Graser Quesions

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.

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'.

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?

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.

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.
...

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?

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.

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.

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.