How to protect your ship against TW-range lasers?

Question

Let's say you live in a war-torn universe, with sub-FTL intertellar travel, big ships, big railguns and big ship-mounted railguns. At some point, people (read engineers) realized that fast moving red-hot lumps of [basically anything] are pretty easy to detect and dodge, if not fired at point blank range (let's assume this to be less that 10s of travel time to target) or anything capable of changing it's trajectory, really. (That means you can still use your shiny gun as a fire and forget bombardment device against, say, planets!)

For more somewhat up-to-date info on this universe, feel free to check the following:

• Railgun launched nuclear warhead
• Force field
• Multi staged railgun thingie

Time to use some lasers. They can output at least 50TW continuously, but can be pulsed if needs be. We assume that since we have capacitor and cooling (read a big buffer) we can "safely" fire those for at least a minute before catastrophic failure, and no need to worry about energy consumption (unless you need to throw a star in your fusion reactor to make it work)

Now I want some armor to protect my ships against those mean photons the enemy vessel is throwing my way. I already have a Whipple Shield to help survive space rocks and maybe hostile projectiles, but I can't figure out if that would help against lasers. Actually I have to idea how to protect against this kind of weapon (and correct me if I'm wrong, but a mirror sounds like a Stupid Idea™)

So, What is the best way to protect a ship against lasers? I'm looking for a suitable material, or a particular construction that's good at not castastrophically failing when fired upon with lasers, for a realtively light wheight (strapping 30m of [insert material here] onto the ship won't do for obvious reasons)

As previous questions, tech level is several centuries ahead of current tech, extrapolating known technology to the limits of physics is okay, and feel free to ask for precisions/clarifications if you need any.

Not a dupe of how effective is a free electron laser in space combat because I ask about ways to protect against lasers, and not about the effectiveness of said lasers (still not a dupe).

Answer 1

By not being there

By far the best way to protect yourself from any direct line of sight firing weapon is to not be in line of sight. Options range from being behind a planet, asteroid or other large body, to not even being in the same solar system. This is where things like artillery, missiles and other "over the horizon" weapons systems come into play. All you have to do is make sure there's a horizon.

Mass and passive heat sinking

Lasers work by heating a small area to failure. Sufficient mass and heat distribution around your vessel prevents the weapon from being directly effective. Of course in the long term if you don't have some way to vent this heat your ship turns into an oven and cooks everyone inside, but hopefully you've won the battle before that happens.

Active heat distribution

If your ship is rotating, for gravity or just because you think it's cool, then the laser won't be hitting a point but a line. Ideally a line moving fast enough that the laser doesn't do much more than clean and polish the surface as it passes over. You could also actively fluid cool the surface, again distributing the heat around the vessel. Eventually this suffers the same fate as passive heat distribution though, slow baked crew.

Active fluid cooling systems could also force the heat to a specific heat sink location, this works until the heat sink exceeds tolerances and fails, at which point you're on you way to the oven again.

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Avoid, Evade, Disperse, Deflect, Absorb, probably in that order of preference.

Answer 2

mirror sounds like a Stupid Idea

Why?

You have an incoming energy flow due to the lasers being fired, then your only options are:

• Absorb it: this what would normally happen, turning your ships into a cloud of energized plasma
• Reflect it: make your ship really shiny, so that all the light is reflected back.

Mind that, even though you might have a reflectivity of 99.99%, you would be left with 0.001% of a TW, which is still a tens of MW.

At this point you need to be sure that you have pretty good cooling of your mirrors, if you want to tell your grandchildren some war stories.

Oh, if you have the technology to bend space-time like a large mass would do, you could locally distort the space time and bend the light away from your ship.

In this way there would be no interaction between the laser and your ship, preventing your from dealing with the heat management issues.

You could even turn the laser around by 180 degrees, firing back to your enemies. That would be a nice trick to play!

Answer 3

According to Atomic Rockets, just keep your distance: http://www.projectrho.com/public_html/rocket/spacegunconvent.php

Lasers need a focal point, and when speaking of space distances lasers have trouble keeping the beam coherent. You need increasingly large focussing arrays for larger lasers and longer distances. So staying at distance reduces the amount of energy per meter and will eventually have most of the laser miss. Its one of the reasons why railguns and the like are considered the long-range options and lasers CIWS against missiles and the like. But considering your laser isnt cooking the entire ship after a minute of firing you might also want these lasers to remain accurate.

Mirrors are reflective, but too much energy will burn the mirror and reduce its reflectiveness and subsequently burn it faster. Mirrored surfaces would decrease the range where a laser is dangerous though.

Theres only two other ways I can think off to protect the ship. First is "simple" ablative layers that bleed off the heat by transforming to different states of matter, and using particular metamaterials that do this effectively. Not sure what kind of materials those could be. The second is extreme heat conduction+cooling and radiating it away. Considering you can fire a multi-TW laser no problem for a minute your heat management is legendarily good. Use that to spread out and lose heat and reduce the effects on the armor. Possibly you could use a Graphene layer (can get a bit hotter than the surface of our Sun, great heat conduction, lightweight and strong enough for armor) for this and have an ablative layer underneath which you keep pusing up against the Graphene so it never reaches critical heat and shows no signs of heat-damage for ships to focus on. Ofcourse there would need to be some channels to get the ablated material out of the ship or the heat will keep rising anyway.

Answer 4

Stop the lazer before the ship by dumping dust where you expect the laser to be!

10TW heating your ship is bad, but 10 TW heating a cloud of dust (even if just meters away from your ship) can be safely ignored.

This of course means you have to survive the initial strike for a couple of seconds or so until you dumped enough dust in the direction of the laser. (Or you just preemtively cloud the area between you and the enemy EDIT: surviving the initial blast is pretty easy, thanks to nzaman's Ablative layer, which itself could already diffuse dust when heated, making the response immediately)

By having your lasers/sensors at the end of the ship (where you don't dump dust) you can still use your weaponry and detection, even if it means a small unprotected part of your ship.

Since the dust-cloud is pretty limited in size (and if the dust is magnetic you can dispel it easily) it won't mess with your sensors etc too much, and the energy requirement is close to zero.

Of course this would have consequences for prolonged or large battles where eventually both fleets are surrounded by an uncontrollable amount of dust, but that would be strategically acceptable imo.

[Bonus of this method that just occured to me: if you already have magnetic dust on board, this setup can also double as a measure to limit the enemy's sensor effectiveness (eg. make your ship appear massively bigger for the enemy or conceal where your ship is precisely, meaning that their non-laser weapons can only target your general location (= the dust cloud) instead of the ship itself, making them a little less reliable]

Answer 5

If you are hit by a 50 TW laser, it's like being hit by a Hiroshima-sized bomb, once a second or so. Dodge until you can get a planet or large asteroid between you and it.

On the other hand, if the attacker's laser is 50% efficient, he has a Hiroshima-sized bomb going off once a second inside his ship. Use whatever cooling system the enemy uses, only on the outside of your ship instead of the inside.

*Edited after PcMan pointed out a $10^3$ error.

Answer 6

Clouds

Lasers aren't great through atmosphere. Armour your ship with big tanks of water** - when punctured, a massive cloud envelops your ship and the laser is diffused over a harmless area.

** There may be a better liquid than water for this, but hey, water is also useful for drinking.

Answer 7

The Glass Ship

Nanomaterials are awesome! Build your ship entirely out of materials transparent to the wavelength of the TW-range lasers.

Works best for missions where you don't need to accommodate cargo or a carbon-based crew.

Answer 8

Deflect it, in time honoured tradition.
Multiple layers of shielding with slightly different refractive index gradually bend the light till it is discharged away from the ship's body.
The problem here is twofold: first the heat generated by the light will warp the semitransparent layers, changing both the shape of the surface and the refractive index of the material. Also of note is that a hit perpendicular to the surface goes straight through. Secondly, the refractive index changes with the frequency of the incident light, so all the enemy really have to do is change the colour of their laser.
Just to be safe, you'd want an ablative layer underneath the refractive layers just to make sure nothing gets through in under a minute.

Answer 9

Many distant layers of whatever

No matter what you use, it'll inevitably evaporate. You may use mirrors hoping to reflect 99% of the energy, but they'll evaporate immediately. Even with 99.99% reflection rate, you'll be left with tens of MW, which is still too much to cool.

So let's let the shield evaporate. The vapors will absorb some energy and let some energy through. This is where the next layer comes into play. It must not be too close to the first layer so it doesn't get destroyed immediately by the heat of the vapors from the first layer. It'll be hit by a fraction of the laser energy and evaporate. The game continues.

For the last layer, you may want to use a cooled mirror, as it gets hit only by the $n$ times weakened beam and can survive. Or maybe not as two or three additional layers may be cheaper and equally effective.

So my design would be something like hundreds of tiny lightweight shields. Maybe aluminium foil layers spaced one meter from the next layer. They take quite some space (which is plentiful in space, isn't it?), but they're cheap and lightweight.

Answer 10

Assuming you have to close the distance and cannot just out range:

Extremely sloped armor can help tremendously by spreading the effective spot size. Add cooling and you can get closer. If the laser wavelength is extremely short, however, this becomes difficult as hard enough x-rays require grazing incidences. Also, if your very sloped armor is a cone, you can rotate to make it a lot easier to spread the heat out. This also only works against an individual laser source, or a very tight cluster.

Damage the laser's optics if possible. A rain of sand from missiles, mass driver launched canisters or Macrons from electrostatic accelerators can damage mirrors and lenses.

Damage the radiators of whatever is shooting the laser at you assuming they're not buried on the surface of a celestial body. Lasers and their power sources require cooling that should be a very easy to spot and target.

Answer 11

Being far away

It is not possible to get a perfectly focused laser beam. Even the most advanced laser technology will have extremely minor deviations, multiplied over the vast distances of space combat. At close rangers, this un-focusing of the beams can be ignored, but if the distance between the ships is sufficient, the beam may be fully disintegrated.

Verdict: Depends on how good the laser is.

Being really far away

If your ships are sufficiently far apart (i.e. a few light-hours, a stone's throw by cosmic standards), then it'll be very hard to hit a ship, especially if its size is not on the same order of magnitude as that of a large planet.

Assuming your ships are just one light-hour apart, it will take an hour for the laser to hit. And on the enemy ship, while they are targeting the victim, the "picture" of the ship (so to speak) will be an hour old, and by making minuscule (but sporadic, hard-to-predict) adjustments in course, it will make hitting the target quite hard.

Although it is hard to avoid something coming at you at the speed of light, it's harder to hit something really really far away that's moving around, especially when your beam's direction cannot be changed after firing. What might work, however, is intentionally defocusing your beam based on the range of the ship such that you have a large beam with lower energy. As stated in this answer, a 1 MW laser can melt 2kg of steel per second. You have 50 TW, orders of magnitude more than the aformentioned steel-melting laser. You can spread those 50 TW into a larger beam, decreasing your required accuracy a lot.

Verdict: Depends on how far away you are and how advanced targeting technologies are.

Mirrors

Mirrors are good at reflecting light. That's a bad thing, because if your weapon is reflected, it doesn't cause damage. The good thing is that mirrors are not 100% effective, and even assuming the enemy has their entire hull coated in 99% reflective material, 1% of 50 TW is still a hefty load (capable of causing quite a lot of damage). In addition, by tuning the laser to other frequencies, the mirrors will be rendered useless.

Verdict: Only works if we're dealing with visible lasers/what your mirror reflects.

What might actually work

The laser needs to be focused. That is its undoing: By installing lenses to de-focus the laser, the energy of the beam can be quickly dissipated. While the lens must be positioned exactly where the laser beam strikes (which is nearly impossible to determine beforehand), coupled with other defense systems (like the mirrors), enough time can be bought to get the lens in place. The only issue is that the lens must be correctly aligned and capable of dissipating the beam enough that the ship isn't damaged.

Spin around

Lasers work by heating a single region to the point of failure. To counter this, you can spin the ship, meaning that there is very little time for each spot to actually heat up and fail before the ship turns around. The faster you spin, the less the damage is.

Clouds

Answer 12

Fusion/Fission

As a first layer, use the 50TW to power the fusion of elements that are heavier than iron, or power the fission of elements that are lighter than iron. That would be the most efficient way to use mass to absorb the energy. As a back-of-the-envelope calculation, I see that a randomly chosen large atomic weapon produced about 63000 TJ. 63000 TJ / 50 TW means that it would take about 20 minutes to absorb enough energy to produce the atomic weapon. So it's certainly in the right ballpark.

For fusion, you'd need to keep the mass constrained in position to prevent it from just scattering and merely serving as ablative shielding. That seems pretty hard, and requires heavy elements anyway, so it seems like it would be a lot easier to use fission. Many of the lighter elements don't absorb much light normally, so perhaps spray out a lot of carbon?

Ironically, rather than reducing the intensity by defocusing the beam, it might be better to focus it on an even smaller point to properly trigger the fission. This also suggests a curious characteristic: higher power levels might be easier to defend against; the nastiest shot would be one that goes below the threshold of fission.

Get Out Of The Way

That's really, really handwavy, so I'll throw in an alternative suggestion: let's say there really isn't any way to block or deflect that much energy. Then the next natural solution would be to not be where it is striking. It would be pretty hard to outrace a laser, so don't try: as soon as a laser hit is detected, reconfigure the innards of your ship to move everything out of the way of the beam, allowing it to pass through causing no further damage. If there are enough self-healing partitions throughout the ship, they can automatically seal up and prevent the loss of air, water, and unhappy crew members.

Pin Cushion Approach

...though if you follow that line of reasoning to its natural conclusion, then it suggests that perhaps the best way to defend against a laser attack is: don't. Rather than a bunch of high-tech machinery that moves parts of your ship out of the way, just let the laser do it. Construct your ship out of material that burns through as quickly and cleanly as possible, without dumping a lot of explosive heat to nearby mass. Let them poke a few holes in you but keep fighting back. Massive redundancy would be helpful.

Combo

Though come to think of it, a combination of the last two approaches might work best. The big threat would not be the pinpoint holes, it would be where the laser moves and cuts a line due to the relative motion of your ship and the attacking ship. So you'd want to quickly detect the trajectory of that line and move things ahead of it out of the way. It could even be a reflex-like action; sensors nearby sensitive things would slam them out of the way in one direction or another; the only smarts would be that you'd wait for the 2nd detector to trigger to know what line the laser is moving in.

Answer 13

You could equip the ship with sheets of tiny dielectric laser mirrors with high reflectivity indexes mounted on the sides of the ship to deflect the photons (think sequins on a dress). I presume the technology for the fabrication of these has advanced enough to make them small and light enough, similar to sequins sown onto clothing. If the mirror can handle the inside of the laser, it should handle what comes out the business end as well. If you're worried about heat damage, stack the sheets to turn it into an ablative defense. If passive is not enough, vibrate the sheets to constantly change the position of the mirrors. In theory, if the mirrors are small enough, the pressure of the photons on the mirror might even be sufficient for passive deflection.

Answer 14

SCS

Solar Panels do a "good enough" job of turning photons into electricity to be used at an industrial level on earth. Assuming we have improvements in solar capability by the time star wars happens we can capture a lot of the excess power from the lasers. This leads to the development of SCS or Solar Cell Shielding.

This excess power can be used return fire at the enemy at a fraction of the cost or could be used to power expensive defense (read electronic heat sink). Whatever you use the power for, whoever fires the first shot is at the disadvantage in this fight.

The next big improvement is changing the wavelength for the laser being fired, which could mean decreased electric conversions for the solar cell shielding resulting in faster critical levels of heat. Making adjustable shielding is then key to accompany the adjustable photon frequencies being sent at ships.

This adjustable shielding would then make good invisibility cloaks outside of combat as they could absorb or reflect background electromagnetic radiation based on it's surroundings.

Answer 15

In addition to building reflective layers and dumping particle screens (water, dust, whatever), if possible keep your ship rotating about an axis perpendicular to the beam. Damage is nonlinearly dependent on dwell time, so by rotating you reduce the duty cycle on any given spot. (technique is actually proposed for current-year Terran missiles to defend against DEWs)

Answer 16

Use a lot of very small retroreflectors on your hull.

A retroreflector is a special type of construct that enables incoming light to be sent back to the overall direction of the source with minimal scaterring.

If your enemy fires a laser into your direction and it hits a retroreflector, he is firing back into his own laser cannon - he will do some damage to you in the process, sure, but in the end his weapons will be taken out of comission in a very explosive way almost at the same instant they fire it.

This has the advantage of instant retribution - hopefully, his lasers won't be able to fire long enough to damage your hull but will fire long enough to destroy themselves. Lasers are delicate things, and probably won't withstand the extra energy being pumped back at them in this sudden manner.

Answer 17

Along with my answer here: In a future where lasers are the weapon of choice, why not wear mirrors?, you will want to consider the wavelength of the lasers, as different materials react to different wavelengths differently.

Mirrors can be reflective to just visible light, just UV, or probably a variety of other ranges of light. The material of the reflective portion of a mirror is also critical. When using my 80 watt CO2 laser cutter, I can't etch the reflective side of a mirror, but I can etch the back of the mirror to remove the reflective material, but only for some types of mirrors.

At the bottom of my linked answer, I did some testing of potential "armor" materials and posted the video to YouTube: https://youtu.be/WkOQffTjsC8.

I would suggest Googling "laser safe materials", then depending on what type of laser you're facing, don't use those materials. Often times, a list of laser safe materials will list materials that aren't safe, too. This unsafe list might also tell you why it's unsafe. For a CO2 laser, metals are unsafe up to a certain wattage of laser due to reflection. PVC, on the other hand, is unsafe because it releases chlorine gas at any wattage able to vaporize the material.

You might even have different laser systems depending on the material of the opponent ship. This could have the effect of your captain asking a science officer what the material makeup of the ship is before firing on them.

The makerspace I use the laser cutter at has their own list: http://wiki.qccolab.com/index.php?title=LC6090#Approved_Materials. This is specific to CO2 laser cutters. If you're using solid state or other lasers, you'll need different lists.

In my linked answer, I also have a list for different protection methods that could be adapted to "space lasers of TW" power. It includes all kind of safety goggles, windows, and other documentation.

http://www.lasersafetyindustries.com/Selecting_Laser_Safety_Glasses_Goggles_and_Protection_s/55.htm

As far as mass and heat sinks are concerned, industrial lasers of the KW range can cut 1" (25.4mm) thick steel and thicker with relative ease. Rotating, changing direction, or anything so "the laser won't be hitting a point but a line" will effectively be cutting your hull, or even your ship, into multiple pieces. A few punctures are much easier to deal with than gouges or a massive amount of punctures. Just ask the Titanic crew and designer.

Solar panels only work with certain waves lengths, only convert a fraction of the light to electricity, and have a maximum amount of light they can deal with.

https://en.wikipedia.org/wiki/Solar_cell_efficiency

As far as the "glass ship" is concerned, what about the organics within? They'll get the full blast of the laser instead of your ship, so will any wiring and anything else that can't be made transparent.

Using water as clouds, coolant, or other materials for the same all take mass that a ship would have to accelerate, which there's a point at which this becomes detrimental to your space fight. What is more important, maneuverability or attempting to deal with the laser directly?

A "space laser" would attempt to be a perfectly collimated beam, so that it would have the same effect at 1 AU as it is at 0.1 AU, as well as 10 AU. Current technology doesn't allow that to happen, but future tech could bring that much closer to ideal. This means that simple distance may not be an option.

https://en.wikipedia.org/wiki/Collimated_light

As for "not be there", it's pretty hard to avoid something that travels at the speed of light. You have no way to detect a laser in time, then move out of it's way unless they miss and you see dust vaporizing in it's path or you have precognition. Even if this happens, the sniper/bombardier/targeting specialist/computer/whatever will be able to re-aim the laser faster than your ship can get out of the way.

Getting behind a planet is a decent idea, but how long is it going to take to do that? And is your opponent going to be following you there? How will you fire your laser back?

What might work is a lens to de-focus the laser. A laser cutter works with a collimated beam of laser, then passes it through a lens to focus it at the surface of the material you are trying to cut. If you do the reverse, it'll spread the laser light to be much less effective over a much larger area. You can move a "small" lens of 12" (304.8mm) (or whatever size you need) and it's framework faster than you can a 1 million ton spaceship.

In a laser cutter, you have to clean the lens on occasion. I've accidentally put the lens in backwards, and then it has next to no cutting power. Even the collimated beam has more cutting power than the light going "backwards" through the focusing lens.

Also, a lens that bends the light to a different angle, like a prism, would help, if you can get it to bend far enough to avoid your hull entirely. Something like fiber optic cable, at a massively enlarged scale, might work. Optic cable has a minimum bending radius, but if you keep that in mind, you could shoot the laser right back, without using mirrors.

http://www.fiber-optic-transceiver-module.com/is-bend-radius-really-a-concern.html

As a reminder, this question has a "science-based" tag, not "hard-science", so please remember this when making comments. I do not pretend to have all the answers, just the ones I wrote down. Unfortunately, with all the answers I wrote down, it would be pretty easy to think I am pretending to have all the answers. ;-)

Answer 18

It's possible to cancel out light waves using other waves 180 degrees out of phase. How about a defensive laser or light turret that calibrates to match incoming laser fire with 180 degree phase difference to cancel out the attack? It wouldn't be perfect and would take a moment to calibrate, which adds a bit of drama and means lasers would still be dangerous.

Answer 19

I think we should consider refractive meta materials, these are entirely manmade materials that refract light around the object without absorption, current designs include similar materials like a teflon substrate with ceramic cylinders, but this can only be designed to defend against one frequency at a time. In the future we may have a material that could refract all or most frequencies.

Answer 20

Jinking, Fairy Dust and Plasma Mirrors

Terawatt lasers requires presence of mind, but even this cannot beat the absence of body. Never be whenever the shooter is aiming at. You do this by taking care never to come too close to potential threat sources, and never following a straight line. Granted, this means you're spending a lot of reaction mass. On the other hand, the ship could be equipped with a secondary tethered ballast ship, and travel in sync with that. By rotating around a common center of gravity and paying out and reeling in at random the connecting tether, you can achieve efficient repositioning and save something on artificial gravity.

Releasing small amounts of fairy dust whenever the local density of cosmic dust is not sufficient allows to easily and safely detect laser beams through Tyndall refraction (those beams that don't hit; those that hit are self-detecting).

Finally, the surface of the ship could be covered with a layer of low-temperature melting metal (gallium or Wood's metal or...). When heated, the metal melts and forms a highly reflective surface; it also vaporizes, creating a local plasma shield that disrupts the incoming beam.

For better performances you can add external electrodes and create a plasma mirror around the ship; this would be ruinously expensive unless you get energy for free, but if you do, it can be made thick enough and dense enough to reflect even higher-powered lasers. Actually, plasma mirrors are being studied for that very purpose - to contain the energies required to ignite nuclear fusion in frozen fuel pellets (10¹⁸ W is one million terawatt).

Answer 21

As noted. there are many problems lasers should have, that said:

Reflective / Refractive Ice

It does not need to be water made. It should have high reflection. It is cheap and can be used for many other problems. As an additional benefit, when the laser hit, it will create gas that will further absorb/distort the laser and hide you.

You might want to have multiple layers for different wavelengths / a way to adjust depending on the wavelength used.

As an additional benefit, your ship would end up looking like a comet when hit ;)

Edit based on comments:

No counter-measure is perfect, any medium glass, nano or what have you would absorb some energy and as a result of the process, the layers of ice/metal/??? reflective material will become vapour. Before that, it will have reflected an amount of energy that has to do with how fast it will deteriorate. This vapour will be standing in the way. As you write, no mirror is 100% effective, and even if it was, it would have to be kept completely dust free. So the thinking is lets sacrifice quality and go for quantity... After some (micro? mili? nano? seconds, the first layer of ice will be peeled in a massive explosion consuming lots of energy. In the milli seconds scale, chunks of ice would be lunched. Long before any of that, more energy will heat the material - think going to plasma form. Also part of the energy will not be absorbed going deeper, part of it also reflected, though a lot absorbed. As opposed to a closed container, most of the force and gasses will be allowed to escape) It is therefore important to have some really massive layer. Good think that you used a cheap material... Often the army will use sandbags to stop bullets, it is not because it is the most effective (though it is pretty effective) but because it can be cheap and easy to deploy and even (re)build on the spot / fixed after the explosions and dealing with casualties etc... You can even trim down your armour before very long trips and enlarge it when you arrive. A laser that big probably is more like what an RPG is to a bullet, so you need a pretty big sandbag :)