The Practicality of various futuristic weapons.

[Aralonia]

There is a huge difference between aiming at a galaxy and a missile probably no more than 10m across. Yes, the quasar is far away, but it's fucking huge.

Trig time - let's assume a distance of .05 light seconds for missile acquisition range. That's... 15,000km.

Draw a triangle, with small angle theta, and pick one of the two remaining angles. It is now 90 degrees. Baseline length is 10m, long side is 15,000,000m. SOH CAH TOA - we're looking for opposite/adjacent so that's... tan[10/15 000 000] = 6.666666 × 10^-7 radians on the angle. How many arc seconds is that? Google Calculator gives me 0.137509857 arc seconds.

ARA MOD EDIT: I was a dipshit and Talhydras hit me over the head with the astronomer stick. Apparently the major emitting source in a quasar is the core. Which is true, and this point source is approximately 1 light-day in diameter. That's 0.00273790926 light years. So we have the equation again - baseline length 0.00273790926 light years, long side of the triangle is an exhilaratingly meaty 12,000,000,000 light years. Tan[0.00273790926/12 000 000 000] = 2.28159 × 10^-13 radians, which translates to the pitiful 4.70611719 × 10^-8 arc seconds. Ouch.

[Anna]

One thing that hasn't been touched on, and might be a possiblity, is firing massive bursts of radiation.

Fun fact: Light is a form of radiation.

Just semantics.

For lulz.

I know what you meant. Other types of radiation that more or less don't interact with non-organic substances.

But still.

Lasers shoot radiation. Just sayin'.

[Talhydras]

Aralonia: I feel kind of dirty saying "he has a good point" when I'm referenced in his damn post, but the numbers he comes up with serve a good point.

He used a saturn V to determine missile size IIRC, and milliarcseconds is indeed QUITE TINY. On the other hand, we don't have the resolvingpower to pick out the emitting region of a quasar at 4 gigaparsecs, so as examples go its not definitive.

Suffice to say, though, that tracking a missile in several tens of thousands of kilometers is possible. Difficult, but not impossible. Phalanx tracks cruise missiles moving Mach .86 and intercepts them at ranges of ~10 km IIRC; compensating for the motion of objects moving 300 times faster at 1,000 times the range doesn't seem like it'd be THAT much harder. Slew speed won't be an issue at that range at any rate; fine turret control will be. The target itself is a lot smaller.

Sponge"
Luke Campbell wrote the following:

"Let's take a 10 MW ERC pumped FEL at just above the lead K-edge. This particular wavelength is used because lead is pretty much the heaviest non-radioactive element you can get, and at just above the highest core level absorption for a material you can get total external reflection at grazing angles - so no absorption or heating of a lead grazing incidence mirror. We will use a 1 meter diameter mirror. The Pb K-edge x-ray transition radiates at 1.4E-11 m. This gives us a divergence angle of 1.4E-11 radians. At 1 light second, we get a spot size of 5 mm, and an intensity of 5E11 W/m2.

Looking at the NIST table of x-ray attenuation coefficients, and noting that 1.4E-11 m is a 88 keV photon, we find an attenuation coefficient of about 0.5 cm2/g for iron (we'll use this for steel), 0.15 cm2/g for graphite (we'll use this for high tech carbon materials) and 0.18 cm2/g for borosilicate glass (a very rough approximation for ceramics). Since graphite has a density of 1.7 g/cm3, we get a 1/e falloff distance (attenuation length) of 4 cm. Iron, with a density of 7.9 g/cm3, has an attenuation length of 0.25 cm. Glass, density 2.2 g/cm3, has an attenuation length of 2.5 cm.

At 1 light second, therefore, the beam is depositing 2E12 W/cm3 in iron at the surface and 7E11 W/cm3 at 0.25 cm depth; 1.2E11 W/cm3 in graphite at the surface and 5E10 W/cm3 at 4 cm depth; and 2E11 W/cm3 in glass at the surface and 7E10 W/cm3 at 2.5 cm depth. Using 6E4 J/cm3 to vaporize iron initially at 300 K, we find that iron flashes to vapor within a microsecond to a depth of 0.9 cm. The glass, assumed to take 4.5E4 J/cm3 to vaporize (roughly appropriate for quartz) will flash to vapor within a microsecond to a depth of 4 cm within a microsecond (sic). Graphite, at 1E5 J/cm3 for vaporization, will flash to vapor to a depth of 0.7 cm within a microsecond (the laser performs better if we let it dwell on graphite for a bit longer, we get a vaporization depth of 10 cm after ten microseconds).

Net conclusion - ravening death beam at one light second."

Sure, 10 MJ isn't a lot of force, but you put it on a pinhead and shit will get busted up it seems. If you take a thin enough section of a warship and exert on it modest forces, grievous damage will still be inflicted. I'd like to say this is my math, but it really isn't. Which... got me thinking.

Mr. Campbell's website got linked. Needless to say, the man's pretty meticulous.

I ran the 10 MW 5 mm spot through that calculator there and the drilling speed of 30.4 m/sec through structural steel sounds like it'd support the cloven starship idea I was postulating, but converting units says that's a small fraction of a centimeter in a microsecond. Hunh. The battleship Iowa had armor half a meter thick on its turrets; I'm not sure how that'd compare to the pusher plate of an orion drive ship but if that damage calculator is right, a 5 mm spot 10 MW beam would drill through that in, well, 17 milliseconds. Assuming 100 km/sec, in that time your ship would coast 1.7 km plus whatever maneuvers it could perform in 17 milliseconds. Assuming maneuver power of 10 Gs transversally, or 100 m/sec^2, let's see just how much a ship could dodge. r=vt+1/2at^2; at time of initial laser impact assume the targeting computer's deduced the ship's recent velocity and is slewing to track thus vtransverse = 0, a = 100 m/sec^2, t=0.017 seconds. Total distance maneuvered = 1.455 centimeters. Where'd you get your 50 cm radius figure?

So... in the time it takes a 10 MW laser -according to an online calculator that shows copious math I personally couldn't recite but looks good to me-, a ship could move transversally 3 widths of the 5mm spot. So... if the Death Star can focus on a target at all, -and- that calculator is right... fans are shitty and the death star is indeed a star of death. You don't need to blow a hole in a chunk of steel to cut all the cabling beneath it; you just need to make a gap. If that's true, I don't think you can say that you need the global power output in laser format to ruin somebody's day.

I've run the calculator for an 8 TW laser and a spot size of 5 mm. Drills steel at 2780km/sec. We've moved past "devastating" when we're talking terawatt range beams. Make the spot a little bigger and you can start carving up minor planets. Not vaporizing large areas of them out right, but definately carving 'em up.

Heat is why the weapon in the story was defensive. You don't really want to make a massive radiator and coolant spraying apparatus acceleration-safe... but towing 433 Eros into Earth orbit and using the entire mass as a heatsink, I think a few shots could be managed even at low efficiencies. Mobile superlasers like that would require LARGE ships. Star destroyers, essentially. That kind of engineering is definately a century away, and by then.... well, Sponge, who knows what military quantum leap is over the horizon XD?

EDIT: Oops. Coupla other quickies.
Just as the european X-ray FEL is not a viable antistarship weapon, modern ICBMs aren't either. The warheads themselves are, but the delivery vehicles suck for space engagements, just like experimental FELs suck for toasting martians. Apples and oranges.

Smaller surface area being struck, or being struck face on as opposed to along the sides, means a shorter gash, means less structural damage and less shit getting cut. Also makes you a smaller target and magnifies the effect of maneuvering. Ultimately the orion pusher plate is the end of the ship you want heading into battle.

[Normandy]

As to the missiles' defense, any sort of point defense system which could be deployed in a large enough scale to actually shoot down thousands of missiles might not have the power to instantaneously destroy a missile. Considering the Star Wars 747 laser, it has to keep trained on its target for quite a while in order to actually destroy it; given the lack of atmosphere in space, a missile could easily (relatively speaking) create erratic movement that could throw off point-defense lasers, or at least occupy the defense gun for significant amounts of time. An analysis is done in the Atomic Rocket page linked earlier (http://www.projectrho.com/rocket/rocket3x.html): search for the term '6.6 seconds in order to kill it'. As said before, a single nuke gets through, you're very much screwed.

As par Aralonia's calculations, you have to take into consideration the massive amounts of energy that pulsar gives off in a nicely (once again, relatively speaking) concentrated beam, the multiple wavelengths of energy it comes in, and the fact that it isn't trying to dodge you. Compare that to the rather insignificant heat signature of a missile, which is not so broad-spectrum, and can easily be covered with chaff. In fact, an interesting tactic might be to throw off coolant as thermal chaff to make it even harder to pinpoint the missile.

EDIT:
ninja'd. Or more accurately, 'left post here for a few minutes'. Do note this post does not take into account any of Talhydras' post. I'll fix it later.

[Noctis]

One thing that hasn't been touched on, and might be a possiblity, is firing massive bursts of radiation.

Fun fact: Light is a form of radiation.

Just semantics.

For lulz.

I know what you meant. Other types of radiation that more or less don't interact with non-organic substances.

But still.

Lasers shoot radiation. Just sayin'.

Ha ha funny.

Still, I wonder what other types of less conventional but obviously awesome stuff could be done. Both lasers and RKV are pretty common, so they kind of lose their "Awwwwwwwwww yeah" factor, simply because of saturation. There are a lot of neat things that could, maybe, theoretically, be done; but we'd need to be a level 3 or so civilization.

[Sponge]

@Noctis
Because in order for something to be a viable space weapon, it needs to be really cool.

@Aralonia
Yeah, I know. It's far away. We also have the benefit of knowing exactly where it's at, because it's pouring out lots and lots and lots of energy. This does a lot to negate that whole "it's far away" problem. The moon is far away, and yet I have an easier time tracking that than I have tracking a car going past my house. Objects as distant as galaxies are essential stationary when they're being observed. You point your telescope at it and you don't see it whiz past. The same cannot be said for a missile. I'm not saying that focusing in on a distant galaxy is easy. I'm saying it's not the same as targeting something close to you moving at appreciable speeds. The first involves precision, but no time constraints. The second requires precision AND it's very time-oriented. And not only do you have to see the missiles, but you have to hit them with a laser.

@Anna
"Way to take it out of context. He was talking about the "Death Star" laser as described in his theoretical story thing. "
Unless I misunderstood his post, I wasn't taking it out of context. He had previously referred to his death star as being 10MW; I was merely carrying that figure on from earlier. Quote: "A 10 MW x-ray FEL like the one the death star had in the story..."

@Talhydras
I pulled the 50cm straight from the depths of my ass, thinking it was a fair assumption. It does seem that I was sufficiently incorrect. Still, I've got to say, 5mm @ 1Ls does not sit well with me. That is the theoretical minimum calculated with the properties of the x-rays themselves, and says nothing to the sort of equipment that would be required to pull this off. If you had a perfectly collimated x-ray beam, then your spot size is 5mm. If you don't, you don't. Or, at least, this is my interpretation of the situation. It's possible I'm missing something. Could it be done? I have no fucking clue. Am I skeptical? Yes.

I understand Mr. Campbell's math only on a very superficial level. I see what he's doing, and it looks to make sense, but I can't verify the validity of his derivations. I do know that he later said, in direct relation to your block quote, the following:
I have since come to realize that at x-ray energies this high, matter cannot act as a mirror even at grazing angles (the x-rays have such a short wavelength that they interact with the atoms individually, rather than seeing them as a flat sheet - and you can't really get grazing incidence off of an individual atom). This is why I now prefer diffraction for focusing.

I'll take his word for it, and attempt to explain the significance of his statement. It seems to get the numbers he was talking about (10MW, 5mm, etc), he was using a technique that was impractical. Essentially blasting an x-ray laser at a mirror at a low angle so that it reflects off of the surface at an equally small angle. I really don't understand what this would even accomplish, and I can't find where he explains why this step is necessary. Is it some sort of collimation procedure? Anyway, x-rays are real small, and so would penetrate the surface of even a particularly shiny mirror, effectively negating all of that shiny and not causing the x-rays to reflect at all.

Are similar results possible with this new "diffraction" method? I don't know. I'm having trouble finding his writings on the topic. Using diffraction as a method of pinpoint focusing seems incredibly strange, and I can find no other reference of such a concept anywhere else on Atomic Rockets.

While on the topic of Atomic Rockets, they point out that Campbell's death-ray would require an accelerator about 1km in length, making it completely impractical for anything other than, well, a death star. That fact that this is a FEL in the first place, and thus requires an accelerator, makes it impractical for extended use in space. The main accelerator at Fermilab was originally build under a man-made lake for the purposes of cooling. When they upgraded the magnets, even the lake was insufficient. Now they use liquid helium. So not only do you need a kilometer-long electron accelerator, but you need to transport all of the tons and tons and tons of heat it creates out of what is essentially a closed system (not really, but I think you know what I'm getting at; you're going to have to expel some sort of coolant, because radiators are just not going to cut it). You've already touched on this, and so I'm preaching to the choir. It does make quite a case against mobile laser platforms that are capable of high damage output, though. Defensive platforms? Possibly. Attack ships? Missiles are your best bet.

[Aralonia]

As par Aralonia's calculations, you have to take into consideration the massive amounts of energy that pulsar gives off in a nicely (once again, relatively speaking) concentrated beam, the multiple wavelengths of energy it comes in, and the fact that it isn't trying to dodge you. Compare that to the rather insignificant heat signature of a missile, which is not so broad-spectrum, and can easily be covered with chaff. In fact, an interesting tactic might be to throw off coolant as thermal chaff to make it even harder to pinpoint the missile.

If I point my telescope at the sky, which am I more likely to see?

A.) Barnard's Star, 6 light years away
B.) A quasar, 12 billion light years away
C.) A Saturn MCLVIXIEVL, 15,000km away, burning its ass off
D.) NGC 224/M31 Andromeda Galaxy, 2.5 million light years away?

@Aralonia
Yeah, I know. It's far away. We also have the benefit of knowing exactly where it's at, because it's pouring out lots and lots and lots of energy. This does a lot to negate that whole "it's far away" problem.

See above multiple choice question

The moon is far away, and yet I have an easier time tracking that than I have tracking a car going past my house. Objects as distant as galaxies are essential stationary when they're being observed. You point your telescope at it and you don't see it whiz past.

Because the Earth totally doesn't rotate and we don't have to compensate for the fact that a miniscule-tiny object is, relative to its size and its apparent speed across the night sky, actually is whizzing the fuck past, and if you're not paying attention for half a minute, you have to re-adjust it.

Compare to your 100 km/s rocket - for half a minute, 3000km of travel time (if in a straight line, I suppose, headed straight at you) is still easy to track. OOH LET ME DO SOME MORE TRIG: Baseline length is 3000km at a distance of 30,000km. Tan[3000/30 000] = 0.100335 radians = 361.20600 arc seconds. That's... really pretty easy to see.

The same cannot be said for a missile. I'm not saying that focusing in on a distant galaxy is easy. I'm saying it's not the same as targeting something close to you moving at appreciable speeds. The first involves precision, but no time constraints. The second requires precision AND it's very time-oriented. And not only do you have to see the missiles, but you have to hit them with a laser.

Because it's very difficult to track objects that are going very fast at distances that are very far away from you

*Aralonia looks at NORAD

Brb moving to Australia. Hey, Anna, can I crash on your couch?

[Noctis]

@Noctis
Because in order for something to be a viable space weapon, it needs to be really cool.

No, but it helps.

[unsunghero10]

Deconstructive/mining nano-clouds, in place of mines.

Just putting that out there.

[Noctis]

Deconstructive/mining nano-clouds, in place of mines.

Just putting that out there.

Nanobots, while cool, are still pretty dang difficult to make. Making something on the nano-scale is difficult be cause there's simply not enough room to make it very complex. It's easier if you can determine the exact particulars of their environment and job, such as seeking out and destroying cancer. But when you have it doing things like mining, that means that logically it will need some sort of thruster for movement, an antennae to pick up remote signals, a way to process those signals, a variety of programs to allow it to move in the vacuum and so on. Nanomachines will generally not be very complex, more like viruses or bacteria.

We could, hypothetically, make something like a bacterium that moved until finding any sort of matter and then devoured it, using the matter to make copies of itself. But that seems like a Grey Goo situation to me.

[zackfire]

For the sake of us all I hope we never invent Gray Goo.

[unsunghero10]

Let me rephrase that,
'non-reproducing' deconstructive nanobots.
We already have nano-motors, which could make nano-drills.

Or better yet, thumb sized robots with tiny drills or tiny lasers.
Too small for PD to notice, and potent in great enough numbers.

[Noctis]

Let me rephrase that,
'non-reproducing' deconstructive nanobots.
We already have nano-motors, which could make nano-drills.

Or better yet, thumb sized robots with tiny drills or tiny lasers.
Too small for PD to notice, and potent in great enough numbers.

Small, non-nano bots are much more likely. The main problem I could see is that we'd need motors strong enough to drill through armor. Maybe lasers, or even easier just explosives.

[zackfire]

That would be even more expensive and less effective than deploying small missiles by the hundreds.

[Noctis]

That would be even more expensive and less effective than deploying small missiles by the hundreds.

I guess it depends on the situation. Releasing them from a ship to target another ship would only be useful if they could sneek in under the opponent's sensors. However, leaving them as a sort of "mine", hidden and running silent until a ship gets close, might be effective. Especially if they can bypass whatever sensors the ship has.

Maybe something like this would be better.

http://www.keiththompsonart.com/pages/needle.html