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Comment by ChuckMcM | Hacker News Reader

I've been following the laser programs for a long time. It always seems they and the rail gun projects are 'any time now' sorts of technologies when presented by the contractor and 'maybe in a couple of decades' when talked about by the generals.

But its very true that having a working 100kW laser would provide troops with basic immunity from overhead threats, and smart projectiles would provide the ability to engage enemies in bunkers, making pretty much every aspect of 'conventional' warfare moot. And making everyone who can afford it, invulnerable to insurgent attack.

That leaves killing civilians as a proxy, which is the biggest irony of all high tech weaponry, when people want to attack and can't hit the troops, there are always the shopkeepers.

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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?

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?

Shhh... Not supposed to talk about that.

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 :-)

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.

How many targets could these hit at once? I imagine it will take a significantly non-zero length of time to hit and heat each shell with the laser, so to get past the lasers you need to know the average airtime of your shells, the number of lasers, and the amount of time it takes to kill each shell.

I mean, that would dramatically change warfare, but I don't think it is making anything moot.

This has been the single largest problem with the program to date, how often you can fire and how quickly you can acquire a target. Early tests with chemical lasers were basically one shot every 10 to 15 minutes. These lasers are better than that, but they still have duty cycle limits which makes it possible to just overwhelm them.

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