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Why do we need X-ray lasers???

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Re: Why do we need X-ray lasers???
Post by Whitecold   » Fri Mar 28, 2014 2:26 pm

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Joat42 wrote:
Whitecold wrote:In the end it boils down to "because the plot says so."

6 orders of magnitude more energy trump about every targeting consideration, and missiles were used before laser heads were invented, and could achieve kills.


Not really unless it's directed in a specific direction. An object traveling at near c velocities hitting a sidewall will do negligible damage to any ship but the impact will look very spectacular and probably mess up sensors but nothing more.

A focused nuclear blast will have a much better chance penetrating a sidewall since it's energy are focused on 1 small area.

In other words, the inverse square law is not very forgiving on undirected energy.


Except the energy is very, very directional. If a nuke can take down a sidewall, then can a kinetic impact. If you scale it down, why should something be susceptible to a ton of TNT, but immune to a Megaton thermonuclear explosion?

Also any sidewall deflecting a missile should generate an awesome amount of radiation, simply due to the fact that particles are accelerated, and the radiation will be focused in direction of the momentum of the missile.
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Re: Why do we need X-ray lasers???
Post by kzt   » Fri Mar 28, 2014 3:09 pm

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I suspect the answer is "Because that is how it works". Which is fine, I don't read the books to learn about high energy physics and I don't think David would think of himself as qualified to write a textbook anyhow.
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Re: Why do we need X-ray lasers???
Post by cralkhi   » Fri Mar 28, 2014 8:27 pm

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Whitecold wrote:Except the energy is very, very directional. If a nuke can take down a sidewall, then can a kinetic impact.

Did the nukes actually take down the sidewall? I thought that actually taking it down needed another gravity effect (wedge, grav lance) -- energy weapons "burn through", and pre-laser head missiles used "sidewall penetrators" -- which I don't think actually destroy/take down the sidewall.

I'm not entirely clear what a contact nuke did after contacting/penetrating the sidewall though.

In any case, kinetic impacts definitely do not take down sidewalls. The sidewall is an area of intense gravity, a kinetic impactor doesn't damage it - it's just torn up by the gravity (or I guess squashed by the gravity and torn up by tidal forces).

Also any sidewall deflecting a missile should generate an awesome amount of radiation, simply due to the fact that particles are accelerated, and the radiation will be focused in direction of the momentum of the missile.


Well, the direction of the (atomized residue of the) missile will be changed by the enormous gravity of the sidewall, so most of it probably misses the ship.

And Honorverse ships have impressive particle shielding anyway -- they need it to move at .8 c.

Laser heads and starship lasers/grasers apparently do damage by dumping in heat/energy so fast the armor basically explodes. They're both very focused weapons.
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Re: Why do we need X-ray lasers???
Post by kzt   » Fri Mar 28, 2014 8:45 pm

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cralkhi wrote:Did the nukes actually take down the sidewall? I thought that actually taking it down needed another gravity effect (wedge, grav lance) -- energy weapons "burn through", and pre-laser head missiles used "sidewall penetrators" -- which I don't think actually destroy/take down the sidewall.

I'm not entirely clear what a contact nuke did after contacting/penetrating the sidewall though.

Nukes can. I'm pretty sure the sidewall burners in Andy's article came out of David's notes. KE doesn't because that it is so written.

What a sidewall penetrator does after penetrating the sidewall is explode. They are multi-megaton yield shaped fusion bombs, so this can be pretty damaging. Or not, it depends on where the ship is inside the sidewall and how close the warhead passes to the ship. If it gets within a km or two before exploding you could do quite a lot of damage to every part of the ship that can see the explosion, plus stuff inside the hull damaged by the resulting shockwave.
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Re: Why do we need X-ray lasers???
Post by Whitecold   » Sat Mar 29, 2014 3:21 am

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cralkhi wrote:In any case, kinetic impacts definitely do not take down sidewalls. The sidewall is an area of intense gravity, a kinetic impactor doesn't damage it - it's just torn up by the gravity (or I guess squashed by the gravity and torn up by tidal forces).

Yes, the particles get deflected. But getting deflected means those particles start radiating, mainly in forward direction, it doesn't matter if they are turned into plasma. They still radiate. The effect is https://en.wikipedia.org/wiki/Bremsstrahlung, at least for deceleration due to EM fields, I don't know what it's called for gravitational fields, but the effect is still there.


cralkhi wrote:Well, the direction of the (atomized residue of the) missile will be changed by the enormous gravity of the sidewall, so most of it probably misses the ship.

And Honorverse ships have impressive particle shielding anyway -- they need it to move at .8 c.

Laser heads and starship lasers/grasers apparently do damage by dumping in heat/energy so fast the armor basically explodes. They're both very focused weapons.


Yes, the direction will be changed, the same as for a laser beam. In the relativistic limit the difference between a massless particle (x-ray photon) and a particle with mass (nuclei, electrons in a missile) vanish. There is a difference in trajectory, but it gets small and can be corrected for.
And for the focused part, what is unfocused in the momentum of a missile?
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Re: Why do we need X-ray lasers???
Post by SWM   » Sat Mar 29, 2014 10:48 am

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Whitecold wrote:
cralkhi wrote:In any case, kinetic impacts definitely do not take down sidewalls. The sidewall is an area of intense gravity, a kinetic impactor doesn't damage it - it's just torn up by the gravity (or I guess squashed by the gravity and torn up by tidal forces).

Yes, the particles get deflected. But getting deflected means those particles start radiating, mainly in forward direction, it doesn't matter if they are turned into plasma. They still radiate. The effect is https://en.wikipedia.org/wiki/Bremsstrahlung, at least for deceleration due to EM fields, I don't know what it's called for gravitational fields, but the effect is still there.


cralkhi wrote:Well, the direction of the (atomized residue of the) missile will be changed by the enormous gravity of the sidewall, so most of it probably misses the ship.

And Honorverse ships have impressive particle shielding anyway -- they need it to move at .8 c.

Laser heads and starship lasers/grasers apparently do damage by dumping in heat/energy so fast the armor basically explodes. They're both very focused weapons.


Yes, the direction will be changed, the same as for a laser beam. In the relativistic limit the difference between a massless particle (x-ray photon) and a particle with mass (nuclei, electrons in a missile) vanish. There is a difference in trajectory, but it gets small and can be corrected for.
And for the focused part, what is unfocused in the momentum of a missile?

Actually, charged particles deflected by a gravitational field do not radiate. Particles affected by a gravitational field are in free-fall. They do not feel an acceleration, and therefore do not radiate. There is no Bremsstrahlung radiation from an object being torn apart by a sidewall. There will be some extra energy generated by the inter-molecular bonds breaking as the solid material is broken apart. But that is a fairly small amount, and is non-directional.
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Re: Why do we need X-ray lasers???
Post by Whitecold   » Sat Mar 29, 2014 11:33 am

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SWM wrote:Actually, charged particles deflected by a gravitational field do not radiate. Particles affected by a gravitational field are in free-fall. They do not feel an acceleration, and therefore do not radiate. There is no Bremsstrahlung radiation from an object being torn apart by a sidewall. There will be some extra energy generated by the inter-molecular bonds breaking as the solid material is broken apart. But that is a fairly small amount, and is non-directional.


The particles still have an electric field, if you transform their rest frame to the frame of the ship, the electromagnetic field is no longer constant.
Photons are not conserved when switching between different accelerated frames.
http://m.iopscience.iop.org/0264-9381/16/1/021
https://physics.stackexchange.com/quest ... ld-radiate
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Re: Why do we need X-ray lasers???
Post by SWM   » Sat Mar 29, 2014 11:33 pm

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Whitecold wrote:
SWM wrote:Actually, charged particles deflected by a gravitational field do not radiate. Particles affected by a gravitational field are in free-fall. They do not feel an acceleration, and therefore do not radiate. There is no Bremsstrahlung radiation from an object being torn apart by a sidewall. There will be some extra energy generated by the inter-molecular bonds breaking as the solid material is broken apart. But that is a fairly small amount, and is non-directional.


The particles still have an electric field, if you transform their rest frame to the frame of the ship, the electromagnetic field is no longer constant.
Photons are not conserved when switching between different accelerated frames.
http://m.iopscience.iop.org/0264-9381/16/1/021
https://physics.stackexchange.com/quest ... ld-radiate

The first article you cite is talking about zones of negative Ricci curvature, which is not a normal gravitational field. Normal gravitational fields have a positive Ricci curvature. That's why it is talking about such zones near a cosmic string, and the fact that the Cerenkov radiation will be a particular signature that identifies it as a cosmic string.

The second website you refer to has several answers to the question, but a quick perusal shows several errors in those answers. For instance, one person says that an electron falling in a gravitational field gives up gravitational potential energy by radiating electromagnetic energy, but that is not correct. It gives up gravitational potential energy in exchange for kinetic energy.

I am still pretty certain that an electron accelerated in an (ordinary) gravitational field does not radiate photons, but I will examine the articles you refer to in greater detail and get back to you.
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Re: Why do we need X-ray lasers???
Post by Michael Everett   » Sun Mar 30, 2014 10:32 am

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Why do we need X-ray lasers?

Because water pistols only work once!
:lol:
(See Bucky O'Hare ep1 for details)
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