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Comment by ttraub | Hacker News Reader

Eventually, the Navy will be doing more than "dazzling" and "blinding" enemy optics. The Tactical High Energy Laser project[1] demonstrated that incoming mortars and Katyushas could be shot down. It seems unlikely that this technology was abandoned, albeit it's probably much bulkier and more expensive than the RHEL.

1. https://en.m.wikipedia.org/wiki/Tactical_High_Energy_Laser

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Couldn't you just start putting a reflective coating on your mortar rounds?

You need a coating that won’t burn off even if it reflects 99.9% of the beam, and rugged enough to survive being field handled.

Those don’t exist, it will be scratched off well before it’s even used.

Not to mention the cost of such material and the cost loss of scrapping or converting existing inventory won’t make it a viable solution.

The majority of mortars fired at US troops today were likely made in the 60’s and 70’s.

You are better off with simply using mortars in large volleys to saturate the system or simply attacking unprotected targets.

Most rounds fired at US troops can’t penetrate their body armor either it doesn’t stop them from trying not did it force them to switch to armor defeating projectiles.

They just are less effective and hope they’ll either land a lucky shot to the face or lower limbs or a debilitating shot to unprotected areas such as the arms and shoulders.

You don't necessarily need the round to survive. If it's reflecting 99.9% of a destructive laser beam, then that poses a risk of that beam bouncing back at the ship and causing damage. It might be a minuscule risk in isolation, but dozens or hundreds of rounds with retroreflectors designed specifically to bounce lasers back whence they came could wreak havoc on all sorts of fragile sensors (including the squishy ones in sailors' eye sockets).

That would make this an illegal weapon system according to the Geneva Convention. Weapons that are intended to injure rather than kill are prohibited.

That’s not the right reading of the convention. The rule is against unnecessary suffering and even excessive lethality. For example hollow point rounds are more effective at killing but solid rounds have the same disabling effect and give the recipient a chance of survival. Hollow point bullets are banned by the convention.

Its also illegal to use excessive calibre bullets against human targets. Even though such large projectiles are much more likely to kill.

The exact phrasing is:

“It is prohibited to employ weapons, projectiles and material and methods of warfare of a nature to cause superfluous injury or unnecessary suffering.”

https://ihl-databases.icrc.org/customary-ihl/eng/docs/v2_rul...

A sizable subset of America's past, present, and future adversaries in war have never ratified any portion the Geneva Convention.

Yes, all the sailors on deck managing the sails, climbing the mast and so on. Wait, is this the 19th century still?

"Sailor" is still commonly used (even in official contexts) to describe personnel on modern naval vessels.

Sailors aren't on deck during a battle any more, so are unlikely to be suffering laser reflections (!) from tiny projectiles thousands of yards away.

Most warships (of the non-submersible variety) have windows, last I checked. In fairness, though, that does make it easier to mitigate that issue.

"Those don’t exist, it will be scratched off well before it’s even used"

Not if there is some sort casing around that is discarded once the projectile is in flight

Don't even need the casing to be discarded. If the casing gets hit by the laser and gets vaporized, that's fine. The reflective layer underneath then becomes visible.

Except the mirror would be coated with vapour deposits - ruining it.

Conceivably, the vaporized material could shield the projectile.

This may be a dumb question, but surely the escalation is “shoot lasers too” not “try to protect my shots with mirrors”?

So if it were me trying to bypass this system rather than trying to make increasingly complex and expensive projectiles to try and defeat the system I'd just make increasingly cheap projectiles to make it easier to spray the target with them and eventually get some through. The article even mentions that a laser can only point at a single target at a time. To your point if you also target the defensive system you're bound to sooner or later damage the system with one you managed to get through. Seems to me that this system is easily defeated with tactics.

It would be kind of hard to fire a laser over obstacles like a mortar. Unless, perhaps, you send up a attach a mirror to a balloon and fly it over the battlefield so you can bounce your laser. :)

The same goes for Katyushas (rockets). Most of them have a range that's well over the horizon, so it would be difficult to fill the same use case with a laser.

It is almost impossible to create a coating that can reflect high-power laser pulses. Even if the coating reflects 99.9% of the light, it absorbs 0.1% of the light. When we are talking about laser pulses strong enough to melt steel projectiles, the absorbed light will quickly destroy the coating and then the projectile is vulnerable again. Also, the coating has to survive the launch/firing of the projectile without getting hazed.

I was using pulse lasers in the lab and traditional silver mirrors would get damaged by pulse energies over 100mJ. They would just turn black. The solution was to use interference mirrors for the exact wavelengths of the beam to reflect, which wouldn't have any absorption and such could survive large pulse energies. But those mirrors are limited to the exact wavelength at precise angles.

You need to find out the wavelength of the laser. Once you know the wavelength you can design a reflective shell around the projectile. Certain ceramics with proper coating are really good in scattering energy and are extremely resistant to heat.

> You need to find out the wavelength of the laser. Once you know the wavelength you can design a reflective shell around the projectile. Certain ceramics with proper coating are really good in scattering energy and are extremely resistant to heat.

That sounds impractical. Either you're trying to coat shells on demand in wartime, or stocking extra quantities targeted to this or that wavelength. If you're already stocking extra ammunition, it sounds better to just overwhelm the defensive system with more shells, like another commenter suggested.

If you're going to design something new, maybe something more like a MIRV launcher that fires three shells in the time it currently takes to fire one.

It's likely that your opponent is fielding only a limited number of laser projectile countermeasure systems, and also likely that they are related and only using a limited number of wavelengths.

But yeah, just throw a bunch of things and swamp their targeting systems.

Had the same question, the answer is yes BUT you would have to accomplish the following:

- reflect every part of the spectrum that the laser can produce (idk if military lasers operate in the visible part of the spectrum)

- keep the coating clean enough throughout flight to maintain reflectivity

- meet the same requirements as the current coating which probably includes aerodynamics, heat resistance, etc.

Idk if such a material exists, but I'm sure every country building lasers is also working on the defensive side as well.

The coating on it would have to reflect the entire EM spectrum. Or whatever frequency a LASER device weapon would use.

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