The manufacturer of the American AIM-9X-2 Sidewinder air-to-air missiles has been ordered to develop a new version that has longer range and uses insensitive munitions in the warhead. The 9X has a max range of 20 kilometers but some heat-seeking missiles have a range of up to 70 kilometers. This can be useful if you are chasing an aircraft that is trying to get away, but most of the time it is not particularly helpful. It's unclear how much longer range the new Sidewinder will have.
Insensitive explosives only detonate when subjected to a certain type of ignition blast. Thus if exposed to high levels of heat, bullets or most other explosives going off nearby, insensitive explosives will, at most, burn or be shattered into pieces. All this is the result of advances in chemistry in the last few decades. Now there are affordable "highly insensitive munitions" available to replace more sensitive explosives.
The first insensitive explosives were developed for use in nuclear weapons. Nuclear weapons use explosives to get the nuclear reaction going. By using insensitive explosives if a bomber crashed there was no chance any of its nuclear bombs would go nuclear just because the explosives were set off by fire. Until recently these "insensitive explosives" were very expensive. That is changing, and now the military is being offered torpedoes, shells, and missiles using slightly more insensitive explosives that are much less likely to go off by accident. Such unintended ammunition explosions have long been a threat to warships, aircraft, and ground troops. So the military sees the benefit of paying more for ammo that is more stable.
The latest version of the Sidewinder, 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 are, 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 costs about half a million dollars each. The next version of the Sidewinder (Block III?) will not only have longer range and use insensitive explosives but will also have some older components replaced with better performing equipment.
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 older 9M is nearly as accurate as the 9X, 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.