Nuclear Weapons As A Unit Of Measurement

Some thoughts:

“In general,” he added, “What I don’t like is … the idea that kiloton or a megaton is just an energy unit, that it’s equivalent to so many joules or something. Because you could do that. You could claim that your house runs so many tons of TNT worth of electricity per year, but it sort of trivializes the notion.”

While I agree that the notion of comparing a bolide explosion to a nuclear event is misleading, I think he misses the boat himself here. It’s not just about an “energy release.” It’s about how fast the energy is released. That is, talking about megatons of TNT is a discussion about power, not energy per se. This is the same confusion that people have with regard to rocketry. They often talk about how much “energy” it takes to get into orbit, when in fact it’s not much more energy than it takes for intercontinental aircraft flight. The difference is that the airplane deploys its energy over many hours, whereas the rocket must do so in a very few minutes. When the Shuttle took off, it generated more power than the entire nation’s electrical grid for the first two minutes. In fact, when I was working propulsion at Rotary Rocket in the nineties, we used to joke about what units we should use to describe the power output of the engine, and thought that “Hoovers” (as in the dam) would be a useful one.

In any event, radiation and heat or no, either exploding meteoroids or nuclear weapons city busters, and events to be concerned about.

19 thoughts on “Nuclear Weapons As A Unit Of Measurement”

  1. It’s not just about an “energy release.” It’s about how fast the energy is released. That is, talking about megatons of TNT is a discussion about power, not energy per se.

    I disagree. It really isn’t going to make that much of a difference to a nearby city, if the energy was released over five seconds or five microseconds. Sure, if it’s released over a long enough span of time, then the energy would go into space, rather than say, breaking buildings. But meteors and nuclear bombs both fall on the wrong side of that particular threshold.

    1. It very much does matter. If the energy is released in 10 microseconds it is all dumped into one location, and if it happens close enough to the ground it’s effectively identical to a nuclear explosion. However, if the energy is released over 10 seconds then instead of being distributed in a sphere the destructive power is distributed over a tube that is perhaps a hundred kilometers long, since the object will be traveling at 11 km/s or more initially.

      In the case of an energy release in the 20 megaton range, for example, the lethal / destructive radius from “ground zero” of an instantaneous explosion will be around 40 km, so even if the detonation is in the stratosphere it would still lead to a significantly sized destructive radius on the ground which would lead to tremendous loss of life if it happened over a heavily populated area. However, if the energy is released over a 100 km tube over 10 seconds then the effective destructive distance from any given point along the meteor track will be significantly shorter than for the instantaneous explosion case. More so, because much of the destructive power is expended in the upper atmosphere the volume enclosing the space where there is lethal destructive power may not even contact the ground at all in this example, vastly reducing the destructive potential of the impact by orders of magnitude.

      1. That’s not what I was speaking of, Robin. Dispersing energy release over a larger area or volume is different from releasing it over differing time spans.

  2. Given that there are thousands of commercial jets in the air continuously, including scores of jumbo jets, I am wondering about your math here:
    “The difference is that the airplane deploys its energy over many hours, whereas the rocket must do so in a very few minutes. When the Shuttle took off, it generated more power than the entire nation’s electrical grid for the first two minutes. “

    1. It may take the same energy to accelerate a payload to LEO as it does to carry that payload on a jet airliner from Chicago to Sydney.

      But . . .

      The jet gets its oxygen from the air. A rocket has to carry its oxygen, which in turn requires accelerating more weight as oxygen partway to orbit, which in turn requires more fuel and in turn more oxygen — OK, OK, I don’t need to explain the Rocket Equation, Mass Fraction, and Staging to anyone in these parts.

      But the answer as to why rockets are “harder” than trans-Pacific airliners is more than the higher energy rate, but I think y’all know that too.

      So why not go to orbit with an air breather? The whole deal with an air breather is essentially to make the economics of space launch the same as that of Quantas.

      Well, there is the LACE concept, where you scoop air and liquify the oxygen fraction to burn in a rocket, but the closer you get to orbital velocity, the more drag you incur scooping the air — essentially accelerating that air to your current speed. As you approach orbital velocity, the compression heating in that scoop approaches the molecular disassociation temperature.

      Then there is the scramjet, the real-life drink from the firehose, where you don’t attempt to scoop the air, only slow it down a little in relation to the vehicle, burn a flame in that hypersonic stream without the flame going out, and try to get some net thrust. Somehow.

      Well, after 50 or so years, there are folks still pottering around with the scramjet, and there are those dudes in England with the Skylon — not fully LACE as they gave up on liquifying the air, but they have some complicated thermodynamic cycle that would make the designer of an advanced steam-cycle electric power plant proud.

      And then there is not getting your air breather to burn up during its ground-to-orbit burn. But, I think you all know all of that . . .

      1. For an air breather of any variety to work well at hypersonic speed, the energy of the incoming air stream must be captured in some form useful to the engine. The propellant, whether coming from a tank or an inlet, must (to first approximation) be brought to the engine’s rest frame before it can be used. A scramjet fudges it somewhat, but even then the air passing through the engine is closer to the engine rest frame than the surrounding air rest frame.

    2. The math is fairly easy. All you have to do is look at the fuel. A Boeing 767-400ER can carry 91,000 liters of fuel. A Falcon 9 carries about 280 tonnes of propellant which includes fuel and oxidizer, adjusting for a typical LOX/Kerosene mixture ratio of 2.7:1 that gives 27% of the propellant mass as fuel mass, which is 76 tonnes or about 95,000 liters.

      So there you have it, the total fuel load on a 767 is about the same as on a Falcon 9, though the 767 has the advantage of using Oxygen from the air, and thus the total energy used will be comparable (depending on how close to the margin the 767 drains its tanks). A 777 or A380 uses considerably more fuel though.

  3. While I appreciated the mathematical argument in the linked article, there is one excellent reason to express impactors in terms of their nuclear-weapons equivalent: the terrifying geopolitical risk they pose. We have only to imagine the exact same event occurring in October 1962, or occurring today anywhere over the Korean Peninsula, almost anywhere in the Middle East, or perhaps worst of all the Indian subcontinent, to grasp its true significance. Shameless plug.

    1. Isn’t another reason, the very fact that the impact would cause damage along the lines OF a massive explosion?

      During the run up to the Trinity Test, they actually stacked 108 TONS of conventional explosives as a ‘calibration’ blast.

      Everything I’ve ever read about the Manhattan Project and the Trinity Site and the first A-Bomb and all the ones since then, says they used the Tons, Kilo-tons, Mega-tons terminology so that, after the fact of the attack(s) on Japan, foreign governments would understand what we had, and what the capability was.

      It made no sense to tell politicians, and most military men wouldn’t understand joules and ergs. But TONS of explosives they understood and still understand.

  4. “The radiation brings sickness, makes land uninhabitable in the long term…”

    Residents of Hiroshima and Nagasaki were unavailable for comment.

    “What does it even mean to say that something is 30 times the size of Hiroshima? Do people have a really strong sense of even what one Hiroshima looks like, and can they then imagine an energy release 30 times that?”

    He knows that expressing such an event in millions of joules would convey even less information to the layman. But he doesn’t like the Hiroshima measure because it implies that the bomb was 30 times smaller than the meteor, and the idea that nuclear weapons are small is bad for people because nuclear weapons are bad.

    Abysmally stupid mommy-state PC crap.

    1. the idea that nuclear weapons are small is bad for people because nuclear weapons are bad.

      That’s the impression I got from the article: It’s wrong to compare meteors to nukes because it trivializes the danger of nukes.

      But what else is suitable to describe a really big meteor? This one detonated at an altitude of about 30 miles, the blast wave took over two minutes to reach the ground, and it still broke windows, damaged buildings, and injured people. What else can you compare it to, if not a nuclear explosion?

  5. I agree. These events are nothing like modern nuclear weapons. They can be actually much worse and more destructive. Say the Chicxulub meteor for instance.
    The effects are not the same? This coming from the same people clamoring about the possibility of “nuclear winter” from dust sent to the atmosphere after a blast? What about shock waves? Or high temperatures upon impact? Yup nothing like a nuclear blast.

    1. The “nuclear winter” anaylsis was based on a cue-ball earth, and had no relationship to reality. Sagan knew it, but had no problem twisting “science” into a pretzel in support of his politics.

  6. If the source of the article had a point, he could have explained exactly how a 500kt nuke at detonated AT THE SAME ALTITUDE AS THE METEOR would have differed in effect. He didn’t. Instead, he showed a pic of a 500kt groundburst and said it didn’t look like the meteor. Gee, ya think? That, to me, says one thing; he’s nothing but a fraud and a hack with an agenda.

    BTW… if the Russian meteor had arrived, say, 30 years ago in the cold war, and done the same thing in the same place… I doubt we would be here. That area had a lot of weapons programs, and so what looked very muck like a high order nuke appearing of a track out of the northeast… that could have very easily triggered WWIII, especially during a time of tension.

  7. This occurred to me when I saw this article. Let me toss it out for thoughts.

    Could we not also say that merely using kilotons/megatons of TNT as a measurement of a nuclear detonation is misleading. Yes, you could hypothetically detonate 10,000 tons of TNT at the same time, but you still not get the same thermal pulse as you would from a nuclear detonation. Nor would you get the radiation pulse, etc.

    And another question that just came to mind. When the early physicists came up with kiloton to measure the Trinity/Hiroshima/Nagasaki bombs, just how did they calculate the energy released? Was it in joules? And did that number of joules released equate to that released by 10, 12 or 15 thousand tons of TNT going off at once? Can anybody with a better backing in that realm elaborate?


    1. Yes, you could hypothetically detonate 10,000 tons of TNT at the same time, but you still not get the same thermal pulse as you would from a nuclear detonation.

      I disagree. It’s worth remembering here that our intuition for nuclear bombs and conventional explosives comes from radically different sizes of each. We think of conventional explosions as detonations up to perhaps tens to hundreds of tons TNT equivalent. But nuclear weapons start to barely work around the few kiloton range. When we scale up conventional explosions to the nuclear bomb range, we’ll start to see the same issues that happen with nuclear bombs. For example, a large enough explosion won’t be able to get rid of heat fast enough via ejection of material. That will create a thermal pulse.

      Consider this, a megaton of TNT would be a ball of TNT about 350 feet in diameter (or almost 105 meters). One could get a similar effect by wrapping a one megaton nuclear bomb in a shell of a similar amount of inert material with similar density to TNT. The latter bomb configuration will actually have less energy for the combination of blast and thermal pulse because it is losing more energy to radiation that penetrates through the shell (neutrons and to a limited extent gamma rays) and more thorough dissociation of the matter of the shell.

      I think it would be very hard to tell a difference between the two bombs, aside from the absence of radioactive fallout for the chemical explosion. You’d still get the thermal burn with severe burns miles away. You’d still get people blinded at tens of miles. You’d still get the blast wave. And you’d probably even see some radiation burn symptoms (the TNT-based fireball would probably radiate well in the UV range).

      There might be some discernible differences in the distribution of energy between blast wave and thermal pulse. But fundamentally, there’s only a few ways to channel energy away from a huge release of energy. No matter how you generated the energy release, they’ll probably look very similar in outcome.

  8. If they don’t like energy level, how about going with toxicity level? For example, you can rate everything by how much you must intake for a 50% toxicity. So instead of tons, for a strike you give a radius where 50% of the people would die?

  9. I thought you were talking about the old Cold War joke, that Germany was so built-up that the towns were just a few kilotons apart…

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