positions and identification data, to other friendly platforms. This upgraded system allowed the Link 16 military tactical data link capability to be added as part of the Block 30/35 upgrade. Prior versions of the E-3 (NATO/US Standard and 20/25) had the Class 1 (Hughes) JTIDS system which was not Link 16 capable.
 * Global Positioning System (GPS) capability was added.
 * Onboard computers and software were overhauled to accommodate the JTIDS Class 2H, Link 16, the new ESM systems and to allow for future enhancements.

RSIP
The Radar System Improvement Program (RSIP) was a joint US/NATO development program. RSIP enhances the operational capability of the E-3 radars' electronic countermeasures, and improves the system's reliability, maintainability, and availability. Essentially, this program replaced the older transistor-transistor logic (TTL) and emitter-coupled logic (MECL) electronic components, long-since out of production, with off-the-shelf computers that utilised a High-level programming language instead of assembly language. Significant improvement came from adding pulse compression to the pulse-Doppler mode. These hardware and software modifications improve the E-3 radars' performance, providing enhanced detection with an emphasis towards low radar cross-section (RCS) targets.

The RAF had also joined the USAF in adding RSIP to upgrade the E-3's radars. The retrofitting of the E-3 squadrons was completed in December 2000. Along with the RSIP upgrade was installation of the Global Positioning System/Inertial Navigation Systems which improved positioning accuracy. In 2002, Boeing was awarded a contract to add RSIP to the small French AWACS squadron. Installation was completed in 2006. Saudi Arabia began RSIP upgrades in 2013; the first aircraft being upgraded by Boeing in Seattle with the four remaining aircraft upgraded in Riyadh between 2014 and 2016.

NATO Mid Term Program
Between 2000 and 2008 NATO upgraded its E-3s to Mid Term Program (MTP) standard. This involved technical upgrades and a total multi-sensor-systems integration

DRAGON
In 2009, the USAF, in cooperation with NATO, entered into a major flight deck avionics modernization program in order to maintain compliance with worldwide airspace mandates. The program, called DRAGON (for DMS Replacement of Avionics for Global Operation and Navigation), was awarded to Boeing and Rockwell Collins in 2010. Drawing on their Flight2 flight management system (FMS), almost all the avionics were replaced with more modern digital equipment from Rockwell Collins. Main upgrades include a Digital Audio Distribution System, Mode-5/ADS-B transponder, Inmarsat and VDL datalinks, and a terrain awareness and warning system (TAWS). The centerpiece flight deck hardware consists of five 6x8 color graphics displays and two color CDUs. DRAGON laid the foundation for subsequent upgrades including GPS M-Code, Iridium ATC, and Autopilot. USAF DRAGON Production began in 2018.

USAF Block 40/45
In 2014 the USAF began upgrading block 30/35 E-3B/Cs into block 40/45 E-3Gs. This upgrade replaces the main flight computer with a Red Hat Linux-based system, as well as replacing the DOS 2.0-like operating system with a Windows 95-like system on the operator workstations. In 2016, a three-week long cybersecurity vulnerability test revealed that the 40/45 block and its supporting ground equipment were vulnerable to cyber threats, and were thus deemed "not survivable." This caused a delay of approximately two years. Twenty-four E-3s are projected to complete this upgrade to 40/45 by the end of fiscal year 2020, while seven aircraft will be retired to save upgrade costs and harvest out-of-production components.

NATO Final Lifetime Extension Program
NATO intends to extend the operational status of its AWACS until 2035 by significantly upgrading fourteen aircraft in the Final Lifetime Extension Program (FLEP) between 2019 and 2026. Upgrades include the expansion of data capacity, expansion of bandwidth for satellite communications, new encryption equipment, new HAVE QUICK radios, upgraded mission computing software and new operator consoles. The supporting ground systems (mission training center and mission planning and evaluation system) will also be upgraded to the latest standard. NATO Airborne Early Warning & Control Program Management Agency (NAPMA) is the preparing and executing authority for the FLEP. FLEP will be combined with the standard planned higher echelon technical maintenance.

United States
In March 1977 the 552nd Airborne Warning and Control Wing received the first E-3 aircraft at Tinker AFB, Oklahoma. The 34th and last USAF Sentry was delivered in June 1984. The USAF has a total of thirty E-3s in active service. Twenty-six are stationed at Tinker AFB and belong to the Air Combat Command (ACC). Four are assigned to the Pacific Air Forces (PACAF) and stationed at Kadena AB, Okinawa and Elmendorf AFB, Alaska. One aircraft (TS-3) was assigned to Boeing for testing and development (retired/scrapped June 2012).

E-3 Sentry aircraft were among the first to deploy during Operation Desert Shield, where they established a radar screen to monitor Iraqi forces. During Operation Desert Storm, E-3s flew 379 missions and logged 5,052 hours of on-station time. The data collection capability of the E-3 radar and computer subsystems allowed an entire air war to be recorded for the first time. In addition to providing senior leadership with time-critical information on the actions of enemy forces, E-3 controllers assisted in 38 of the 41 air-to-air kills recorded during the conflict.

NATO, UK, French and USAF AWACS played an important role in the air campaign against Serbia and Montenegro in the former republic of FR Yugoslavia. From March to June 1999 the aircraft were deployed in the NATO bombing of Yugoslavia (operation Allied Force) directing allied strike and air defence aircraft to and from their targets. Over 1,000 aircraft operating from bases in Germany and Italy took part in the air campaign which was intended to destroy Yugoslav air defenses and high-value targets such as the bridges across the Danube river, factories, power stations, telecommunications facilities, and military installations.

On 18 November 2015, an E-3G was deployed to the Middle East to begin flying combat missions in support of Operation Inherent Resolve against ISIL, marking the first combat deployment of the upgraded Block 40/45 aircraft.

United Kingdom

In February 1987 the UK and France ordered E-3 aircraft in a joint project which saw deliveries start in 1991. The British requirement arose due to the cancellation of the BAE Nimrod AEW3 project. UK E-3Ds contributed to the NATO Airborne Early Warning and Control Force (NAEWCF), receiving much of their tasking directly from NATO. However, RAF E-3Ds remained UK-crewed and capable of independent, national tasking.

In 2009, the UK effectively limited the service life of the E-3D fleet by de-funding the Project Eagle upgrade which would have seen it upgraded in line with the USAF Block 40/45 standard. AirForces Monthly reported that by December 2020, just 2 aircraft were available for operations at any one time. The Strategic Defence and Security Review 2015 had announced the intention to retain the E-3D fleet until 2035, however in March 2019, the Ministry of Defence announced that the E-3Ds would be replaced by five E-7 Wedgetails from 2023. The £1.51 billion contract was awarded to Boeing without a competitive procurement process, a decision criticised by both competitors of Boeing and the UK's Defence Select Committee. The 2021 Integrated Defence Review confirmed a reduced order of three aircraft. On 27 January 2015, the RAF deployed an E-3D Sentry to Cyprus in support of U.S.-led coalition airstrikes against Islamic State militants in Iraq and Syria. The last operational flight by an RAF E3 Sentry was in July 2021 with the Sentry subsequently retired from service.

France
In February 1987 the UK and France ordered E-3 aircraft in a joint project which saw deliveries start in 1991. France operates its E-3F aircraft independently of NATO. France operates four aircraft, all fitted with the newer CFM56-2 engines.

In early 2024, there were reports that France is looking to the Swedish Saab GlobalEye to replace its AWACS aircraft.

Chile
3 Boeing E-3D Sentry (Sentry AEW.1) aircraft, acquired second hand from the United Kingdom in September 2021, arrived in Chile in July 2022; units ZH103 and ZH106 will join the "Grupo de Aviación N.º 10" of the II Air Brigade.

NATO
NATO acquired 18 E-3As and support equipment, with the first aircraft delivered in January 1982. The aircraft are registered in Luxembourg. The eighteen E-3s were operated by Number 1, 2 and 3 Squadrons of NATO's E-3 Component, based at NATO Air Base Geilenkirchen.

NATO E-3s participated in Operation Eagle Assist after the September 11 attacks on the World Trade Center towers and the Pentagon. NATO and RAF E-3s participated in the military intervention in Libya.

From January 2011 to September 2014, NATO E-3s were deployed to Mazar-i-Sharif International Airport, Afghanistan, as part of NATO's International Security Assistance Force (ISAF) mission. The aircraft were used for air traffic control of military aircraft over the country, as well as surveillance, and tactical management of friendly aircraft. During the mission to Afghanistan, NATO E-3s flew 1,240 missions and accumulated 12,240 flying hours.

Presently, 14 NATO E-3As are in the inventory, since one E-3 was lost in a crash and three were retired from service in 2015, 2017, and 2018. The first was due for its six-year cycle Depot Level Maintenance (DLM) inspection which would have been very costly. The "449 Retirement Project" resulted in reclamation of critical parts with a value of upwards of $40 million which will be used to support the remaining active aircraft. Some of the parts to be removed are no longer on the market or have become very expensive.

Variants

 * EC-137D
 * 2 prototype AWACS aircraft with JT3D engines, 1 fitted with a Westinghouse Electric radar and 1 with a Hughes Aircraft Company radar. Both converted to E-3A standard with TF33 engines.

 * E-3A
 * Production aircraft with TF33 engines and AN/APY-1 radar, 24 built for USAF (later converted to E-3B standard), total of 34 ordered but the last 9 completed as E-3C. One additional aircraft retained by Boeing for testing, 18 built for NATO with TF33 engines and 5 for Saudi Arabia with CFM56 engines.

 * KE-3A
 * These are not AWACS aircraft but CFM56 powered tankers based on the E-3 design. 8 were sold to Saudi Arabia.

 * RE-3A
 * Three KE-3 airframes delivered as CFM56–powered strategic reconnaissance aircraft. Systems and external appearance are similar to the USAF’s RC-135V/W Rivet Joint platform. At least one of the RE-3As has received the extended "hog nose" as fitted to the RC-135.

 * E-3B
 * USAF Block 30 modification. E-3As with improvements, 24 conversions.

 * E-3C
 * USAF Block 35 modification. Production aircraft with AN/APY-2 radar, additional electronic consoles and system improvements, ten built.

 * JE-3C
 * One E-3A aircraft used by Boeing for trials later redesignated E-3C.

 * E-3D
 * Production aircraft for the RAF to E-3C standard with CFM56 engines and British modifications designated Sentry AEW.1, 7 built. Modifications included the addition of a refueling probe next to the existing boom AAR recipticle, CFM-56 engines, wingtip ESM pods, an enhanced Maritime Surveillance Capability (MSC) offering Maritime Scan-Scan Processing (MSSP), JTIDS and Havequick 2 radios.

 * E-3F
 * Production aircraft for the French Air and Space Force to E-3C standard with CFM56 engines and French modifications, 4 built.

 * E-3G
 * USAF Block 40/45 modification. Includes hardware and software upgrades to improve communications, computer processing power, threat tracking, and others, and automates some previously manual functions. Initial operating capability (IOC) declared in July 2014. E-3G(II) Block 40/45 modification that included a glass cockpit modification that reduced the crew size by one, and added a new avionics suite.

Operators

 * 🇨🇱 Chile: The Chilean Air Force purchased three retired E-3D Sentry aircraft from the Royal Air Force.

 * 🇫🇷 France: The French Air and Space Force purchased four E-3F aircraft.
 * Escadron de détection et de contrôle aéroportés 36 Berry (36th Airborne Detection and Control Squadron "Berry") based at Avord Air Base.

 * NATO
 * 18 E-3 AWACS were purchased – 1 was written off in Greece, 3 were retired from service. Mainly responsible for monitoring European NATO airspace, they have also been deployed outside the area in support of NATO commitments. The 20 multinational crews are provided by 15 of the 31 NATO member states.

 * NATO Airborne Early Warning and Control Force – E-3A Component. Based at Geilenkirchen (Germany), with forward operating bases at Konya (Turkey), Preveza/Aktion (Greece) and Trapani/Birgi (Italy) and a forward operating location at Ørland (Norway).
 * Aircrew Training Squadron
 * Flying Squadron 1
 * Flying Squadron 2
 * Flying Squadron 3 – disbanded in 2015

 * 🇸🇦 Saudi Arabia: The Royal Saudi Air Force purchased five E-3A aircraft in 1983. In 2004, modifications began to convert KE-3A tankers into RE-3 electronic intelligence gathering aircraft.
 * RSAF No. 6 Wing (Prince Sultan Air Base – Al Kharj)
 * السرب الثامن عشر (al-Sarab al-Ththamin Eshr – No. 18 Squadron)
 * No. 19 Squadron – RE-3A/B (as well as Beechcraft 350ER-ISR)
 * No. 23 Squadron – KE-3A

 * The United States Air Force has 21 operational E-3s as of June 2024
 * Tactical Air Command 1976–1992
 * Air Combat Command 1992–present

 * 552d Air Control Wing – Tinker Air Force Base, Oklahoma
 * 960th Airborne Air Control Squadron 2001–present (NAS Keflavik, Iceland 1979–1992)
 * 963d Airborne Air Control Squadron 1976–present
 * 964th Airborne Air Control Squadron 1977–present
 * 965th Airborne Air Control Squadron 1978–1979, 1984–present
 * 966th Airborne Air Control Squadron 1976–present

 * 380th Air Expeditionary Wing 2002–present Al Dhafra Air Base, United Arab Emirates
 * 968th Expeditionary Airborne Air Control Squadron 2013–present (Thumrait Air Base, Oman 2002–2003)
 * Air Force Reserve Command

 * 513th Air Control Group (Associate) – Tinker AFB, Oklahoma
 * 970th Airborne Air Control Squadron 1996–present (Personnel only, aircraft loaned by co-located 552nd ACW as needed)

 * 413th Flight Test Group – Robins AFB, Georgia
 * 10th Flight Test Squadron – Tinker AFB, Oklahoma 1994–present
 * Pacific Air Forces

 * 3d Wing – Elmendorf AFB, Alaska
 * 962d Airborne Air Control Squadron 1986–present

 * 18th Wing – Kadena AB, Japan
 * 961st Airborne Air Control Squadron 1979–present

Former operators

 * 🇬🇧 United Kingdom: The Royal Air Force purchased seven E-3Ds by October 1987, designated Sentry AEW.1 in British service. As of December 2020, only three remained in service after one was withdrawn from service in 2009 to be used as spares, two were withdrawn in March 2019 and a further one withdrawn in January 2020.  The fleet had been given an out of service date (OSD) of December 2022. They formed the E-3D Component of the NATO Airborne Early Warning and Control Force. However, that date was accelerated pursuant to the 2021 defence review and the aircraft made its final flight in U.K. service in August 2021.
 * RAF Waddington, Lincolnshire, England
 * No. 8 Squadron (1991–2021)
 * No. 23 Squadron (1996–2009)
 * No. 54 Squadron (Operational Conversion Unit 2005–?)
 * No. 56 Squadron (Operational Evaluation Unit 2008–?)

Incidents and accidents

E-3s have been involved in three hull-loss accidents, and one radar antenna was destroyed during RSIP development (see photo under Avionics).
 * On 22 September 1995, a U.S. Air Force E-3 Sentry (callsign Yukla 27, serial number 77-0354), crashed shortly after takeoff from Elmendorf AFB, Alaska. The plane lost power to both left side engines after ingesting several Canada geese during takeoff. The aircraft went down about 2 mile northeast of the runway, killing all 24 crew members on board.
 * On 14 July 1996, a NATO E-3 Sentry (tail number LX-N90457) overran the runway and crashed into a sea wall at Preveza-Aktion Airport in Greece when the pilot attempted to abort takeoff after mistakenly believing that the aircraft had suffered a bird strike. The aircraft overran the runway and struck a sea wall, where it came to a halt. There were no injuries and the aircraft was written off. Investigators could find no evidence that a bird strike and ingestion had occurred.
 * On 28 August 2009, a U.S. Air Force E-3C Sentry (serial number 83-0008) participating in a Red Flag exercise at Nellis Air Force Base, Nevada experienced a nose gear collapse on landing, resulting in a fire and damaging the aircraft beyond repair. All 32 crew members evacuated safely.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Boeing E-3 Sentry


text:
Northrop Grumman E-8 Joint STARS

The Northrop Grumman E-8 Joint Surveillance Target Attack Radar System (Joint STARS) is a retired United States Air Force (USAF) airborne ground surveillance, battle management and command and control aircraft. It tracks ground vehicles and some aircraft, collects imagery, and relays tactical pictures to ground and air theater commanders. The aircraft was operated by both active duty USAF and Air National Guard units and also carried specially trained U.S. Army personnel as additional flight crew until its retirement in 2023.

Development
Joint STARS evolved from separate U.S. Army and Air Force (USAF) programs to develop technology to detect, locate and attack enemy armor at ranges beyond the front line of a battle. In 1982, the programs were merged and the USAF became the lead agent. The concept and sensor technology for the E-8 was developed and tested on the Tacit Blue experimental aircraft. The prime contract was awarded to Grumman Aerospace Corporation in September 1985 for two E-8A development systems.

In late 2005, Northrop Grumman was awarded a contract for upgrading engines and other systems. Pratt & Whitney, in a joint venture with Seven Q Seven (SQS), was contracted to produce and deliver JT8D-219 engines for the E-8s. Their greater efficiency would have allowed the Joint STARS to spend more time on station, take off from a wider range of runways, climb faster, fly higher, all with a much reduced cost per flying hour.

In December 2008, an E-8C test aircraft took its first flight with the new engines. In 2009, the company began engine replacement and additional upgrade efforts. The re-engining funding was halted in 2009 as the Air Force began to consider other options for performing the JSTARS mission.

Design

The E-8C is an aircraft modified from the Boeing 707-300 series commercial airliner. The E-8 carries specialized radar, communications, operations and control subsystems. The most prominent external feature is the 40 ft (12 m) canoe-shaped radome under the forward fuselage that houses the 24 ft (7.3 m) APY-7 active electronically scanned array side looking airborne radar antenna.

The E-8C can respond quickly and effectively to support worldwide military contingency operations. It is a jam-resistant system capable of operating while experiencing heavy electronic countermeasures. The E-8C can fly a mission profile for 9 hours without refueling. Its range and on-station time can be substantially increased through in-flight refueling.

Radar and systems

The AN/APY-7 radar can operate in wide area surveillance, ground moving target indicator (GMTI), fixed target indicator (FTI) target classification, and synthetic aperture radar (SAR) modes.

To pick up moving targets, the Doppler radar looks at the Doppler frequency shift of the returned signal. It can look from a long-range, which the military refers to as a high standoff capability. The antenna can be tilted to either side of the aircraft for a 120-degree field of view covering nearly 19,305 square miles (50,000 km2) and can simultaneously track at more than 152 miles (250 km). The GMTI modes cannot pick up objects that are too small, insufficiently dense, or stationary. Data processing allows the APY-7 to differentiate between armored vehicles (tracked tanks) and trucks, allowing targeting personnel to better select the appropriate ordnance for various targets.

The system's SAR modes can produce images of stationary objects. Objects with many angles (for example, the interior of a pick-up bed) will give a much better radar signature, or specular return. In addition to being able to detect, locate and track large numbers of ground vehicles, the radar has a limited capability to detect helicopters, rotating antennas and low, slow-moving fixed-wing aircraft.

The radar and computer subsystems on the E-8C can gather and display broad and detailed battlefield information. Data is collected as events occur. This includes position and tracking information on enemy and friendly ground forces. The information is relayed in near-real time to the US Army's common ground stations via the secure jam-resistant surveillance and control data link (SCDL) and to other ground C4I nodes beyond line-of-sight via ultra high-frequency satellite communications.

Other major E-8C prime mission equipment are the communications/datalink (COMM/DLX) and operations and control (O&C) subsystems. Eighteen operator workstations display computer-processed data in graphic and tabular format on video screens. Operators and technicians perform battle management, surveillance, weapons, intelligence, communications and maintenance functions.

Northrop Grumman has tested the installation of a MS-177 camera on an E-8C to provide real time visual target confirmation.

Battle management
In missions from peacekeeping operations to major theater war, the E-8C can provide targeting data and intelligence for attack aviation, naval surface fire, field artillery and friendly maneuver forces. The information helps air and land commanders to control the battlespace.

The E-8's ground-moving radar can tell approximate number of vehicles, location, speed, and direction of travel. It cannot identify exactly what type of vehicle a target is, tell what equipment it has, or discern whether it is friendly, hostile, or a bystander, so commanders often crosscheck the JSTARS data against other sources. In the Army, JSTARS data is analyzed in and disseminated from a Ground Station Module (GSM).

Operational history

The two E-8A development aircraft were deployed in 1991 to participate in Operation Desert Storm under the direction of USAF Colonel Harry H. Heimple, Program Director, even though they were still in development. The joint program accurately tracked mobile Iraqi forces, including tanks and Scud missiles. Crews flew developmental aircraft on 49 combat sorties, accumulating more than 500 combat hours and a 100% mission effectiveness rate.

These Joint STARS developmental aircraft also participated in Operation Joint Endeavor, a NATO peacekeeping mission, in December 1995. While flying in friendly air space, the test-bed E-8A and pre-production E-8C aircraft monitored ground movements to confirm compliance with the Dayton Peace Accords agreements. Crews flew 95 consecutive operational sorties and more than 1,000 flight hours with a 98% mission effectiveness rate.

The 93d Air Control Wing, which activated 29 January 1996, accepted its first aircraft on 11 June 1996, and deployed in support of Operation Joint Endeavor in October. The provisional 93d Air Expeditionary Group monitored treaty compliance while NATO rotated troops through Bosnia and Herzegovina. The first production E-8C and a pre-production E-8C flew 36 operational sorties and more than 470 flight hours with a 100% effectiveness rate. The wing declared initial operational capability 18 December 1997 after receiving the second production aircraft. Operation Allied Force saw Joint STARS in action again from February to June 1999 accumulating more than 1,000 flight hours and a 94.5% mission-effectiveness rate in support of the U.S.-lead Kosovo War.

The twelfth production aircraft, outfitted with an upgraded operations and control subsystem, was delivered to the USAF on 5 November 2001.

On 1 October 2002, the 93d Air Control Wing (93 ACW) was "blended" with the 116th Bomb Wing in a ceremony at Robins Air Force Base, Georgia. The 116 BW was an Air National Guard wing equipped with the B-1B Lancer bomber at Robins AFB. As a result of a USAF reorganization of the B-1B force, all B-1Bs were assigned to active duty wings, resulting in the 116 BW lacking a current mission. The newly created wing was designated as the 116th Air Control Wing (116 ACW). The 93 ACW was inactivated the same day. The 116 ACW constituted the first fully blended wing of active duty and Air National Guard airmen. The wing took delivery of the 17th and final E-8C on 23 March 2005.

The E-8C Joint STARS routinely supports various taskings of the Combined Force Command Korea during the North Korean winter exercise cycle and for the United Nations enforcing resolutions on Iraq.

In March 2009, a Joint STARS aircraft was damaged beyond economical repair when a test plug was left on a fuel tank vent, subsequently causing the fuel tank to rupture during in-flight refueling. There were no casualties but the aircraft sustained $25 million in damage.

In September 2009, Loren B. Thompson of the Lexington Institute raised the question of why most of the Joint STARS fleet was sitting idle instead of being used to track insurgents in Afghanistan. Thompson states that the Joint STARS' radar has an inherent capacity to find what the Army calls 'dismounted' targets—insurgents walking around or placing roadside bombs. Thompson's neutrality has been questioned by some since Lexington Institute has been heavily funded by defense contractors, including Northrop Grumman.

Recent trials of Joint STARS in Afghanistan are destined to develop tactics, techniques and procedures in tracking dismounted, moving groups of Taliban.

In January 2011, Northrop Grumman's E-8C Joint Surveillance Target Attack Radar System (Joint STARS) test bed aircraft completed the second of two deployments to Naval Air Station Point Mugu, California, in support of the U.S. Navy Joint Surface Warfare Joint Capability Technology Demonstration to test its Network-Enabled Weapon (NEW) architecture. The Joint STARS aircraft executed three Operational Utility Assessment flights and demonstrated its ability to guide anti-ship weapons against surface combatants at a variety of standoff distances in the NEW architecture.

From 2001 to January 2011 the Joint STARS fleet flew more than 63,000 hours in 5,200 combat missions in support of Operations Iraqi Freedom, Enduring Freedom and New Dawn.

On 1 October 2011, the "blended" wing construct of the 116th Air Control Wing (116 ACW), combining Air National Guard and Regular Air Force personnel in a single unit was discontinued. On this date, the 461st Air Control Wing (461 ACW) was established at Robins AFB as the Air Force's sole active duty E-8 Joint STARS wing while the 116 ACW reverted to a traditional Air National Guard wing within the Georgia Air National Guard. Both units share the same E-8 aircraft and will often fly with mixed crews, but now function as separate units.

On 1 October 2019, JSTARS ended its continuous presence in the United States Central Command (USCENTCOM) areas of responsibility. The 18–year deployment was the second-longest deployment in U.S. Air Force history. In that time, the crews and aircraft flew 10,938 sorties, and 114,426.6 combat hours.

On 11 February 2022, the first of four JSTARS out of the remaining 16 operational JSTARS was retired as detailed in the Fiscal Year 2022 National Defence Authorisation Act (NDAA). The plane (serial number 92-3289/GA) which was the first to arrive at Robins AFB in 1996 has now been transferred to the 309th Aerospace Maintenance and Regeneration Group at Davis–Monthan Air Force Base.

From late 2021 to early 2022, E-8C JSTARS aircraft deployed to Europe during the 2021-2022 Russo-Ukrainian crisis. 30 years after entering service, it was performing the type of mission it had originally been intended to: monitoring Russian military activity in Eastern Europe, which it did while operating over Ukrainian airspace until the start of the 2022 Russian invasion of Ukraine in late February 2022.

Retirement
The USAF began an analysis of alternatives (AOA) in March 2010 for its next generation ground GMTI radar aircraft fleet. The study was completed in March 2012 and recommended buying a new business jet-based ISR aircraft, such as a version of the Boeing 737, and the Gulfstream 550. The Air Force said Joint STARS was expected to remain in operation through 2030.

On 23 January 2014, the USAF revealed a plan for the acquisition of a new business jet-class replacement for the E-8C Joint STARS. The program was called Joint STARS Recap and planned for the aircraft to reach initial operating capability (IOC) by 2022. The airframe would be more efficient, and separate contracts would be awarded for developing the aircraft, airborne sensor, battle management command and control (BMC2) system, and communications subsystem.

On 8 April 2014, the Air Force held an industry day for companies interested in competing for JSTARS Recap; attendees included Boeing, Bombardier Aerospace, and Gulfstream Aerospace. Air Force procurement documents called for a replacement for the Boeing 707-based E-8C as a "business jet class" airframe that is "significantly smaller and more efficient." Indicative specification were for an aircraft with a 10-13 person crew with a 3.96 - 6.1 m radar array and capable of flying at 38,000 ft for eight hours. In August 2015, the Air Force issued contracts to Boeing, Lockheed Martin, and Northrop Grumman for a one-year pre-engineering and manufacturing development effort to mature and test competing designs ahead of a downselect in late 2017.

During the fiscal 2019 budget rollout briefing it was announced that the Air Force will not move forward with an E-8C replacement aircraft. Funding for the JSTARS recapitalization program was instead be diverted to pay for development of an Advanced Battle Management System.

The E-8C JSTARS began to be retired in February 2022, and flew its last operational sortie on 21 September 2023. Rather than procure a replacement aircraft, the USAF intends to use a network of satellites, aircraft sensors and ground radars as a cheaper and more resilient approach to collecting similar targeting and tracking data. The JSTARS performed its last flight on 15 November 2023. The aircraft conducted some 14,000 operational sorties flying more than 141,000 hours over 32 years of service.

Variants

 * E-8A
 * Original platform configuration.

 * TE-8A
 * Single aircraft with mission equipment removed, used for flight crew training.

 * YE-8B
 * Single aircraft, was to be a U.S. Navy Boing E-6 Mercury but transferred to the U.S. Air Force as a development aircraft before it was decided to convert second-hand Boeing 707s (one from a Canadian Boeing CC-137) for the JSTARS role.

 * E-8C
 * Production Joint STARS platform configuration converted from second-hand Boeing 707s (1 from a CC-137).

Operators

 * United States Air Force 1991-2023
 * 93d Air Control Wing - Robins Air Force Base, Georgia 1996-2002
 * 12th Airborne Command and Control Squadron
 * 16th Airborne Command and Control Squadron
 * 461st Air Control Wing - Robins Air Force Base, Georgia 2002-2023
 * 12th Airborne Command and Control Squadron
 * 16th Airborne Command and Control Squadron
 * Air National Guard - 2006-2023
 * 116th Air Control Wing - Robins Air Force Base, Georgia
 * 128th Airborne Command and Control Squadron
 * 128th Airborne Command and Control Squadron

Aircraft on display

 * E-8C 00-2000 is preserved at the Museum of Aviation at Robins Air Force Base, Georgia. It was transported from the base to the museum's facilities in July 2023.
 * TE-8A 86-0416 was transferred to the Sowela Technical Community College in Lake Charles, Louisiana on 19 September 2023. It will be used as a ground aircraft maintenance training tool as part of the college's Aviation Maintenance Technology program. This aircraft was one of the original two pre-production E-8A which took part in Operation Desert Storm in 1991, and also saw action during Operation Joint Endeavor in 1995. Afterward, it was converted into a TE-8A training aircraft and used to qualify E-8C pilots, navigators, and flight engineers.
 * E-8C 02-9111, the last JSTARS aircraft in service, was transferred to Kelly Field, San Antonio, Texas, on 15 November 2023, where it serves as a ground training aircraft in the 37th Training Wing.

Accidents
One E-8C was damaged beyond economical repair during an operational sortie.
 * On 13 March 2009, E-8C tail 93-0597, while assigned to the USAF 379th Air Expeditionary Wing, experienced a near catastrophic fuel tank over-pressurization during aerial refueling. While refueling from a Boeing KC-135T Stratotanker an test plug left in the fuel vent system caused overpressure resulting in severe internal damage to the number two fuel tank and surrounding wing structure. The JSTARS crew were able to make a successful emergency landing at Al Udeid Air Base, and the aircraft was written off.

title: Northrop Grumman E-8 Joint STARS