ship's lasers

[jatay3]

How does a laser do offennsive damage? I can see two ways: the kinetic force caused by energy being suddenly "pumped" into a ship, and the sudden increase in temperature.
As a side note; what would be the viability of using reflective surfaces as armor in a manner analogical to a mirror?

 

[selunatic2397]

In Larry Niven's Mote In God's Eye and the sequel he uses a room temperature superconductor to coat a ship's hull, with more superconductor linked to a large amount of ice. His end result is that the ship can endure hotter temperatures and only be at the temp of boiling water...until you run out of ice/water. How would that work to stop a ship's laser? Would that be better than a chromed out ship's hull?

Just a stray thought crossing my sleep deprived mind.

 

[Ptah]

Originally posted by jatay3:
How does a laser do offennsive damage? I can see two ways: the kinetic force caused by energy being suddenly "pumped" into a ship, and the sudden increase in temperature.
As a side note; what would be the viability of using reflective surfaces as armor in a manner analogical to a mirror?

I'm sure you'll get a lot of input on this. The precise nature of the interaction depends a great deal on laser wavelength and hull material but a general description is as follows.

One mechanism will be explosive vaporization of material from the target. This material will have a high "temperature" and most strongly eject in a plume along the laser beam, but there will be ejectin in all directions it's just not equal in all directions. So stuff will be coming off. The vaporization can occcur two ways, the rapid conversion of the material to a gas and by ionization of material followed by a Coulomb explosion. Both probably occur. Energy transfer from the site of impact to other sites may not provide enough energy to vaporize material but enough to melt it. So you'll get a hole with edges where melted material is blown out. If there is enough heating/thermal shock/expansion you may get material being ejected from the inside of the ship, spalling I believe it is called.

On the question whether reflective surfaces will work as a practical defense: the short answer is no; based on the following. Current mirrors are not perfect reflectors, some energy is always absorbed. If the power of the laser is sufficient this imperfection can be enough power to ruin/degrade the reflectivity, the mirror then absorbs energy damaging the surface, the reflectivity is ruined more, the mirror absorbs even more energy, etc. In addition, even if the surface as applied was reflective enough, other things may damage this surface, dust impacts, other weapons, poor maintenance. Finally, current technology finds some wavelengths very hard to reflect. Laser weapons would likeley exploit any such weakness/gaps in mirror technology.

If you wanted to make reflective surfaces a defense here are some suggestions. The mirrors are very good and you have a way of dynamcially repairing the surface. Maybe it is a liquid material you can extrude and surface tension spreads it. You have a way to carry away excess heat, maybe a thermally superconducting layer underneath.

To expand the topic. I've often wondered if a thermally and electrically superconducting material might provide added protection against lasers by a mechanism where the energy is rapidly transfered across the entire hull so coated. The transfer may be rappid enough in these materials to make this a possibility. Any thoughts out there?

The best analogy I can think of is how ballistic cloth works. The kinetic energy of the bullet is spread out across the cloth instead of all being directed into a small area and thus penetrating.

I don't know if "high temperature" superconducters where common enough knowledge for later editions of Traveller or discussed. I recall Larry Niven had some interesting descriptions of the properties of superconductors in the Known Space works and Ringworld series. But this was long before we discoverred that superconductivity was possible above liquid Helium temperatures.

 

[Ptah]

Originally posted by selunatic2397:
In Larry Niven's Mote In God's Eye and the sequel he uses a room temperature superconductor to coat a ship's hull, with more superconductor linked to a large amount of ice. His end result is that the ship can endure hotter temperatures and only be at the temp of boiling water...until you run out of ice/water. How would that work to stop a ship's laser? Would that be better than a chromed out ship's hull?

Just a stray thought crossing my sleep deprived mind.

Yep, that's the Larry Niven stuff. Oh the irony of cross posting. You could also replace the ice with something that has a higher heat capacity, higher phase transition energies and/or lower vaporization temperature. But ice is probably cheap, has a darn good heat capacity and you can drink the water.

Certainly better than a chromed out hull, maybe not as pretty though.

 

[Anthony]

Originally posted by selunatic2397:
In Larry Niven's Mote In God's Eye and the sequel he uses a room temperature superconductor to coat a ship's hull, with more superconductor linked to a large amount of ice. His end result is that the ship can endure hotter temperatures and only be at the temp of boiling water...until you run out of ice/water. How would that work to stop a ship's laser?

Realistically, superconductors are not good heat conductors, so it would be totally useless. If you have a material that's an extraordinary thermal conductor, it might give superior resistance to lasers, but since we're talking Unobtainium, there's no real way to guess.

 

[Scott Martin]

Your supercon sheathing would work if it was hooked to a mind-blowingly efficient peltier type junction and used to bleed of the generated energy

Oh wait, isn't that an alternate description of a black globe generator

Scott Martin

 

[coldwar]

Lasers are Lasers the just cut and have no heat at all. In Ship Combat there'll be used cut turrets off and make hull breaches (the Ship can be cut but the ships Structure bones would be coatted in high reflectiv materials or light absorbing such as ablitiv armours.)
They can be used to cut thrusters off, or anything that sticks out, though there will be more damage repersenting electrical short outs for that system, ie overloads, burnouts, electrical fire.

nathan

 

[Badbru]

Originally posted by Deathwisher:
Lasers are Lasers the just cut and have no heat at all.
nathan

Maybe that's how they work In Your Traveller Universe. I doubt you'd find many adherents around this forum though. Certainly no adherents among any of the TNE players or Refs.

Never asked yourself HOW they cut Nathan?

 

[Ptah]

Originally posted by Scott Martin:
Your supercon sheathing would work if it was hooked to a mind-blowingly efficient peltier type junction and used to bleed of the generated energy

Are you viewing the superconductor as part of a device to convert heat to current (Seebeck effect) to transfer the heating of the ships hull to the ice via generation of a current in the superconductor? If so, the situation becomes more complicated because what makes common materials "hot" is different than what is required to heat a superconductor. Laser wavelengths corresponding to rotational and vibrational excitation will heat (microwave, infrared), those that are geared towards electronic excitation (UV, x-ray) will not necessarily heat a superconductor. Superconducters then may be part of a composite armor with a portion geared to IR and microwaves.

Or are you talking about the heat evolution at the junction of the superconductor and the ice? If the latter, the Joule Effect (resitive heating) is the dominant effect for a non-conductor.

 

[Scott Martin]

I subtly changed the topic on you Ptah

I postulated using junction heat pump technology to rapidly convert the transferred heat into electricity (outer layer, A Peltier type junction) and dump the resultant current onto an underlying (electrically) superconducting grid. If your fusion power plant has a way of dumping waste heat / power, then the "added" waste energy from a laser (even a MJ level one) should be trivial to deal with.

This would basically be a "surface treatment" black globe screen without the loss of maneiverability or sensors. It would, of course only work on Lasers, and you may need an outer layer of some material guarenteed to strongly absorb laser wavelengths (a metarial with really good black body properties and an insane heat of sublimation. Bonded superdense?)

This relys on being able to dump heat (as electrical power) into the supercon grid faster than the outer layer can sublimate / ionize, so we're *well* into the realms of fantasy here. Maybe not so much so at TL 15 or so, but who knows? I can think of a lot of applications for a material with that kind of response time (sub-nanosecond?) in detectors alone.

Needless to say I don't buy (or even rent) Niven's Thermal and Electrical "twin miracle" room temperature supercons. But they do make for good fantasy.

Scott Martin

 

[TheEngineer]

Hi !

Usually higher TL use small wavelength or X-ray laser, which have much better focussing abilities and a little different behaviour impact like VIS lasers.
As Ptah explained and known from real life laser surface treatment or laser drilling experiments high energy lasers work abrasive not only surface material is melted and vaporized, but also because of sub-surface vaporations, caused by inperfect material structure and heat flow differences. This effect in not always wanted in e.g. laser welding, so its a bit work finding the correct "setting".

The sub-surface vaporization effect would be quite more effectful with an intense x-ray beam, as beam intensity penetrates "outer" regions and decreases only with exp(-kx) (were k is a linear coeffizient related to a special materials and the energy class of the beam photons). Below 1 MeV intensity decrease is mainly caused by compton scattering, photo effect and a running down reaction cascades down to thermal levels.
E.g. a value for lead and 1 MeV photons is around 1 /cm, meaning beam intensity drops to 50% at 0,7 cm and to 0,01% at around 4 cm.
Soft x-rays usually are related to higher values, so at 0,1 MeV the factor is around 70, causing the intensity dropping more rapidly in the material, finally resulting in a surface concentrated effect.

At reasonable high surface intensities x rays laser hits could produce more nasty explosive "inner hull armor" vaporization cascades, helping to move thru the material more quickly = higher penetration.
A side effect of intense ionisation and kinetic transfer is the destruction of molecule bindings/cristal structures, which is not good for a piece of starship hull, especially if its a mechanically stressed part.
This effect could not be prevented even by a super thermal conducter...
What I would like to check is, if x-ray lasers might create kind of significant electrical currents in a target material...

Anyway, if the surface intensity is too low and x-rays are too "hard" the effect might be merely a in depth temperature increase. So, if a laser battery could not create intensities needed, it might be more wise to use soft x rays, which cause surface centered reactions like a VIS laser.

A bit problematic might be, that one just could guess about the actual absolute energies deployed in HG/MT starship combat...
Anybody already made his mind upon that ?

Regards,

Mert

 

[daltoncalford]

IMTU,
Lasers are mostly short range weapons that are used in conjuction with other weapon systems.

For example, sandcasters fired offensively, causing opposing ships to slow down in order to avoid damage due to high-velocity collisions with large quantities of particulate matter combined with missiles guided by laser pointer act as a good low tech one-two punch.

If damage is needed, the laser is used against surface fixtures where the amount of armor is minimal while the damage is very telling (hard to hit someone when all your sensor arrays are overheated/melted).

I do not allow high-pen lasers IMTU as I do not believe that anything less than a nuke-pumped laser has any chance of real penetration, and the nuke portion is far more dangerous than the laser.

Now, a plasma or fusion gun, although very short ranged, has the benefit of kenetic punch combined with heat and extensive radiation.

So, IMTU lasers are not a 'kill' weapon but are a 'tactical' weapon. Most combat is based on missiles with some dogfights occuring withing the km range and not the km's range.

For our group, sandcasters have been used from floating sensor shields to shotgun blasts using the targets own velocity to ablat their own armor away while lasers only come into play when the sand has caused enough surface damage to allow for the heat differentials to cause hull stress or even small punctures.

Lasers have their place, but, not as a good space weapon. That is the reason why the Imperium does not mind them as civilian weapons (only on small point defense turrents (LBB 2 1 ton design)).
Repulsers, Tractors, and homing missiles that use explosive power to generate a massive grav field (you should see what that does to a 'nice' ships vector - really plays havoc with enemy plans).

Oh well, I have gotten totally off topic but, I think you guys see where I am coming from when it comes to laser damage as related to how Traveller has always portrayed it.

best regards

Dalton

 

[Anthony]

Originally posted by TheEngineer:
A bit problematic might be, that one just could guess about the actual absolute energies deployed in HG/MT starship combat...
Anybody already made his mind upon that ?

FF&S2 makes the wavelength of lasers pretty clear. X-ray lasers are 1A, or 12.4 kEv. Non-X-ray lasers vary by TL; at TL 15 they are 10nm (EUV), at TL 11-14 they are 100 nm (UV)

 

[Ptah]

Originally posted by Scott Martin:
I subtly changed the topic on you Ptah

I postulated using junction heat pump technology to rapidly convert the transferred heat into electricity (outer layer, A Peltier type junction) and dump the resultant current onto an underlying (electrically) superconducting grid. If your fusion power plant has a way of dumping waste heat / power, then the "added" waste energy from a laser (even a MJ level one) should be trivial to deal with.

I agree that such heat pump technology wouldn't work, at least with the materials we have or ones even with orders of magnitude better Seebeck coefficients. The unconverted heat would be enough to damage the hull.

Originally posted by Scott Martin:

This relys on being able to dump heat (as electrical power) into the supercon grid faster than the outer layer can sublimate / ionize, so we're *well* into the realms of fantasy here. Maybe not so much so at TL 15 or so, but who knows? I can think of a lot of applications for a material with that kind of response time (sub-nanosecond?) in detectors alone.

Verily (been wanting to use that word for awhile. ). The advances in materials that such a capability implies leads to the postulate that laser defense may just be better met by advanced armors instead of a complex heat shunting system.

Originally posted by Scott Martin:

Needless to say I don't buy (or even rent) Niven's Thermal and Electrical "twin miracle" room temperature supercons. But they do make for good fantasy.

Scott Martin

I love Larry Niven's books but have also wondered about the thermal superconducting aspect, it doesn't fall-out from electrical supercondiuctivity as far as I know. Since I really only know enough about superconductors to be dangerous, nice to see others weighing with their take.

 

[Ptah]

Originally posted by Anthony:
FF&S2 makes the wavelength of lasers pretty clear. X-ray lasers are 1A, or 12.4 kEv. Non-X-ray lasers vary by TL; at TL 15 they are 10nm (EUV), at TL 11-14 they are 100 nm (UV)

Interesting. Does the wavelength impact space combat in any way?
I don't belive CT ever talked about wavelength. IMTU I postulate that lasers weapons at higher TL are designed to have multiple wavelengths to better defeat wavelength dependent defences. Sort of avoids the whole problem of the wavelength and material dependent interactions.

 

[Ptah]

Originally posted by Dalton:
IMTU,
...homing missiles that use explosive power to generate a massive grav field (you should see what that does to a 'nice' ships vector - really plays havoc with enemy plans)....

best regards

Dalton

That's a cool off-topic idea. How are these rated/work?

 

[daltoncalford]

Ok,

Well you know that my system is a little different than most, but, if I was doing it as a book 5 design, I would rate them as nuke missile batteries, with the USP code standing for the reduction in agility of the target vessel if penetration occurs. If agility is reduced below 0, then all other weapons get the absolute value of the hit as a bonus to hit and penetrate for all other weapons brought to bear against the target vessel for one turn. The target vessel recieves a negative modifier for all to hit rolls equal to the amount that agility is reduced below 0.

For LBB2, I would use the LBB5 USP code as a direct G-Vector towards the missile reduced by 1 g per 2 cm of distance. If the missile G template overlaps a planet, the missile template is immediatly centered on the planet and affects all ships in range (making it illegal to have such a destructive weapon around).
If the final vector change is greater than the target vessel(s) G rating, the inertial dampers cannot cancel out the excessive forces causing a (final G effect - Maneauver Drive Rating -1) die modifier on all task rolls for the next turn.
If any vessels are attempting a jump, treat the jump as if it occured within 100 dia.

Just a quick thought for the rules for those of you who are not using my home system.

best regards

Dalton

 

[Anthony]

Originally posted by Ptah:
Interesting. Does the wavelength impact space combat in any way?

Mostly determines effective range of weapons. Also affects happens when the beam hits atmosphere.

 

[TheEngineer]

Hi !

Would like to repeat the question...
Anybody has an idea or information about the absolut amount of energy "transfered" to a target ?
E.g. MT presents the energy requirement of a single laser with 250 MW. But how many MJ does one laser hit represent ?

Is anybody perhaps able to backtrack that from the damage values ?

Regards,

Mert

 

[far-trader]

I think there's just not enough information to work backwards. It would be full of assumptions. Such as what the damage represents, how many shots are actually fired in a turn that is several minutes long, what is the efficiency of the input energy to output power, and so on. I suspect if you start applying math to it you'll find that the lasers do little more than warm up a broad area of a ship's hull and trying to justify damage from that.