Nuclear AA

[Jackmc]

with a bitty little subcritical warhead using 'induced fission' of something like say U-240 or a similarly 'techy' isotope. 

You really don't want the fizzle bombs unless you are sure of a contact hit.  For prox kills you want to go the neutron bomb route to increase your x-ray yield so that the warhead punches outside of its weight class.

But isn't that somewhat irrelevant to the discussion?  I thought that BT nukes were laser-fusion devices?

-Jackmc

[RunandFindOut]

You really don't want the fizzle bombs unless you are sure of a contact hit.  For prox kills you want to go the neutron bomb route to increase your x-ray yield so that the warhead punches outside of its weight class.

That argument is invalid.  Reread my post, with the proper design using existing IS tech you could fit little bitty induced fission nukes onto LRMs and smaller Thunderbolts.  Those are missiles that make contact hits of ASF all the time.  A salvo of nuclear T-Bolt 5 is going to hit with at least one and you only need 1.

But isn't that somewhat irrelevant to the discussion?  I thought that BT nukes were laser-fusion devices?

Nope, the ones in most common use and that we are given stats for are laser-fusion devices.  But there are at least two factions that kept huge stockpiles of fission and fission-fusion nukes.  The Regulans and the Taurians.  The IS has no problem at all making fission devices, they just normally use pure fusion devices because they are cleaner.

If you start mounting multiple 'mech scale weapons onto a platform to engage fighters, wouldn't you be better off using standard fighters and drone controllers? You get your ranged launch, your multiple target engagement, and the ability to get multiple shots if your lucky.

The problem is one of doctrine and thought process, you're not making a platform to engage fighters.  You're taking a cheap missile that can reliably get contact hits on fighters (LRMs & Thunderbolts) sticking a fizzle bomb that can reliably one-shot most fighters on it.  Then taking a big one-shot box of the things and sticking it on a capitol missile as a booster stage to get it out to long range so they can engage fighters before those fighters are in range for their own weapons.  It's still cheaper to engage several fighters with one expensive munition than to deploy enough conventional ASFs to blunt their attacks.  And if you're going to start using mech-scale nuclear weapons widely then fighters even the most heavily armored are going to drop like swatted flies.  You actually end up saving money by shooting them with a missile that acts as a booster stage for a box of little nuke missiles than to take the inevitable losses of nuclear armed ASF going at each other.

[Jackmc]

Nope, the ones in most common use and that we are given stats for are laser-fusion devices.  But there are at least two factions that kept huge stockpiles of fission and fission-fusion nukes.

Then only the Regs and Taurians would mess with sub-crits.  The main beauty of laser-fusion is the micronization of the warhead that it enables.

As for the validity, I see your logic, but I'm not entirely convinced you're getting direct contact hits with LRM's.  I think it's more a case of ABF warheads which make more sense when going against ablative armor whether in space or on the ground.

Thunderbolts, OTOH, might be ideal and back before they were neutered into their current form, they were my SAM/AAM of choice.


-Jackmc

[RunandFindOut]

Then only the Regs and Taurians would mess with sub-crits.  The main beauty of laser-fusion is the micronization of the warhead that it enables.

If it were done in setting they would do it First, but essentially any faction making them would result in all faction adopting them fairly swiftly once they were used.  But yes if anybody did it the Taurians would probably be it, or the Regulans during the Jihad.

As for the validity, I see your logic, but I'm not entirely convinced you're getting direct contact hits with LRM's.  I think it's more a case of ABF warheads which make more sense when going against ablative armor whether in space or on the ground.

That would contradict pretty much every piece of setting detail we have regarding LRMs.  they're pretty explicitly both not continuous rod warheads or proximity fused.  The standard missile for both ground and space use is a contact fused weapon.

Thunderbolts, OTOH, might be ideal and back before they were neutered into their current form, they were my SAM/AAM of choice.

Yeah I like Thunderbolts, they were a good idea and whenever possible I houserule them back into non-neutered form.  I also make them cheaper and the primary missile of choice for mercs (take a gander at the mass of a LRM or SRM compared to various Thunderbolts, they're much tinier.  Which means every component has to be far more miniaturized and thus more expensive.  Thunderbolts should be lower tech, cheaper, and more available.)

[Jackmc]

That would contradict pretty much every piece of setting detail we have regarding LRMs.  they're pretty explicitly both not continuous rod warheads or proximity fused.  The standard missile for both ground and space use is a contact fused weapon.

The problem with that is that you just don't have much mass to work with.  An individual LRM weighs 8 kg which is essentially the long version of the 70mm Hydra rocket which doesn't have the required seeker head or vectored thrust steering.  It's also roughly half the mass of a Stinger or Mistral MPAAD SAM. 

If you crunch the numbers on the Hydra's motor, it's acceleration is actually pretty close to what you'd need to fly to an LRM's max space range in 30 seconds.  Budgeting a very modest amount for the seeker head and thrust vectoring means that realistically, you're looking at a warhead of 3 kg max with a max diameter of 90 mm but more realistically 60-70 mm.  That's awful small even for a laser-triggered device and allowing for realistic tech advance even a futuristically modernized version of a W54 is about a third too heavy and way too bulky.  You need to get into higher end super science before you start see thing's like Traveller's 20mm nukes.

-Jackmc

[RunandFindOut]

The problem with that is that you just don't have much mass to work with.  An individual LRM weighs 8 kg which is essentially the long version of the 70mm Hydra rocket which doesn't have the required seeker head or vectored thrust steering.  It's also roughly half the mass of a Stinger or Mistral MPAAD SAM. 

If you crunch the numbers on the Hydra's motor, it's acceleration is actually pretty close to what you'd need to fly to an LRM's max space range in 30 seconds.  Budgeting a very modest amount for the seeker head and thrust vectoring means that realistically, you're looking at a warhead of 3 kg max with a max diameter of 90 mm but more realistically 60-70 mm.  That's awful small even for a laser-triggered device and allowing for realistic tech advance even a futuristically modernized version of a W54 is about a third too heavy and way too bulky.  You need to get into higher end super science before you start see thing's like Traveller's 20mm nukes.

-Jackmc

Actually you have JUST enough size and mass inside an LRM for a particle induced fission explosive using U-240.  Now just the thought of manufacturing that stuff makes me want to not be anywhere near it.  Because it has the habit of spontaneously fissioning, but a disk of that approximately 2 inches in diameter hit with a weak particle beam would cause induced fission.

Thunderbolts are what I would preferably use as you don't have to get that exotic and COULD use standard BT laser-induced fusion.  At 83kg a Thunderbolt 5 has much more mass budget to work with. 

[Jackmc]

Actually you have JUST enough size and mass inside an LRM for a particle induced fission explosive using U-240.  Now just the thought of manufacturing that stuff makes me want to not be anywhere near it.  Because it has the habit of spontaneously fissioning, but a disk of that approximately 2 inches in diameter hit with a weak particle beam would cause induced fission.

Possibly, but I'd be very leery.  One of the reasons that U-240 doesn't enter spontaneous fission more often is the shielding from cosmic rays produced by the earth rock and atmosphere.  Without that shielding, or the mass budget to simulate it, I'd be real concerned about such a weapon in space.

-Jackmc

[RunandFindOut]

Possibly, but I'd be very leery.  One of the reasons that U-240 doesn't enter spontaneous fission more often is the shielding from cosmic rays produced by the earth rock and atmosphere.  Without that shielding, or the mass budget to simulate it, I'd be real concerned about such a weapon in space.

-Jackmc

So would I the very idea gives me the crawling willies as that stuff if about as stable as a housecat on meth.  I was using it as an example of it being possible to do a nuclear LRM within the tech base of the IS.  Even if it wouldn't be a good idea to do it.  My preference would always be a Thunderbolt as those are much larger and have room for a real warhead that isn't made out of a substance that's angry it exists.

[Wrangler]

Thinking about it.  I remember that in the novel, Blood of Skye,  that Malvina did in fact use nuke to knockout a incoming DropShip while her forces were based on Glengarry.

[Liam's Ghost]

Nope, the ones in most common use and that we are given stats for are laser-fusion devices.  But there are at least two factions that kept huge stockpiles of fission and fission-fusion nukes.  The Regulans and the Taurians. 

Source?

[The_Caveman]

Okay, here's a thought: instead of attempting to use the radiation flux from the nuke itself as the kill mechanism, what about turning the warhead into a miniature Orion Drive and hurling a shotgun blast of Kinetic Kill Vehicles at the fighter squadron?

A little napkin math indicates a 1MT warhead would be capable of launching a metric ton of tungsten-carbide darts at around 2,000 km/sec (assuming 50% of the detonation energy is lost). So you'd be unleashing something like 100,000 10-gram projectiles, each with an impact energy of 20 gigajoules*. Assuming you launched them in a cone that would spread them across an entire space hex, you'd get a spacing of about one projectile every 40 meters. Which, given the size of the average ASF, is at least a 50/50 chance of hitting every ship in the squadron. Along with everything else in the hex.

Assuming the squadron had a tighter spacing, you could detonate the nuke half as far away and get a 20 meter spacing, which virtually guarantees the annihilation of every fighter.

It's the LB-X autocannon from hell.

*for reference, a Gauss slug moving at the (hilarious) inferred space map velocity of ~6 km/s would pack about 2 GJ. So this is a weapon equivalent to 1 million Gauss rifles. Ouch.

[VhenRa]

Someone actually used that in a fanfic, or rather. They modified NACs to fire something similar.

[Maingunnery]

Okay, here's a thought: instead of attempting to use the radiation flux from the nuke itself as the kill mechanism, what about turning the warhead into a miniature Orion Drive and hurling a shotgun blast of Kinetic Kill Vehicles at the fighter squadron?

A little napkin math indicates a 1MT warhead would be capable of launching a metric ton of tungsten-carbide darts at around 2,000 km/sec (assuming 50% of the detonation energy is lost). So you'd be unleashing something like 100,000 10-gram projectiles, each with an impact energy of 20 gigajoules*. Assuming you launched them in a cone that would spread them across an entire space hex, you'd get a spacing of about one projectile every 40 meters. Which, given the size of the average ASF, is at least a 50/50 chance of hitting every ship in the squadron. Along with everything else in the hex.

Assuming the squadron had a tighter spacing, you could detonate the nuke half as far away and get a 20 meter spacing, which virtually guarantees the annihilation of every fighter.

It's the LB-X autocannon from hell.

*for reference, a Gauss slug moving at the (hilarious) inferred space map velocity of ~6 km/s would pack about 2 GJ. So this is a weapon equivalent to 1 million Gauss rifles. Ouch.

So basically NAC with a canister round. Considering you want a metric ton of projectiles you will need to use a NAC/40. However there is a problem with your damage assumptions, BT armor is very good at dealing with high-velocity impacts, so the effects will be less.

ps. gauss slug would be moving a whole lot faster, just to be able to hit, projectile don't travel an entire turn.

[The_Caveman]

So basically NAC with a canister round. Considering you want a metric ton of projectiles you will need to use a NAC/40. However there is a problem with your damage assumptions, BT armor is very good at dealing with high-velocity impacts, so the effects will be less.

Not that high of velocity. Not even close to that high. 2000 km/s is 0.6% of light-speed. Obviously I wouldn't stat the weapon at 15 million damage points, but it wouldn't be as reduced as you think. (strictly speaking, I wouldn't stat this at all, because it'd be game-breaking)

Also, with the 1 megaton warhead, I was assuming this'd be the payload for a Killer Whale missile, not a NAC round.
 

ps. gauss slug would be moving a whole lot faster, just to be able to hit, projectile don't travel an entire turn.

I was using exceedingly conservative velocity numbers to preserve my sanity. 'Mech Gauss rifles do not have a muzzle velocity over 20 km/s. They just don't, and attempting to tell me otherwise will result in severe injury.

[Maingunnery]

Not that high of velocity. Not even close to that high. 2000 km/s is 0.6% of light-speed. Obviously I wouldn't stat the weapon at 15 million damage points, but it wouldn't be as reduced as you think. (strictly speaking, I wouldn't stat this at all, because it'd be game-breaking)

You also need to take into account that high speed projectiles behave like a liquid and thus it is possible for it to destroy itself when hitting the right armor. Also this assumes that the projectile survives the initial acceleration and won't turn into plasma.   

Also, with the 1 megaton warhead, I was assuming this'd be the payload for a Killer Whale missile, not a NAC round.

That would increase the 'effective' range.

I was using exceedingly conservative velocity numbers to preserve my sanity. 'Mech Gauss rifles do not have a muzzle velocity over 20 km/s. They just don't, and attempting to tell me otherwise will result in severe injury.

If you want to keep your sanity, then just assume that Gauss rifles (and other BT weapons) use different settings when used in space. Or they would need to use slugs with guidance systems just to hit their targets.  ;D

[Jackmc]

Caveman, I'd double check you math. 

BT space hexes are 18 km across and a sphere that size has a volume of ~24,4000 km.  100,000 projectiles isn't even going to come close to saturation.

Also, your math doesn't match FASA Fysics as the NAC class weapons already use nuclear charges to launch kinetic kill projectiles and their damage is capping out at 400 standard points of damage.

-Jackmc

[The_Caveman]

Caveman, I'd double check you math. 

BT space hexes are 18 km across and a sphere that size has a volume of ~24,4000 km.  100,000 projectiles isn't even going to come close to saturation.

You're confusing volume with area. What matters for scoring hits is the cross-sectional area, not the swept volume.

When the warhead detonates and scatters the projectiles, it will do so in the form of a cone which has been calibrated to have a frustum 18km in diameter at the target distance (the midpoint width of a space hex). The area of the cone's frustum, being a circle, is equal to pi times half the cone's width squared. That produces a circle whose area is ~255 million square meters. Divided by 100,000 projectile paths, that works out to ~2544 square meters per projectile. Taking the square root of that area gives an average separation of 50 meters between any two projectiles at the midpoint of the hex. I originally used a 17-kilometer hex as that figure was mentioned upthread, so my original separation was a bit tighter.
The amount of change in the spread of each projectile path through the entire hex will depend on the distance from the target at which the warhead is detonated, but it should be small enough that we can treat the projectile paths as approximately parallel (ie, an angle of separation of no more than a couple degrees between any two paths).
However, we can be pretty certain the fighter squadron is not spread exactly across the midpoint plane of the space hex, so its actual separation will be considerably less than 18km, and thus we can release the projectiles in a tighter cone, greatly reducing the separation between projectile paths and increasing the odds of scoring multiple hits.

Also, your math doesn't match FASA Fysics as the NAC class weapons already use nuclear charges to launch kinetic kill projectiles and their damage is capping out at 400 standard points of damage.

Source? I've never seen capital cannons mentioned as being anything besides chemical.

Edit: TacOps confirms this. The description does not mention anything about a nuclear charge, in fact from the way it reads I'm dead certain they're talking about light gas guns.

[Jackmc]

You're confusing volume with area. What matters for scoring hits is the cross-sectional area, not the swept volume.

But it does matter because you are assuming that everything is aligned perfectly in order to use the cross sectional area rather than the swept area.  Each one of your 50 m projectile spaces is actually a lane that's 18 km long.  But even ignoring that and going with you cross sectional argument, you've got a projectile occupying a fraction of a square meter in a 50 meter kill box vs a target that has a relative cross section of 5-10 square meters.

Source? I've never seen capital cannons mentioned as being anything besides chemical.

Per the author, and Strat Ops IIRC, they're essentially Orion mortars.  You can PM the author if you like, he goes by the handle Cray on these boards.

-Jackmc

[The_Caveman]

Per the author, and Strat Ops IIRC, they're essentially Orion mortars.  You can PM the author if you like, he goes by the handle Cray on these boards.

-Jackmc

Oh, Cray. That explains it. Cray and I have some very different views on how certain parts of the BT universe work.

Strat ops, btw, is silent on the topic of how naval weapons function in-universe, it just presents the game rules. TacOps does give a description in its equipment section. Specifically it calls the propulsion method a "controlled plasma explosion" which is just meaningless technobabble. Black powder firearms use a controlled plasma explosion ;)

But based on everything else that's been written about them in the prior 30 years of BT, NACs call out to me pretty strongly as some sort of Gerald Bull-ish light gas guns.

[Maingunnery]

Oh, Cray. That explains it. Cray and I have some very different views on how certain parts of the BT universe work.

Strat ops, btw, is silent on the topic of how naval weapons function in-universe, it just presents the game rules. TacOps does give a description in its equipment section. Specifically it calls the propulsion method a "controlled plasma explosion" which is just meaningless technobabble. Black powder firearms use a controlled plasma explosion ;)

But based on everything else that's been written about them in the prior 30 years of BT, NACs call out to me pretty strongly as some sort of Gerald Bull-ish light gas guns.

Its quite clear, the plasma comes from laser-triggered fusion.

[Liam's Ghost]

Oh, Cray. That explains it. Cray and I have some very different views on how certain parts of the BT universe work.

You're free to disagree with him, but if his explanation is the canon explanation, then it's still the canon explanation.

[The_Caveman]

Its quite clear, the plasma comes from laser-triggered fusion.

Quite clear as mud.

In any case, even if naval autocannons were nuclear-powered, that doesn't mean the charge is anything close to one megaton. BattleTech doesn't exist at the kind of tech level to contain a 1MT nuke inside a gun barrel without the ship itself becoming collateral damage. That's Star Trek level stuff.

[Fallen_Raven]

BattleTech doesn't exist at the kind of tech level to contain a 1MT nuke inside a gun barrel without the ship itself becoming collateral damage. That's Star Trek level stuff.

We have FTL drives and fusion powered cars as commercial products.. The tech level is whatever the plot requires.

[The_Caveman]

I thought I had read something like this before, but it took some digging through my pdf archive to find it.

Technical Readout 2750, in the intro bit before the WarShip section, describes naval autocannon as using "huge neo-cordite (nitroglycerine and other explosives in a stabilizing jelly) charges to propel the projectiles much further than conventional autocannon".

So yeah. This fusion-powered cannon stuff? Not part of the BattleTech universe I grew up with. Admittedly, either description is just technobabble, but one fits with the feel of everything I knew and loved about the setting and the other describes something new and totally different. Not that warships loaded down with relativistic guns powered by fusion charges isn't a cool idea, but to me it's not BattleTech.

[HobbesHurlbut]

I thought I had read something like this before, but it took some digging through my pdf archive to find it.

Technical Readout 2750, in the intro bit before the WarShip section, describes naval autocannon as using "huge neo-cordite (nitroglycerine and other explosives in a stabilizing jelly) charges to propel the projectiles much further than conventional autocannon".

So yeah. This fusion-powered cannon stuff? Not part of the BattleTech universe I grew up with. Admittedly, either description is just technobabble, but one fits with the feel of everything I knew and loved about the setting and the other describes something new and totally different. Not that warships loaded down with relativistic guns powered by fusion charges isn't a cool idea, but to me it's not BattleTech.

The fluff in the current rulebooks explain the performance of NAC much better than the TRO fluff.

[Jackmc]

I thought I had read something like this before, but it took some digging through my pdf archive to find it.

Technical Readout 2750

Which has since had most of its info rewritten.  The game's policy is that newer material trumps older so it's largely invalid.  I totally get the "game I use to know and love" thing, but unfortunately that sentiment brings zero to a discussion regarding the current game/fluff.



-Jackmc

[HobbesHurlbut]

Which has since had most of its info rewritten.  The game's policy is that newer material trumps older so it's largely invalid.  I totally get the "game I use to know and love" thing, but unfortunately that sentiment brings zero to a discussion regarding the current game/fluff.



-Jackmc

And rulebooks trump TROs.

[The_Caveman]

Which has since had most of its info rewritten.  The game's policy is that newer material trumps older so it's largely invalid.  I totally get the "game I use to know and love" thing, but unfortunately that sentiment brings zero to a discussion regarding the current game/fluff.

Rules clarifications are one thing, but I'm going to continue to take exception to shoving a few powers of ten into the universe here and there just so it looks better in "versus" arguments against other sci-fi franchises. I'll stop here before I embarrass myself by having a total meltdown over a minor point of lore.