A beyond-visual-range missile usually refers to an air-to-air missile that is capable of engaging at ranges beyond 20 nautical miles (37 km). This range has been achieved using dual pulse rocket motors or booster rocket motor and ramjet sustainer motor.
In addition to the range capability, the missile must also be capable of tracking its target at this range or of acquiring the target in flight. Systems in which a mid-course correction is transmitted to the missile have been used.
Early air-to-air missiles used semi-active radar guidance, that is the missile used the radiation produced by the launching aircraft to guide it to the target. The latest generation of BVR missiles use a combination of semi-active and active radar.
The first such missiles were relatively simple beam riding designs that were soon replaced by semi-active radar homing (SARH). This is where the launching aircraft's radar is "locked" onto the target in a single target track (STT) mode, directing a radar energy at the target that the missile seeker can "see" as it reflects off the target. The radar antenna must "illuminate" the target until impact. Missiles like the Raytheon AIM-7 Sparrow and Vympel R-27 (NATO designation AA-10 'Alamo') home in on the reflected radiation, much as a laser-guided bomb homes in on the reflected laser radiation. Some of the longest-range missiles in use today still use this technology.
The first air-to-air missile to introduce a terminal active seeker of its own was the AIM-54 Phoenix carried by the F-14 Tomcat, which entered service in 1972. This relieved the launch platform of the need to illuminate the target until impact putting it at risk. The Phoenix and its associated Tomcat radar, the AWG-9 was capable of multiple track and launch capability, which was unique to the Tomcat/Phoenix until the advent of AMRAAM in 1991.
Newer fire-and-forget type missiles like the Raytheon AIM-120 AMRAAM and the Vympel R-77 (NATO designation AA-12 'Adder') instead use an inertial navigation system (INS) combined with initial target information from the launching aircraft and updates from a one or two-way data link in order to launch beyond visual range, and then switch to a terminal homing mode, typically active radar guidance. These types of missiles have the advantage of not requiring the launching aircraft to illuminate the target with radar energy for the entire flight of the missile, and in fact do not require a radar lock to launch at all, only target tracking information. This gives the target less warning that a missile has been launched and also allows the launching aircraft to turn away once the missile is in its terminal homing phase or engage other aircraft. The very longest-range missiles like the Hughes (now Raytheon) AIM-54 Phoenix missile and Vympel R-33 (NATO designation AA-9 'Amos') use this technique also.
Some variants of the Vympel R-27 use semi-active radar homing (SARH) for the initial guidance and then passive infra-red guidance for the final stage. This type of missile requires active guidance for a longer part of the flight than fire-and-forget missiles but will still guide to the target even if radar lock is broken in the crucial final seconds of the engagement and may be harder to spoof with chaff due to the dual-type guidance.
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