Particle Beams, Pulse Lasers and Beam Lasers

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alex_greene
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Postby alex_greene » Fri Jun 04, 2010 12:26 pm

Rikki Tikki Traveller wrote:Particle beams in Traveller use neutrons, so there is no decay, so a Nuclear Damper would have no effect.
Free neutrons do decay. They have a half life measured at about 15 minutes. You could hypothesise that nuclear dampers' disruption of the strong nuclear force causes immediate neutron decay even among bound neutrons. Nuclear dampers would work on the unstable "surface" neutrons with the highest energy of the nucleus; perhaps disintegrators work on the deeper, lower energy-band neutrons closer to the "core" of the nuclei.

But yeah, neutron radiation would get blocked if it crossed through a nuclear damper field.
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Postby Lord High Munchkin » Fri Jun 04, 2010 12:35 pm

Wouldn't nuclear-pumped lasers be a better option?

I think they had them in '2300AD'.
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Postby Rikki Tikki Traveller » Fri Jun 04, 2010 2:13 pm

Bomb Pumped Lasers are also mentioned in HG (page 49 in the box text) for torpedoes anyway.

Basically, the nuclear blast powers an x-ray laser. This focuses the blast and helps concentrate the energy onto the target (less of the blast goes into empty space).

Regarding hull material protecting against X-rays.

Yes, a couple of centimeters of steel or lead will protect from normal levels of X-rays, but the energy still has to be absorbed by the hull, so thermal effects will still happen and that could cause hull/structure damage or internal hits if a section of the hull buckles under the thermal stress.

The energy of the blast doesn't just go away when it hits the hull/armour, it still has to go somewhere.

Just like hitting a brick wall with your car, the wall may not be destroyed, but it might be cracked or at least weakened because it absorbed some of the energy from the collision just like your car did. When you car gets smashed up, that is the energy of the impact going into deformation of the metal in the car.
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Postby Lord High Munchkin » Fri Jun 04, 2010 3:46 pm

So, in effect a nuclear missile might be a nuclear-pumped laser with a close-proximity fuse?

I don't have HG, so you might want to ignore the above if it contradicts.
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Postby BP » Fri Jun 04, 2010 8:36 pm

Just for clarification:
Rikki Tikki Traveller wrote:...The energy of the blast doesn't just go away when it hits the hull/armour, it still has to go somewhere.
RTT is, I believe, specifically referring to the smaller percentage of radiation that is absorbed by the hull/armour, which can cause warping, ablation, and embrittlement.

Most of the radiation will just go through...

So make sure the crew has taken their KI pills!
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Postby Egil Skallagrimsson » Sun Jun 06, 2010 8:33 pm

Many thanks to all for the wide range of replies, lots to think about there.

Still going to increase the damage of nukes, 4d6 missiles and 16d6 torpedoes (contact hit), but will keep particle beams as is (3I space opera conventions), they are clearly very much part of the spirit of the game

In a non-3I setting will be more radical (probably scrap particle beams entirely)

Looking at HG again, noticed the radiation shielding option gives 6pt protection against nukes, particle beams and fusion guns, as well as 1000 rads of protection for crew. IMHO a must for any military ship likely to face particle beams. A snip at 0.25 MCr per ton of hull!

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Postby apoc527 » Mon Jun 07, 2010 12:32 am

Actually, if you believe the math, an x-ray laser (like those generated by x-ray laser warheads) is a ravening death beam:

Bottom line is an x-ray laser is technologically very challenging, but if you manage to make one you have an Unstoppable Death Ray of Stupendous Range.

Luke Campbell:

Let's take a 10 MW ERC pumped FEL at just above the lead K-edge. This particular wavelength is used because lead is pretty much the heaviest non-radioactive element you can get, and at just above the highest core level absorption for a material you can get total external reflection at grazing angles - so no absorption or heating of a lead grazing incidence mirror. We will use a 1 meter diameter mirror. The Pb K-edge x-ray transition radiates at 1.4E-11 m. This gives us a divergence angle of 1.4E-11 radians. At 1 light second, we get a spot size of 5 mm, and an intensity of 5E11 W/m2.

Looking at the NIST table of x-ray attenuation coefficients, and noting that 1.4E-11 m is a 88 keV photon, we find an attenuation coefficient of about 0.5 cm2/g for iron (we'll use this for steel), 0.15 cm2/g for graphite (we'll use this for high tech carbon materials) and 0.18 cm2/g for borosilicate glass (a very rough approximation for ceramics). Since graphite has a density of 1.7 g/cm3, we get a 1/e falloff distance (attenuation length) of 4 cm. Iron, with a density of 7.9 g/cm3, has an attenuation length of 0.25 cm. Glass, density 2.2 g/cm3, has an attenuation length of 2.5 cm.

At 1 light second, therefore, the beam is depositing 2E12 W/cm3 in iron at the surface and 7E11 W/cm3 at 0.25 cm depth; 1.2E11 W/cm3 in graphite at the surface and 5E10 W/cm3 at 4 cm depth; and 2E11 W/cm3 in glass at the surface and 7E10 W/cm3 at 2.5 cm depth. Using 6E4 J/cm3 to vaporize iron initially at 300 K, we find that iron flashes to vapor within a microsecond to a depth of 0.9 cm. The glass, assumed to take 4.5E4 J/cm3 to vaporize (roughly appropriate for quartz) will flash to vapor within a microsecond to a depth of 4 cm within a microsecond. Graphite, at 1E5 J/cm3 for vaporization, will flash to vapor to a depth of 0.7 cm within a microsecond (the laser performs better if we let it dwell on graphite for a bit longer, we get a vaporization depth of 10 cm after ten microseconds).

Net conclusion - ravening death beam at one light second.

Now lets look at one light minute. The beam is now 30 cm across. This is much deeper than the attenuation length in all cases, so we will just find the radiant intensity and the equilibrium black body temperature of that intensity. We have an area of 7E-2 m2, and an intensity of 1.4E8 W/m2. You need to reach 7000 K before the irradiated surface is radiating as much energy away as heat as it is receiving as coherent x-rays. The boiling point of iron is 3023 K, the boiling point of quartz is 2503 K, and the sublimation temperature of graphite is 3640 K. All of these will be vaporized long before they stop gaining heat. At this range, the iron is subject to 5.6E8 W/cm3 at the surface, the graphite to 3.3E7 W/cm3 at the surface, and the glass to 5.6E7 W/cm3 at the surface. Using the above values for energy of vaporization, we get about 0.1 milliseconds before the iron starts to vaporize, 0.8 milliseconds before the glass starts to vaporize, and 3 milliseconds before the graphite begins to vaporize (because of its long attenuation length, once it begins to sublimate, graphite sublimates rapidly to a deep depth, while you essentially have to remove the iron layer by layer).

Net conclusion - still a ravening death beam at one light minute.

What about at one light hour? The beam is 18 meters across. The equilibrium black body temperature is 900 K. This is well below the melting point of most structural materials. Ten megawatts, however, is a lot of ionizing radiation. Any unhardened vehicle will be radiation killed at these ranges.

However, he goes on to note that in order to boost electrons to the velocities required for an X-ray free electron laser, you will need an acceleration ring approximately one freaking kilometer in diameter. So this X-ray laser would only be suitable for exceedingly huge warships, orbital fortresses, and Death Stars.

Since the time he wrote the above, Luke Campbell has reconsidered the use of lead grazing incidence mirror. Now he favors using diffraction.

Luke Campbell:

I have since come to realize that at x-ray energies this high, matter cannot act as a mirror even at grazing angles (the x-rays have such a short wavelength that they interact with the atoms individually, rather than seeing them as a flat sheet - and you can't really get grazing incidence off of an individual atom). This is why I now prefer diffraction for focusing.
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Postby rinku » Mon Jun 07, 2010 3:37 am

Stepping aside from the nuke stuff for the other question re pulse/beam lasers...

Traveller has a long history of not giving us consistant rules on this point. Supposedly, beam lasers are more accurate, but pulse lasers do more damage in the event that they hit. However the various rules sets never really bore this out, often just not giving any rule about it.
The only thing that has been consistant is that the Pulse Laser is the cheap one (MCr0.5 vs MCr1.0 for the beamer).

I would say that with the Mongoose High Guard mods, someone has finally provided rules that make sense in game design terms and which back up the original stated difference between the two as provided in OT book 2. One assumes that both models have the same power requirements, but that the pulse laser shoots twice as hot, half as often.

Is the MGT HG Pulse laser (on average) crappier? Yes. It's woefully inaccurate compared to the Beam laser. Thus its cheapness and low-techness. However, it is not pointless because of the higher damage value in the event it does hit.

It's also worth considering that for point defense (where damage caused has no real meaning - one hit kills one missile), you want beam lasers (which makes sense!). If you're on a buget, or have unusally high Gunnery skill, maybe the Pulse Laser is your friend...

There could be room here for a variable pulse laser that could switch between modes. Tech 13 is a popular breakpoint for laser tech in Traveller, so maybe TL13, MCr2?
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Postby locarno24 » Mon Jun 07, 2010 9:59 am

So, in effect a nuclear missile might be a nuclear-pumped laser with a close-proximity fuse?

It must be detonating in close proximity (or else the radiation hit wouldn't apply), and you can either visualise it as a big nuke powering a laser but detonating close enough to allow point defence to engage it normally (which seems a little foolish since you can obviously make a missile that doesn't - see bomb-pumped torp rules), or a small nuke going for contact detonations. Personally, I think the latter seems simpler.
Looking at HG again, noticed the radiation shielding option gives 6pt protection against nukes, particle beams and fusion guns, as well as 1000 rads of protection for crew. IMHO a must for any military ship likely to face particle beams. A snip at 0.25 MCr per ton of hull!
Yes. In any setting where nuclear weapons are the standard arm of a fleet, not taking specific radiation-hardening along with conventional armour is just daft.
Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.
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Postby Egil Skallagrimsson » Mon Jun 07, 2010 6:37 pm

Well, there are a lot of daft miltary ship designs in HG, T & G and FS! Almost none have radiation shielding. Admittedly, this adds a lot more MCr to the price, but if Joe Zhodani shows up with radiation shielding, and you don't, you'll be the one floating arround in a irradiated escape pod.

My starting point for this line of thinking was running some naval engagements, during the course of which it became obvious that most ships in FS are ridiculously underarmoured, and a number in the other books could do with more. As a guide now, any line of battle vessel without its TL value of crystal iron or bonded super dense has been built on the cheap.

Not so much "age of sail", more "age of ironclads".

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Postby Mongoose Pete » Mon Jun 07, 2010 10:52 pm

Egil Skallagrimsson wrote:Well, there are a lot of daft miltary ship designs in HG, T & G and FS! Almost none have radiation shielding. Admittedly, this adds a lot more MCr to the price, but if Joe Zhodani shows up with radiation shielding, and you don't, you'll be the one floating arround in a irradiated escape pod.
The military ships in Darrians have proper armour and radiation shielding. In a toe to toe fight the Darrian SDBs will pretty much wipe the floor with most of the vessels in T&G or FS... and hopefully any small Zhodani escorts which start poking their noses about too! :wink:
Nice to get a reminder that these rules were written assuming a quite different sort of campaign from the munchkin "It's in the rules so you have to let me do it, look at me buffing my character I'm going to go kill now arrgrgrgrh" approach. -dbhoward
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Postby AndrewW » Tue Jun 08, 2010 12:24 am

Mongoose Pete wrote:The military ships in Darrians have proper armour and radiation shielding. In a toe to toe fight the Darrian SDBs will pretty much wipe the floor with most of the vessels in T&G or FS... and hopefully any small Zhodani escorts which start poking their noses about too! :wink:
Eeeep, you had to go and remind me of that chapter...

But yes radiation shielding is common in the Darrian ships.
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Postby locarno24 » Tue Jun 08, 2010 7:04 am

As a guide now, any line of battle vessel without its TL value of crystal iron or bonded super dense has been built on the cheap.
I suppose you could say it depends on the expected opposition - but frankly it doesn't. 12+ armour makes you immune to 2D6 damage weapons unless they're delivered in a barrage by competent gunners (and largely immune even then). Any decent sized ship will usually pack a shedload of laser turrets as part of its point defences, and if it actually has a target those popguns can hurt, can shred it like a buzz-saw - light weapons are by far the most efficient in terms of damage per ton against an unprotected target.
Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.
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Postby Rikki Tikki Traveller » Tue Jun 08, 2010 1:09 pm

AndrewW wrote:
Mongoose Pete wrote:The military ships in Darrians have proper armour and radiation shielding. In a toe to toe fight the Darrian SDBs will pretty much wipe the floor with most of the vessels in T&G or FS... and hopefully any small Zhodani escorts which start poking their noses about too! :wink:
Eeeep, you had to go and remind me of that chapter...

But yes radiation shielding is common in the Darrian ships.
After what happened to their civilization, I bet every computer is a FIB and every HOUSE and BICYLCLE has radiation shielding.
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Postby Mongoose Pete » Tue Jun 08, 2010 1:58 pm

Rikki Tikki Traveller wrote:After what happened to their civilization, I bet every computer is a FIB and every HOUSE and BICYLCLE has radiation shielding.
Pretty much, yes... :wink:
Nice to get a reminder that these rules were written assuming a quite different sort of campaign from the munchkin "It's in the rules so you have to let me do it, look at me buffing my character I'm going to go kill now arrgrgrgrh" approach. -dbhoward
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Postby rinku » Thu Jun 10, 2010 2:43 am

Totally agree that ANY capital warship should have rad shielding. It's only a cost, not a tonnage or power upgrade. However, this might not apply to police ships, escorts and other sub-capitals, who would not expect to face nukes and heavy particle beams (or who would not expect to survive in a capital ship environment even with rad shielding...)

So... just add it. It will have zero effect on the players, unless they're somehow purchasing Imperial warships.

The armour issue is slightly different, since it *is* a tonnage issue, so gets into the area of jump capacity vs weapons vs agility vs protection.
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Postby apoc527 » Thu Jun 10, 2010 4:24 am

rinku wrote: The armour issue is slightly different, since it *is* a tonnage issue, so gets into the area of jump capacity vs weapons vs agility vs protection.
Which I think is a perfectly valid set of design constraints!
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Postby DFW » Thu Jun 10, 2010 5:40 pm

By TL 10 all interplanetary & interstellar space craft would have rad shielding. Otherwise, one decent sized solar flare and you can say bye, bye.

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Postby AndrewW » Thu Jun 10, 2010 5:59 pm

DFW wrote:By TL 10 all interplanetary & interstellar space craft would have rad shielding. Otherwise, one decent sized solar flare and you can say bye, bye.
Just ask the Darrians.
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Postby alex_greene » Thu Jun 10, 2010 7:25 pm

AndrewW wrote:But yes radiation shielding is common in the Darrian ships.
Seeing as radiation reduced their society's TL from 16 to near zero in an hour, yeah ... I imagine rad shielding would be common.
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