The Practicality of various futuristic weapons.

[thanto_]

Thanto: 10 MW xray FEL spot size 5mm has a temperature of nearly 60,000 kelvin.

Thanks for playing! Bye bye now.

Sorry, but that's not how transfer of thermal energy works. 10MW is 10MJ/s. That is, the laser is dumping 10MJ per second of thermal energy on a substance. The actual change in temperature is determined by the specific heat capacity (also known simply as "specific heat") of the substance - more Joules of heat means higher temperature, but specific heat varies greatly by substance. And them you have to consider thermal conductivity - while the laser may be pointing at a 5mm spot, how much of the heat directed at that spot gets transmitted to the surrounding substance? How much is radiated? A number of Watts of heat doesn't just magically give you a temperature regardless of your target. Also, 10MW could provide 10J of heat of you run for 1µs, which would raise the temperature of a 5mm radius circle 1mm deep by ~60K (assuming my calculations are right).


In this case, LI-900 is made of silica glass, also known as fused quartz or clear fused silica. We can make estimations based on that, I suppose, though I believe that some properties may be significantly changed, like the thermal conductivity (see the image from the original TPS article where the man safely handles a cube at someting like 1260C). We know the specific heat of this substance is 45.3 J/(mol·K) (compared to 4.228 for water). We also know the thermal conductivity is 1.3 W/(m·K).

[Noctis]

Also, its not my mistake if people connect two phrases that I didn't intend to have connected.

Yes it is. That's either bad communication (which can be fixed), or a lack of thought actually poured into what you're writing (i.e. you're not being self-critical). Remember: We're not psychic. We don't know what you're trying to say. Clarity of thought is something we appreciate, as it makes it easier for us to address the content of your argument, rather than your silliness.

How much more seperate could I have made the phrases? It was an entirely different paragraph, spaced twice down, making absolutely no reference to space or anything like it. In fact, only in the first paragraph did I even mention space, the second one was about how nano-bots would need supplies, with no mention of their environment. So overall I had three tiny little, sometimes one sentence, paragraphs that talked about reasons why nanobots can't work and somehow you connect the first paragraph to the last sentence and jump to conclusions.

I'll remember to use monosyllabic words and nice clear sentences next time. Excuse my blunt anger, but I have the flu and I'm not in a good mood.

[Talhydras]

Normandy:
Thermal conductivity is incredibly important to what you're saying (that when a laser hits a ship with a glass layer, apparently the entire hull gets heated evenly because magical gnomes move all that heat before any damage occurs). Like you said, it determines heat transfer from matter to matter; like heat transfer from the matter getting bathed in photons to the matter right next to it that's just chilling.

I don't really know how to divorce you of the notion that high conductivity materials will spread heat around the ship fast enough to protect it from drilling; think of the bloody space shuttle disasters. One thermal tile gets punctured by debris on the Columbia and it's all over. Let me quote the equation I used in my first post in this thread to try and convince you.

Beam power at the target = Beam power at aperture / (pi * ( range * tan (theta/2))^2). Theta is the divergence angle, simply 1.22 * wavelength / Radius of the lens. Assuming a 1M radius lens, theta = 1.22 * 1.4E-11 = 1.708E-11 radians.

Beam power at target = 10 MW / (pi * (1 light second * tan (1.708E-11/2))^2) = 485.6 gigawatts per square meter. Re your tanning booth comment, sunlight is 0.0014 W/m^2. That would make the spot of this laser 346 trillion times brighter than the sun.

In order to convince you that I didn't just make that shit up: Beam radius at target = 0.61 * distance to target * wavelength / lens radius; 0.61 * 1 light second * 0.014 nanometers / 1m = 2.5 and change mm. (2.5mm)^2 (the size of the spot our power is distributed over) / (0.5 m)^2 (the size of our emitting lens that distributes the power) * 486 GW (an irresponsible amount of energy = 12ish megawatts, or our starting intensity.

Now, since we only had 10 MW of power to start with we haven't magically increased our power so we're not going to actually dump 485.6 gigawatts onto a square meter of target. We're just gonna take a teeny weensy bit of the target and, even if it is made out of unobtanium, wreck it. In ten nanoseconds, 5000 joules/m^2 are exerted on that spot. There is no 5mm circle of material that can wick away heat fast enough to survive that intensity, let alone a beam 5 or 10 times more intense. While total force doesn't exceed 10 megajoules, the amount of force experienced by the tiny area of target material is extreme. A meter deep hole drilled by this weapon is only about 20 cubic centimeters of volume; LI-900 is 144.2 kg/m^3. Making a meter deep hole in the stuff constitutes vaporizing or ejecting a whole 3 grams of it. With 10 million joules per second available, I imagine that's readily possible. Since the whole point of LI-900 is to not conduct reentry heat to the aluminum structure of the space shuttle, I'm not sure how much the impact heat of the laser would get shared around before the impact point vaporized. It's a small point (5mm dia); low density armor simply hasn't got enough stuff in contact to conduct the heat away fast enough.

Thanto:
I'm not sure you'd want thermal armor made out of material that when heated to over a thousand degrees can be safely handled by a man. The oven that brick was heated in was brought slowly to a controlled temperature. Armoring tiles will be brought rapidly to the blackbody temperature, which in the case of a 10 MW laser on a teeny weensy spot is 54750 kelvin. High conductivity armor, IE armor that burned the fuck out of that man's hand while he was holding it, would wick away that heat to underlying structures (kinda bad) as well as adjacent regions of armor (very good, essentially spreading the target area) before damage was inflicted in the impact point. I'd be very interested to run the numbers for LI-900; if you can find heat of fusion and heat of vaporization that'd do the trick; I don't know how important the stuff on viscosity required actually is.

[Sponge]

@Aralonia and anyone else railing me on astronomy stuff.
I'll be the first to admit that I'm no astronomer (just did, in fact). This has led me to make a couple of conclusions that were based on misconceptions, and for that, I apologize. At the same time, it certainly didn't help that Talhydras's initial comment which prompted this whole astronomy discussion was technically not relevant to my argument in the first place. I can't fault him for that, as I've only just realized it myself, but there is a clear logical disconnect here. In reality, observing a distant galaxy is terribly different than shooting down a missile. Observation in the first sense is a rather, for lack of a better word, inexact procedure. I don't mean to imply that the angles of viewing are somehow less exact than those required for downing a missile, but rather that, when you are viewing a galaxy, you're viewing it as it was millions if not billions of years ago. You're not trying to estimate its current location and shoot it with a laser; you're trying to look at it, and you'll have to be satisfied with what it looked like in years past. With a missile, we have an entirely different case. Observing it may be somewhat trivial, but that's not the hard part. The hard part is trying to shoot something with what is essentially a 5mm projectile when, at any given time, you don't know where your target is. Missiles are moving fast and they're highly maneuverable. With a relatively minimal fuel expenditure, they can adjust their course just enough to give you no clue where they are after each shot you fire. It's like shooting into a swarm of gnats with a BB gun. If you hit one, it's by pure dumb luck, not because of some sophisticated targeting maneuver. Granted, the closer they get the better your odds, but if you've got a few hundred missiles coming at you, and their paths are growing increasingly erratic, you're in for a rough ride. Conventional point defense mechanisms (along the lines of railguns or small-ish chemical ordinances) are likely going to be required. Taking potshots with a laser is an inefficient use of energy.

@Talhydras
Have you seen this yet?: http://www.wyrdysm.com/phpBB2/viewtopic ... 895#100895
I have found something that calls into question the validity of Luke Campbell's claims, and it is Luke Campbell himself. I do not know whether or not your 5mm spot size assumption is at all a fair number. Do you have a link for any of Campbell's more recent writings on the subject of death rays? Preferably something explaining this "diffraction" method? I'm having a tough time navigating his site, and I'm betting you've read more of his work than I have.
EDIT: Didn't see your most recent post (I left this sitting for quite some time). Might edit later if I get time.

@Anyone who thinks nanobots are a good idea
lololololololo

Terribly impractical. First up, how? How do you develop something so small, and somehow outfit it with the ability to damage a ship's armor? I could see maybe outfitting them with a small chemical explosive, but then they don't last very long, and their effectiveness is still pretty questionable. Corrosives could be only in impossibly small quantities. Lasers would require more energy than the little things could produce to be effective. So on, so forth. Any cloud dense enough to cause damage would be very visible, and thus just as avoidable as a mine. Next up is why? Why would you go out of your way to develop the infrastructure to build millions if not billions of these expensive little fuckers? What's wrong with nukes or railguns or any of a large number of short range weapons? And finally, when? This is more futuristic than a death ray, which really defeats the purpose of even speculating.

@Noctis
Get used to it. Semantical arguments centering on minor unclarities in otherwise cogent arguments are the preferred straw men of the internet.

[thanto_]

Talhydras:

LI-900 was the only material I could think of that exists right now that can withstand ridiculous amounts of heat being dumped into it, especially at high speed. There's LI-200 as well, but IIRC, that's impregnated with some other stuff that makes it heavier and also probably changes the thermal properties a fair bit. The other one is reinforced carbon-carbon, but I wasn't able to get much of any useful thermal info on that (other than that it is used in disc brake systems for super-expensive sports cars). The stuff I have on LI-900 is based only on non-crystalline SiO2, which doesn't exactly seem right for LI-900. For example, the melting point of Si02 is something like 1250C, whereas the "softening point" for LI-900 is 1260C, meaning it's not melted at that point. It's supposed to be able to survive heat of upwards of 3000C as well without being completely destroyed, so it seems to me that basing its thermal properties solely on Si02 is a bad idea. I haven't really seen anything discussing the structure of LI-900, whether it's some sort of crazy special crystalline structure or what, which may provide more degrees of freedom in which to store thermal energy.


Either way, we have materials right now that are pretty good for protecting against ridiculous amounts of heat. Given the technological breakthroughs required for functional deathrays in space, I'd imagine we'd develop equally fantastic materials for thermal protection, if not specifically against deathrays.


Sorry to bring up Mass Effect again, but a solution to deathrays brought up in that game is a kind of ablative armor that melts or vaporizes when heated by lasers, creating a vapor cloud that diffracts the laser (or something), thereby mitigating damage. I'm really not sure how that would work. I doubt we have any existing materials that exhibit that kind of property anyway, but supposing we invented one, what effect would the diffracting vapor have on the laser?


Or, what effect would negative index metamaterials have?

[Wicky_42]

@Anyone who thinks nanobots are a good idea
lololololololo

Terribly impractical. First up, how? How do you develop something so small, and somehow outfit it with the ability to damage a ship's armor? I could see maybe outfitting them with a small chemical explosive, but then they don't last very long, and their effectiveness is still pretty questionable. Corrosives could be only in impossibly small quantities. Lasers would require more energy than the little things could produce to be effective. So on, so forth. Any cloud dense enough to cause damage would be very visible, and thus just as avoidable as a mine. Next up is why? Why would you go out of your way to develop the infrastructure to build millions if not billions of these expensive little fuckers? What's wrong with nukes or railguns or any of a large number of short range weapons? And finally, when? This is more futuristic than a death ray, which really defeats the purpose of even speculating.

Eh, I think you're railing against nanobots for ENTIRELY the wrong reasons, lol. They don't need lasers or explosives or acids to damage shit, they disassemble each molecule in the ship one by one though the magic of nano-technology. Give them self-replicate and even one could pose a serious threat in a reasonable time-frame.

As to expense, not really. Once you've got the infrastructure to begin manufacture (presumably using other nanobots) all you need to do is feed them raw materials and new bots would be produced in their millions.

The other weapons systems you suggest are all limited by needing a large, detectable delivery system that can be engaged conventionally from afar, whilst a self-replicating nano-bot swarm could be spread thin with no energy emissions and so would be very hard to detect.

As to when, as with lasers we're already beginning to experiment with nano-scale tech, so it's not far-fetched to imagine functional nano-destructors.

However, that all said, the point has already been made that nano-bots are very, VERY squishy and wouldn't survive long in space as we currently see them. Perhaps there will be future advances, more robust materials, shielded micro-scale delivery systems, whatever, but for this discussion I think they can be discounted.
____________

Negative index metamaterials would/could be SWEET, potentially negating lasers significantly. I believe I brought them up yonks back during the last tech discussion. A material that diffracts light through 180 degrees, rather than reflecting it? sounds like a plan. The real trick, however, would be making it effective for a sufficient spectrum of electro-magnetic radiation at sufficient planes of incidence to provide full cover.

[Noctis]

@Anyone who thinks nanobots are a good idea
lololololololo

Terribly impractical. First up, how? How do you develop something so small, and somehow outfit it with the ability to damage a ship's armor? I could see maybe outfitting them with a small chemical explosive, but then they don't last very long, and their effectiveness is still pretty questionable. Corrosives could be only in impossibly small quantities. Lasers would require more energy than the little things could produce to be effective. So on, so forth. Any cloud dense enough to cause damage would be very visible, and thus just as avoidable as a mine. Next up is why? Why would you go out of your way to develop the infrastructure to build millions if not billions of these expensive little fuckers? What's wrong with nukes or railguns or any of a large number of short range weapons? And finally, when? This is more futuristic than a death ray, which really defeats the purpose of even speculating.

Eh, I think you're railing against nanobots for ENTIRELY the wrong reasons, lol. They don't need lasers or explosives or acids to damage shit, they disassemble each molecule in the ship one by one though the magic of nano-technology. Give them self-replicate and even one could pose a serious threat in a reasonable time-frame.

As to expense, not really. Once you've got the infrastructure to begin manufacture (presumably using other nanobots) all you need to do is feed them raw materials and new bots would be produced in their millions.

The other weapons systems you suggest are all limited by needing a large, detectable delivery system that can be engaged conventionally from afar, whilst a self-replicating nano-bot swarm could be spread thin with no energy emissions and so would be very hard to detect.

As to when, as with lasers we're already beginning to experiment with nano-scale tech, so it's not far-fetched to imagine functional nano-destructors.

However, that all said, the point has already been made that nano-bots are very, VERY squishy and wouldn't survive long in space as we currently see them. Perhaps there will be future advances, more robust materials, shielded micro-scale delivery systems, whatever, but for this discussion I think they can be discounted.
____________

Negative index metamaterials would/could be SWEET, potentially negating lasers significantly. I believe I brought them up yonks back during the last tech discussion. A material that diffracts light through 180 degrees, rather than reflecting it? sounds like a plan. The real trick, however, would be making it effective for a sufficient spectrum of electro-magnetic radiation at sufficient planes of incidence to provide full cover.

Self replicating nanobots are a rather ominous. In B4 Skynet

[unsunghero10]

Skynet? Heck no.

Replicators, heck yes!
They actually use everything, and don't bother making skeletons.
(Stargate)

[Aralonia]

@Sponge: Okay, let's see here - We can find a missile in space pretty easily with LIDAR/RADAR or whatever ranging system you want to use (but if you use SONAR I'm going to fucking kill you). And we're firing on them with hitscan weapons (lol), which operate only a bit faster than a BB gun. Why operate something as point defense that can be easily dodged (bullets, missiles) when we already have lightspeed weapons? And I think the Talhydras Death Star has enough energy to burn with the laser.

@Wicky: NANOBOTS ARE NOT EFFECTIVE LIGHTSECOND RANGE WEAPONS

[Sponge]

@Wicky_42
wut

No, lets throw sensible mechanisms, such as making them explode when they come in contact with an enemy vessel, out the window. Instead, we should consider something capable of dissembling an enemy ship on atomic (or even molecular) level, magically transmuting those base elements into something completely different, and then building more of itself. This doesn't make any sense at all. You have something that is literally nanometers across. How is it going to get the energy to somehow pull individual molecules apart, convert the elements into something useful, and then build itself a friend? So yes, I agree. I think they can be discounted. Entirely.

@Sponge: Okay, let's see here - We can find a missile in space pretty easily with LIDAR/RADAR or whatever ranging system you want to use (but if you use SONAR I'm going to fucking kill you).

If you read my post, you'll find that I described this phase as "somewhat trivial."

And we're firing on them with hitscan weapons (lol),

No we are not. These "projectiles" move at 299 792 458 m/s, which really needs to be taken into account when you're firing at anything more than a fraction of a Ls out.

which operate only a bit faster than a BB gun.

On a comparable scale, I'm actually being generous. The laser will take a second to reach the missiles, where the BB will take a far smaller amount of time to reach the swarm of gnats. In any case, you're missing the analogy entirely. The point I'm making is that by the time your projectile has reached the target, the target is no longer where you predicted it would be. Your sensor data is, at that point in time, two seconds old (assuming 1 Ls).

Why operate something as point defense that can be easily dodged (bullets, missiles) when we already have lightspeed weapons?

Short range. Conventional point defense would do nothing at long range, but would be quite effective when the missiles get close and you don't have enough power to charge up thirty or forty lasers. Lay down a field of fast-moving metal and watch as your enemy's rockets start getting gutted. Or maybe you do have an arsenal of point defense lasers, which might actually be quite practical. One thing's for sure; they wouldn't be death rays.

And I think the Talhydras Death Star has enough energy to burn with the laser.

It's not that there isn't enough power to spare; it's that you're building up tons and tons of waste heat in a fruitless endeavor.

[Aralonia]

In my post I specifically stated that we were playing with a long-side-of-the-triangle range of 0.05 light seconds, or 15,000km. I haven't wavered from that number since. The missiles are still going at 100 km/s, so the Death Star still has 150 seconds to react. And since we've got some rock-faces-off lasers here, we have enough time to shoot down your shit.

Fast-moving metal has a far, far, far longer travel time to hit a far, far, far smaller target than we want. Do you want me to do the trig for the arc second width of a gnat at 50 meters? Let's do the motherfucking trig.

We will assume that the gnat is approximately 5 millimeters in size. This is 0.005 meters. Tan[0.005/50] = 0.0001 radians = 20.6264806 arcseconds. This target is approximately 50 times larger than the missile at the engagement range I specified.

Let's keep going, because I am having SO MUCH fun. With a muzzle velocity of 150 meters per second, we have the BB gun reaching gnat distance at 1/3 of a second. On the other hand, we do have the laser reaching .05 light seconds in, well, you know. On the other hand, your manhole cover swarm going at... what speed do you want? I'll go with the muzzle velocity of the British Goalkeeper CIWS, which is at best 1225 meters per second as according to this http://navweaps.com/Weapons/WNNeth_30mm_Goalkeeper.htm <-- site, my favourite naval gun resource. Since we're engaging a target at .05 light seconds, 15,000 kilometers away, 15,000,000 meters away, even if I'm being nice and giving you a 30mm gun with 5 times the muzzle velocity, it's still going to take 2448.98 seconds for your bullet to hit the target. That's... what, 4897.96 times slower than the laser.

My 1000th post on this forum involves gnat trigonometry.

This is the first time I've ever hit 1000 posts on a forum.

I feel accomplished as fuck

[Normandy]

Don't forget kids, you have to keep the laser pointed on the missile for a rather significant amount of time in order to actually destroy it; unless you use rather high-voltage lasers for your point defense. Which sort of limits the amount you can deploy.

@thanto_:
The problem is that right now, we're discussing a laser that's being developed right now. A simple 10MW x-ray laser.

@Talhydras:
I never said it would completely stop the drilling. It would significantly reduce the impact of it. I'm not sure how a space shuttle getting its thermal tile punctured and being hit by a laser beam compare, though. Once again, in atmospheric reentry a low thermal conductivity is wanted as you wish to prevent that super-hot outer layer from contacting the inner layers. In defending against a laser beam, you want that super-hot point to become not so super-hot. Your example has no bearing on the discussion at hand.

Which does get me thinking. You're using x-rays on a spongy material. Now my physics may be sketchy (taking high school physics this year), but x-rays don't tend to get stopped easily by such material. It's why our soft spongy flesh allows x-rays to pass, but our bones do not. Given that said spongy material is, well, spongy, one could probably have a few meters of the stuff with no weight problems (compared to your death laser). There is no 'spot' which heats up to your absurdly high temperatures. Your energy is deposited safely throughout the armor which, thanks to its high thermal conductivity, safely returns to a near baseline temperature, ready to take another hit.

As par Sponge's post, if you get a lake of liquid helium, I think we can get an absurdly thick plate of spongy carbon material.

EDIT:
@Aralonia:
I don't think you understand Sponge's statement. By the time the laser reaches a missile 1 ls away, your data is 2s old. On a similar vein, a missile 0.05 ls away, your data is a tenth of a second old. I'm not sure about you, but with speeds like 100km/s, you're going to be a good 10 km off with your shot.

[Talhydras]

Sponge: This sort of thing could be used for a focusing element on a large x-ray laser turret, though the material you'd make it out of would probably have to be a large very precisely machined crystal. Additionally, x-ray mirrors exist, so I'm not sure what the cutoff energy level is that Campbell was talking about. I'm not an engineer so I have no real information to give you about it. Which is why I'm getting on my research pants! Cruising on down here on the european XFEL site, it seems they're using... nothing at all to focus their beams beyond the electrons in the undulator. Since they don't need to focus their beam very much and X-rays are so bloody short wavelength they don't attenuate very much, this works for their purposes.

Let's talk about diffraction for a moment; assuming that its possible to machine a nanoscale diffraction element; in order to bend the beam you'd need to be making grooves on the same scale as the wavelengths which would require TRICKSY engineers. Thinking about it, you MIGHT be able to get away with a flexible lens changing spot size, but you might not. This would make death-star type lasers need to be built for a single desired focus and range. Outside that range, they'd quickly lose focus and damaging capabilities.

However, there would be no moving components in this turret, so the death star would likely have a number of different turrets the electron beam generated in its guts would be routed to, each with a different focus. Super long rage "interplanetary graffiti" turret, a number of .1 LS turrets for missile interception, and probably one for light second range "maybe we'll get lucky" shots. Similarly, if you wanted to invest in a number of undulators, you could split the electron beam and route it through multiple point defense turret, allowing you to very nicely combine and disperse laser power.

The kilometer accelerator ring is a valid point; you'll note that earlier I proposed that sort of weapon on star destroyers and battlestars for just that reason.

This is a fun little application to use for calculating laser coolant capacity. Being a sheep I'm using lithium like they use on atomic rocket, and assume the death star can have a 100 ton block of lithium as its coolant. Heavy, yes, but keep in mind that the Saturn V is 30 times more massive than that. Assuming 10 MW shots lasting 1.25 seconds we can try and calculate waste heat per shot: Wh = Tf * (Bp/eff * dc) * (1 - eff), where Wh = waste heat, Tf = firing time, Bp = aperture power, eff = efficiency, and dc = duty cycle.

Tf = 1.25 s, Bp = 10 MW, eff = 10% (.1), dc = oh hell, call it 2 seconds. Wh = 220.5 MWseconds; I'm not sure I picked anywhere near an appropriate duty cycle considering the accelerator will first have to be spun up. This will probably require a great BIG radiator all of its own.

Anyway, we have waste heat values. Let's plug them into that coolant calculator I linked just a bit ago. Running the numbers, it gives 667 activations, for a continuous activation time of 1400 seconds, over 20 minutes, per 100t chunk of lithium. Plugging in 433 Eros like I suggested as a base for such an orbital installation gives access to a 6.69E15 kg chunk of silicate rock. I'm gonna use water as a representative sample of that; it's programmed into the calculator and I'm having a bitch of a time looking up applicable feldspars to use as a substitute. As 1000 tons of water gives 1830 activations and an hour of firing, I'm going to assume that 6690 trillion tons of water will give 6.69 trillion hours of firing, or 763 million years of continuous firing. This means that the accelerators for the laser(s) could be reasonably left running indefinately, giving the time required for the death star to react to a detected threat to be on the order of the time it takes a controller to click the "zap that shit" icon on his desktop. Fearsome indeed.

Now, that's assuming relatively small amounts of warm up time per shot and 10% efficiency for the entire system. But -still-, that kind of massive thermal reservoir would completely alleviate all needs for thermal systems. Assuming you placed the thing in an orbit where it had a great view of the earth area at all times and drilled through from pole to pole for maximum coverage you could construct many and larger death ray lasers on Eros, turning it into a relatively unassailable object. A number of such orbital fortifications built out of redirected apollo-amor asteroids would actually make things quite safe from whatever.

Cost of such a thing would be substantial; smaller rocks would do just fine and be easier to redirect though many of the A-A asteroids are quite close in terms of required delta-V (sneer sneer) to get them into an earth orbit. By no means would the rock hold all the requisite materials either; you'd need to manufacture a fairly significant amount of electronics and probably accelerator elements either on the moon or Earth; boosting that would be a royal bitch. Would such a massive endeavor be as expensive as a fleet of killships with missile swarms? I'm almost entirely positive it'd be far more expensive, but it'd also be an investment that was a lot sturdier. Teraton rocks would require enormous energy to pulverise from missile strikes; impact shocks would probably destroy any installations far before the missiles even scratched the thing. Massive kinetic impact (read: another rock) would probably be a better bet, but such a thing would have to take a ballistic course to the target over a prodigious distance and thus the death rays woud be able to engage.

Such an engagement would be quite tactical; while the laser's impact would produce thrust on the impactor, should the attackers have the asteroid suitably de-spun they would be able to attach a rocket with similar output to the laser on the opposite side and compensate. Small-spot lasers would take many, many, many consecutive hits to burn through all of that rock and aiming at huge range would be a bitch and a half. Additionally such a super rock would require the ability to correct course relatively well; anyone going to the trouble of building such a death star would do well to include docking arrangements for tugs capable of moving it out of the way of the impending death projectile. Otherwise a laser fort's only defense would be point blank thermonuclear salvo attempting to deflect the thing (long shot) or a really, really good insurance policy.

Thanto: That was sort of why I plugged the death ray in vs. fullerite (nanotubes), about the badassin'est armor I can imagine. Again, to fight lasers you need armor that can wick away heat DAMN FAST. Vapor does not contrary to popular belief disperse all incident radiation. In fact, molten metal is closer to a black body and thus VERY GOOD at absorbing radiation. In other words, it would have to be vaporized by the beam.

Except, that's how the damn beam drills through armor in the first place; a pulse melts the outermost layer which expands, vaporizes, creates massive localized pressure and fragmentation which drives out particles of armor, and then the melt front propagates through the target. High energy beams pulsing at greater than a MHz will cause the individual shocks of each pulse's explosion to coalesce into a single wave propagating through the hull.

Again, laser impact != reentry. Reentry is friction across the surface of the space shuttle, laser spot = rapid spot heating. Both are deadly and involve large numbers of degrees ganging up to break shit, but the laser does it in a way that is far harder to effectively defend against because 1) it's faster and 2) it's localized.

In conclusion: You don't want Mass Effect armor that vaporizes when it gets hit by a laser as it is doing the laser's job for it. Lasers are not like relativistic impactors, they are not defeated by whipple plating or ablative layers. You'd probably want something with a very large vaporization energy for its mass. You would also want to be in tight control of what aspect you present to the laser; this is why I recommended the orion drive ship attacking with its pusher plate towards the target. The pusher plate needs to be a massive chunk of metal anyway; you're not going to realistically afford similar protection for the front of the ship. If you didn't use an orion drive, you would likely end up with a super-armored ship prow ith whipple plating to deal with kinetic weaponry and dust collisions (nothing to sneer at at 100s of km/sec relative speed), Awesome Shit (carbon or boron are the best current material) to absorb laser energy, and shock absorbers to help mitigate the blast effects of a contact nuclear detonation. For that last one, you will need a very large vessel with lots of armor.

Normandy: Oooh you're getting the yeast in my science loaf to really rise!

Moving away from plagiarism, the interaction with x-rays and atoms is tricky. For while they will hang around depositing energy in dense stuff, they also slam right into the atmosphere. Just cause it isn't dense doesn't mean the material is transparent to that radiation wavelength.

I'm honestly not sure how diffracted the beam would be by such a spongey substance; any energy deposition at all would probably lead to rapid heating or vaporization of the material because it's being hit by a freaking laser and lasers vaporize shit.

For a HS physics student, you're making pretty thoughtful points.

EDIT: On the subject of the immense thermal capacity of 433 Eros: Being a S-type asteroid, aka a carbonaceous chondrite, it has a significant amount of water. Hollow out a large volume in the interior and fill it with water. Submerse the accelerator in this water, then agitate it to spread out heat. To defend against impact shock from surface nuclear detonation, surround this chamber with foam-filled voids. A friend points out that the scree from asteroid mining would work nicely in lieu of foam; all it needs to do is give a little to reduce shock effects.

Defeating such a thing would reduce to destroying the turrets, of which it could have many. Very, very, very, very many. Teraton asteroids are difficult to engage as an entity. Terawatt range lasers would probably be the best bet, as they have beastly cutting power. A friend suggests a barrage of X0 or X00 ton asteroids and assorted shot to attack the turrets directly and attempt to saturate defenses before delivering a coup de grace kinetic impact. Attacking the turrets with your own lasers would work well too.

[Sponge]

In my post I specifically stated that we were playing with a long-side-of-the-triangle range of 0.05 light seconds, or 15,000km.

Because I have repeatedly used this number every time I've referenced missiles, right? Seeing as how I have never, ever even mentioned a range of .05 Ls, and your posts have typically been in direct response to mine, I have no idea why you feel it an appropriate number to use. Clearly your intent, which you have not wavered from, was not to refute my claims, but to employ a mechanism known as a "straw man." I understand you have an interest in trigonometry, but this interest is of no relevance to my initial argument. This is because looking at a distant nebula is fundamentally different than shooting down a missile that's hurdling toward you. I apologize for thinking that it was, and thereby making statements with more basis in misconception than in fact.

we have enough time to shoot down your shit.

By this, you invariably mean "I have time to pick apart your post, take metaphors and analogies as literally as possible, and intentionally misconstrue the various minutia of your post, so that I can formulate some irrelevant argument and make you look dumb because this is the internet." Oh wait, you were talking about missiles.

Fast-moving metal has a far, far, far longer travel time to hit a far, far, far smaller target than we want.

Is this in response to the point defense comment? If so, look at it this way. Even setting non-moving chunks of metal between your ship and the direction the missiles are moving in would be an effective counter-measure. I do recall mentioning close range, and that still stands. The more metal, the more chances you have of hitting something that will make you go boom. If you have a problem with this concept, go ahead and take it up with Talhydras, as I recall him using manhole covers and banana peels for a similar purpose, and I'm done defending this painfully simple concept from your ever-increasing urge to argue about everything.

Do you want me to do the trig for the arc second width of a gnat at 50 meters?

No, I don't. I never, anywhere, said that I was 50 meters away from the gnats. I couldn't even see a fucking swarm of gnats 50 meters away. Just for the sake of argument, I was envisioning these gnats being at a rather point-blank range, so as to illustrate the futility of trying to hit one. But now you're going to point out that those missiles aren't at point blank range, and that taking the analogy literally makes it no longer valid. And then I'll respond with some quip about how analogies aren't supposed to be taken literally, and you'll argue about my usage of the word "supposed," and so on, and so forth.

Let's do the motherfucking trig.

OKAY!

We will assume that the gnat is approximately 5 millimeters in size. This is 0.005 meters. Tan[0.005/50] = 0.0001 radians = 20.6264806 arcseconds. This target is approximately 50 times larger than the missile at the engagement range I specified.

Excellent job!

Let's keep going, because I am having SO MUCH fun.

I know how you feel! Trig makes me feel all warm inside, too. In fact, it's a weekend hobby. If I do enough of it, I'll enter into a sort of drunken stupor and, after fumbling around with a calculator for a few minutes while feeling warm and fuzzy, I'll go mad with anger, cutting down everyone in my path with carefully accurate trigonometric calculations!

With a muzzle velocity of 150 meters per second, we have the BB gun reaching gnat distance at 1/3 of a second. On the other hand, we do have the laser reaching .05 light seconds in, well, you know. On the other hand, your manhole cover swarm going at... what speed do you want? I'll go with the muzzle velocity of the British Goalkeeper CIWS, which is at best 1225 meters per second as according to this http://navweaps.com/Weapons/WNNeth_30mm_Goalkeeper.htm <-- site, my favourite naval gun resource. Since we're engaging a target at .05 light seconds, 15,000 kilometers away, 15,000,000 meters away, even if I'm being nice and giving you a 30mm gun with 5 times the muzzle velocity, it's still going to take 2.44898 seconds for your bullet to hit the target. That's... what, 48.9796 times slower than the laser.

Good show! You have totally proven me wrong by selecting some small aspect of my post, plugging in your own value of 50m, and running some numbers! And how does this factor into the whole missiles vs laser debate? It doesn't? You mean to say your taking a metaphor as literally as possible, substituting in missing information, and doing some trig really has no bearing on the "big picture," and in fact just serves as a vector for you to argue about something entirely unimportant?

This is the first time I've ever hit 1000 posts on a forum.

'Gratz.

@Talhydras
EDIT: Just saw your post there. Look forward to seeing what you've found out, and will try to get back to you soon.

[Normandy]

[OOC: I do like how multiple arguments seem to be going on all at the same time.]

@Talhydras:
Oh. I misread your post.

Heh, I was going to suggest that the vapors disperse radiation, when I remembered that vapors tend to be invisible.

Well, I do suppose now we're getting into some stuff that hasn't been done yet, experimentally at least. I'm not sure it'd be too wise of me to continue arguing for this point until some harder research comes out.

I'm not sure that traditional ideas of point defense will be applicable in space, for the same reason that mines are not. There are just simply too many possible places the object you're trying to shoot down can be. Once again, at the rather ridiculous speeds things will be moving out there, even a small change in trajectory will alter an object's position drastically. Not to mention information lag. You might just need all of those activations to shoot down a single missile.

I know how you feel! Trig makes me feel all warm inside, too. In fact, it's a weekend hobby. If I do enough of it, I'll enter into a sort of drunken stupor and, after fumbling around with a calculator for a few minutes while feeling warm and fuzzy, I'll go mad with anger, cutting down everyone in my path with carefully accurate trigonometric calculations!

Hey, I do that occasionally.