Really big upper-atmosphere detonations

[Shannon]

(Mods please move if I've put this in the wrong forum)

Mike's page on Planet Killers on the main site got me thinking:

http://www.stardestroyer.net/Empire/Ess ... llers.html

Mike lists effects of an asteroid impact. I'm interested in which of those apply if you had an upper-atmosphere detonation of significant magnitude (I'm thinking 1E6 to 1E7 megatons' worth), say by the explosion of a starship's power core (leaving aside how such a catastrophe occurred in the first place). The nuclear weapons effects calculator gives lots of good data on the actual explosion, but I'm interested in the aforementioned additional effects, many of which are long-term. Obviously some won't apply; but would, for example, electrodynamic interactions occur?

What other effects might there be if this occurred on (or above) Earth? Are the ultimate long-term effects dependent on altitude of detonation?

Thanks in advance.

[Simon_Jester]

For one...

Everything in line of sight is going to get the hell scorched out of it- and line of sight at those altitudes is extremely long, something like a thousand miles across. Within that area, you're going to see an average of hundreds of kilotons of radiation hitting the surface per square kilometer- which is, yes, about equivalent to carpet-bombing with nukes.

The area 'immediately' underneath the blast will take disproportionately more of the beating, excavating a very large crater.

Basically, anyone who is in line of sight and isn't either in a deep bunker or under Super Magic Shields is dead. Pretty much any normal buildings, vegetation, or terrain features is going to get burnt into an unrecognizable cinders. Rivers would boil off, as would most lakes; oceans might not boil off but you'd get enormous damn clouds of steam and large currents rushing in to replace flash-vaporized water.

Stuff in orbit would be exposed to intense bombardment of particles caught up in the planetary magnetic field- likewise fried, unless covered by Super Magic Shields. This can even wreck shit on the other side of the planet, because magnetic fields are quite capable of taking charged particles and bank-shotting them around to the other side of the Earth. Indeed, they do exactly that with the solar wind.

It bears remembering that this hypothetical one to ten teraton bomb has the same relationship in yield to the Hiroshima bomb that the Hiroshima bomb does to a hand grenade. It is really fucking big.

[LaCroix]

Now you know why SW has planetary shields around most of their important worlds. To protect against traffic accidents...

[Shannon]

Will it permanently blow off a big chunk of atmosphere?

If not, how much bigger would it need to be? 1E8?

(Yes, I know I'm talking ridiculously huge explosions here. Humour me. )

Also, if I'm reading the nuclear weapons calculator right, a 10 teraton blast, which can generate 3rd degree burns to a radius of 8646.6km, is pretty much going to fry the best part of a hemisphere of an Earth-sized planet, correct?

[Shannon]

If not, how much bigger would it need to be? 1E8?

Edit: That should of course be 1E8 megatons.

[LaCroix]

I think I'll go out on a limb and propose that it would even blow some parts of the planet permanently off - surface water, topsoil, everything flammable that can be taken with the ejecta...

[Sithking Zero]

This, amongst many other reasons, is why an Orion Drive is considered a Really, REALLY bad idea.

For those who don't know what an Orion Drive is, it's basically the idea that the propulsion of your ship is maintained by dropping nukes behind your ship and riding the blast wave. While awesome... you can probably see the downsides. Nuclear fallout, the fact that it uses freaking nukes, etc, etc, etc.

[Sarevok]

Orion is not a bad idea in deep space however.

[Sithking Zero]

Well, no, but in-atmo, as this topic refers to, it can be, uh, what's the word what's the word what's the word, Oh yeah, BAD.

[madd0ct0r]

trying to fly a giant nuke driven spaceship through the atmosphere is bad?

well, i learned something new today.

[Sarevok]

Depends on the planet though. Orion would not be too bad on Mars or Titan. It might even be an economical way to lift large payloads from surface of such worlds.

[Sithking Zero]

trying to fly a giant nuke driven spaceship through the atmosphere is bad?

well, i learned something new today.

And Knowing is half the battle!

G.I. JOOOOOOOOOOOOE!

[doom3607]

I still argue in favor of Orion. Get a reasonably clean nuke, and make the South Pole the new launch area to avoid irradiating anywhere that matters- it's not like an Orion really needs to curve east or west while taking off like PUNY ROCKETS.

[Sarevok]

Antarctica is the last pristine environment on Earth. You want to irradiate the only continent not touched by human activity ?

There IS a reason why treaties prohibiting mining, military basing and nuclear testing on the Antarctic were signed.

[Connor MacLeod]

if you had an upper-atmosphere detonation of significant magnitude (I'm thinking 1E6 to 1E7 megatons' worth), say by the explosion of a starship's power core (leaving aside how such a catastrophe occurred in the first place). The nuclear weapons effects calculator gives lots of good data on the actual explosion, but I'm interested in the aforementioned additional effects, many of which are long-term. Obviously some won't apply; but would, for example, electrodynamic interactions occur?

Mike notes that many of the effects would not occur with nuclear detonations largely because of yield. Given the information he lists for electrodynamic interactions, you won't have the ionized wake or the shockwaves from an impactor, or probably as much ejecta (The ship isn't impacting the ground. an asteroid impact throws up alot of ejecta both from crater formation as well as the asteroid's own mass vaporizing) However, depending on how the reactor "blows up" I would expect some ionization and possibly shockwaves from those events, some of which is likely to cause what Mike described.

Bear in mind alot of this depends on how high up we're talking, because atmospheric density is not uniform. How intense (compared to an asteroid impactor) I can't say, because I don't have sufficient data.

What other effects might there be if this occurred on (or above) Earth? Are the ultimate long-term effects dependent on altitude of detonation?

Thanks in advance.

Simon covered the rest, but it's really hard to say because it depends on how your hypothetical reactor worked. If its something magical it could be arbitrary. That said, there could be the risk of atmospheric pollution or contamination from particularily toxic parts of the ship, or (if you have a big enough target) particulate matter (vaporized metal, plastic, coolant, etc.) Look at Curtis Saxton's "Endor Holocaust" for some idea of that (bearing in mind that it will also depend on alot of factors, especially how big a ship we're talking about.)

Hell, I suspect it may be possible that not all reactors will behave totally like a nuclear explosion, because nuclear explosions (liek any explosion) rely on certain specific factors (short timeframes and small volumes particularly) to achive some of their most devastating effects.

Will it permanently blow off a big chunk of atmosphere?

If not, how much bigger would it need to be? 1E8?

How big a chunk are you defining as "big". To "blow off" the atmosphere, you have to overcome gravity becaus ethat's what holds it (like everything else) in place. Ignoring inefficiencies you need somewhere between at least e26-e27 joules to "blow off" the Earth's atmosphere totally. In theory, a "multi teraton" blast will blow a smaller fraction of that off.. a thousandth to a millionth, say, and even then that is probably generous. STill, that is alot of air, and could still be a "big chunk" such as it were. We can say at least SOME atmosphere will escape, though.

Also, if I'm reading the nuclear weapons calculator right, a 10 teraton blast, which can generate 3rd degree burns to a radius of 8646.6km, is pretty much going to fry the best part of a hemisphere of an Earth-sized planet, correct?

Could be. The fireball itself will be huge, but line of sight will block most of the radiation up to a point. I'd expect atmospheric heating to be more of an issue than the fireball itself (which is going to be "bigger" than the atmosphere by that point.)

[doom3607]

Antarctica is the last pristine environment on Earth. You want to irradiate the only continent not touched by human activity ?

There IS a reason why treaties prohibiting mining, military basing and nuclear testing on the Antarctic were signed.

Damn right. The human race is the only thing that should matter for the human race. To hell with the penguins, colonization of other worlds is more important for our long-term survival.

[Bluewolf]

Damn right. The human race is the only thing that should matter for the human race. To hell with the penguins, colonization of other worlds is more important for our long-term survival.

Amusing you are actually serious then please consider that It'd might just nice for once to not to keep spoiling the planet. The attitude that the Earth is perfectly fine to spoil is a rather sad one. I can understand the desire for humanity to live on but you don't automatically need Orion drives to do it (hell, even a massive boost into space funding in general would help immensely). Also please respect that preserving the planet would help reduce some of the need to actually colonize other worlds.

[Shannon]

Thank you, Connor.

I'm assuming that the explosion will behave like a nuke simply for the sake of convenience. Assume a magical reactor that has identical effects. I also assumed that the vessel itself is completely vaporised by the blast, or at least that the effects of falling debris are minimal compared to the blast itself.

IIRC, Mike also mentioned that air is pretty much transparent to thermal radiation, which is why I looked at the 3rd degree burn radius. Since the explosion would have to be 100km up or less to actually be within the atmosphere (well, at least some of it), I wondered how much of the hemisphere would be hit.

Of course, the higher the blast, the less atmosphere displaced, right? When I looked at the numbers it did occur to me that the fireball would extend into space, hence my question about escaping atmosphere - that's still a lot of displaced air. When you factor in atmospheric heating, it would probably be fair to say that there would be a massive effect on global weather patterns, then? Even if the planet corrected itself eventually, I imagine the short-term effects would be pretty catastrophic.

[Connor MacLeod]

Thank you, Connor.

I'm assuming that the explosion will behave like a nuke simply for the sake of convenience. Assume a magical reactor that has identical effects. I also assumed that the vessel itself is completely vaporised by the blast, or at least that the effects of falling debris are minimal compared to the blast itself.

Then that, I think, would take care of many of the "long-term" consequences. Problems like fallout and long term radiation effects are significant worries there. There would still be some contamination due to the particulate matter (although how widespread or dangerous, I have no idea - like I said it depends on how big the starship. And of course effects on climate and weather. I don't think there would be much dust loading or ejecta with a high-altitude detonation.

IIRC, Mike also mentioned that air is pretty much transparent to thermal radiation, which is why I looked at the 3rd degree burn radius. Since the explosion would have to be 100km up or less to actually be within the atmosphere (well, at least some of it), I wondered how much of the hemisphere would be hit.

Air, as Mike noted, is very transparent at upper altitudes because of how thin it is. That's why airbursts can be so widespread in their effects. Closer to the ground though, air tends to be much more opaque. I believe much of a nuclear weapon's radiation tends to be absorbed within the first few feet of ground zero. Of course, that also depends greatly on what form the radiation takes. Modern nukes are mostly soft x-rays which don't penetrate atmosphere well. Other forms of radiation would interact differently.

As for how much hemisphere would be hit? At its highest I'd guess the fireball would have a line of sight to the horizon of many hundreds of km, potentially. That doesn't include the effects from heating the atmosphere around the fireball.

Bear in mind that at the height you're talking about, about half the energy will be radiated back into space rather than interact with the atmosphere.

Of course, the higher the blast, the less atmosphere displaced, right?

Yes. The fireball will also be much more diffuse (which is why it so much bigger in area of effect) so it won't behave like it would closer to the ground (or whatever Mike is assuming optimum burst height)

When I looked at the numbers it did occur to me that the fireball would extend into space, hence my question about escaping atmosphere - that's still a lot of displaced air. When you factor in atmospheric heating, it would probably be fair to say that there would be a massive effect on global weather patterns, then? Even if the planet corrected itself eventually, I imagine the short-term effects would be pretty catastrophic.

Any sufficiently large quantity of energy, especially delivered in the right way, will impact weather and climate. Your average severe weather (thunderstorms, hurricaines, or tornadoes) have total energy releases somewhere equal to nuclear weaponry, only spread out over longer priods of time (for example). Hell, volcanic eruptions can do that (many are in the megaton range IIRC.) although the effects of those can be due to the sheer volume of matter ejected into the air as much as the energy.

Bear in mind that there's alot I am not sure of or am making assumptions about, so while I think it's right, don't just take my word on it. I'm just a layperson in these matters.

[Simon_Jester]

Antarctica is the last pristine environment on Earth. You want to irradiate the only continent not touched by human activity ?

There IS a reason why treaties prohibiting mining, military basing and nuclear testing on the Antarctic were signed.

Damn right. The human race is the only thing that should matter for the human race. To hell with the penguins, colonization of other worlds is more important for our long-term survival.

Is it, really?

For the semi-foreseeable future, Earth is far more survivable than any other planet we know of, certainly more so than any other planet we could conceivably reach on a useful scale. Large disasters striking Earth would not mean the end of humanity; we are surprisingly good at maintaining some minimum scale of habitable living space even in very inhospitable conditions.

Whereas cheerfully pissing all over the environmental viability of Earth, and thus reducing its carrying capacity, in favor of getting a few thousand tons of ironmongery into orbit... that is just too foolish for words.

[Enigma]

Depends on the planet though. Orion would not be too bad on Mars or Titan. It might even be an economical way to lift large payloads from surface of such worlds.

Except, you'll get a bunch of environmentalists and NASA on your ass for polluting a pristine planet.

[Sarevok]

Nah i don't think so. Most of the opposition to RTGs come from groups who fear spacecraft crashing on Earth. Even the most luddite environmental groups are not loony enough to protest polluting an irradiated wasteland on another planet with our nukes.

[Starglider]

The Orion drive thing is a total red herring. The energy output required for most earth-to-orbit Orion drive concepts is under a megaton total, i.e. smaller than many cold war nuclear tests, of which there were hundreds. Doing thousands of Orion launches will start to cause global environmental problems, but a mere handful are not going to have a noticable effect on the environment (assuming use of boosters to avoid groundburst fallout).

[Sarevok]

The Orion drive thing is a total red herring. The energy output required for most earth-to-orbit Orion drive concepts is under a megaton total, i.e. smaller than many cold war nuclear tests, of which there were hundreds. Doing thousands of Orion launches will start to cause global environmental problems, but a mere handful are not going to have a noticable effect on the environment (assuming use of boosters to avoid groundburst fallout).

Will not hundreds of small nuclear detonations cause much more fallout than one or two megaton yield blasts ?

[Starglider]

Will not hundreds of small nuclear detonations cause much more fallout than one or two megaton yield blasts ?

Well, it's true that smaller nuclear devices tend to have a lower fusion fraction, but that's countered by the fact that Orion propulsion units would be expressly engineered to minimise fallout, vs nuclear weapons where fallout is at worst a desired part of the kill mechanism and at best a secondary factor behind yield and compactness.