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What can counter Laser weapons?


WestAir

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Smoke would work on the ground, though blinding light in the visible spectrum would likely be an issue.

In space, ablative armor, chaff, or a bigger laser would probably be your best bet.

On the subject of nukes, they have a minimal shockwave in space and the EMP effects outside altitudes equivalent to low earth orbit are unknown. That said, they do cause EMPs and create areas contaminated by radiation at those altitudes.

Sub-orbital nuclear testing by both the U.S. and Russia during the Cold War has been documented to cause general mayhem with electronics, frying sensitive equipment including satellites. The most famous test with these effects is probably Starfish Prime

Wild stuff. I had no idea. Also this resulted in permanent artificial radiation belts in orbit!?

Some scary stuff really.

So what would happen to the radiation if a similar detonation occurred outside the Earth's magnetic field? Or very high in the Earth's magnetic field?

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Smoke would work fine in space, it is just a dispersal of microscopic particles that would have no problems being scattered in a microgravity environment.

Mirrors would in fact not work reliably.

The reason for this is a mirror only reflects a percentage of the energy to strike them, and the actual reflective layer is very thin.

If held in one spot long enough the mirror's reflective layer will overheat and burn out, allowing the laser to penetrate the mirror as if it was ordinary window glass.

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Just cover your ship in mirrors. +1 for easier hiding from enemies without sensors, too. Not to mention if you're about to board the ship and want to make sure you want to look good, the window will serve you well.

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Wild stuff. I had no idea. Also this resulted in permanent artificial radiation belts in orbit!?

Some scary stuff really.

So what would happen to the radiation if a similar detonation occurred outside the Earth's magnetic field? Or very high in the Earth's magnetic field?

Not permanent, they dispersed eventually.

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In essence, the point of a weapon is to dump enough energy into something so it breaks. Light is a horrible, horrible way to do that. The MIRACL laser can produce about 1 megawatt of beam power over 70 seconds giving it a total energy transfer of 70 megajoulle. A 10kg slug only needs to travel at:

v = sqrt ( 2 * E/m) = sqrt (2*70*10^6*10^-1) ~ 3.8km/s to contain the same energy. Not to mention that a slug is also excellent at delivering all that energy over various surface sizes. If you want to hit a large area you just fragment the slug a short time before impact, or you leave it intact to trash a small area.

All you need to ward off a laser is a large heatsink on the surface that can take some heating. That MIRACL laser on a full 70 sec duration outputs enough energy to boil about 200 liters of water (starting at room temperature). So if you are in a spaceship you just make the water tanks cover the hull. This is beneficial due to radiation shielding anyway. Then you just need to circulate the stuff and maybe vent some to lower the temperature and you're set vs lasers.

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I think one of the things that will complicate space warfare is that first strike is absolutely critical.

Let's say you're in a hypothetical space version of a coast guard cruiser stationed at Venus. You've got super sci-fi terawatt lasers that can poke a hole in most anything in a split second pulse (assuming it's not 3 light-seconds away still and actively random dodging with variable thrust; it's not like you can accurately predict where a dodging target will be 3 seconds from now...) You're also carrying kinetic kill missiles and multi-megaton nuclear missiles. You have an efficient fusion drive that can do 5 g's even with a full fuel load, and that's carrying enough fuel to burn for a solid 24 hours. There are colonies on the moon, mars, and in orbit around venus, and asteroid mining - but you and others like you are on station because there's also been some incidents of space piracy, and people need rescuing sometimes, and to keep the colonies from turning into lawless frontiers.

Something is seen boosting for earth from the asteroid belt; they tried to hide the burn by making it a long slow orbit that only burned when Earth was on the far side of the sun, but they didn't know you have automatic detection gear in orbit around Mars. According to your computers in 6 months' time it's going to pass near Venus; course projections say that another burn there would let it pass through Earth's vicinity at a high relative speed 4 months later.

Based on the rate of delta-V your detectors caught it was only able to burn at 2 g's; your coast guard cruiser can out-manuever it easily. You are launched on an orbit that will let you intercept them one month before they reach Venus, assuming they do no further burns. They don't; 5 months worth of your three-man crew playing cards and getting on each other's nerves later, it's time to intercept.

You start matching speeds while you're still a few light-seconds away and demand that they surrender, and get your first good long-range telescope views; It looks like a salvage job, two asteroid miner ships were welded together at some point. They've got a relatively weak NERVA engine putting out some radiation even at idle, must have used chemical boosters to do the initial burn, and no visible weapons, and they say "Thank god, yes, we surrender!" as soon as you ask them to over a fairly low power radio... looks like they may have been trying to make it back to be rescued.

Once you've matched orbits and are only a kilometer away and one of you is suited up to go over and inspect them using suit thrusters, the seam where two ships were joined pops open like it was being held together with explosive bolts, two 100 kiloton nukes pop out and detonate in a split second. the bulk of the miner ship was nothing but shielding to make the nukes undetectable against the NERVA's background radiation.

Your ship might pop some leaks from being superheated along one side, but it's not gonna matter; that much x-ray and neutron radiation has your crew almost instantly unconscious, and they die without ever waking from the coma. but you just saved some colony on the moon or in orbit around the earth from the same fate. It's the space equivalent of a check point stopping a car bomber before they can get to their intended target.

Small space engagements will go to whoever shoots first; You had that booby trap outgunned in every possible way, but they lulled you into letting them shoot first. if you'd opened fire on them from 10000 km away they could have set off those nukes and barely hurt you, due to inverse square law giving you a tiny fraction of the radiation you took at 1 km. It's going to make everyone trigger-happy whenever anything the least bit unusual happens, and the scenario I outlined above will mean you desperately need those coast guard equivalents to prevent direct kinetic-kill kamikazes against colonies and space stations (and then you'll have to be ready to shoot down your own coast guard if a crew goes rogue or one of those ships gets hijacked.)

Back to the original question - the best defense against a laser is to be a few light-seconds away and randomly altering your thrust. if you're 5 light-seconds away, 10 meters long and changing your speed by 0-30 meters per second at random, they'd have to just take a random guess where you'd be and have a lucky shot to take you out even with an impossibly strong laser, or blanket the whole potential spread of your positions with random pulses (so, as long as the laser is strong enough to still kill you even with only 1/1000th of its power hitting you, that could work.)

Edited by khyron42
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I think one of the things that will complicate space warfare is that first strike is absolutely critical.

Definitely. A lot of people seem to be stuck in a naval mindset when thinking of space engagements, but aerial warfare would be a better analogue. Nobody would have armour (although some lightweight countermeasures would be available), everybody would have long-range weapons powerful enough to kill any opponent. The main thing limiting the effectiveness of weapons would be the effectiveness of the sensor array/network they were coupled to.

First look would give you first shot, and that would give a high probability of a kill. Stealth, speed, ECM and networked sensors would be the decisive factors.

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Just cover your ship in mirrors. +1 for easier hiding from enemies without sensors, too. Not to mention if you're about to board the ship and want to make sure you want to look good, the window will serve you well.

Good point. Won't get hit with weapons if the "enemy" doesn't know you are there.

The subterfuge won't last long if the opposing forces are using RADAR or LIDAR, but it would buy you time to get away.

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Again, mirrors won't do jack against a weaponized laser; it'll just burn clean on through. Heatsinks won't really do jack against a weaponized laser, either, because it'll burn through the heatsink faster than the heatsink can disperse the energy. Your only real defenses are 1) don't be there when the laser arrives, 2) get behind something, 3) destroy the laser before it fires.

As for nukes, they're great space weapons, since you don't have to directly hit your target to mission-kill them. Even better are Casaba howitzers, for when you want to fire a beam of howling plasma death to ruin someone's day.

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Definitely. A lot of people seem to be stuck in a naval mindset when thinking of space engagements, but aerial warfare would be a better analogue. Nobody would have armour (although some lightweight countermeasures would be available), everybody would have long-range weapons powerful enough to kill any opponent. The main thing limiting the effectiveness of weapons would be the effectiveness of the sensor array/network they were coupled to.

First look would give you first shot, and that would give a high probability of a kill. Stealth, speed, ECM and networked sensors would be the decisive factors.

I think the reason people keep equating naval and space warfare is simply the nomenclature - spaceSHIP. And that's how we've always seen it pictured in sci-fi - as large naval vessels duelling one another in pitched battles using heavy gunnery (usually energy weapons, Star Wars being the best example - turbolaser turrets, anyone?).

I think space warfare will be all about who has the better stealth systems - getting the drop on your opponent SHOULD guarantee victory. If that fails, it'll likely devolve into WW2-style dogfighting at short range using maneuvering thrusters and small unguided kinetics. Whoever tears out the enemy's life support/control computer first wins. In point of fact, the WW2 air warfare analogy works on almost all levels - you're trying to get the drop on your enemy, and if that fails, kill him as quickly as possible using short maneuvers and unguided weapons, with little more than radar support from the ground (or your base station). The only armoured vehicles would be base stations/carrier ships, but they would also be poorly armed - unguided kinetics only really work in space if you can maneuver fast enough to track your enemy, and deflection-shoot far enough ahead to hit him. They would rely on swarms of fighters/drones to do the actual combat - finish off the enemy's fighters, then finish him with something a bit bigger (though I doubt anything nuclear - too risky for you, and not terribly effective without a medium for blast pressure to propagate through). Maybe just stick a retrorocket to him and shove him back down to the surface.

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AFAIK the only outright weapon sent into space wasn't a laser, but the 23mm autocannons on the Almaz stations.

Funny you mention that... the soviets did put cannons on the Almaz stations, but they also tried to launch a megawatt-class carbon dioxide laser system in 1987. https://en.wikipedia.org/wiki/Polyus_%28spacecraft%29

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I've seen enough references to stealth that I have to second the suggestion early on in this thread: read the projectrho website, in particular: http://www.projectrho.com/public_html/rocket/spacewardetect.php#id--There_Ain%27t_No_Stealth_In_Space

I deliberately pointed out the failure of stealth in my example story. Any active drive will get spotted if a sensor happens to be pointed its way at the right time, and between active and passive scanners ships will get found.

While that page is not god-given truth and he might be wrong about some things, he is very right about detectability. Any kind of high-energy engine shouts, to the whole solar system worth of passive sensors, "Hi, I have a weapons-grade engine on this thing, and by watching how long I leave it running for and how much I move during that time you know I'll be arriving at (destination) in (time frame)." You can always do a big burn with your heavy engine and then fine-tune with RCS to surprise people on when you'll be arriving by a few days, but they'll know you're coming. The more efficient drives burn even hotter and are more easily detected, and usually have to be left running for hours or days to make major orbit changes; but even the relatively weak space shuttle main engines could be detected from Pluto with current technology if you had sensors aimed at earth during the right 10 minutes. Any war zones is going to have automatic sensors to pick up on things like missiles heading their way from the other side of the solar system.

When you're not boosting, you still can get spotted. Power systems always eventually result in heat directly proportional to their power output, and you can't just throw away heat into the surrounding space via conduction or convection. Between power systems to keep your crew alive, power systems to operate your electronics, and power systems to operate your weaponry (if not chemical-rocket missiles, which goes back to detectable by seeing the exhaust) you have at least kilowatts of heat to radiate away, and more likely on a warship mega- or gigawatts. The closest you'll get to stealthing that is putting all your radiators on one side of the ship and trying to keep the ship between them and your enemy. And every sensor the enemy has scattered around the area.

For reference, the ISS has solar arrays capable of producing about 100 kW of power. (For comparison, the average house in the US has a power main capable of supplying 20-40 kW.) That's a tiny amount of heat to radiate away compared with what you'd need for basic non-missile weaponry, but it takes 168 square meters of active radiator surfaces to get rid of 70 kW of it (the other 30 uses passive radiator systems.) My math says those panels are likely running a bit warmer than human skin temperature, not very visible.

http://whatif.xkcd.com/35/ gives good examples of what happens when radiating larger amounts of waste heat from a small surface. you're either going to have giant, flimsy, very poorly stealthed heat radiators or small, extremely hot ones. Keep in mind that anything you do to hide your infrared signal just means that you have to run hotter somewhere on the ship to cool the parts you're trying to keep from showing up on passive IR sensors, too.

Now - if you want to go with magic drives that can do massive acceleration with no hot exhaust and no massive power usage, or magic stealth technologies that let you hide all your heat from IR sensors, you're welcome to move into science fantasy, but science doesn't seem to allow for that right now. Everyone will know some object, warm enough that it must be using x amount of power, is boosting towards them or is coasting along on an easily detected trajectory.

Your best bet would be to never launch the attack ship in the first place - instead, use an engine burn from your big bright engine to hide the missile launches. Not stealth, but subterfuge, will rule.

Edit: I got curious just how infrared detection of the current ISS would look, and found an image. Note the radiators shining like beacons. High-end amateur gear got this image from 400-600 km away, but could have at least seen a bright IR source moving against the background from hundreds of times further. http://www.awesky.com/Planets/Misc/International+Space+Station/

Edited by khyron42
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Bah. All you have to do for stealthy radiation is get your radiator running really hot (use a heat pump) and then set up reflectors to radiate heat away from anyone who's looking for you. It's not terribly energy-efficient, but if your goal is not to be detected, it's pretty straight forward.

Engines are trickier, since they generally leave hot exhaust, and that stuff will radiate in all directions. But ion drive can run with exhaust having really low effective temperature. So that'd be my first option if I was trying to sneak up on somebody in space.

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I hate to dig deeper into the weeds, but here I go. Point one about radiators: Let's look at three space warfare scenarios.

1. Two well-organized, well-funded opposing groups are attempting to attack one another within an otherwise orderly interplanetary society. Both groups have high-sensitivity fixed sensor platforms widely separated within the system.

2. A relatively weak organization is attempting to stealthily attack a well-organized, well-funded opposing group.

3. Two organizations are attempting to continue hostilities even though both sides have lost (or never had) robust detection capabilities.

Only in the third instance does "aim your radiators away from the enemy detectors" work, because in the first two they have detectors at Mars, the Moon, L4, L5, and LEO. and maybe L1 for good measure. By the time you're any closer than the Moon you're surrounded on all sides and have to somehow store all your excess heat to even pass as a non-warship, let alone attack.

Oh yeah, and I didn't even mention active detection. Current stealth planes play tricks on the radars they're hiding from, giving echos like a flock of birds or faulty equipment getting groundscatter. Not an option in space; a wider array of frequencies can be used and there's no random scatter to hide your echo in. While warships wouldn't want to use active scans, stationary platforms at most target planets would be blanketing the nearby area with active scans.

Regarding Ion drives, most scenarios for use of them on a military-grade vessel involve running extremely hot nuclear reactors to power them, making the IR detection problem that much worse - but yes, they are indeed the lowest-signal interplanetary drive option. You'd still want other high thrust options available for once you dropped stealth to start your attack, though.

Back on the original topic of laser weaponry - I know that most lasers use mirrors to bounce photons back and for to create the beam (thus hella power loss from every photon not going the right direction) and then other mirrors to aim them - given how much discussion has been made about mirror armor not being able to deflect the beam, I'm curious how the mirrors that create and aim these high-powered lasers don't melt as well. Does anyone know how it works? The only thing that came to mind was actively-cooled mirrors, but then we just use actively-cooled mirror armor to counter it?

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Only in the third instance does "aim your radiators away from the enemy detectors" work, because in the first two they have detectors at Mars, the Moon, L4, L5, and LEO. and maybe L1 for good measure. By the time you're any closer than the Moon you're surrounded on all sides and have to somehow store all your excess heat to even pass as a non-warship, let alone attack.

Heat is radiated away at a wavelength of less than 10 microns. With a 1m parabolic reflector I can send all my heat into the region of space about 2 arc seconds across. Are you telling me that I can't find 2 arc seconds without sensors in it? Are we talking about operating inside a Dyson sphere, or something?

Oh yeah, and I didn't even mention active detection. Current stealth planes play tricks on the radars they're hiding from, giving echos like a flock of birds or faulty equipment getting groundscatter. Not an option in space; a wider array of frequencies can be used and there's no random scatter to hide your echo in. While warships wouldn't want to use active scans, stationary platforms at most target planets would be blanketing the nearby area with active scans.

Active detection of a ship that isn't transponding? If this was possible, we wouldn't be having so much difficulty looking for asteroids that present danger to us. The only reason radar works so well here on Earth is that the distances are so laughably short. Say I have a ship 50m across 1 light minute away. I'm going to look for it using a dish or an array that's 100m across. If I wish to scan the sky in any reasonable amount of time, the signal should be focused on something like 1 minute of arc. I'm going to pump 100MW of power into transmitted signal.

So 1 light minute away, my signal is covering about 5,000 km. Or 105 the size of the ship. So the ship gets hit by 10 mW of radiation which it scatters around in all of the directions. 1 light minute back at the radar, I pick up 2x10-20W of reflected signal. This isn't even close to being distinguishable from cosmic background radiation.

Active detection in space is a pure fantasy. The only way you are going to see something is if it reflects sun light, obstructs a significant background source, or emits something you can pick up. In other words, passive methods only.

Back on the original topic of laser weaponry - I know that most lasers use mirrors to bounce photons back and for to create the beam (thus hella power loss from every photon not going the right direction) and then other mirrors to aim them - given how much discussion has been made about mirror armor not being able to deflect the beam, I'm curious how the mirrors that create and aim these high-powered lasers don't melt as well. Does anyone know how it works? The only thing that came to mind was actively-cooled mirrors, but then we just use actively-cooled mirror armor to counter it?

This is a question with two answers. First, in terms of IR and visible lasers. The idea there is that while mirrors can be used to reflect anything you throw at them, mirrors of sufficient quality will be heavy. If you are talking about something like missile defense, covering entire missile with high quality mirrors is just not practical. Best you can do is cover them with some foil, and sufficiently powerful laser will get through that. So an IR laser can be used to shoot these down.

If you are talking about something like ship-to-ship combat, things get more complicated. Here, covering ship with mirrors is much more plausible. At least from direction you expect attacks from. The solution is going into UV and soft X-Ray where mirrors just don't work. This, of course, brings up problem of building the actual laser. There are several solutions.

1. Forget the mirrors. Make lasing medium long enough to lase on a single pass.

2. Build a loop. Soft X-Ray can be reflected at small angles, making it possible to loop around in multiple reflections.

Both of these are going to result in something rather large. Probably not suitable for actual ship-to-ship, but could be used as orbital defense or something similar.

And then you can forego an actual laser. You don't really need a laser beam. Just any old beam with sufficient energy density will do. And if you need a really powerful beam of soft X-Ray or hard UV, the best way is to build an undulator. Of course, you do need a small particle accelerator to power it.

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Any kind of high-energy engine shouts, to the whole solar system worth of passive sensors

Indeed, again we get back to a good analogue with aerial warfare (and to a less extent ASW). Certain systems (main engines, radar, etc) will render you instantly visible to passive search. Modern combat aircraft use their radar as little as possible unless they actually want to be spotted (for deterrent value) or have already been spotted. Likewise a combat spacecraft isn't going to light up it's radar or engines unless it's ok with being seen.

When you're not boosting, you still can get spotted. Power systems always eventually result in heat directly proportional to their power output, and you can't just throw away heat into the surrounding space via conduction or convection. Between power systems to keep your crew alive, power systems to operate your electronics, and power systems to operate your weaponry (if not chemical-rocket missiles, which goes back to detectable by seeing the exhaust) you have at least kilowatts of heat to radiate away, and more likely on a warship mega- or gigawatts.

First of all, what possible reason would you have to put crew on a combat spacecraft? They'd just be a liability. Your ship would be bigger, heavily, slower, more vulnerable, less stealthy, require vastly more support and be able to keep station for a lot shorter time if you manned it. No combat spacecraft will ever be manned. Even if you were talking about combat somewhere beyond Earth's orbit you'd still be better off providing a human in the loop from a remote location that was within an acceptable control distance (eg: under 10 light seconds). Absolutely no need to have them riding in the actual combat vehicle pressing the trigger.

I don't think a small robotic combat spacecraft cruising with most systems powered down would present a large thermal signature. Spacecraft are inherently low power. One that had a low thermal signature included in the design from the start should have no problem being quite stealthy. I think this alone would rule out the idea of large "warship" type combat space vehicles. They'd just be too easy to find compared to small ones. FWIW naval combat on Earth has already gone this way. The advent of small, fast moving stealthy vehicles with powerful weapons (aircraft) has already forced warships to become as small as they practically can. That's why you don't get the big battleships any more, smaller ships are ton for ton more powerful.

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Vaild points all, though though the engineering challenges of keep the rest of your ship's hull sub-zero while heating that emitter to thousands of degrees are not exactly trivial. I can only hope to live for centuries or millennia, and see how the real-world arms race that always happens between concealment and detection play out in this new environment.

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I can only hope to live for centuries or millennia, and see how the real-world arms race that always happens between concealment and detection play out in this new environment.

To be honest I don't think you'll have to wait that long. Satellite reconnaissance and navigation both have immense strategic value. Currently we can knock down satellites from the ground, all it would take would be an innovation that rendered asat missiles ineffective and you'd probably see armed spacecraft in orbit pretty quickly.

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Seret,

My thoughts on your first reply are this: There is no hiding in space. Any space power is going to be watching everyone everywhere, they will always know where your going and generally what you are. Even doing a burn behind a planet won't help a warship once it comes back out behind the planet, due to vector changes. The best you can possibly do is disguise yourself as something your not, like a commercial vessel packed full of missiles or something.

Second reply: Unless you have human level AI, using drone combat ships wouldn't be so great for the whole fleet. They could easily jam your radio transmissions, and shoot off any laser receivers. You might be able to armor them, but it's still a major weakness. Not to mention what you would do if they split their fleet and went after your CnC ship.

Space is very cold, and I doubt you could cool down a nuclear reactor anyway. Plus, they would still know where you were going, and any major course changes would require you to light up. Spacecraft are low power, warships probably won't be. Lasers and railguns are very thirsty electricity wise, and I doubt batteries are going to hold them over when they are pumping out 100+ megawatts of power each second. As far as size goes, if you have checked out any of our modern warships, they are rapidly approaching the sizes of WW2 heavy cruisers. We are getting bigger again.

On topic: Lasers generate vast amounts of heat. ProjectRHO, Ken Burnside describes weapon lasers as blast furnaces that produce coherent light as a byproduct. Rick Robinson describes them as an observatory telescope with a jet engine at the eyepiece. Laser cannons are going to need seriously huge heat radiators. And don't forget that heat radiators really cannot be armored. Any serious laser cannons or batteries are going to generate vast amounts of waste heat, limiting you to firing only a certain number of times before you and your crew burn up. Even unmanned ships would have to stop at some point, electronics and base materials can still melt.

So, with that in mind, you can either armor yourself up and take a beating, waiting to get in range for missiles, kinetics, and or your own lasers. Most vessels might want to draw in their radiators when they can actually be shot up, to avoid overheating later on, so your limited to whatever your internal heatsinks are. So you can just saturate any point defense units with kinetics or missiles.

Another option is to counter the lasers themselves, with other lasers. If you shoot down the laser beam of the attacking ship, you can wreck their lasers. Same thing with point defense units. You could also target sensors and telescopes with lasers. A blind ship is a dead ship in space.

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Back on the original topic of laser weaponry - I know that most lasers use mirrors to bounce photons back and for to create the beam (thus hella power loss from every photon not going the right direction) and then other mirrors to aim them - given how much discussion has been made about mirror armor not being able to deflect the beam, I'm curious how the mirrors that create and aim these high-powered lasers don't melt as well. Does anyone know how it works? The only thing that came to mind was actively-cooled mirrors, but then we just use actively-cooled mirror armor to counter it?

I assume the beam intensity inside the laser is kept to a level that its mirrors can handle (and I imagine active cooling comes into play here). Once you project the beam, you can then focus it onto the target at a high-enough intensity that they can't defend against it.

Heat is radiated away at a wavelength of less than 10 microns. With a 1m parabolic reflector I can send all my heat into the region of space about 2 arc seconds across. Are you telling me that I can't find 2 arc seconds without sensors in it? Are we talking about operating inside a Dyson sphere, or something?

That's going to murder the efficiency of your radiators, and then you'll cook in your own waste heat. XD

Edited by qeveren
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