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Old 09-06-2017, 09:34 PM   #11
Michael Thayne
 
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Anthony View Post
Presumably there's tech improvements if they're making them as weapons at all, but yes, you'd expect a FEL at gamma wavelengths to be larger than an X-ray installation.
Sorry, there was a typo in the original post that mangled the question. If I'm reading the equations on Wikipedia right, going from say 1nm to 0.1nm requires an FEL 10 times as long, correct?
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Old 09-06-2017, 09:38 PM   #12
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by sir_pudding View Post
Sure but as you say, weaponization in the first place implies there are some ways to compact it.

Nor are two mile spaceships unheard of in fiction.
The whole Spaceships line assumes they're uncommon, though. Two miles translates to SM +19 or +20, which is easy enough to extrapolate but which we have no worked examples of. Even the suggestion for turning an Adversary-class warship into a planet-killer using cosmic power only uses SM+18.
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Old 09-06-2017, 09:49 PM   #13
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Michael Thayne View Post
The whole Spaceships line assumes they're uncommon, though. Two miles translates to SM +19 or +20, which is easy enough to extrapolate but which we have no worked examples of. Even the suggestion for turning an Adversary-class warship into a planet-killer using cosmic power only uses SM+18.
Nope. Spaceships really only hints at length. Streamlined ships or just long thin cylinders can be 2x as long as mostly box-like ones. 3x or more compared to spheres.
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Old 09-06-2017, 10:34 PM   #14
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Michael Thayne View Post
[*]How implausible are smaller versions of these weapons?
If you're willing to take a cut in efficiency, you could use laser wakefield accelerators to get a particle beam with lengths around 1 to 3 meters (SM -2 to +1).
https://en.wikipedia.org/wiki/Plasma_acceleration
We're still working out some of the kinks at TL 8 - we can get particle energies of a GeV in a few cm, but the emittance may not be tight enough to be usable as a spacecraft-to-spacecraft weapon. Also, the theoretical maximum amount of energy you can transfer from your laser pulse to a particle bunch is 50%, in practice current wakefield accelerators are more like 10% to 20%. At this point you need to ask yourself if you should just use that laser to fry your enemies instead.

If you use the particle beam from a wakefield accelerator to drive an x-ray free electron laser, you can get around the emittance problems - FELs self-organize their electron bunches to draw energy from the particles and transfer it to the x-ray field.

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Originally Posted by Michael Thayne View Post
[*]How plausible would it be to lift the limits 1 TL after a weapon is originally introduced?
Why not? TLs are supposed to represent advancement, and a lot of advancement is all sorts of stuff that is unexpected at lower TLs.

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Originally Posted by Michael Thayne View Post
[*]SS7 gives the same size limits for all weapons covered by the optional rule. Is this realistic? I can see particle and antiparticle beams having the same minimum size (depending on how the antiparticles are generated), but would X-ray lasers and grasers have the same minimum size?
Modern x-ray lasers are mostly generated by particle beams, so if you don't have the minimum size for the particle beam you don't get the laser.

We don't have gamma ray lasers, but you can use particle beams to get narrow gamma ray beams using laser Compton backscatter (in principle, you can also use positron annihilation in flight, but that's a tech path that we are not currently pursuing in favor of Compton backscatter).

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Originally Posted by Michael Thayne View Post
[*]I've heard one possibility for x-ray laser weapons involves a "free electron laser", but IIUC these both have (a) an even larger minimum size than given in SS7 and (b) are tunable, so such a weapon could also function on other wavelengths for say planetary bombardment, a capability Spaceships lasers don't have. So how could an ~SM +10 x-ray laser with the capability in Spaceships work?[/LIST]
How could it work? You accelerate up a bunch of electrons and send it through the gap between two Halbach arrays of magnets (a "wiggler").
https://en.wikipedia.org/wiki/Halbach_array
This forces the electrons to move in a sinusoidal pattern. The modes of the electromagnetic field whose force is constantly opposing the motion of the electrons will have work done on them and be amplified. With a suitably long wiggler or a resonant cavity, you can get a very narrow band of modes, like a laser beam. If the radiation field is intense enough and the wiggler is long enough, the electrons will self-organize into bunches to produce super-radiant coherent motion. Now you have a free electron laser.

For a tuneable FEL, you will need separate wigglers for different frequency bands. The wiggler for the x-rays will have a pitch way too short for when you need visible light, so you would divert the electron bunches to a visible light wiggler. (The visible light wiggler would probably also be inside a Fabry-Perot resonant cavity,
https://en.wikipedia.org/wiki/Fabry%...interferometer
allowing you to achieve your laser behavior threshold with a much shorter wiggler.)

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Old 09-07-2017, 10:27 AM   #15
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Fred Brackin View Post
Nope. Spaceships really only hints at length. Streamlined ships or just long thin cylinders can be 2x as long as mostly box-like ones. 3x or more compared to spheres.
I'd forgotten the thing about streamlined ships, but the lengths in the table are for "typical cylinders". There's no indication you can stretch them out significantly beyond what's in the table without the same DR handicap streamlined ships face. Note: two miles is 3,520 yards. SM+19 is 3,000 yards, while SM+20 is 5,000 yards. An SM+18 ship that was two miles long would be 175% of the typical length for an unstreamlined ship, which I think would be an issue for DR.
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Old 09-07-2017, 10:34 AM   #16
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

Assuming a loaded spaceship has the same density as water (which probably overestimates the volume of a warship), a two-mile long cylindrical SM+18 ship would only have a radius of 100 yards. I guess that's not so bad–you can visualize it as bundle of ~4 #2 pencils.

Edit: Still, doubling the length of a skinny cylinder holding volume is increasing the surface area by approximately sqrt(2). More precisely, as [radius divided by length] of the original cylinder goes to 0, the ratio of their surface areas goes to sqrt(2). Which probably justifies the reduction in DR of streamlined ships.

Last edited by Michael Thayne; 09-07-2017 at 12:07 PM.
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Old 09-07-2017, 10:47 AM   #17
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by lwcamp View Post
Modern x-ray lasers are mostly generated by particle beams, so if you don't have the minimum size for the particle beam you don't get the laser.

We don't have gamma ray lasers, but you can use particle beams to get narrow gamma ray beams using laser Compton backscatter (in principle, you can also use positron annihilation in flight, but that's a tech path that we are not currently pursuing in favor of Compton backscatter).
How likely is it that the size of particle accelerator you'd need for a particle beam weapon is significantly larger/smaller than the one you'd need for an x-ray laser weapon? Similarly, am I correct that the accelerator for a graser would likely need to be orders of magnitude larger than the one for an x-ray laser? Does Compton backscatter present its own issues with miniaturization? How does positron annihilation in flight lead to a coherent beam?

Quote:
How could it work? You accelerate up a bunch of electrons and send it through the gap between two Halbach arrays of magnets (a "wiggler").
https://en.wikipedia.org/wiki/Halbach_array
This forces the electrons to move in a sinusoidal pattern. The modes of the electromagnetic field whose force is constantly opposing the motion of the electrons will have work done on them and be amplified. With a suitably long wiggler or a resonant cavity, you can get a very narrow band of modes, like a laser beam. If the radiation field is intense enough and the wiggler is long enough, the electrons will self-organize into bunches to produce super-radiant coherent motion. Now you have a free electron laser.

For a tuneable FEL, you will need separate wigglers for different frequency bands. The wiggler for the x-rays will have a pitch way too short for when you need visible light, so you would divert the electron bunches to a visible light wiggler. (The visible light wiggler would probably also be inside a Fabry-Perot resonant cavity,
https://en.wikipedia.org/wiki/Fabry%...interferometer
allowing you to achieve your laser behavior threshold with a much shorter wiggler.)

Luke
So TLDR; if you want to justify a non-tunable x-ray laser you could assume the multiple wigglers was not worth the trouble?
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Old 09-07-2017, 11:17 AM   #18
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Michael Thayne View Post
Assuming a loaded spaceship has the same density as water (which probably overestimates the volume of a warship), a two-mile long cylindrical SM+18 ship would only have a radius of 100 yards. I guess that's not so bad–you can visualize it as bundle of ~4 #2 pencils.

Edit: Still, doubling the length of a skinny cylinder holding volume is increasing the surface area by approximately sqrt(2). More precisely, as [radius divided by length] of the original cylinder goes to 0, the ratio of their surface areas goes to sqrt(2). Which probably justifies the reduction in DR of unstreamlined ships.
That would be of streamlined ships?

And, well, sort of. If, like an MBT, your spaceship armor plan cares about protection in one direction above all others, a cylinder with a single massively armored endcap is a pretty good design...
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Old 09-07-2017, 12:10 PM   #19
Michael Thayne
 
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Ulzgoroth View Post
That would be of streamlined ships?

And, well, sort of. If, like an MBT, your spaceship armor plan cares about protection in one direction above all others, a cylinder with a single massively armored endcap is a pretty good design...
Whoops, yes, streamlined. Fixed via edit.

And that's a good point. I've previously suggested a "tank hull" design feature that double DR from the front and rear while halving it on the top and bottom. I should look more at the SDV hulls in THS 3e to figure out what a simple way to model would look like.
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Old 09-07-2017, 12:11 PM   #20
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Default Re: [Ultra-Tech] [Spaceships] Weapons that are hard or impossible to miniaturize

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Originally Posted by Ulzgoroth View Post
That would be of streamlined ships?

And, well, sort of. If, like an MBT, your spaceship armor plan cares about protection in one direction above all others, a cylinder with a single massively armored endcap is a pretty good design...
This has the side effect that tactics favors multiple firing platforms so you can hit the side armor.
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