AAM-4

Not to be confused with AAM-N-4 Oriole.

The Mitsubishi AAM-4 (Type 99 air-to-air missile, 99式空対空誘導弾 (99 Shiki Kūtaikū Yūdōdan)) is a medium-range active radar homing air-to-air missile. It is a modern beyond-visual-range missile developed in Japan and intended to replace the semi-active radar homing AIM-7 Sparrow missile in service. It has been operational since 1999. The main contractor is Mitsubishi Electric. The AAM-4 had a development cost of 36.2 billion yen.^[3] The 2010 AAM-4B was the world's first air-to-air missile with an AESA radar seeker.

AAM-4
Type	Beyond-visual-range air-to-air missile/surface-to-air missile
Place of origin	Japan
Service history
In service	September 1999 (1999-09)–present
Used by	See Operators
Production history
Manufacturer	1999–present – Mitsubishi Heavy Industries
Unit cost	US$450,000
Variants	AAM-4, XRIM-4, AAM-4B, AAM-4TDR, JNAAM
Specifications
Mass	489 lb (222 kg)
Length	12 ft (3,667 mm)
Diameter	8 in (203 mm)
Wingspan	30 in (770 mm)
Warhead	High explosive Directional blast-fragmentation
Warhead weight	69 lb (31.3 kg)
Detonation mechanism	4-Quadrant Radar Proximity fuse, impact fuse
Blast yield	16.2kg TNT Equivalent
Engine	Two-stage Solid-fuel rocket motor
Operational range	AAM-4 46 nmi (85 km) AAM-4B 57 nmi (105 km) AAM-4TDR 92 nmi (170 km) JNAAM 110 nmi (200 km)
Maximum speed	Mach 4.5 (5,063 ft/s; 1,544 m/s)
Guidance system	Mid-Course:Inertial guidance, datalink, SARH Terminal: active radar homing, Inertial guidance, datalink
Steering system	Fuzzy Guidance Logic XAAM-4: 20G Maximum Overload AAM-4/4B: 25G maximum Overload
Launch platform	F-15J, F-2
References	Japanese Ministry of Defense,[1] MHI[2]

The AAM-4's fins are too large to fit in the internal weapons bay of the F-35 Lightning II. This, along with other factors, led to a program with MBDA UK to adapt the AAM-4B's AESA seeker technology to MBDA's Meteor missile airframe to produce the JNAAM. However this project has since been canceled. The AAM-4 is instead expected to be succeeded by a new domestic medium range air to air missile, which is slated for use on GCAP.

In addition to its air-to-air capabilities, the missile also has the capabilities to intercept cruise missiles and other ASMs. However it can only engage them from the front aspect, lacking sufficient energy to hit them from side or rear aspects.^[1]

Development

Technical research into a future medium-range AAM started in Japan in 1985, however it wasn't until 1994 that the design for the AAM-4 itself started, with early live testing of the XAAM-4 being done as early as late 1996 from a modified F-4EJ Kai. It initially saw service on the Mitsubishi F-15J,^[4] on post J-MSIP models, or else models which had undergone IRAN. It was not on the Mitsubishi F-2 initially due to it lacking a place for the J/ARG-1 radio transceiver,^[5] however it was later added when the radar was upgraded to the J/APG-2, which included the necessary components.^[6] Its fins are too large to be fitted to the F-35 Lightning II without changes to the mounting pylons, and additionally requires the J/ARG-1 radio transceiver to function, which can not be mounted on the F-35.^[7]

The AAM-4 uses a fuzzy guidance logic control system, as opposed to PID or binary logic. With over 70 values being taken into account to calculate its control logic. This allows for superior energy retention over other guidance logics. Additionally it greatly improves ECCM, by allowing for soft comparisons of datalink, inertial, active, and semi-active targeting information, cross referencing error rates from detected interference and target velocity information to estimate the most accurate information to guide itself.^[2] It uses a directional blast fragmentation warhead, with roughly 16.2 kg TNT equivalent of explosive surrounded by 600 fragmentation segments, each with up to 7.7mm of steel penetration. It is detonated with a variable detonation system, using either a 4-quadrant radar proximity fuse, or an impact fuse, to direct the blast in the direction of the detected target. The proximity fuse additionally uses frequency modulation to resist electronic countermeasures. This fuse has a 4-6s arming period after being fired.^[1]

The datalink for the missile is provided by the J/ARG-1 radio transceiver, an X-Ku band radio transceiver which uses frequency modulation to reduce its detectability by hostiles, as well as to resist interference from electronic countermeasures. The missile can be fired without this transceiver, however when doing so greatly decreases its effectiveness.^[4]

The seeker of the AAM-4 is, like its proximity fuse and datalink system, operated using frequency modulation to minimize its ability to be detected by hostile Radar warning receivers.^[8] Unlike the AIM-120 AMRAAM, which uses a Traveling-wave tube transmitter, the AAM-4 uses a small, high-output, and inexpensive gallium arsenide semiconductor FET improving lock-on performance, ECCM and anti-clutter performance. The seeker has a detection range of 15 km against a target 2.5m^2 in size.^[2]

The improved AAM-4B was the world's first air-to-air missile with an AESA radar seeker.^[7] The AAM-4B entered production in 2010 for service on the F-15J and F-2.^[9] It has a range of 1.2x that of the regular AAM-4, thanks to improved guidance logic, as well as a 1.4x increase in autonomous detection range (up to 21 kilometers). Using GaN semi-conductors, it operates in the Ka band, and is capable of SAR imaging. The Type 12 surface-to-ship missile and ASM-3 use the same seeker, using its imaging capabilities to allow for the detection of stealth ships, being successfully capable of spotting a Mogami-class frigate.

On 17 July 2014, Japan announced a collaboration with the United Kingdom^[9] to study the development of a new Joint New Air-to-Air Missile (JNAAM). MBDA UK is prime contractor on the Meteor missile which entered service on the Saab JAS 39 Gripen in 2016 and on the Eurofighter Typhoon and Dassault Rafale in 2018,^[10] and can fit in the internal weapons bay of the F-35.^[11] It has a unique variable-flow ramjet motor that according to MBDA gives the Meteor the largest no-escape zone of any air-to-air missile.^[12] The JNAAM will "[combine] the UK's missile-related technologies and Japanese seeker technologies",^[13] possibly with some adjustments to help the missile fit better in the F-35 weapons bay.

Variants

AAM-4B prototype

• AAM-4 – Original version with 85 km (53 mi) range that entered service in 1999.
• AAM-4B – Improved version introduced in 2010 with a Ka band millimetric frequency AESA seeker^[4] and 105 km (65 mi) range.^[14] The seeker also utilized to the Type 12 surface-to-ship missile. As well as on the ASM-3.
• XRIM-4 – Naval surface-launched variant, project was previously canceled but effectively resurrected in 2016.^[15]
• AAM-4TDR – Throttleable Ducted Rocket (TDR) Test model, based on the XRIM-4, had Thrust vectoring and BTT (Bank to turn) capabilities. Range estimated to be around 1.6-2x that of the AAM-4.^[16]

Operators

 Japan

Japan Air Self-Defense Force

• F-15J Eagle
• Mitsubishi F-2

Specifications

• Length: 3,667 mm
• Diameter: 203 mm
• Wing span: 770 mm
• Weight: 222 kg (489 lb)
• Guidance: inertial guidance, datalink, semi-active radar homing, active radar homing^[17][18]
• Range: 70 km (AAM-4), 85 km (AAM-4B^[19][20])
• Speed: Mach 4.5

See also

• AAM-1 – (Japan)
• AAM-2 – (Japan)
• AAM-3 – (Japan)
• AAM-5 – (Japan) – short range heatseeking missile introduced 2004
• AIM-120 AMRAAM – (United States)
• Sky Sword II – (Taiwan)
• Meteor (missile) – (France, United Kingdom, Italy, Germany, Spain, Sweden)
• PL-12 – (China)
• PL-15 – (China)
• R-77 – (Russia)