Thread: Space Combat - Lasers vs Reflective armor

Maybe a bit of an oddball topic around here but it just popped into my head and was wondering if you brainiacs know the answer. :-D

I saw a documentary about space combat. Certain weapons were addressed, like rail guns, asteroid projectiles and what not. The most efficient weapon to me seems to be lasers. Not only don't they need ammo (well not in the traditional sense) but they are also unavoidable since they move at the speed of light, so the target can never see it coming.

The question however is: How effective is reflective armor versus lasers?
Can a laser become more powerful than any material can reflect/withstand? Or will dedicated anti-laser material/armor always be more effective than the laser itself?

What is the most reflective material we know right now? I'm assuming that even when it's 99%, that 1% that will get through will heat up the material, and then it's just a matter of a more powerful laser till the material melts. Right..?

Can anyone shed some light on this issue? :wink:
The future of space combat: Lasers or not?

Personally, I'd use a laser that uses frequencies that can't be reflected so easily, such as x rays or gamma, and kill everyone inside. Then, simply board and steal the enemy ship.

Of course, the logical step to take in defense of this tactic would be to make the hull thick/dense enough to block out practically all gamma. Then it might be useful to have a back-up weapon, e.g. a laser, and, should they have reflective armour (which, by the way, would offer significant protection, as the majority of the light is reflected back), then it might also be useful to have another back-up weapon which can damage the mirrored hull sufficiently that your lasers become effective.

So, basically, in your scenario, it would be incredibly benefitial to have a range of weapons available.

Originally Posted by AjL

Maybe a bit of an oddball topic around here but it just popped into my head and was wondering if you brainiacs know the answer. :-D

I saw a documentary about space combat. Certain weapons were addressed, like rail guns, asteroid projectiles and what not. The most efficient weapon to me seems to be lasers. Not only don't they need ammo (well not in the traditional sense) but they are also unavoidable since they move at the speed of light, so the target can never see it coming.

The question however is: How effective is reflective armor versus lasers?
Can a laser become more powerful than any material can reflect/withstand? Or will dedicated anti-laser material/armor always be more effective than the laser itself?

What is the most reflective material we know right now? I'm assuming that even when it's 99%, that 1% that will get through will heat up the material, and then it's just a matter of a more powerful laser till the material melts. Right..?

Can anyone shed some light on this issue? :wink:
The future of space combat: Lasers or not?

Lasers are only effective against targets in which damage to a small area can be catastrophic. So they are effective as "eye poppers" agains the pilot of an aircraft, or against a pressurinzed rocket motor case IF they can be focused on one spot long enough to burn through. Spinning a rocket is an effective countermeasure. Goggles can effectively protect one's eyes.

Even a well-focused laser beam has some angular dispersion, and so the effective range of a laser is limited, even in space. The Air Force has experimented with laser weapons for anti-missile and anti-satellite defense, but the successful systems have used hit-to-kill kinetic energy warheads powered by rockets.

The only viable space warfare scenario at this time would be destruction of communication, and spy satellites. That would almost certainly involve ground-based rockets.

With current technology spacecraft are made as lght as possible (therefore ar not armored), and except for the satellites mentioned above have no military value, so are not targets. However, if two spacecraft for some bizarre reason were to engage in combat either could take out the other with almost anything, including a kid's slighshot, it they could hit the other guy, simply because closing velocities would probably be enormous.

Additionally, it's not true that lasers can't miss. At long enough ranges, light speed lag comes into effect, and as a laser isn't steerable, it's not that hard to dodge, at least most of the time.

Great answers so far guys. Thanks!
DrRocket, I probably should have been more detailed in that I'm talking about space battles in the distant future with enourmous more technological advances. Just think of a warship with a thousand fusion reactors on board or something.

I'm interested in what the limits are of the weapons/lasers vs the possible defence options. Of course we can't know what new technologies we discover but we can extrapolate from the limits we know that apply today.

Is the power of a laser limited or unlimited? Will the machine that makes the laser at a certain point have it's own limit (like material melting points) that means the laser can not possibly be increased any further? But we can stack multiple lasers meaning the power of a laserbeam can theoratically be unlimited?

Originally Posted by MagiMaster

Additionally, it's not true that lasers can't miss. At long enough ranges, light speed lag comes into effect, and as a laser isn't steerable, it's not that hard to dodge, at least most of the time.

But you can't dodge something you can't see coming in advance.

The only system I can think of that can prevent long range laser sniping is an automatic dodge pattern. Meaning the warship will always have to 'shake' through space. Of course this 'pattern' should be randomized or else it will be cracked and therefore be predicted.

Originally Posted by MagiMaster

it's not that hard to dodge, at least most of the time.

You can't dodge it unless you know where it's going to be, and you can't know that untill it hits you, because the light travels at c.

Originally Posted by AjL

Great answers so far guys. Thanks!
DrRocket, I probably should have been more detailed in that I'm talking about space battles in the distant future with enourmous more technological advances. Just think of a warship with a thousand fusion reactors on board or something.

I'm interested in what the limits are of the weapons/lasers vs the possible defence options. Of course we can't know what new technologies we discover but we can extrapolate from the limits we know that apply today.

Is the power of a laser limited or unlimited? Will the machine that makes the laser at a certain point have it's own limit (like material melting points) that means the laser can not possibly be increased any further? But we can stack multiple lasers meaning the power of a laserbeam can theoratically be unlimited?

Originally Posted by MagiMaster

Additionally, it's not true that lasers can't miss. At long enough ranges, light speed lag comes into effect, and as a laser isn't steerable, it's not that hard to dodge, at least most of the time.

But you can't dodge something you can't see coming in advance.

The only system I can think of that can prevent long range laser sniping is an automatic dodge pattern. Meaning the warship will always have to 'shake' through space. Of course this 'pattern' should be randomized or else it will be cracked and therefore be predicted.

Yes, lasers are limited in power. And there are lots of different kinds of lasers, based on very different technologies with very different limits. They all have dispersion as well, and therefore loose energy density with range, and it is energy density, not just energy that is important in their application as a weapon (or almost anything else). Lasers are not the obvious long range weapon that you seem to think them to be.

If I were going to hazard a guess, I would think that a neutron bomb delivered by a rocket would be more effective.

The other thing that has been complicated would be to download Windows to the computer of the enemy ship and wait for the computers to overload and crash.

@AjL, yeah, that's the basic idea. If you're zig-zagging enough, light speed lag will prevent them from accurately targetting you and they'll have to spread their lasers out more to increase their chance to hit, reducing the damage done in the process.

@drowsy turtle, Yes, at distances of over about 1 light-second, you can easily dodge lasers, since they can't aim at you because they don't know where you're going to be, or even where you really are. Just where you were a second ago. (Of course, you can start predicting paths, but then you can start making evasive maneuvers, etc.) Rather than me trying to explain it all, just go read all about space based laser combat here: http://www.projectrho.com/rocket/rocket3x1.html#laser.

Originally Posted by DrRocket

The Air Force has experimented with laser weapons for anti-missile and anti-satellite defense, but the successful systems have used hit-to-kill kinetic energy warheads powered by rockets.

The airforce has indeed destroyed ballistic missiles with airborn laser systems. Although there's a relatively narrow window to kill the missile, because they have to hit it after it's high enough that it's out of the thicker parts of the atmosphere (in order to prevent the atmosphere from interfering with the beam) but before it releases its warheads (which it does pretty soon after it reaches space).

Originally Posted by Scifor Refugee

Originally Posted by DrRocket

The Air Force has experimented with laser weapons for anti-missile and anti-satellite defense, but the successful systems have used hit-to-kill kinetic energy warheads powered by rockets.

The airforce has indeed destroyed ballistic missiles with airborn laser systems. Although there's a relatively narrow window to kill the missile, because they have to hit it after it's high enough that it's out of the thicker parts of the atmosphere (in order to prevent the atmosphere from interfering with the beam) but before it releases its warheads (which it does pretty soon after it reaches space).

I think your use of the plural is over-optimistic. One was destroyed several weeks ago.

http://www.boeing.com/defense-space/...B_overview.pdf

I don't know what the target missile was. That would be interesting to know. It is described as a short-range threat-representative ballistic missile, which to me is a contradiction in terms, launched from an at-sea mobile platform, which again limits the possibilities.

I personally rather skeptical about the practicality of this. The boost phase of an ICBM only lasts about 3 minutes (about one minute, give or take, per stage). To effectively hit the missile in the boost phase you have to be rather near the launch site. If that launch site is a silo well inland that will be hard to do. If it is near the coast, that will be easier but will take some strong defense of the 747 platform (or other cargo plane) and knowledge of the likelihood of an enemy launch.

If, as you say, the engagement needs to take place at altitude that would basically require engagement during either second or third stage burn, so that eliminates the first minute. That is indeed a small window. It is also a fast target at that point.

Originally Posted by AjL

The question however is: How effective is reflective armor versus lasers?
Can a laser become more powerful than any material can reflect/withstand? Or will dedicated anti-laser material/armor always be more effective than the laser itself?

What is the most reflective material we know right now? I'm assuming that even when it's 99%, that 1% that will get through will heat up the material, and then it's just a matter of a more powerful laser till the material melts. Right..?

Can anyone shed some light on this issue? :wink:
The future of space combat: Lasers or not?

Reflectivity has to do with several factors, but before we get there, if visible or non-visible electromagnetic wave energy weapons are available and used, then so will electromagnetic shields. A strong enough field can bend EM radiation so it doesn't strike the 99% effective hull plating. It will at least mitigate the energy. If we assume the shields are also 99% effective, then you end up with a pretty small amount of energy left.

Beam me up Scotty...

Originally Posted by Wild Cobra

Reflectivity has to do with several factors, but before we get there, if visible or non-visible electromagnetic wave energy weapons are available and used, then so will electromagnetic shields. A strong enough field can bend EM radiation so it doesn't strike the 99% effective hull plating. It will at least mitigate the energy. If we assume the shields are also 99% effective, then you end up with a pretty small amount of energy left.

Beam me up Scotty...

Shielding is used now, and it is in general pretty effective. The key to an effective shield is to pay attention to the construction of the penetrations of the shield that are required to construct it. Leaky doors and cable penetrations can make an otherwise good shield ineffective, particularly at high frequency. But with tight penetrations and appropriate filters on cabling, shielding against unwanted fields is not difficult. The EMP that you sometimes hear about in the popular press, is not difficult to handle.

Light is very high frequency and shielding at those frequencies is another kettle of fish entirely -- the usual technique of encasing the item to be protected in a conductive blanket just is not applicable. X-ray shielding requires high atomic number materials, and attention to some specialized issues. An x-ray laser might make a formidable weapon, but the (conceptual) designs that I have heard about are powered by a nuclear explosion, and therefore are not amenable to situations requiring multiple shots or long duration beams.

What would be really hard to handle would be an incoming body of any appreciable mass as the closing velocities that are typical between two spacecraft. A rock moving at several km/s would penetrate a lot of things. I would not want to be in a tank that was hit by a baseball-sized rock those speeds, and it would be rather difficult to armor a spacecraft to the level that tanks are armored.

Originally Posted by drowsy turtle

Personally, I'd use a laser that uses frequencies that can't be reflected so easily, such as x rays or gamma, and kill everyone inside. Then, simply board and steal the enemy ship.

Of course, the logical step to take in defense of this tactic would be to make the hull thick/dense enough to block out practically all gamma. Then it might be useful to have a back-up weapon, e.g. a laser, and, should they have reflective armour (which, by the way, would offer significant protection, as the majority of the light is reflected back), then it might also be useful to have another back-up weapon which can damage the mirrored hull sufficiently that your lasers become effective.

So, basically, in your scenario, it would be incredibly benefitial to have a range of weapons available.

well said i would not mind playing a strategy game like that that takes the though out steps like that lol that would be quite fun

From the same page comes Rick Robinson's First Law of Space Combat: "An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT," as well as the unit of measurement the Rick, which is a multiplier on its mass to TNT conversion (which scales with the square of velocity). It mentions somewhere on the page of simply dumping the kitty litter out the airlock at relativistic velocities.

Edit: Oh, that was on the next page where it mentions that the previous formula is only accurate at non-relativistic velocities.

Originally Posted by MagiMaster

@AjL, yeah, that's the basic idea. If you're zig-zagging enough, light speed lag will prevent them from accurately targetting you and they'll have to spread their lasers out more to increase their chance to hit, reducing the damage done in the process.

@drowsy turtle, Yes, at distances of over about 1 light-second, you can easily dodge lasers, since they can't aim at you because they don't know where you're going to be, or even where you really are. Just where you were a second ago. (Of course, you can start predicting paths, but then you can start making evasive maneuvers, etc.) Rather than me trying to explain it all, just go read all about space based laser combat here: http://www.projectrho.com/rocket/rocket3x1.html#laser.

Yeah. The odds of somebody randomly managing to target you if you're moving around unpredictably are about the same as a blind person managing to target you if you were sitting still.

Hey mate, take a look at this video about the Israeli Tactical High Energy Laser

http://www.youtube.com/watch?v=nVxZ9...eature=related

Israel is using a very expensive, but effective laser defense system against ICBM and even small rockets. I hope you will like it.

Regards

Originally Posted by jgabase

Hey mate, take a look at this video about the Israeli Tactical High Energy Laser

http://www.youtube.com/watch?v=nVxZ9...eature=related

Israel is using a very expensive, but effective laser defense system against ICBM and even small rockets. I hope you will like it.

Regards

Apparently someone forgot to tell Israel that they are using this system.

http://www.janes.com/articles/Janes-...ed-States.html

Originally Posted by jgabase

Hey mate, take a look at this video about the Israeli Tactical High Energy Laser

http://www.youtube.com/watch?v=nVxZ9...eature=related

Israel is using a very expensive, but effective laser defense system against ICBM and even small rockets. I hope you will like it.

Regards

From watching the clip (gotta love the music :-P ) it looks like it only works at short range. They focused mostly on small rockets, artillery shells, and mortar rounds. Still very impressive, but I doubt the cost/benefit ratio is good enough that they would seriously consider deploying one.

If you put one of those close to an actual fire fight, you run the risk the enemy might manage to destroy it. Plus, it looks like it has one fundamental vulnerability: it can be overwhelmed by a large enough number of simultaneous attacks. They got up to 3 mortar rounds at once, but do you think they could manage 4 or 5?

I've come across a 'Sci Fi Science' episode that covers some of the questions I asked about.

It's called: Physics of the impossible: How to blow up a planet.
Here's a short youtube video: http://www.youtube.com/watch?v=BneZVc1Fe1M

Michio Kaku clearly states that the power of a laser beam is theoratically unlimited. Which is not what some of you here claim.

You can download the episode here for those interested:

http://torrent.zoink.it/Sci.Fi.Scien....720p.AC3.HDTV.[MVGroup.org].torrent

Originally Posted by AjL

I've come across a 'Sci Fi Science' episode that covers some of the questions I asked about.

It's called: Physics of the impossible: How to blow up a planet.
Here's a short youtube video: http://www.youtube.com/watch?v=BneZVc1Fe1M

Michio Kaku clearly states that the power of a laser beam is theoratically unlimited. Which is not what some of you here claim.

Err, I don't remember anyone claiming otherwise. It's just that theoretically unlimited and practically unlimited are two very different things and there are many factors to consider besides power.

Originally Posted by AjL

I've come across a 'Sci Fi Science' episode that covers some of the questions I asked about.

It's called: Physics of the impossible: How to blow up a planet.
Here's a short youtube video: http://www.youtube.com/watch?v=BneZVc1Fe1M

Michio Kaku clearly states that the power of a laser beam is theoratically unlimited. Which is not what some of you here claim.

Michio Kaku likes to sell books and make sensational statements.

Being theoretically unlimited is not much of a constraint. All you have to do is, theoretically, make it bigger.

There are all sorts of practical engineering problems with making very large lasers.

Originally Posted by MagiMaster

It's just that theoretically unlimited and practically unlimited are two very different things

I asked a theoretical question. We don't have space combat right now, so obviously current practical limits are meaningless.

Current limits are meaningless, but we can make an educated guess at what the limits will be in the future.

Originally Posted by MagiMaster

Current limits are meaningless, but we can make an educated guess at what the limits will be in the future.

Yes, based on what we know of laser construction and what limits current lasers. So current limits are not so meaningless after all -- they are the basis for understanding future limits.

Unlike the computer world, many technologies are limited by material properties. Lots of very advanced design concepts have been put forward, many some time ago, and await future development of materials to make them feasible. In such cases limits are pretty well understood.

Are lasers limited to the visible spectrum, or could a focused gamma ray beam be considered a "laser weapon"?

Originally Posted by GiantEvil

Are lasers limited to the visible spectrum, or could a focused gamma ray beam be considered a "laser weapon"?

No, lasers are not limited to the visible spectrum. Infrared lasers are fairly common. X-ray lasers have been contemplaed, but only one tested with inconclusive results.

A focused beam is not necessarily a laser beam -- it may lack phase coherence.

I don't know of anything that would, in principle. preclude a gamma ray laser. Bulding one given current technology is another issue.

Well, since it's the future. I'm gonna put gamma lasers on my X-wing. Now, are gamma ray's still just photons, and charge neutral? Or could electromagnetic shielding be used to repell the gamma laser?

Originally Posted by GiantEvil

Well, since it's the future. I'm gonna put gamma lasers on my X-wing. Now, are gamma ray's still just photons, and charge neutral? Or could electromagnetic shielding be used to repell the gamma laser?

afaik photons are the medium and electromagnetic shielding would be useless.

Originally Posted by GiantEvil

Well, since it's the future. I'm gonna put gamma lasers on my X-wing. Now, are gamma ray's still just photons, and charge neutral? Or could electromagnetic shielding be used to repell the gamma laser?

Gamma rays are very high energy photons or, equivalently, very short wavelength electromagnetic waves.

So, depending on what you mean, electromagnetic shielding would shield against gamma rays. But what is usually meant by "electromagnetic shielding" is some sort of conductive material which is effective against much longer wavelengths. X-rays for instance, go through metals of moderate thickness and gamma rays penetrate more easily than do x-rays.

Since your interest in this case is science fiction, with emphasis on the fiction, you will probably need to violate some principles of physics in order to get a good story anyway.

I had gamma ray's, and cosmic ray's a little mixed. I meant a generated electromagnetic field, which wouldn't have effect's on photons, which are charge neutral. Now the idea of a material that absorbs and converts gamma length EM would be a feasible thing in the far future. So I think laser,s are not a useful combat weapon, at least not against shielded opponents.

Anything that absorbs energy gets hotter. If it gets hot enough or hot fast enough it'll melt or break.

For a sci-fi story, the best advice I ever heard is that you should limit yourself to as few miracles as possible. A material that would absorb weapons-grade gamma ray lasers well enough to make those lasers ineffective would be close to one miracle, I think.

Originally Posted by MagiMaster

Anything that absorbs energy gets hotter. If it gets hot enough or hot fast enough it'll melt or break.

For a sci-fi story, the best advice I ever heard is that you should limit yourself to as few miracles as possible. A material that would absorb weapons-grade gamma ray lasers well enough to make those lasers ineffective would be close to one miracle, I think.

Any sort of shield would not absorb the gamma rays since as you say that energy has to go somewhere. In fact the reason that a gamma ray laser would be an effective weapon is because the energy would be absorbed and thereby do damage. An effective shield would pretty much have to be reflective. The problem is finding something that would reflect gamma rays.

Well then, I want a gamma ray weapon on my spacefighter. I wasn't planning on writing any science fiction. But it sound's like a good idea. Thank's.

It's highly likely that a gamma ray laser would be too big to fit on a fighter. The site I linked to earlier had a lot of reasons why fighters would probably be impractical in general.

Hmmm. It seems that energy weapons are impractical even in the future. And vectoring a craft in a vacuum presents a whole range of challenges. How would a craft be vectored in a vacuum without using thrust and massive amounts of fuel?

Originally Posted by MagiMaster

It's highly likely that a gamma ray laser would be too big to fit on a fighter. The site I linked to earlier had a lot of reasons why fighters would probably be impractical in general.

For starts, there is noboby to fight. yet.

Originally Posted by GiantEvil

Hmmm. It seems that energy weapons are impractical even in the future. And vectoring a craft in a vacuum presents a whole range of challenges. How would a craft be vectored in a vacuum without using thrust and massive amounts of fuel?

You can't maneuver an airplane in the atmosphere without using thrust and massive amounts of fuel either. Fuel consumption for modern high-performance aircraft is pretty high.

Originally Posted by DrRocket

Originally Posted by MagiMaster

It's highly likely that a gamma ray laser would be too big to fit on a fighter. The site I linked to earlier had a lot of reasons why fighters would probably be impractical in general.

For starts, there is noboby to fight. yet.

Just to clarify, I meant fighter in the "small, one-person craft" sense and impractical within a scenario in which some kind of combat spacecraft is called for.