A Gigajoule of Damage

[whswhs]

Originally Posted by Anders

The most powerful nuke ever made was the Tsar Bomba, somewhere in the vicinity of 50-58 Megatons of TNT. In theory it could have had a 100 MT yield, but in order to reduce radioactive fallout one of the mechanisms for boosting yield was left out. 50 MT is about 210 Petajoules, or 210,000 Gigajoules.

Yes, that's about right, since a gram of yield is a kcal, or about 4200 J.

[TGLS]

Originally Posted by edk926

What was the rating of the nukes dropped on Japan in ww2?

Little Boy was 15 kt, Fat Man was 20 kt.

Originally Posted by edk926

How powerful would the modern nuke be?

OK, the Tsar Bomba has been brought up but it's important to keep in mind that was from an era when nuclear bombs were to be delivered individually in single bombers, such that maximizing the damage done by each bomber was critical.

Modern nuclear bombs are delivered in missiles usually with MIRV capabilities (i.e. deploying bombs that target multiple separate locations), and this necessitates smaller bombs to avoid fratricide (i.e. one detonation knocking out the other devices) and to reduce weight. Thus, most modern US nuclear bombs are believed to be in the 500 kt range, but each missile fired drops like a dozen. Countries that pursue a single bomb design (i.e. China until the mid 2010s for example) usually go for around a 5 Mt device.

[Rupert]

Originally Posted by TGLS

Modern nuclear bombs are delivered in missiles usually with MIRV capabilities (i.e. deploying bombs that target multiple separate locations), and this necessitates smaller bombs to avoid fratricide (i.e. one detonation knocking out the other devices) and to reduce weight. Thus, most modern US nuclear bombs are believed to be in the 500 kt range, but each missile fired drops like a dozen. Countries that pursue a single bomb design (i.e. China until the mid 2010s for example) usually go for around a 5 Mt device.

This also depends on the missile carrying the bomb and the intended target. Submarine launched missiles tended to have smaller warheads due to size restrictions, and because they were intended primarily for use against cities, which aren't hardened. These days they can also be used against missile silos because accuracy is higher than it was in the Cold War (in large part due to the use of GPS to precisely pinpoint the launching sub's position before launch - which leads to potential issues with accuracy if they aren't used early in an 'all-in' war before the GPS satellites are killed). ICBMs intended for use vs enemy missile silos tended to have megaton plus yields because their targets were hardened (Soviet missiles tended to have higher yields as they were less accurate). Increasing accuracy is partly why late Cold War ICBMs had smaller yields than earlier ones, and this also allowed the use of MIRVs and the addition of penaids (decoys, chaff, etc. to confuse any ABM systems the enemy might have).

[Fred Brackin]

Originally Posted by TGLS

Thus, most modern US nuclear bombs are believed to be in the 500 kt range, but each missile fired drops like a dozen. e.

6 to 10 or just 3 for any Minutemans still in service.

[Fred Brackin]

Originally Posted by Varyon

Maybe you simply need a higher concentration of neutrinos than what's present at daytime on a habitable planet

The concentration of neutrinos at night is the same as the concentration during the day. I've read that it would take 600 light-years of solid lead to stop 50% of neutrinos.

We (and probably everyone else) has already had that higher concentration anyway. During Supernova 1987j our neutrino detectors got more neutrinos in 10 seconds or so than they did in a year without supernovas that were only 170,000 ly away.

The levels when the Crab Nebula supernova went (only c. 6000 ly distant) would have been higher than that and when the supernova (or multiples) that formed the Local Bubble exploded during pre-history (c. 500 ly) there would have been even more.

Perhaps we can't be truly sure of anything except that such levels of neutrinos don't kill cavemen but neutrinos just don't interact with normal matter enough to produce much effect.

[Varyon]

Originally Posted by Fred Brackin

The concentration of neutrinos at night is the same as the concentration during the day. I've read that it would take 600 light-years of solid lead to stop 50% of neutrinos.

Yeah, that went through a few revisions for what I was trying to say, and it looks like I failed to correct some of it (the "during the day" bit was in a draft where I was talking about visible light there).

Originally Posted by Fred Brackin

Perhaps we can't be truly sure of anything except that such levels of neutrinos don't kill cavemen but neutrinos just don't interact with normal matter enough to produce much effect.

I was thinking of something more exotic than ordinary matter. Like, maybe superscience forcefields that are extremely resilient to projectiles are actually pretty easy to make, but said forcefields are so weak to neutrinos they can't actually form in our solar system until you get out near Jupiter's orbit, due to the high neutrino concentration near Sol. So you could have a setting where ships are practically invulnerable to conventional weapons, but the forcefields can have holes punched in them by particle accelerators (which from my understanding generate a high concentration of neutrinos), and the ships are much more fragile once you get roughly within the snow line of a star - with the side effect of answering "How was this easy technology never discovered before, to the extent humans thought it was impossible?" with "Because it is impossible... when you're close to a star, which humans have been up through our present."

Of course, then you'd probably just end up with spaceships using nukes against each other, as nukes apparently produce a lot of neutrinos, so the shields would be useless against them.

[Fred Brackin]

Originally Posted by Varyon

Of course, then you'd probably just end up with spaceships using nukes against each other, as nukes apparently produce a lot of neutrinos, so the shields would be useless against them.

Yes, all or nearly all nuclear reactions produce at least some neutrinos. The first neutrinos (technically anti-neutrinos) were detected when the detector was placed next to an early fission reactor.

I wouldn't think it was the particle accelerators that produced the neutrinos so much as the high energy collisions between particles when the beam reaches its' target. A force field might prevent those collisions.

<shrug>Every thousand years there'll be a supernova somewhere in the galaxy (maybe more often when you count the Magellanic clouds) and all the force fields would go "Poof" anyway.

[David Johnston2]

Originally Posted by Prince Charon

It could be interesting to come up with something that could plausibly be damaged by neutrinos, though (other than by straight GM fiat like 'energy beings naturally interact with neutrinos, and have blasters made of energy that shoot coherent neutrino beams').

Neutrinos are insubstantial. Insubstantial things can hurt other insubstantial things. Thus neutrino blasters are the way to give an owie to ghosts.

[Anaraxes]

Originally Posted by Fred Brackin

Every thousand years there'll be a supernova somewhere in the galaxy... and all the force fields would go "Poof" anyway.

I'm pretty sure the militaries would be happy with a device that had an MTBF of a thousand years.

There's no doubt a section of one of their manuals that outlines the doctrine for what to do if your forcefield is disabled (which could be because of other flaws in the device, maintenance or logistics problems, enemy action, sabotage, etc). Supernovae taking them out isn't a reason not to put them on the ships, any more than all those other reasons would be.

[Fred Brackin]

Originally Posted by Anaraxes

I'm pretty sure the militaries would be happy with a device that had an MTBF of a thousand years.

There's no doubt a section of one of their manuals that outlines the doctrine for what to do if your forcefield is disabled (which could be because of other flaws in the device, maintenance or logistics problems, enemy action, sabotage, etc). Supernovae taking them out isn't a reason not to put them on the ships, any more than all those other reasons would be.

1000 years was only the average that comes from observing other galaxies. The actual occurrence locally over the past thousand years is around 4 or 5. even 6 if Andromeda is close enough. This may not be a negation of that thousand year figure but just the result of supernovas "clumping" together.

You also get the "problem" (common to FTL but not the worst of the FTL problems)that once you've observed a supernova somewhere you'll know when that supernova's neutrino front will arrive everywhere else. Very patient species could use this knowledge to prepare for combat when they know force fields wii be out (which will probably not be at anywhere near the same time for their home system) but their targets may be surprised.

The supernova thing may not be a reason to omit fields on ships but it's a fairly good reason not to rely on force fields to protect habitats floating in the atmospheres of hostile planets like you sometimes see (as in the vignette at the front of UT's Defenses chapter).