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Graser Quesions

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Re: Graser Quesions
Post by kzt   » Mon Aug 13, 2018 12:15 pm

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JohnRoth wrote:I suspect that a good deal of the reason for the granitic lens is aiming, These things would be pretty useless if they couldn't be aimed, or if aiming them involved moving several tons of emitter hardware on 3-dimensional gimbals to aim them.

Yeah, the pointing accuracy you need for these is pretty extreme. Given that we can accurately aim telescopes at stars it's pretty clear we can do this, but a telescope also doesn't have a 8 meter wide field of view at a million km and has some strong feedback as to whether it's aimed correctly.
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Re: Graser Quesions
Post by ericth   » Mon Aug 13, 2018 12:20 pm

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kzt wrote:Anyhow, so the SD works by absorbing the energy in it's enormous amounts of armor. This results in lots of chunks of armor (generally metal) and pieces of the carbon nano-composite called battlesteel (which forms structural elements of the ship) moving at high velocity, hopefully to be contained by further layers of the armor system.

When say a destroyer gets hit by that same graser you don't have to worry about being killed by fragments of your armor.
Apparently instead the graser converts a 4m cylinder all the way through the destroyer to a few million degrees plasma. This then has roughly the effect of having a good sized nuclear weapon go off inside the ship. This generally results in an overall bad day for everyone on board, often involving the phrase 'lost with all hands'.


This actually brings up a point that I've been puzzling over. It has to do with the deep penetration abilities of the latest laserheads described in the books. IIRC recent textev described through-and-through hits. I'm not an expert on laers, but it seems to me that the pulse duration of a laserhead strike should not be long enough for that.

Shipboard Grazers are multipluse weapons, so when Hexapuma gutted the Peoples Navy in Exile for a third of her length it made sense that multiple pulses were responsible.

However, my intuitive sense is that the short single pulse of a laserhead should not have the deep penetrating power.

Anyone care to elaborate?
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Re: Graser Quesions
Post by kzt   » Mon Aug 13, 2018 12:43 pm

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ericth wrote:However, my intuitive sense is that the short single pulse of a laserhead should not have the deep penetrating power.

Anyone care to elaborate?

I'm told the essay was written by a nuclear power officer in the US Navy who has enough background in the physics of high energy plasma's and energy weapons to likely know what he's talking about.
The description in the essay (about an obsolete RMN missile) says:
Returning to our Mk-13 anti-ship missile example for specifics we discover that precise numbers are hard to come by without a security clearance. Publically available statements indicate that the Mk-13 uses one Mk-86 general purpose fusion warhead with a yield of 15 megatons pumping six Mk-73 laser rods to produce X-ray beams. This last is unsurprising since all practical bomb-pumped laser beams are in the X-ray range. The exact wavelength of the Mk-73’s Special Laser Material output is classified. Weapon characteristics are classified to frustrate enemy countermeasures, but they also frustrate attempts to understand and predict performance. What can be stated with some certainty from known physics is that the Mk-73’s beams probably have a wavelength around ten picometers. Total energy on target and laser power figures are not even hinted at in public and useful speculation is nearly impossible. Public speculation has these weapons depositing terajoules or petajoules into their targets at powers in the petawatt to exawatt or possibly higher range. Detailed computer simulations are required to fully describe laser penetration profiles and these simulations require a great deal of information about the beam and the target for accuracy. The best such simulations are, of course, classified. The author’s speculations are enough however to give a hint of what happens when a Mk-73’s laser beam strikes a target.
1. Ten-picometer photons are energetic enough to fully and completely ionize most common spacecraft materials. This means that all of the atoms in the area illuminated by the beam have all of their chemical bonds broken as their electrons are all stripped off. This is of particular importance for two competing reasons. First, ionizations generally consume massive amounts of beam energy without doing much further damage to the target. The material is ionized. Any structure made from it is destroyed after the first ionization, but the beam goes right on stripping electrons from the ionized matter as it rapidly expands away from the rest of the ship. Hence, materials which can soak up the most beam energy in ionizations usually make excellent armor. However, continuing to pour energy into the ionized cloud of target atoms can be useful from the weapon’s perspective. It happens that, once a target is completely ionized by the first photons in a short wavelength beam, it can become largely transparent to the rest of that beam. Called “bleaching” this phenomenon means that if one puts enough short wavelength photons into the target material, one continues to burn through it.
2. Most spacecraft materials are opaque to 10 picometer photons. That means that the X-ray photons in these laser beams will be absorbed within a short distance (perhaps one millimeter) of the target’s surface.
3. The massive terajoule or petajoule DETT of the Mk-73 render the weapon capable of completely disintegrating huge amounts of the target. Perhaps the following reflection will supply perspective: one source close to the author mentioned test firings of Mk-73 laser heads which punched holes clear through stony iron asteroids dozens of meters across.
4. Couple the above-mentioned high energy with petawatt to exawatt power and one gets beams that convert any matter into plasma that resembles stellar core material. Nonintuitive things happen here—solid matter flows and expands like a gas, thermal radiation from the superheated matter pushes radiation shock waves through the material at the local speed of light, and mechanical shock waves travel long distances carrying tremendous energy of their own. While none of these shocks carry as much energy as the original beam they often carry more than enough to shatter the target’s structure into splinters many meters away from the original impact site.
5. Ten-picometer photons are not energetic enough to penetrate the nuclei of target atoms. This means that the target does not, in addition to worrying about being ionized or torn apart by shock waves, need to worry about having its elements transmuted into something radioactive to complicate damage control or repair efforts.
A picture of the Mk-73’s interaction with a target’s armor now emerges. The first photons in the beam atomize and then fully and completely ionize a thin outer layer of armor and bleach the resulting plasma. This takes a few billionths of a second and it clears a path for the photons that follow to repeat the process on the newly exposed material deeper inside the armor. Later photons repeat this cycle and the beam “burns through” a target very much like an incredibly high-speed cutting torch. The whole laser pulse takes roughly a tenth of a microsecond or so. The huge total energies possible in bomb pumped beams can propagate this process to tremendous depths. Thermal and mechanical shock waves race out from the nearly instantaneously ionized column or cone of material, inducing tremendous stresses in the target and often shattering it.
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Re: Graser Quesions
Post by Bill Woods   » Mon Aug 13, 2018 10:56 pm

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kzt wrote:I'm told the essay was written by a nuclear power officer in the US Navy who has enough background in the physics of high energy plasma's and energy weapons to likely know what he's talking about.
The description in the essay (about an obsolete RMN missile) says:
Returning to our Mk-13 anti-ship missile example for specifics we discover that precise numbers are hard to come by without a security clearance. Publically available statements indicate that the Mk-13 uses one Mk-86 general purpose fusion warhead with a yield of 15 megatons pumping six Mk-73 laser rods to produce X-ray beams. This last is unsurprising since all practical bomb-pumped laser beams are in the X-ray range. The exact wavelength of the Mk-73’s Special Laser Material output is classified. Weapon characteristics are classified to frustrate enemy countermeasures, but they also frustrate attempts to understand and predict performance. What can be stated with some certainty from known physics is that the Mk-73’s beams probably have a wavelength around ten picometers. Total energy on target and laser power figures are not even hinted at in public and useful speculation is nearly impossible. Public speculation has these weapons depositing terajoules or petajoules into their targets at powers in the petawatt to exawatt or possibly higher range. Detailed computer simulations are required to fully describe laser penetration profiles and these simulations require a great deal of information about the beam and the target for accuracy. The best such simulations are, of course, classified.
...
An upper limit of the laser power can be estimated. The size, distance, and orientation of the rods relative to the warhead gets you to the fraction of the warhead's energy intercepted by the rods. (Multiply that by the focussing effect of the warhead's gravity generators. A factor of two? Three?)
Multiply that by an estimate for the efficiency of turning that energy into the laser beam.

N.b. a wavelength of 10 pm ~ an energy of 100 keV per photon.
----
Imagined conversation:
Admiral [noting yet another Manty tech surprise]:
XO, what's the budget for the ONI?
Vice Admiral: I don't recall exactly, sir. Several billion quatloos.
Admiral: ... What do you suppose they did with all that money?
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Re: Graser Quesions
Post by evilauthor   » Tue Aug 14, 2018 1:39 am

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ericth wrote:However, my intuitive sense is that the short single pulse of a laserhead should not have the deep penetrating power.

Anyone care to elaborate?


X-Rays and Gamma Rays are deeply penetrative by nature. You don't need a long pulse to penetrate deeply because even single photons of X-Ray and Gamma wavelengths can penetrate go through a lot of material before being absorbed by said material.

So even with a short pulse of a bomb pumped X-Ray laser, the laser is being absorbed by armor several meters deep ALL AT ONCE, not depositing its energy on the outer surface and burning its way in. And there's gotta be a lot of energy in that short pulse to create explosive vaporization in several cubic meters of armor all at once.

And the really impressive part is how the armor absorbs all that energy, to the point that no one ever worries about radiation poisoning. Worried about explosive decompression and flying debris, yes, but not getting dosed by any X-Rays and Gamma Rays that have been attenuated by the armor from "instantly lethal" to merely "poisonous".
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Re: Graser Quesions
Post by Hegemon   » Tue Aug 14, 2018 1:09 pm

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kzt wrote:
JohnRoth wrote:I suspect that a good deal of the reason for the granitic lens is aiming, These things would be pretty useless if they couldn't be aimed, or if aiming them involved moving several tons of emitter hardware on 3-dimensional gimbals to aim them.

Yeah, the pointing accuracy you need for these is pretty extreme. Given that we can accurately aim telescopes at stars it's pretty clear we can do this, but a telescope also doesn't have a 8 meter wide field of view at a million km and has some strong feedback as to whether it's aimed correctly.


I would like to ask you a question on ship-mounted grasers versus laser heads:

In Short Victorious War you have a scene where a HMS Bellerophon's sidewall and armor shrugs off the massed fire of ship-mounted lasers and grasers from 4 Havenite BCs and then proceeds to casually destroy them using its own (much more powerful) ship-mounted weapons.
(BTW, I love the chapter's ending: "A quarter-second later, Battlecruiser Divisions 141 and 142 of the People's Navy ceased to exist.")

I don't know the broadside of the Sultan-class, but supposing that it is the same as the newer Warlord-class (6 Grasers and 6 Lasers per broadside), it would mean 24 Grasers and 24 Lasers shrugged off with minimal damage by a DN's sidewalls and armor. However, the same DN (or its bigger SD cousin) can only take ~250 MDM laser heads (each with ~9 lasing rods) before being destroyed. So the obvious question is how is it possible that a MDM laser head that weights maybe 50 tons seem to be in the same destructiveness ballpark as a ship-mounted Graser (even it is only a BC-size Graser) that weights maybe 1000-2000 tons and has access to the enormous energy stored in the ship's capacitors.

Thank you very much for your time.
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Re: Graser Quesions
Post by TFLYTSNBN   » Wed Aug 15, 2018 9:41 am

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Grasers just like lasers, optical telescopes and microscopes, and radar are limited by the phenomenon of diffraction. Photons that pass through an aperature spread out. There are complications of diminishing intensity from beam center as well as side lobes caused by constructive interference. However; the simple rule of thumb is that a photon beam will spread out at a rate given by the equation:

Beam Spread Angle = 2.44 x wavelength / aperature diameter.

Obviously lenses and mirrors can focus a light beam into a spot much smaller than the optical elements. However; the phenomenon of diffraction dictates how small that spot size can be.

Diffraction also dictates how accurately an optical system can resolve details or direction.

What this means for Honorverse ships is that X-ray lasers and Grasers can be effective at much longer ranges than optical wavelength lasers.

Take a hypothetical laser mounted on an SD with a wavelength of one-tenth of a micron and a 10 meter diameter optical system.

Diffraction Limitation = 2.44 x 1eex-7 meters / 10 meters

Beam Divergence Angle = 2.44eex-8 radians.

At a range of one million kilometers or 1eex9 meters, spot diameter = 24.4 meters. That is a lot of beam area to spread the energy over so unless you have Petawatt class lasers, this is not going to do much to an armored target.

Compare this to the laser mounted on a pinnance as described in THE SHADOW OF SAGANAMI. If I recall correctly, Weber described the laser mount as having a 10 centimeter aperature.

The Beam Divergence Angle would be 2.44eex-6 radians.

At a range of one million kilometers, the spot diameter is 2,440 meters! Since the energy density of the laser is inversely proportional to the beam front area, the actual intensity for a given power output is one ten thousandth of the 10 meter optical system.

There are a few tricks that can increase the effective optical diameter of a laser. One trick would be to have multiple lasers spaced a distance apart that are optically linked to act as one. This is essentially how the Very Large Array radio telescope in New Mexico functions. We now have multiple element optical telescopes that operate on the same principle. (Thanks to President Ronald Reagan and his SDI research propgram). Unfortunately; this trick would require Honorvese ships to take their sidewalls down. Using this system on chase armaments might be practical.

The other alternative is to decrease the wavelength of the energy beam. X-ray lasers as used on laserheads use this trick. However; there small diameter optical systems and chaotic conditions during lasing limits their range to a few thousand kilometers or perhaps tens of thousands of kilometers. When combined with multimeter diameter optical systems, even longer wavelength X-ray lasers would be very destructive at ranges measured in millions of kilometers.

Weber uses the word "Graser", but the dstinction between X-rays and Gamma rays is a bit slippery. There is no specific wavelength that seperates X-rays from Gamma rays. By convention X-rays are emitted by energy level transitions of electrons while Gamma Rays are emitted by energy transitions within atomic nuclei. The dividing line is about 1eex-10 meters, but that is fuzzy.

Weber's use of the word "Graser" suggests a weapon system that operates on energy state transitions within atomic nuclei. The phenomenon of energy transitions within certain nuclear Isomeres suggests that this is possible. I could forgive Weber for using the word "Graser" because "Xaser" is impossible to pronounce.

As KZT and others who shall not be named speculated years ago on this forum, Gamma Ray lasers with optical systems meters in diameter could be extremely destructive at distances of many astronomical units. However; this presumes "optical" systems that are diffraction limited. It is quite plausible that the focusing systems on Grasers are extremely blurry resulting in performance that falls far short of diffraction limit. We can accept Weber imposing range limitations that might seem arbitrary.
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Re: Graser Quesions
Post by TFLYTSNBN   » Wed Aug 15, 2018 9:46 am

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One other point.

KZT pointed out that there is no possibility of a physical optical system focusing a Graser. I would respectfully point out that X-ray telescopes that using grazing incidence reflection MIGHT be able to do the job.

However; a far more plausible concept would be a phased array Graser. You might have dozens or even hundreds of graser emitters that are bundled together and optically linked. You might call isuch a weapons system a "PHASER".
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Re: Graser Quesions
Post by Louis R   » Wed Aug 15, 2018 8:45 pm

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Actually, Himself's use of graser suggests that he's adopted the astronomical definition of gamma ray - photon energy > 100keV - and says nothing about mode of generation. My guess is that shipboard energy mounts are all FELs on steroids.

Weber uses the word "Graser", but the dstinction between X-rays and Gamma rays is a bit slippery. There is no specific wavelength that seperates X-rays from Gamma rays. By convention X-rays are emitted by energy level transitions of electrons while Gamma Rays are emitted by energy transitions within atomic nuclei. The dividing line is about 1eex-10 meters, but that is fuzzy.

Weber's use of the word "Graser" suggests a weapon system that operates on energy state transitions within atomic nuclei. The phenomenon of energy transitions within certain nuclear Isomeres suggests that this is possible. I could forgive Weber for using the word "Graser" because "Xaser" is impossible to pronounce.

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Re: Graser Quesions
Post by Jonathan_S   » Thu Aug 16, 2018 1:42 pm

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Hegemon wrote:I would like to ask you a question on ship-mounted grasers versus laser heads:

In Short Victorious War you have a scene where a HMS Bellerophon's sidewall and armor shrugs off the massed fire of ship-mounted lasers and grasers from 4 Havenite BCs and then proceeds to casually destroy them using its own (much more powerful) ship-mounted weapons.
(BTW, I love the chapter's ending: "A quarter-second later, Battlecruiser Divisions 141 and 142 of the People's Navy ceased to exist.")

I don't know the broadside of the Sultan-class, but supposing that it is the same as the newer Warlord-class (6 Grasers and 6 Lasers per broadside), it would mean 24 Grasers and 24 Lasers shrugged off with minimal damage by a DN's sidewalls and armor. However, the same DN (or its bigger SD cousin) can only take ~250 MDM laser heads (each with ~9 lasing rods) before being destroyed. So the obvious question is how is it possible that a MDM laser head that weights maybe 50 tons seem to be in the same destructiveness ballpark as a ship-mounted Graser (even it is only a BC-size Graser) that weights maybe 1000-2000 tons and has access to the enormous energy stored in the ship's capacitors.

Thank you very much for your time.

From a physics standpoint this doesn't make a lot of sense - TFLYTSNBN covered how the energy gets lost or spread by distance, but in the Honorverse that seems to happen much more quickly than you'd expect; giving the firing range of the energy weapon is fired a massive influence over its effectiveness.

So a BC broadside laser fired at 500,000 km seems to have less effective impact than a bomb-pumped laserhead which goes off at no more than 30,000 km (in SVW. By WoH some had improved their standoff range to 50,000 km).
(I think there's even a mention that a DD's energy weapons can't normally penetrate the sidewall of an SD unless she gets really close)


The energy weapons probably shouldn't be dissipating power that quickly over those ranges - but in the novels they seem to.
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