AIM-9 Sidewinder, US Air to Air Missile

The AIM-9 Sidewinder is a heat-seeking, short-range, air-to-air missile carried mostly by fighter aircraft and recently, certain gunship helicopters. Variants and upgrades remain in active service with many air forces after five decades. When a Sidewinder missile is being launched, NATO pilots use the brevity code Fox Two in radio communication, as with all "heat-seeking" missiles.

AIM-9 Sidewinder
Type	Short-range air-to-air missile
Place of origin	United States
Service history
In service	1956 (AIM-9B) – present
Production history
Manufacturer	Nammo Raytheon Company Ford Aerospace Loral Corp.
Unit cost	US$85,000
Produced	September 1953
Specifications
Weight	190 pounds (86.2 kg)
Length	9 feet 4.2 inches (2.850 m)
Diameter	5 in (127.0 mm)
Warhead	annular blast-frag
Warhead weight	20.8 lb (9.4 kg)
Detonation mechanism	Magnetic influence (old models) Active infrared (AIM-9L onwards)
Engine	Solid-fuel rocket
Wingspan	24.8 in (629.9 mm)
Operational range	0.6 to 11.3 miles (1.0 to 18.2 km)
Speed	Mach 2.5
Guidance system	Infrared homing
Launch platform	Aircraft, helicopter gunships

AIM-9 Sidewinder Design

The AIM-9 Sidewinder 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.

Guidance and Control Unit (GCU)

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” focal-plane 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 (35 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.

Target Detector

Target detector with four IR emitters and detectors that detect if 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.

Warhead

The AIM-9H model contained a 25-pound (11 kg) expanding rod-blast fragmentary warhead. All other models up to the AIM-9M contained a 22-pound (10 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 of spirally wound spring steel filled with 8 pounds (4 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 kilometers.

Rocket Motor

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 that prevents the serpentine motion that gave the Sidewinder its name in the early days. The wings and fins of the AIM-9X are much smaller to accommodate one in each side bay of the F-22 Raptor as originally planned, AIM-9X 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.