Missile lock-on!

Friday, August 31st, 2018

I was listening to the audio version of David Suarez’s techno-thriller Kill Decision, when the pilot of the good guys’ C-130 announced “missile lock-on!” How exactly does missile lock-on work, and how does the target know it’s locked on?

Aircraft radars typically have two modes: search and track. In search mode, the radar sweeps a radio beam across the sky in a zig-zag pattern. When the radio beam is reflected by a target aircraft, an indication is shown on the radar display. In search mode, no single aircraft is being tracked, but the pilot can usually tell generally what a particular radar return is doing because with each successive sweep, the radar return moves slightly.


In track mode, the radar focuses its energy on a particular target. Because the radar is actually tracking a target, and not just displaying bricks when it gets a reflection back, it can tell the pilot a lot more about the target.


An important thing to note is that a radar lock is not always required to launch weapons at a target. For guns kills, if the aircraft has a radar lock on a target, it can accurately gauge range to the target, and provide the pilot with the appropriate corrections for lead and gravity drop, to get an accurate guns kill. Without the radar, the pilot simply has to rely on his or her own judgement.


And what about missiles? Again, a radar lock is not required. For heat-seeking missiles, a radar lock is only used to train the seeker head onto the target. Without a radar lock, the seeker head scans the sky looking for “bright” (hot) objects, and when it finds one, it plays a distinctive whining tone to the pilot. The pilot does not need radar in this case, he just needs to maneuver his aircraft until he has “good tone,” and then fire the missile. The radar only makes this process faster.

Now, radar-guided missiles come in two varieties: passive and active. Passive radar missiles do require a radar lock, because these missiles use the aircraft’s reflected radar energy to track the target.

Active radar missiles however have their own onboard radar, which locks and tracks a target. But this radar is on a one-way trip, so it’s considerably less expensive (and less powerful) than the aircraft’s radar. So, these missiles normally get some guidance help from the launching aircraft until they fly close enough to the target where they can turn on their own radar and “go active.” (This allows the launching aircraft to turn away and defend itself.) It is possible to fire an active radar missile with no radar lock (so-called “maddog”); in this case, the missile will fly until it’s nearly out of fuel, and then it will turn on its radar and pursue the first target it sees. This is not a recommended strategy if there are friendly aircraft in close proximity to the enemy.


Radar is just radio waves, and just as your FM radio converts radio waves into sound, so can an aircraft analyze incoming radio signals to figure out who’s doing what. This is called an RWR, or radar warning receiver, and has both a video and audio component.


Each time a new radar signal is detected, it is converted into an audio wave and played for the pilot. Because different radars “sound” different, pilots learn to recognize different airborne or surface threats by their distinctive tones. The sound is also an important cue to tell the pilot what the radar is doing: If the sound plays once, or intermittently, it means the radar is only painting our aircraft (in search mode). If a sound plays continuously, the radar has locked onto our aircraft and is in track mode, and thus the pilot’s immediate attention is demanded. In some cases, the RWR can tell if the radar is in launch mode (sending radar data to a passive radar-guided missile), or if the radar is that of an active radar-guided missile. In either of these cases, a distinctive missile launch tone is played and the pilot is advised to immediately act to counter the threat. Note that the RWR has no way of knowing if a heat-seeking missile is on its way to our aircraft.


  1. Bill says:

    Suarez predicted the idea of drone assassination in this novel; it was recently tried in Venezuela a few weeks ago against its president.

  2. Bruce says:

    Tried or faked. A drone exploding a half-mile away in the air is a lot easier on a faking politician’s nerves than the rifle bullet zooming riskily close (near spoiler) in Donald Hamilton’s classic Line of Fire.

  3. Lucklucky says:

    Not anymore true with electronic scanned radars and low signature radars so it is increasingly difficult to know when someone is just scanning you.

    That is one of the reasons for https://en.wikipedia.org/wiki/Missile_approach_warning_system

    They need to detect the missile.

  4. Sam J. says:

    I happened to be thinking about missile systems lately. In the past missle systems seemed an insurmountable task to defeat. Hence the vast sums spent on cruise missles and stealth. Today this seems to not be true but I haven’t heard anyone else say so or comment on it. High ground always has the stronger hand. With a CCD camera, possibly with some limited thermal capability and a cheap processor with some limited neural net software, why in world should anyone worry about missiles? Just carry a few small anti-missile missiles on the plane. If a missile is fired the plane tells the mini missile killer where it’s coming from, launches and the mini-missile killer optically tracks the missile on the way down and hits it. Missile gone. You need a hell of a lot less energy to fire down than up. The cost of the ground launched missile will always be higher. You could carry a lot of them or one plane could carry a lot of missiles, to clear the ground missiles, while another, higher, carried the bombs

  5. Ritchie says:

    Pye Wacket was the codename for an experimental lenticular-form air-to-air missile developed by the Convair Division of the General Dynamics Corporation [1] in 1957. Intended as a defensive missile for the B-70 Valkyrie Mach 3 bomber, the program saw extensive wind-tunnel testing and seemed promising; however the cancellation of the B-70 removed the requirement for the missile, and the project was cancelled.

  6. Sam J. says:


    That’s thinking out of the box for sure. Very interesting. I never heard of these. Thanks.

    These things would be great for aircraft. They’re really impressive. You could make a slot in the wing and launch them from the front or rear. To launch from the rear or the front just rotate the plate. The slot would be small so it wouldn’t harm the planes drag much. Since they stack like plates you could have a magazine of them in the bomb bay that fed them into the launch slot. Let’s say you had a high risk target. One plane could fill it’s bomb bay with these magazines and launch masses of these plate bombs while another carried the bombs for the target. Since the magazines fit into the bomb bay the whole bomb bay could be re-configurable for different weapons systems for different attack scenarios.

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