How does the SAM (surface to air missile) not fire on friendly aircraft and only on enemy aircraft?
In: Technology
There is an IFF (Identify friend or foe) system. This allows it to ignore heat signatures that are identified as “friendly”.
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To add to the comments about IFF, modern radar systems can examine the radio signatures emitted by aircraft. Those signatures are surprisingly unique, at least as far as radio emitters go….all you need from there is a database of known radios on known aircraft and you can get a fairly accurate understanding of what is flying around. Not good enough for a safe automated SAM system, but good enough to at least go “Oh hey these radio emissions look like those of a friendly craft so we better not fire”.
If it’s flying completely silent though (all radios off), this won’t work as a detection method. IFF is generally coordinated with this to make the system more accurate, and typically unless the system is 100% certain it won’t automatically fire (and would require an operator to fire).
Identify Friend or Foe (IFF) transponder. The IFF responds to a query sent by a the targeting station (either automatically or manually by an operator). The query is encrypted, and the IFF decrypts the signal, processes it, and sends an appropriate response, which is also encrypted.
If the IFF successfully decrypts and reads the signal, it knows the aircraft is being pinged by a friendly system and doesn’t sound an alarm in the cockpit. If the ground station successfully decrypts the response, it knows the aircraft is friendly and not to blow it’s bitch ass out of the sky.
As others have mentioned IFF exists to identify aircraft. But it’s also worth pointing out the launcher isnt operating alone, it’s linked to a detector, usually radar. This is the eyes, it has a computer brain and the iff coming off the contact is part of the information set that makes decisions.
Some missiles then themselves have smaller detector/decision setups and can change their minds after launch
All these things together make them pick legitimate threats out and stop them whacking flocks of birds etc etc
It doesn’t.
The operator can feed it identification data on targets presumed friendly that then, assuming everything goes right, are not engaged.
Only in Hollywood is that system anywhere near perfect – in reality even the most sophisticated systems are “dumb” to the point that SAMs are not used when friendly aircraft are in the same bit of airspace.
Iran Air Flight 655 for a sad recent example: a USN cruiser shooting down a civilian airliner due to being unable to tell it apart from fighters that could have lounched from the same airport.
The Launcher is part of a system –
* The radar or IR sensor find the target
* the IFF module “interrogates” the target (sends a signal & listens for a response to tel friend from foe)
* the crew manning the system has procedues to make a “shoot/don’t shoot” decision. E.g. bogeys (unidentified aircraft) flying outside of certain altitudes or locations get looked at, if they don’t respond they get shot at.
* Depending on the system there is a way to “lock out” bogeys that are confirmed friendlies. The PATRIOT radar has “ENGAGE HOLD” to stop the system from shooting at a friendly.
The missile doesn’t “tell” friend from foe – that’s the job of the shooter.
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