Half a croissant, on a plate, with a sign in front of it saying '50c'
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Remote laser tagging

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(+4, -1)
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So, I was mulling over things like "smart" projectiles which can steer themselves. The example I had in mind was a smart arrow, but smart bullets have been proposed and/or implemented too.

One common problem is that, if the target is moving, the smart projectile has to be able to follow it. This is doable if the shooter keeps a laser aimed at the moving target (the projectile can aim towards the laser dot), but this requires skill.

Ideally, one would prefer to walk up to the target, stick an adhesive marker dot on them, then step back and shoot a projectile that homes in on that dot. However, the need to walk up and attach the dot somewhat defeats the purpose of the smart projectile.

So, can you "dot" a target remotely? I think you can. instead of a regular targeting laser, have a laser powerful enough to heat the surface of the target by at least 50- 100°C. This can be done in a single pulse, which means that fairly modest lasers can be used.

For a few tens of milliseconds after the pulse, the target spot will remain hot, and should have a strong infrared signal. The smart projectile is fired at the moment the heat pulse is delivered, ensuring that an infrared-bright hotspot remains on the target until the projectile reaches it. It doesn't matter if the target moves once the heat pulse has been delivered - the shooter doesn't need to track the target until the projectile reaches it.

For added discrimination (for example, if there are other hot objects around), the heat-pulse can write a barcode or other pattern, in heat, on the target. The smart projectile can then track this, with less risk of being distracted by other heat sources.

MaxwellBuchanan, Dec 01 2013


       Bejeesus that was a high-velocity bun!
MaxwellBuchanan, Dec 01 2013

       Call the target on their cell phone, and say something to anger or embarrass them, then lock on to the heat bloom
lurch, Dec 01 2013

       ...and not just a high-velocity bun, a laser-tracking armor-piercing high-velocity bun.   

       // a heat barcode would be worthless at the time of writing. // Why? If I heat up the surface of a piece of clothing (or an area or fur, or whatever) quickly, it will retain that heat for at least a fraction of a second. In fact, I have seen thermal (IR) videos which show the thermal "fingerprints" left by a warm hand on an object. I see no reason why a barcode or other readable signal couldn't be "heat printed" - its lifetime would be limited (perhaps to a hundred msec or so) by the time needed for the heat to disperse or to spread and blur the image.   

       //fire and forget missile// Yes, but I am looking for a way to laser-designate a target that can be hit by a smart bullet. Reliable optical tracking, I would guess, is harder to implement in a small device.
MaxwellBuchanan, Dec 02 2013

       //any fine grain pattern will blur pretty quickly//   

       We're talking about tens of milliseconds here - the time it takes the bullet to travel to the target. If the laser-made target has features on the scale of a centimetre, it won't dissipate in that time. As I mentioned, infrared hand "prints" left on cold objects are visible for seconds.
MaxwellBuchanan, Dec 02 2013

       It seems like a smart projectile could use pattern recognition to home in. Even if a thing changes its appearance (eg turns tail to run) it changes incrementally and this could be tracked.
bungston, Dec 02 2013

       At the risk of being accused of haplotism or epheuresis, can I suggest, [bung] that you look at some of the superhended annotations? Image recognition software is a bulky and, at best, underelegant solution to the problem. Far simpler to tag the target and then have the projectile tract that [distinctive] tag.
MaxwellBuchanan, Dec 05 2013


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