Gigaton bomb

[TheMuffinKing]

What king of damage would a gigaton bomb do if detonated in Earth's atmoshpere, with a "standard" airburst at 1500 feet? I know its huge, but I'm curious as to how much larger the explosion would be. What kind of increase in destruction would we be looking at (crater, fireball, blast wave)? Bah, this is probably worded badly...

[Duckie]

According to Mike Wong's Nuclear Weapons Effects Calculator:

198.1 km- Thermal radiation radius (3rd degree burns)
70.6 km- Air blast radius (widespread destruction)
26.7 km- Air blast radius (near-total fatalities)
11.6 km- Ionizing radiation radius (500 rem)
100.7 seconds- Fireball duration
6.9 km- Fireball radius (minimum)
8.4 km- Fireball radius (airburst)
11 km- Fireball radius (ground-contact airburst)

All figures assume optimum burst height

Thermal radiation is non-ionizing electromagnetic radiation which has a significant heating effect. Air is virtually transparent to thermal radiation. At the destructive radius, the thermal radiation intensity is sufficient to cause lethal burns.

The first air blast is 4.6psi overpressure, which is sufficient to collapse most residential and industrial structures. Note that exposed humans can actually survive such a blast, about 1/3 bar above standard. However, that much pressure exerted against the face of a building exerts very high force (a 40 foot tall, 50 foot wide structure would be hit with more than 600 tons-force).

The second air blast category is 20psi overpressure, which is sufficient to destroy virtually any large above-ground structure and cause nearly 100% fatalities.

Ionizing radiation is electromagnetic radiation of sufficient frequency (and hence energy) to literally "knock off" electrons from atoms, thus ionizing them. Ionizing radiation is extremely dangerous but it is also strongly absorbed by air, unlike thermal radiation. At the 500rem dosage, mortality is between 50% and 90%, although this can be mitigated with prompt and sophisticated medical care (which may not be available in the aftermath of a nuclear attack).

Fireball duration is based on emission intensity reduction to 10% of peak.

Fireball radius is based on a scaling law from "The Effects of Nuclear Weapons" (1977), Chapter IIc, from excerpts reprinted at EnviroWeb. According to that source, fireball radius scales with (Y^0.4), where Y is yield. Also note that a ground-contact airburst creates a larger fireball because some of the energy is reflected back up from the surface.

http://www.stardestroyer.net/Empire/Science/Nuke.html

[Sea Skimmer]

What king of damage would a gigaton bomb do if detonated in Earth's atmoshpere, with a "standard" airburst at 1500 feet? I know its huge, but I'm curious as to how much larger the explosion would be. What kind of increase in destruction would we be looking at (crater, fireball, blast wave)? Bah, this is probably worded badly...

How do you expect to get a relative answer when you’ve given nothing to compare the burst too? 1500 feet would be a ground burst BTW, because a very large portion of the fireball would touch the ground.

[TheMuffinKing]

How do you expect to get a relative answer when you’ve given nothing to compare the burst too? 1500 feet would be a ground burst BTW, because a very large portion of the fireball would touch the ground.

Doh! Lets compare it to the bomb dropped on Hiroshima.

[Kuroneko]

According to The Effects of Nuclear Weapons, 10psi peak overpressure occurs at 1000ft for 1KT groundburst. Simply scaling that gives 190miles. A peak overpressure of 10psi is enough to break pretty much any structure; even at 2psi (470mi away), there would be significant damage. The problem with such scaling is that the horizon should be a limiting factor. Additionally, this assumes that the terrain is relatively level. In a more realistic military situation, an airburst would be much more effective.

[Sea Skimmer]

Doh! Lets compare it to the bomb dropped on Hiroshima.

Your talking about a 50,000 fold differance in yield, a hand grenade against a very large bomb dropped from an airplane basically. The max diameter of the fireball from a 1 gigaton nuke would be about 42 miles inside more or less nothing would survive. The crater would be about 13,000 feet across and 3,000 feet deep for a low level airburst, terrian depending. But in the end 10 100 megaton nukes would inflict far more damage against any type of target.

[darthdavid]

Doh! Lets compare it to the bomb dropped on Hiroshima.

Your talking about a 50,000 fold differance in yield, a hand grenade against a very large bomb dropped from an airplane basically. The max diameter of the fireball from a 1 gigaton nuke would be about 42 miles inside more or less nothing would survive. The crater would be about 13,000 feet across and 3,000 feet deep for a low level airburst, terrian depending. But in the end 10 100 megaton nukes would inflict far more damage against any type of target.

37. There is no "overkill". There is only "open fire" and "I need to reload."

[Adrian Laguna]

How does that break Rule 37? If 10 100MT bombs do more damage, then they are clearly superior to a single 1GT bomb. Unless of course you are in a sci-fi situation where the concentrated 1GT bomb would be better suited to blasting a hole in that starship than 10 100MT bombs.

[petesampras]

Are there practical upper limits for the size a Nuclear bomb can be?
With a sufficiently large bomb, would material get blown away before the chain reaction had finished for all the material?

[Elheru Aran]

Are there practical upper limits for the size a Nuclear bomb can be?
With a sufficiently large bomb, would material get blown away before the chain reaction had finished for all the material?

Yes. The upper limit, in large part, is weight. You can only get so big before a.) the plane or missile won't be able to carry it, or b.) the explosion would consume the plane carrying it before it could get away.

[Ariphaos]

How do you expect to get a relative answer when you’ve given nothing to compare the burst too? 1500 feet would be a ground burst BTW, because a very large portion of the fireball would touch the ground.

It's still going to generate a mach effect.

[tharkûn]

Yes. The upper limit, in large part, is weight. You can only get so big before a.) the plane or missile won't be able to carry it, or b.) the explosion would consume the plane carrying it before it could get away.

Ahh but you forget that one can conceivably hide such a device in a supertanker and merely sail it into San Francisco bay. The crew need not even know how they volunteered for glorious martyrdom. I think the real limit is machining, eventually getting the precise overpressures needed to set off additional larger stages is going to fall through.

[Admiral Valdemar]

I remember people floating ideas of having loads of smaller bombs detonate precisely to give a colossal single explosion. If they were nanoseconds out, it wouldn't work, so it's pretty much impossible today, assuming you even wanted a supertanker full of H-bombs.