What can counter Laser weapons? MKII

[rasheed]

Since the last thread died due to guys arguing about Einstein and that stuff. I decided to make another.

How to counter a Laser?

I think that we can make a material that has a very high melting point.

[jwenting]

you would still have the heat build up in your structure, damaging everything else. So you need something to disperse the incoming energy away from your vehicle body, which likely means ablative armour.

And you'd need ablative armour that's tuned to react to the frequency profile of the laser it's exposed to, which with tunable lasers is next to impossible (and of course if there's multiple different laser systems out there you're out of luck too).

Added disadvantage is that ablative armour is only good to stop a very few spots (same flaw as explosive reactive armour that's currently used against shaped charge warheads).

And if applied to an air vehicle, the ablation would change the aerodynamic properties of the vehicle, and probably its radar signature as well.

[Seret]

How to counter a Laser?

I think it would help to define some conditions. Are you talking about a laser in space or on Earth? What sort of a laser? How powerful?

[rdfox]

The way I'd do it is counter it with a laser, using the same destructive interference technique as noise-cancelling headphones use.

Or, alternatively, you could counter it with a bigger laser. Or a really, REALLY fast missile. Or anything else that lets you destroy the other guy before the heat buildup from his laser destroys you.

[bias12]

There are specially designed mirrors that can reflect powerful lasers. One of these could be used to dissipate a laser weapon harmlessly into the atmosphere. You could conceivably cover an entire vehicle in an angular, mirrored armour. I'm thinking the aesthetics of the F117 nighthawk, but instead of black radar reflective coating - laser mirrors.

[jwenting]

There are specially designed mirrors that can reflect powerful lasers. One of these could be used to dissipate a laser weapon harmlessly into the atmosphere. You could conceivably cover an entire vehicle in an angular, mirrored armour. I'm thinking the aesthetics of the F117 nighthawk, but instead of black radar reflective coating - laser mirrors.

uh, no. A mirror only reflects a single very narrow band of frequencies. Counter to that is to use multiple lasers in different parts of the spectrum, or a single laser that can be tuned while firing over a range of frequencies.

First is extremely simple to do, second a bit harder but can be managed already.

So mirrors are useless.

[bias12]

uh, no. A mirror only reflects a single very narrow band of frequencies. Counter to that is to use multiple lasers in different parts of the spectrum, or a single laser that can be tuned while firing over a range of frequencies.

First is extremely simple to do, second a bit harder but can be managed already.

So mirrors are useless.

Broadband laser mirrors have been available for some time, covering 90+% of the spectrum from near UV to near infrared. Plus these are commercially available, any dedicated broadband laser armour would surely be able to squeeze that even further. Mirror armour would still be susceptible to frequencies outside of their protective range though so I see your point.

What would be the difficulties in an adaptive laser system? What might the power requirement implications be for a multiple laser system?

I would think the weight and fragility of the mirror armour might make it ineffectual anyway, even small deformations of the surface would render it useless! Still if a broadband mirror could be made light and strong, it might make the effort of frequency shift or multiple lasers no long worth the results.

[randomness5555]

Maybe a hollow armour made of glass and filled with water? The glass would shatter but the water would vaporise and block the rest of the laser? (Actually, maybe not water. Maybe just gravel or something that would flow out but be thick and opaque enough to stop the beam) Still, this would only work once unless sectioned up.

[Seret]

Any laser countermeasure would have to not reduce the vehicles overall survivability to be viable. So anything which made the vehicle easier to detect or more vulnerable to kinetic energy weapons is a bad idea. Personally I don't think armour is the way to go if we're talking about space vehicles, they just don't have the weight budget for it. ECM, countermeasures, and stealth would be more effective. Lasers would need extremely accurate targeting, disrupting that would be more sensible than attempting to neutralise the beam. If you're being hit by the beam you've already lost.

The best countermeasure is of course to shoot first.

[SpaceGremlin]

Speed. You prevent the laser from focusing on one spot of your defenses for too long (assuming we're talking about a realistic laser and not some extremely high energy pulse like a Star Wars turbolaser).

[jwenting]

Broadband laser mirrors have been available for some time, covering 90+% of the spectrum from near UV to near infrared.

that's called glass...

And that doesn't cover the entire band you'd need to cover by far, which includes everything from millimeter wave to hard gamma rays.

[BlackBicycle]

How to counter a Laser?

Any semi-decent mirror will do.

[Seret]

Speed. You prevent the laser from focusing on one spot of your defenses for too long (assuming we're talking about a realistic laser and not some extremely high energy pulse like a Star Wars turbolaser).

At long engagement ranges even very high speed won't translate into a lot of radial movement at the firer's end. You'd need to be jinking, which probably isn't an option for a spacecraft. I think you can guarantee that you'll have pretty high relative motion in most orbital engagements, so their targeting would be designed to track a moving target over several seconds of lasing.

Tumbling or spinning might help, as it would spread the energy across the whole vehicle. Still, it's likely that a laser could get a mission kill by damaging sensitive gear like optics and PV arrays without doing any structural damage.

I still think you can't go past the sledgehammer vs butterfly of a KE weapon in space. Lasers are too complicated and not really powerful enough.

[Seret]

Any semi-decent mirror will do.

Even without the weight problem, there are a lot of spacecraft components you couldn't mirror, such as optics and PV arrays.

[andrewas]

Any semi-decent mirror will do.

Only if the enemy cooperate and fire lasers at frequencies your mirror is effective against. In reality, its more likely they'll fire multiple lasers at you, ensuring any mirror will be ineffective against one of them.

[Kryten]

Any semi-decent mirror will do.

No mirror is perfect, and one doesn't have to absorb terribly large amounts of energy to stop working as one.

[BlackBicycle]

I appreciate the lot of answers countering my simple mirror idea. Do tell me though, how come laser weapons aren't widespread now? Powerful lasers have been around for a while. If there wasn't an easy counter, they would be in use now, no? Yes, in space warfare speed (or rather, sharp changes of the vector) is the key. See, I watch Discovery too... How about other possible spheres of military application? There is some easy counter. IMHO, it is exactly that - reflective surfaces.

[TimMartland]

A big-ass mirror.

[sal_vager]

Do tell me though, how come laser weapons aren't widespread now?

Probably for the same reason we don't have widespread electric cars (not counting hybrids here), the technology to power the lasers is still pants, unless you have a large immobile bank of capacitors handy or a gas turbine powered alternator you're out of luck as far as laser weapons go.

Battery powered laser guns are still a long way off.

[Soda Popinski]

I appreciate the lot of answers countering my simple mirror idea. Do tell me though, how come laser weapons aren't widespread now? Powerful lasers have been around for a while. If there wasn't an easy counter, they would be in use now, no? Yes, in space warfare speed (or rather, sharp changes of the vector) is the key. See, I watch Discovery too... How about other possible spheres of military application? There is some easy counter. IMHO, it is exactly that - reflective surfaces.

We're not conducting war in space. Within the atmosphere, you get a lot of attenuation of the laser. There are some lasers mounted on Humvees the military has been experimenting with. Some of them to temporarily / permanently blind enemy soldiers on a battlefield. I do recall some talk of using a directed energy weapon on the Airforce version of the F-35 some years ago - as it had a lot of extra horsepower, since it doesn't sport the vertical lift fan required in the Marine version, or the heavy structure of the Naval version (for carrier landings).

But I figure the reason we don't field laser weapons is because we don't have to. They're expensive to develop, pretty big and bulky for regular infantry use, and unnecessary for the type of wars America is fighting now (urban, not on the plains of Europe, and definitely not space based).

[KASASpace]

Okay, let's please not have a billion people prick apart my posts, now.

How about something along the lines of solar sails?

Not a solar sail per se, but something that works on the same principle.

[andrewas]

The problem is energy density. A weapons laser is designed to deposit as much energy as possible into as small an area as possible. A solar sail is essentially a big mirror, one intended for propulsion has to be fragile in order to be light enough to be useful. Since there's no such thing as a perfect mirror, a solar sail will quickly heat up to the point of being destroyed. A modification for defensive purposes can only delay the inevitable, again, if you're being hit by a laser you're picking up energy, and while a defensive mirror can be much more robust than a solar sail, there are limits to how high a temperature it can withstand and how quickly you can cool it. Mirrors can only make you harder to destroy with a laser, they cannot make you invulnerable. So, is that enough? Depends on the specifics, but lasers can always be made more powerful, mirrors can only improve up to a point, this is an arms race the laser will win in the end.

Also, mirrors only work on parts of the spectrum, if the enemy can't simply burn through your mirror, they can always fire a laser on a frequency you are vulnerable to. A common silvered glass mirror works on visible light, but is black to light below 300mm so a high ultraviolet laser will punch right through it. A mirror effective against UV lasers will fail against optical or IR lasers. And, if the tech exists, the enemy may fire x-ray or even gamma lasers at you, and there's no mirror against those.

[KASASpace]

The problem is energy density. A weapons laser is designed to deposit as much energy as possible into as small an area as possible. A solar sail is essentially a big mirror, one intended for propulsion has to be fragile in order to be light enough to be useful. Since there's no such thing as a perfect mirror, a solar sail will quickly heat up to the point of being destroyed. A modification for defensive purposes can only delay the inevitable, again, if you're being hit by a laser you're picking up energy, and while a defensive mirror can be much more robust than a solar sail, there are limits to how high a temperature it can withstand and how quickly you can cool it. Mirrors can only make you harder to destroy with a laser, they cannot make you invulnerable. So, is that enough? Depends on the specifics, but lasers can always be made more powerful, mirrors can only improve up to a point, this is an arms race the laser will win in the end.

Also, mirrors only work on parts of the spectrum, if the enemy can't simply burn through your mirror, they can always fire a laser on a frequency you are vulnerable to. A common silvered glass mirror works on visible light, but is black to light below 300mm so a high ultraviolet laser will punch right through it. A mirror effective against UV lasers will fail against optical or IR lasers. And, if the tech exists, the enemy may fire x-ray or even gamma lasers at you, and there's no mirror against those.

Well I mentioned them because of the fact that they can actually use lasers to be propelled. It's an ultra-thin mirror, so the light-pressure (it exists!) is used.

[sjwt]

Well I mentioned them because of the fact that they can actually use lasers to be propelled. It's an ultra-thin mirror, so the light-pressure (it exists!) is used.

Indeed, but at Stella distances for the laser, with extremely low energy per cm^2

[KASASpace]

Indeed, but at Stella distances for the laser, with extremely low energy per cm^2

Yes, but the sun is powerful, and is used for Solar Sails.........

Lasers are just extremely focused, less erratic.