April 11, 2012: The latest version of the U.S. Sidewinder air-to-air missile, the AIM-9X-2, has come a long way from the first Sidewinder of the 1950s. The 9X-2 can lock-on-after-launch. That is, the missile can be fired and then directed to a target via a datalink. That means it can be fired at ground targets or at an enemy aircraft behind you. The X-2 version also makes improvements in the warhead fuze and other components. As impressive as all these features most are already found in similar missiles made in several other countries (including Russia and China). In effect, the X-2 version is just keeping up. What the U.S. sells, in addition, is an impressive track record of reliability and actually performing as expected in combat. Over 4,000 X model Sidewinders have been built since it entered service in 2003. Block II (X-2) entered service four years ago and cost about half a million dollars each.
The AIM-9 is a heat seeking missile, and the heat sensors have become much more sensitive since the first AIM-9 entered service half a century ago. The current versions of the missile work by detecting a heat source at the point where the pilot is looking. This is done using the JHMCS (Joint Helmet Mounted Cueing Systems), which allows a pilot to see, displayed on his visor, critical flight and navigation information. Sort of like a see-through computer monitor or HUD (Head Up Display). Most importantly, the pilot can turn his head towards a target, get an enemy aircraft or ground target into the crosshairs displayed on the visor and fire a missile that will promptly go after target the pilot was looking at. For Sidewinder the pilot has to be looking at something giving off enough heat to catch the attention of the missile's heat sensor. With the X-2 Sidewinder the pilot can launch the missile before he has located the target via the JHMCS, saving a critical few seconds.
The JHMCS is already used with some air-to-ground missiles, although no special air-to-ground software was needed for Sidewinders fired at ground targets. Instead, the air-to-air software was modified. This is important because one of the reasons for this mod was to give the F-15C, which carries no air-to-ground weapons (it's strictly an air-to-air fighter) some air-to-ground capability. In addition, fighter-bombers (like the F-18, F-16, F-22, and F-35) will now be able to use their air-to-air weapons in a pinch, once all their actual air-to-ground weapons are gone.
Although over half a century old, the Sidewinder has been the most effective air-to-air missile ever produced. The first Sidewinder (AIM-9B) was 3 meters (9.3 feet) long, weighed 71 kg (156 pounds), and had a max range of five kilometers. The most current model, the AIM-9X, is the same size, weighs 87 kg (191 pounds), and has a max range of over 20 kilometers. All models have a warhead weighing about 10 kg (22 pounds). The AIM-9X can go after the target from all angles, while the AIM-9B could only be used from directly behind the target. The AIM-9X is about seven times more likely to bring down the target than the AIM-9B. The 9X entered service in 2000, but the older 9M is nearly as accurate, although without the additional flexibility and capabilities.
While air force planners would like to do away with short range, heat seeking missiles, depending on longer ranged, radar guided missiles instead, that is not likely to happen any time soon. Radars and other sensors are still not reliable enough to prevent hostile aircraft from first becoming aware of each other when they are quite close. At that point the cheaper, smaller and increasingly very capable heat seekers are the weapon of choice.