The AIM-9 Sidewinder (for Air Intercept Missile) is a short-range air-to-air missile which entered service with the US Navy in 1956 and subsequently was adopted by the US Air Force in 1964. Since then the Sidewinder has proved to be an enduring international success, and its latest variants are still standard equipment in most western-aligned air forces. The Soviet K-13, a reverse-engineered copy of the AIM-9, was also widely adopted by a number of nations.
The United States Navy hosted a 50th-anniversary celebration for the Sidewinder in 2002. Boeing won a contract in March 2010 to support Sidewinder operations through to 2055, guaranteeing that the weapons system will remain in operation until at least that date. Air Force Spokeswoman Stephanie Powell noted that due to its relatively low cost, versatility, and reliability it is “very possible that the Sidewinder will remain in Air Force inventories through the late 21st century”.
The guidance and control unit (GCU) contains most of the electronics and mechanics that enable the missile to function. At the very front is the IR seeker head utilizing the rotating reticle, mirror, and five CdS cells or “pan and scan” staring array (AIM-9X), electric motor, and armature, all protruding into a glass dome. Directly behind this are the electronics that gather data, interpret signals, and generate the control signals that steer the missile. An umbilical on the side of the GCU attaches to the launcher, which detaches from the missile at launch. To cool the seeker head, a 5,000 psi (34 MPa) argon bottle (TMU-72/B or A/B) is carried internally in Air Force AIM-9L/M variants, while the Navy uses a rail-mounted nitrogen bottle. The AIM-9X model contains a Stirling cryo-engine to cool the seeker elements. Two electric servos power the canards to steer the missile (except AIM-9X). At the back of the GCU is a gas grain generator or thermal battery (AIM-9X) to provide electrical power. The AIM-9X features high off-boresight capability; together with JHMCS (Joint Helmet-Mounted Cueing System), this missile is capable of locking on to a target that is in its field of regard said to be up to 90 degrees off boresight. The AIM-9X has several unique design features including built-in test to aid in maintenance and reliability, an electronic safe and arm device, an additional digital umbilical similar to the AMRAAM and jet vane control.
The AIM-9 is made up of a number of different components manufactured by different companies, including Aerojet and Raytheon. The missile is divided into four main sections: guidance, target detector, warhead, and rocket motor.
Next is a target detector with four IR emitters and detectors that detect whether the target is moving farther away. When it detects this action taking place, it sends a signal to the warhead safe and arm device to detonate the warhead. Versions older than the AIM-9L featured an influence fuze that relied on the target’s magnetic field as input. Current trends in shielded wires and non-magnetic metals in aircraft construction rendered this obsolete.
The AIM-9H model contained a 25 lb (11 kg) expanding rod-blast fragmentary warhead. All other models up to the AIM-9M contained a 22 lb (10.0 kg) annular-blast fragmentary warhead. The missile’s warhead rods can break rotor blades (an immediately fatal event for any helicopter).
Recent models of the AIM-9 are configured with an annular-blast fragmentation warhead, the WDU-17B by Argotech Corporation. The case is made from spirally wound spring steel filled with 8 lb (3.6 kg) of PBXN-3 explosive. The warhead features a safe/arm device requiring five seconds at 20 g (~200 m/s²) acceleration before the fuze is armed, giving a minimum range of approximately 2.5 km (1.6 mi).
The Mk36 solid-propellant rocket motor provides propulsion for the missile. A reduced-smoke propellant makes it difficult for a target to see and avoid the missile. This section also features the launch lugs used to hold the missile to the rail of the missile launcher. The forward of the three lugs has two contact buttons that electrically activate the motor igniter. The fins provide stability from an aerodynamic point of view, but it is the “rollerons” at the end of the wings providing gyroscopic precession to free-hinging control surfaces in the tail that prevent the missile from spinning in flight. The wings and fins of the AIM-9X are much smaller and control surfaces are reversed from earlier Sidewinders with the control section located in the rear, while the wings up front provide stability. The AIM-9X also features vectored thrust or jet vane control to increase maneuverability and accuracy, with four vanes inside the exhaust that move as the fins move. The last upgrade to the missile motor on the AIM-9X is the addition of a wire harness that allows communication between the guidance section and the control section, as well as a new 1760 bus to connect the guidance section with the launcher’s digital umbilical.
The Sidewinder improved on the World War II-era Madrid IR range fuze used by Messerschmitt’s Enzian experimental surface-to-air missile. The first innovation was to replace the “steering” mirror with a forward-facing mirror rotating around a shaft pointed out the front of the missile. The detector was mounted in front of the mirror. When the long axis of the mirror, the missile axis and the line of sight to the target all fell in the same plane, the reflected rays from the target reached the detector (provided the target was not very far off axis). Therefore, the angle of the mirror at the instant of detection (w1) estimated the direction of the target in the roll axis of the missile.
The yaw/pitch (angle w2) direction of the target depended on how far to the outer edge of the mirror the target was. If the target was further off axis, the rays reaching the detector would be reflected from the outer edge of the mirror. If the target was closer on axis, the rays would be reflected from closer to the centre of the mirror. Rotating on a fixed shaft, the mirror’s linear speed was higher at the outer edge. Therefore, if a target was further off-axis, its “flash” in the detector occurred for a briefer time, or longer if it was closer to the center. The off-axis angle could then be estimated by the duration of the reflected pulse of infrared.
The Sidewinder also included a dramatically improved guidance algorithm. The Enzian attempted to fly directly at its target, feeding the direction of the telescope into the control system as it if were a joystick. This meant the missile always flew directly at its target, and under most conditions would end up behind it, “chasing” it down. This meant that the missile had to have enough of a speed advantage over its target that it did not run out of fuel during the interception.
The Sidewinder is not guided on the actual position recorded by the detector, but on the change in position since the last sighting. So if the target remained at 5 degrees left between two rotations of the mirror, the electronics would not output any signal to the control system. Consider a missile fired at right angles to its target; if the missile is flying at the same speed as the target, it should “lead” it by 45 degrees, flying to an impact point far in front of where the target was when it was fired. If the missile is traveling four times the speed of the target, it should follow an angle about 11 degrees in front. In either case, the missile should keep that angle all the way to interception, which means that the angle that the target makes against the detector is constant. It was this constant angle that the Sidewinder attempted to maintain. This “proportional pursuit” system is very easy to implement, yet it offers high-performance lead calculation almost for free and can respond to changes in the target’s flight path, which is much more efficient and makes the missile “lead” the target.
However, this system also requires the missile to have a fixed roll-axis orientation. If the missile spins at all, the timing based on the speed of rotation of the mirror is no longer accurate. Correcting for this spin would normally require some sort of sensor to tell which way is “down” and then adding controls to correct it. Instead, small control surfaces were placed at the rear of the missile with spinning disks on their outer surface; these are known as rollerons. Airflow over the disk spins them to a high speed. If the missile starts to roll, the gyroscopic force of the disk drives the control surface into the airflow, cancelling the motion. Thus the Sidewinder team replaced a potentially complex control system with a simple mechanical solution.
As a Semi-Active Radar Homing (SARH) missile, the AIM-9C could be used from the frontal aspect of the target, provided a radar lock of sufficient quality was obtained.
The next major advance in IR Sidewinder development was the AIM-9L (“Lima”) model which was in full production in 1977. This was the first “all-aspect” Sidewinder with the ability to attack from all directions, including head-on, which had a dramatic effect on close-in combat tactics. Its first combat use was by a pair of US Navy F-14s in the Gulf of Sidra in 1981 versus two Libyan Su-22 Fighters, both of the latter being destroyed by AIM-9Ls. Its first use in a large-scale conflict was by the United Kingdom during the 1982 Falklands War. In this campaign the “Lima” reportedly achieved kills from 80% of launches, a dramatic improvement over the 10–15% levels of earlier versions, scoring 17 kills and 2 shared kills against Argentine aircraft.
In combat uses of the AIM-9L, opponents had not developed tactics for the evasion of head-on missile shots with it, making them more vulnerable. The AIM-9L was also the first Sidewinder that was a joint variant used by both the US Navy and Air Force since the AIM-9B. The “Lima” was distinguished from earlier Sidewinder variants by its double delta forward canard configuration and natural metal finish of the guidance and control section. The Lima was also built under license in Europe by a team headed by Diehl BGT Defence. There are a number of “Lima” variants in operational service at present. First developed was the 9L Tactical, which is an upgraded version of the basic 9L missile. Next was the 9L Genetic, which has increased infra-red counter-counter measures (IRCCM); this upgrade consisted of a removable module in the Guidance Control Section (GCS) which provided flare-rejection capability. Next came the 9L(I), which had its IRCCM module hardwired into the GCS, providing improved counter-countermeasures as well as an upgraded seeker system. Diehl BGT also markets the AIM-9L(I)-1 which again upgrades the 9L(I)GCS and is considered an operational equivalent to the initially “US only” AIM-9M.
The subsequent AIM-9M (“Mike”) has the all-aspect capability of the L model while providing all-around higher performance. The M model has improved capability against infrared countermeasures, enhanced background discrimination capability, and a reduced-smoke rocket motor. These modifications increase its ability to locate and lock-on to a target and decrease the chance of missile detection. Deliveries of the initial AIM-9M-1 began in 1982. The only changes from the AIM-9L to the AIM-9M were related to the Guidance Control Section (GCS). Several models were introduced in pairs with even numbers designating Navy versions and odd for USAF: AIM-9M-2/3, AIM-9M-4/5, and AIM-9M-6/7 which was rushed to the Persian Gulf area during Operation Desert Shield (1991) to address specific threats expected to be present.
The AIM-9M-8/9 incorporated replacement of five circuit cards and the related motherboard to update infrared counter-countermeasures (IRCCM) capability to improve 9M capability against the latest threat IRCM. The first AIM-9M-8/9 modifications, fielded in 1995, involved deskinning[clarification needed] the guidance section and substitution of circuit cards at the depot level, which is labor-intensive and expensive—as well as removing missiles from inventory during the upgrade period. The AIM-9X concept is to use reprogrammable software to permit upgrades without disassembly.
The Navy began development of AIM-9R, a Sidewinder seeker upgrade in 1987 that featured a focal-plane array (FPA) seeker using video-camera type charge-coupled device (CCD) detectors and featuring increased off-boresight capability. The technology at the time was restricted to visual (daylight) use only and the USAF did not agree on this requirement, preferring another technology path. AIM-9R reached flight test stage before it was cancelled and subsequently both services agreed to a joint development of the AIM-9X variant.
China Lake developed an improved compressed carriage control configuration titled BOA. (“Compressed carriage” missiles have smaller control surfaces to allow more missiles to fit in a given space. The surfaces may be permanently “clipped”, or may fold out when the missile is launched.)
The BOA design reduced size of control surfaces, eliminating the rollerons, and returned to simple forward-canard design. Although the Navy and Air Force had jointly developed and procured AIM-9L/M, BOA was a Navy-only effort supported by internal China Lake Independent Research & Development (IR&D) funding. Meanwhile, the Air Force was pursuing a parallel effort to develop a compressed carriage version of Sidewinder, called Boxoffice, for the F-22. The Joint Chiefs of Staff directed that the services collaborate on AIM-9X, which ended these separate efforts. The results of BOA and Boxoffice were provided to the industry teams competing for AIM-9X, and elements of both can be found in the AIM-9X design.
After looking at advanced short range missile designs during the AIM portion of the ACEVAL/AIMVAL Joint Test and Evaluation at Nellis AFB in the 1974–78 timeframe, the Air Force and Navy agreed on the need for the Advanced Medium Range Air-to-Air Missile AMRAAM. However, agreement over development of an Advanced Short Range Air-to-Air Missile ASRAAM was problematic and disagreement between the Air Force and Navy over design concepts (Air Force had developed AIM-82 and Navy had flight-tested Agile and flown it in AIMVAL). Congress eventually insisted the services work on a joint effort resulting in the AIM-9M, thereby compromising without exploring the improved off boresight and kinematic capability potential offered by Agile. In 1985, the Soviet Union did field a short range missile (SRM) (AA-11 Archer/R-73) that was very similar to Agile. At that point, the Soviet Union took the lead in SRM technology and correspondingly fielded improved infrared countermeasures (IRCM) to defeat or reduce the effectiveness of the latest Sidewinders. With the reunification of Germany and improved relations in the aftermath of the Soviet Union, the West became aware of how potent both the AA-11 and IRCM were and SRM requirements were readdressed.
For a brief period in the late 1980s, an ASRAAM effort led by a European consortium was in play under a Memorandum Of Agreement with the United States in which AMRAAM development would be led by the US and ASRAAM by the Europeans. The UK worked with the aft end of the ASRAAM and Germany developed the seeker (Germany had first-hand experience improving the Sidewinder seeker of the AIM-9J/AIM-9F). By 1990, technical and funding issues had stymied ASRAAM and the program appeared stalled, so in light of the threat of AA-11 and improved IRCM, the US embarked on determining requirements for AIM-9X as a counter to both the AA-11 and improved IRCM features. The first draft of the requirement was ready by 1991 and the primary competitors were Raytheon and Hughes. Later, the UK resolved to revive the ASRAAM development and selected Hughes to provide the seeker technology in the form of a high off-boresight capable Focal Plane Array. However, the UK did not choose to improve the turning kinematic capability of ASRAAM to compete with AA-11. As part of the AIM-9X program, the US conducted a foreign cooperative test of the ASRAAM seeker to evaluate its potential, and an advanced version featuring improved kinematics was proposed as part of the AIM-9X competition. In the end, the Hughes-evolved Sidewinder design, featuring virtually the same British funded seeker as used by ASRAAM, was selected as the winner.
The AIM-9X Sidewinder, developed by Raytheon engineers, entered service in November 2003 with the USAF (lead platform is the F-15C; the USN lead platform is the F/A-18C) and is a substantial upgrade to the Sidewinder family featuring an imaging infrared focal-plane array (FPA) seeker with claimed 90° off-boresight capability, compatibility with helmet-mounted displays such as the new U.S. Joint Helmet Mounted Cueing System, and a totally new three-dimensional thrust-vectoring control (TVC) system providing increased turn capability over traditional control surfaces. Utilizing the JHMCS, a pilot can point the AIM-9X missile’s seeker and “lock on” by simply looking at a target, thereby increasing air combat effectiveness. It retains the same rocket motor, fuze and warhead of the 9-“Mike”, but its lower drag gives it improved range and speed. AIM-9X also includes an internal cooling system, eliminating the need for use of launch-rail nitrogen bottles (U.S. Navy and Marines) or internal argon bottle (USAF). It also features an electronic safe and arm device similar to the AMRAAM, allowing reduction in minimum range and reprogrammable infrared Counter Counter Measures (IRCCM) capability that coupled with the FPA provide improved look down into clutter and performance against the latest IRCM. Though not part of the original requirement, AIM-9X demonstrated potential for a Lock-on After Launch capability, allowing for possible internal use for the F-35, F-22 Raptor and even in a submarine-launched configuration for use against ASW platforms. The AIM-9X has been tested for a surface attack capability, with mixed results.
Testing work on the AIM-9X Block II version began in September 2008. The Block II adds Lock-on After Launch capability with a datalink, so the missile can be launched first and then directed to its target afterwards by an aircraft with the proper equipment for 360 degree engagements, such as the F-35 and F-22. By January 2013, the AIM-9X Block II was about halfway through its operational testing and performing better than expected. NAVAIR reported that the missile was exceeding performance requirements in all areas, including lock-on after launch (LOAL). One area where the Block II needs improvement is helmetless high off-boresight (HHOBS) performance. It is functioning well on the missile, but performance is below that of the Block I AIM-9X. The HHOBS deficiency does not impact any other Block II capabilities, and is planned to be improved upon by a software clean-up build. Objectives of the operational test were due to be completed by the third quarter of 2013. However, as of May 2014 there have been plans to resume operational testing and evaluation (including surface-to-air missile system compatibility). As of June 2013, Raytheon has delivered 5,000 AIM-9X missiles to the armed services.
In February 2015, the U.S. Army successfully launched an AIM-9X Block II Sidewinder from the new Multi-Mission Launcher (MML), a truck-mounted missile launch container that can hold 15 of the missiles. The MML is part of the Indirect Fire Protection Capability Increment 2-Intercept (IFPC Inc. 2-I) to protect ground forces against cruise missile and unmanned aerial vehicle threats. The X-model Block II Sidewinder has been determined by the Army to be the best solution to CM and UAV threats because of its passive IIR seeker. The MML will complement the AN/TWQ-1 Avenger air defense system and is expected to begin fielding in 2019.
In September 2012, Raytheon was ordered to continue developing the Sidewinder into a Block III variant, even though the Block II had not yet entered service. The USN projected that the new missile would have a 60 percent longer range, modern components to replace old ones, and an insensitive munitions warhead, which is more stable and less likely to detonate by accident, making it safer for ground crews. The need for the AIM-9 to have an increased range was from digital radio frequency memory (DRFM) jammers that can blind the onboard radar of an AIM-120D AMRAAM, so the Sidewinder Block III’s passive imaging infrared homing guidance system was a useful alternative. Although it could supplement the AMRAAM for beyond visual range (BVR) engagements, it would still be capable at performing within visual range (WVR). Modifying the AIM-9X was seen as a cost-effective alternative to developing a new missile in a time of declining budgets. To achieve the range increase, the rocket motor would have a combination of increased performance and missile power management. The Block III would “leverage” the Block II’s guidance unit and electronics, including the AMRAAM-derived datalink. The Block III was scheduled to achieve initial operational capability (IOC) in 2022, following the increased number of F-35 Lightning II Joint Strike Fighters to enter service. The Navy pressed for this upgrade in response to a projected threat which analysts have speculated will be due to the difficulty of targeting upcoming Chinese Fifth-generation jet fighters (Chengdu J-20, Shenyang J-31) with the radar guided AMRAAM, specifically that Chinese advances in electronics will mean Chinese fighters will use their AESA radars as jammers to degrade the AIM-120’s kill probability. However, the Navy’s FY 2016 budget cancelled the AIM-9X Block III as they cut down buys of the F-35C, as it was primarily intended to permit the fighter to carry six BVR missiles; the insensitive munition warhead will be retained for the AIM-9X program.
|Seeker design features|
|Reticle speed (Hz)||100||125||125||100||Focal-plane array|
|Track rate (°/s)||16.5||Classified||Classified||>16.5||Classified|
|Electronics||Hybrid||Solid state||Solid state||Solid state||Solid state|
|Warhead||4.5 kg (9.9 lb)
|9.4 kg (21 lb) WDU-17/B
|9.4 kg (21 lb) WDU-17/B
|Annular blast-fragmentation||Annular blast-fragmentation|
|Type||Mk.17||Mk.36 Mod.7,8||Mk.36 Mod.9||SR.116||Mk.36 Mod.9|
|Length||3 m (9.8 ft)||2.89 m (9.5 ft)||2.89 m (9.5 ft)||3 m (9.8 ft)||2.89 m (9.5 ft)|
|Span||0.58 m (1.9 ft)||0.64 m (2.1 ft)||0.64 m (2.1 ft)||0.58 m (1.9 ft)||0.64 m (2.1 ft)|
|Weight||77 kg (170 lb)||86 kg (190 lb)||86 kg (190 lb)||86 kg (190 lb)||86 kg (190 lb)|
- Australian Air Force
- United Kingdom
- UK Royal AIr Force
- UK Royal Navy
- United States