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Comment by 3pt14159 | Hacker News Reader

Question about laser weapons: how do they handle heat shielded shells? For example, I make a shell out of depleted uranium, then I coat it with a coating of strong heat insulator, then I coat it with a very reflective surface, then I "spin" it while I fire it. First the laser reflects, but even if enough energy gets to the absorption layer, how does it penetrate through the material? You would need gigawatts at the very least to have a physical force (since light particles have such little mass). Is it because even thermally resistive stuff burns at some temperature and the interface layer smokes off, no matter how thermally insulative?

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You don't file kinetic penetrator shells on parabolic trajectories since they don't have explosive payloads. They're near-direct fire weapons.

Your problem is you've invested all this effort into making a heavy, heat-proof shell, but how much explosive and how much range are you going to get from such a thing?

Could a laser system be effective against small arms/sniper fire?

I recall an article in wired from ~2005 which talked about a tracking system that could track all bullets flying in the air over a vast area. Couple this with a laser and could you shoot pistol/rifle/sniper fire out of the air?

They have the tracking system, it's called ShotSpotter. There are domestic and military versions.

As for defense, its all about heat over time. A 100kW delivered into a small, say 10mm spot. Is very difficult to effectively reflect away, even if your mirror reflects 99% of the light energy away you are still getting a kilowatt of energy dumped into your reflector.

As for shooting bullets out of the sky, that might be a bit tougher. It works for mortar shells because they have an explosive you can set off, but turning a lead bullet travelling along into a blob of lead travelling along, not very effective. However, there is a paper from the Army Ballistics Lab that discusses reducing the effectiveness of bullets by putting divots into them. Basically if you can deform a bullet in flight it will begin tumbling and likely hit further from where it was aimed than it would have if it had not become deformed.

Of course an unsophisticated adversary with RPGs isn't going to be buying 'laser proof' RPGs any time soon :-)

Shhh... Not supposed to talk about that.

No reflective coating is going to be 100% effective against a close in range laser. At some point the thermal energy is going to warp any coating and it will lose its effectiveness. This is more of a concern against longer range missiles and mortars that can afford to be coated enough that it becomes difficult to disable the projectile at the longer range particularly with atmospheric interference.

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