atomic bomb question

[BH]

I was watching a rerun of Meteor the other night and a question popped into my head. How much of a nuclear bomb's destructive power is composed with how it interacts with the immediate atmosphere (like blast winds, oxygen around for things to catch fire) compared to what its destructive power would be, say hitting an asteroid, out in the vacuum of space?

 

[Sarpedon]

Without a medium to transfer the energy, I would expect that the energy hitting the asteroid would be simply governed by the inverse square law, with the blast being over instantaneously. Whereas on earth, heated gas spreading out would both increase the intensity and the duration of the damage.

 

[Bronzeage]

A nuclear weapon's destructiveness comes from the shock wave(kinetic energy) and the heat(thermal energy). Neither of these will be reduced because there is no atmosphere. It probably won't be as spectacular as a Terrestrial explosion, but we can expect a lot of vaporized matter, which is composed of various elements, mainly metals and silicon. These will emit different colors. A good amount of oxygen may be liberated by the blast, so there could be a short lived flame if there is sufficient carbon in the debris.

I presume it would explode on impact, not a distance from the surface. The lessens the need for an atmosphere to transfer energy.

 

[Jimmy Higgins]

I was watching a rerun of Meteor the other night and a question popped into my head. How much of a nuclear bomb's destructive power is composed with how it interacts with the immediate atmosphere (like blast winds, oxygen around for things to catch fire) compared to what its destructive power would be, say hitting an asteroid, out in the vacuum of space?

As an example, the sun is a fusion reaction in a vacuum.

 

[Loren Pechtel]

There's little blast wave from a nuke in space as the only available material is the bomb itself. While the bomb bits are moving very fast when they hit they have so little mass the effect is unimportant. Also, normally a lot of energy is converted from radiation to shock wave as the atmosphere is pretty opaque at those frequencies--but in space this doesn't happen.

Thus in practice almost all the energy of the bomb is carried off as photons. Some are very hot and will fry you if you're too close (which is why the blast energy is unimportant--if you're close enough to be hurt by it you'll be dead from radiation), the majority simply makes things very hot.

While I think I've seen the movie before I don't recall the details. IMDB says the threat is a 8mi asteroid.

Against a threat of this size you do *NOT* want to hit it. Think love pats, not punches. Unless you're sure it's truly a solid rock you need to keep your nudges down to no more than a few meters per second (you need to keep them well below escape velocity, you do *NOT* want to split off a piece!) I'm getting a mass of around 4 teratons so our maximum safe impulse is about 10 petanewtons. At 100% efficiency that's a 2.39 megaton bomb. Since you haven't carefully carved an engine cavity out of the rock the theoretical best you can do is to catch 50% of that energy (half goes up into space) so you're up to 5mt per shot--but that's with the bomb sitting on the surface and throwing fragments. I think the 10% that was the low end of the efficiency numbers for Orion is more realisitic--call it 25mt/bomb.

Such love pats don't sound like they would do much--but if you have enough time they will. Lets say you hit it a year before impact. 2.5m/s * 60 sec/min * 60 min/hour * 24 hour/day * 365 days/year = 78,840,000 meters. That's 6 earth diameters--plenty to cause a miss. 2 months out it likely can generate a miss. One month out you'll need a minimum of two missiles. One week out you'll need at least 9.

 

[fast]

I was watching a rerun of Meteor the other night and a question popped into my head. How much of a nuclear bomb's destructive power is composed with how it interacts with the immediate atmosphere (like blast winds, oxygen around for things to catch fire) compared to what its destructive power would be, say hitting an asteroid, out in the vacuum of space?

As an example, the sun is a fusion reaction in a vacuum.

Fusion isn't fission, and although some nuclear bombs use fusion, the thread title leads me to think he's excluding nuclear bombs that use fusion. Also, I shouldn't let titles mislead me, so carry on: as I have no point to make.

 

[bilby]

Most of the damage from terrestrial bombs - particularly the larger ones - is blast; this would be negligible outside the atmosphere, and the effects are basically going to be from heat, and subject to the inverse square law.

 

[bilby]

A nuclear weapon's destructiveness comes from the shock wave(kinetic energy) and the heat(thermal energy). Neither of these will be reduced because there is no atmosphere. It probably won't be as spectacular as a Terrestrial explosion, but we can expect a lot of vaporized matter, which is composed of various elements, mainly metals and silicon. These will emit different colors. A good amount of oxygen may be liberated by the blast, so there could be a short lived flame if there is sufficient carbon in the debris.

I presume it would explode on impact, not a distance from the surface. The lessens the need for an atmosphere to transfer energy.

The amount of light chemical elements produced by atomic bombs is small; the amount of Oxygen or Carbon produced is insignificant; and even if the ENTIRE mass of the warhead was converted to pure Oxygen and Carbon at the optimum ratio for combustion, the chemical reaction energy would be utterly minuscule in relation to the energy from the atomic reaction in the bomb - indeed, the heat in the vicinity of the bomb would be sufficient to dissociate any oxides already present into their component elements (ie the combustion reactions would run backwards to their usual direction in terrestrial chemical reactions, due to the massive input of heat from the nuke), and these elements would then be rapidly dispersed before they could cool enough to re-combine chemically. So no, a chemical flame is not even vaguely possible.

Getting an atom bomb explosion in space to result in a chemical flame would be a bit like trying to strike a match in a hurricane, only far more difficult.

 

[Bronzeage]

A nuclear weapon's destructiveness comes from the shock wave(kinetic energy) and the heat(thermal energy). Neither of these will be reduced because there is no atmosphere. It probably won't be as spectacular as a Terrestrial explosion, but we can expect a lot of vaporized matter, which is composed of various elements, mainly metals and silicon. These will emit different colors. A good amount of oxygen may be liberated by the blast, so there could be a short lived flame if there is sufficient carbon in the debris.

I presume it would explode on impact, not a distance from the surface. The lessens the need for an atmosphere to transfer energy.

The amount of light chemical elements produced by atomic bombs is small; the amount of Oxygen or Carbon produced is insignificant; and even if the ENTIRE mass of the warhead was converted to pure Oxygen and Carbon at the optimum ratio for combustion, the chemical reaction energy would be utterly minuscule in relation to the energy from the atomic reaction in the bomb - indeed, the heat in the vicinity of the bomb would be sufficient to dissociate any oxides already present into their component elements (ie the combustion reactions would run backwards to their usual direction in terrestrial chemical reactions, due to the massive input of heat from the nuke), and these elements would then be rapidly dispersed before they could cool enough to re-combine chemically. So no, a chemical flame is not even vaguely possible.

Getting an atom bomb explosion in space to result in a chemical flame would be a bit like trying to strike a match in a hurricane, only far more difficult.

"Short lived" could be nanoseconds. There's no real advantage to setting an asteroid on fire.

 

[bilby]

The amount of light chemical elements produced by atomic bombs is small; the amount of Oxygen or Carbon produced is insignificant; and even if the ENTIRE mass of the warhead was converted to pure Oxygen and Carbon at the optimum ratio for combustion, the chemical reaction energy would be utterly minuscule in relation to the energy from the atomic reaction in the bomb - indeed, the heat in the vicinity of the bomb would be sufficient to dissociate any oxides already present into their component elements (ie the combustion reactions would run backwards to their usual direction in terrestrial chemical reactions, due to the massive input of heat from the nuke), and these elements would then be rapidly dispersed before they could cool enough to re-combine chemically. So no, a chemical flame is not even vaguely possible.

Getting an atom bomb explosion in space to result in a chemical flame would be a bit like trying to strike a match in a hurricane, only far more difficult.

"Short lived" could be nanoseconds. There's no real advantage to setting an asteroid on fire.

Yes, it could. But it won't be, because it is impossible.

All chemical reactions are reversible:

Carbon + Oxygen > Carbon Oxides + Heat;

Therefore

Carbon Oxides + Heat > Carbon + Oxygen.

The second reaction is swamped by the first, absent a significant heat source. An atomic bomb is such a source. In space, any Carbon and Oxygen present at the blast will remain separated chemically until they are too dispersed by the explosion to react.

There will not be a flame due to anything burning in oxygen when a nuke goes off in space. Not even for a nanosecond.

 

[Bronzeage]

"Short lived" could be nanoseconds. There's no real advantage to setting an asteroid on fire.

Yes, it could. But it won't be, because it is impossible.

All chemical reactions are reversible:

Carbon + Oxygen > Carbon Oxides + Heat;

Therefore

Carbon Oxides + Heat > Carbon + Oxygen.

The second reaction is swamped by the first, absent a significant heat source. An atomic bomb is such a source. In space, any Carbon and Oxygen present at the blast will remain separated chemically until they are too dispersed by the explosion to react.

There will not be a flame due to anything burning in oxygen when a nuke goes off in space. Not even for a nanosecond.

Ok, no flame. Got it. What about the pretty colors?

 

[repoman]

I think that much of the key to the damage done by nuclear weapons is from the extremely high rate they explode. This allows the radiation to be very high frequency and the blast forces to be very high.

 

[bilby]

Yes, it could. But it won't be, because it is impossible.

All chemical reactions are reversible:

Carbon + Oxygen > Carbon Oxides + Heat;

Therefore

Carbon Oxides + Heat > Carbon + Oxygen.

The second reaction is swamped by the first, absent a significant heat source. An atomic bomb is such a source. In space, any Carbon and Oxygen present at the blast will remain separated chemically until they are too dispersed by the explosion to react.

There will not be a flame due to anything burning in oxygen when a nuke goes off in space. Not even for a nanosecond.

Ok, no flame. Got it. What about the pretty colors?

I reckon you would get an interesting spectrum; you would need to split the light with a prism or grating to see anything other than a white flash though. Nukes produce lots of photons across the entire visible spectrum.

Indeed, the one nuclear explosion in space with which we are all familiar is not only white; it DEFINES what white is. Sunlight is white, because white is the colour of sunlight (Lots of people think sunlight is yellow, but it's not).

This is easy to demonstrate, using just a sheet of paper. 'White' paper is paper that reflects all colours equally. Shine an coloured light on a piece of 'white' paper, and the paper appears the colour of the light. In red light, white paper looks red; in green light, white paper looks green. Now, take the paper out into the sunlight. What colour does it look?

 

[Keith&Co.]

Now, take the paper out into the sunlight. What colour does it look?

Right now It looks cloudy...

 

[Shadowy Man]

Indeed, the one nuclear explosion in space with which we are all familiar is not only white; it DEFINES what white is.

The Sun isn't white because that's the color of a nuclear explosion. The Sun is white because nuclear reactions are warming an optically thick ball of gas to about 6000 degrees Kelvin, and something that is 6000 K emits a spectrum that looks white.

 

[fromderinside]

Is the sun white?

Eyup.

Why?

from  Color temperature

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source .... The color temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in Kelvin, or alternatively in mireds (micro-reciprocal Kelvin).^[4]This permits the definition of a standard by which light sources are compared. .... The Sun closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is about 5,780 K.^[5] The color temperature of sunlight above the atmosphere is about 5,900 K.^[6] ....

So bilby and Shadowy Man between them got it right while they didn't say it right.

Mr. Whizzzzz, oh, did I fall asleep and why are my hands wet ....

 

[skepticalbip]

Is the sun white?

Eyup.

Why?

from  Color temperature

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source .... The color temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in Kelvin, or alternatively in mireds (micro-reciprocal Kelvin).^[4]This permits the definition of a standard by which light sources are compared. .... The Sun closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is about 5,780 K.^[5] The color temperature of sunlight above the atmosphere is about 5,900 K.^[6] ....

So bilby and Shadowy Man between them got it right while they didn't say it right.

Mr. Whizzzzz, oh, did I fall asleep and why are my hands wet ....

Right.

The black body radiation curve:

 

[Shadowy Man]

So bilby and Shadowy Man between them got it right while they didn't say it right.

In what way was what I said not right?

 

[Shake]

I didn't see Meteor but in the film, Armeggedon, I think they had a better plan in regards to the effectiveness of such a weapon: to drill into the body and plant the bomb inside. In the film, the scientific idea was to use the nuke to split the asteroid in two. While it appears this may not be possible on an object the size of the one in the film, I think the concept would yield a better result than exploding a nuke either nearby or even just at impact on the surface.

That said, I'm not sure how practical it would be to try to put a bomb plus drilling equipment up into space and then still have to have it bore into the object. I think the idea of sending astronauts up to do the drilling is even more ludicrous.

 

[bilby]

Splitting the meteor in two sounds like a pretty dangerous strategy; The effect of multiple simultaneous small impacts is actually WORSE than the effect of a single large impact, so you would need to be very, very, confident that you are only going to end up with a manageable number of large pieces, and that the explosion that separates them will impart the right impulse to each fragment to ensure that they miss the planet - that's fairly easy to arrange if the meteor is many months away, but with days (or worse, hours) to go to impact, breaking the object up is far more likely to do harm than it is to do any good.

Lots of smaller impacts are worse, because in a large impact, the effects are localised, and you are just as dead at 100psi overpressure and 3,000K as you are at 1,000,000psi and 50,000K, so concentrating the impact energy in one spot actually reduces the number of immediate deaths. Of course, if the single impact can take out the whole human race, then making things 'worse' is irrelevant; but if you are talking about a fragment that's going to 'only' devastate New York City (and let's face it, it's a disaster movie, so you almost certainly are), breaking it up into a large number of fragments that will devastate the entire continental US, is not going to win any votes.

Even with a planet-killer, breaking it up shortly before impact likely just turns one existential problem into a larger number of equally existential problems.