Nuclear explosion vs. Pure energy blast

Factual Questions
1

Okay, here’s the dealie: How would the effects of a nuclear bomb compare to a strike from, say, a laser with the same amount of energy behind it? Say you managed to build a laser in orbit around Earth and it was capable of pumping out 4 x 10[sup]15[/sup] joules of energy ('bout the same as a 1 megaton explosion). What would the effects of this blast be when it hits the ground? Would you get the same mushroom cloud effect? Obviously you wouldn’t have any radioactive materials left over, since there’s no radioactive fuel to begin with, so there’d be no fallout, but what about the size of the resulting crater? Where would the energy go? How big of a blast area would there be?

Essentially, I’m trying to figure out how science fiction weaponry (like the guns in Star Wars, for example) would compare to modern weaponry, in terms of results.

2

>Essentially, I’m trying to figure out how science fiction weaponry >(like the guns in Star Wars, for example) would compare to >modern weaponry, in terms of results.

As I recall, the weapons on the Star War fighters were immovable, line-of-sight and had a limited range. About like a WW2 Mustang firing .50s.

An atomic blast releases energy at the point of the reaction which is (hopefully) the target. A laser projects energy FROM the point of the reaction and it weakens over distance. The size of the impact area would depend on the laser, but it would not be very big at all. The result would probably be the vaporization of whatever was in the beam path and the main effect would be down rather than out if the area being lased remained steady.

The shooter could probably do some great laser engraving on a big scale.

3

So any sort of “shockwave” or blast radius would result from the rapid expansion of vaporized material? Gotcha…

4

You’d still get the mushroom cloud from the blast - that’s a charactaristic of any high-energy explosion. One question you have to answer is the duration of the laser - it’ll make a big difference if the energy is deposited nearly instantaneously or over a period of a few seconds or more. If the laser takes more than a small fraction of a second to depositi it’s energy into the target, you’ll get most of that energy going into hearting up the air rather than the ground as vaporized material rising from the impact site blocks the beam path.

5

The results of a multi mega joule laser strike would be different than the same level of energy from a nuclear reaction, but the differences would be far more theoretical than pragmatic.

Laser strikes would heat atmosphere from the point where the beam first entered it, until the beam struck a solid target. “Bloom” is the name of the phenomenon where energy beams are dispersed because of the optical effects of heated air. In this scenario we have a tower of expanding plasma reaching down from the sky, and terminating on the ground. It would be a ragged, but essentially straight line, and it would expand with terrific force, and leave a vacuum behind, for a brief time.

When the beam struck the ground it would be absorbed by the surface, reflect back up in a dispersed cone, and the material would vaporize in a very chaotic manner, as different materials absorbed heat at varying rates. The vapor would be further energized, and become disassociated plasma, expanding very rapidly, from the center of the ground target. The beam would penetrate to some extent, variable with the density, and absorptive characteristics of its make-up. That would be a small distance, in most cases, only hundreds of feet at most.

From a distance, you would have a bright flash of super lightning coming down from the sky, followed almost instantaneously by a ball of fire rising from the point where the beam struck. I think it might follow the path of the beam back upwards to some extent, since it was already expanding outward as the blast came up from below. But the beam, for as long as it existed would even more extensively heat plasma moving upward.

If we assume similar time frames for the nuclear, and beam weapons to act, we must assume that the beam would stop before physical effects from the ground reached significant altitudes. That would be an engineering variable, modified to achieve the greatest effectivity as a weapon. So, the flash and boom has a much more tower like shape to begin with. I think you would have a much different blast front than that of a surface blast nuke, Much taller, and narrower, with a cylindrical wall expanding more horizontally than vertically, directing its force more outward than a spherical blast. Tactically, that might be desirable, against surface targets, like cities or military formations over large areas.

The post blast effects would be less different. The air would still rush back in, and the rebound blast would still return outward, and the convection pattern would be essentially similar, although perhaps a bit taller than the familiar one from Bikini, or Alamogordo. Fires would ignite over the entire area, and secondary ignition would still be a devastating effect. Radiation would be the only destructive factor missing.

Tris

“You don’t need a weatherman to know which way the wind blows.” ~ Bob Dylan ~

6

The above assumes that the beam is question is some kind of photons, which interact readily with matter. You could have interesting effects if you postulated some kind of obscure form of energy with a much weaker coupling to ordinary matter. If your hypothetical beam had an average absorbtion of only 50% for every kilometer of rock it penetrated, then instead of a plasma fireball you could heat cubic kilometers of rock into magma. That’s the sort of thing you’d want to destroy very deep fortifications, or devastate large areas without ejecting huge amounts of dust into the stratosphere.

7

Interesting, Trisk and Lumpy… how (not that I’m doubting you at all) did you reach these conclusions?

8

Funny, I was asking myself that as well. Commendable stuff, albeit a little worrying. Very vivid and capturing description as well, you rightfully put ILM to shame.

9

Spoofe

I made it up, of course!
OK, in fact, I extrapolated. I was fairly well trained on the mechanics of nuclear explosions, as you might have noticed from previous big bomb stuff threads. This information came from good ol’ Unka Sam. I also tend to keep up on the published, and to a very small, (and strictly legal!) extent military-industrial skuttle butt, on the related subjects.

Things that go bang in the night are very heavily studied. I must admit my extrapolation might be entirely wrong, for reasons I did not consider, or simply do not know. It was a conservative estimation. I also did not mention that the fictional weapon described, like most fictional weapons has been considered by the Military, as a possible eventual development ( on a smaller scale, perhaps.)

The cylindrical blast wave is the wildest assed part of the guess. The rest is pretty straight forward, really. You have a linear energy source of the same order of magnitude as nuke, with the highest proportion of its energy delivered at the bottom. The geometry is pretty simple. It takes place with a small region near vacuum directly above a very rapidly expanding cloud of plasma. I could be wrong, but that seems like a shaped charge, that would expand outward as a blast wave, and upward as high energy plasma particles.

That much energy in that much time is a big explosion, one way or another.

Tris.

10

I would think that the ground-burst would be more along the lines of an icecream cone, rather than cylindrical.

While the vapor/plasma rising up the axis of the beam would be progressively more energized, most of the material would be ejected from the beam path close to the target, and so expand the base of the blast preferentially. Further, as vapor rises off the target and becomes energized, the target is no longer being struck by the full energy flux, and so vaporizes more slowly, as more and more energy is absorbed and scattered by the vapor cloud. Penetration would be quite shallow in comparison to the amount of energy deposited, and there should be some really spectacular spalling as any hard materials such as concrete and rock shatter under heat stress and are carried away in the blastwave. The net effect should be to have a fairly standard fireball at the surface, with a tapering cone on the axis of the beam perched atop it, shortly thereafter followed by a fairly standard mushroom cloud (which may be distorted by the atmospheric effects of the beam’s path).

The shockwave from the beam’s path through the atmosphere should be fairly inconsequential in comparison to that from the groundburst, based on the relatively small volume of displaced air (assuming the beam has a reasonably tight focus), and depending on lighting conditions, the beam’s path might not even be all that noticeable.

For all intents and purposes, it should behave similarly to a clean nuke ground burst, minus the fallout.

11

Good stuff guys, but you’ve all forgotten something:

If the beam is fired from space it will also make a whole in the ozone layer and give skin cancer to anyone that will live in the area afterwards…

So all survivors will be red and mad like this guy: :mad: , unles they had sunglasses in which case they would be orange and happy like this guy: :cool:

12

Tranq,

Interesting.

A lot depends on the duration, over which the total energy is delivered, which is an engineering variable. In fact, the power need not be assumed to be delivered uniformly over that duration, if it might be militarily useful to do otherwise.

The cone shape you describe would be disadvantageous, although I think it would be a very narrow cone. If the beam is maintained for several hundred milliseconds, as opposed to the hundreds of microseconds more common in nuclear blast times, the effect can be altered pretty much at will, within the parameters that a great big bang is pretty much gonna be common to all solutions.

If you deliberately create a wide-to-narrow focus, over a simultaneous low to high ratio power output, you can affect a large column of atmosphere, and a narrow center of impact on the ground. That should give you the more useful columnar blast wave. It might be possible to engineer an inverted cone, which would be exceptionally effective in extending the radius of destruction. The Mushroom cloud remains the same, I think.

We should begin construction of the Death Star immediately, so that testing can be done.

Tris

" The worst policy is to attack cities. Attack cities only when there is no alternative." ~ Sun-tzu ~

13

Ah, the dreaded neutrino ray cannon…

14

SPOOFE one physical principle that has yet to be mentioned is that your basic run of the mill energy dissipation device like a bomb works the same no matter what the source of the energy. That’s the beauty of energy conversion. If I could build a device that delivered the same amount of explosive power to an area as a thermonuclear blast without the thermonuclear part of the story, I would still have the same effects because the energy would be converted into dissipative forms (mostly light, heat, and sending debris out of the potential gravity well). There differences between these weapons comes into play when you talk about concentration of energy and side-effects, but in terms of big booms and blasts, it doesn’t matter what your source of energy is, you will end up with the same destruction.

15

Heh!

Heheheheheh!

BWAH-hahahahahahahaaaa!

OK! Your orbit, or mine…?

Some other fun-n-games the can be played with beams:

  • What about an anular beam? That might convert all the marterial, air, varpor, etc. to a plasma collumn trapped with in the beam. You could get some really fun shockwave paterns from that when you turn the beam off…

  • What about pulsing the beam? Or simply rotating it rapidly about a central point? Instant megajoule drill! Pulsing would add the advantage of heat and shock spalling, with shockwaves to carry off the debris, greatly increasing penetration, while rotating the beam would tend to cut more (still producing spalling from thermal expansion). Combine the two measures…? Whoah! Nasty!

Shorter pulse length for same energy delivered would greatly increase the efficiency, making beam weapons a better choice for sheer destructiveness…

What fun! :wink:

16

Oooo! Oooo!

What about a wide angle beam, of very short duration, from above the stratuspheret. That way you get a very wide atmospheric effect, and the shock wave is directed downward over a very large area, several miles in diameter. You would loose a lot of power upward, of course, probably nearly half. But the directed blast wave would literally flatten everything inside of its radius, and probably have very reduced effects outside of that. Like stompin’ down on a single circular zone, leaving the rest untouched. You might even be able to use your annular beam here, to enhance the effect. A shaped charge aimed directly downward.

I wonder if it would still have the flash fire effect?

I should have been a war monger.

Tris

“On all the borders of the Communist countries, the European ones in any case, you can find electronic killing devices. These are automatic devices for killing anyone who goes across. But people here say: ‘That doesn’t threaten us either, we are not afraid of that.’” ~ Aleksandr Solzhenitsyn ~

17

That’s not entirely true. An optimally deployed bomb will always have greater destructive effects than an equivalently powered laser/energy weapon. The reason is altitude detonations.

A smaller bomb detonated at a height of 1500 feet has a much greater blast effect than a significantly larger bomb at ground level. This is because of a blast front that “reflects” off the ground. I don’t know the physics details behind it, but it was discussed (and demonstrated) on “Trinity and Beyond: The Atomic Bomb Movie”.

Blast effects of a beam weapon will always originate from the target, not above it.

18

Now, Joe, that ain’t necessarily so. There are no specifications for how this “beam” weapon in the OP works. Detonation could be triggered by means of some sort of energetic coupling with the air at the altitude of 1500 feet.

You are indeed correct that altitude detonation makes a difference, but that has to do with energy transfer and not strictly with energy release. In terms of pure destructive ability, there is equivalency. The physics of high-energy shockwaves are really interesting and are related (not surprisingly) to sound-speed studies, but we needn’t get into them here. Basically, all of this is up to precise weapon and deployment specifications and has nothing to do with destructive capacity.

19

Three things: First, wouldn’t having the radiation directly strike the region you want to destroy be more efficient than striking a small region and relying on the resulting blast to destroy a larger area?

Second, I’d expect there’d be an awful lot of recoil, so that the satellite itself, unless DeathStar sized, would be thrown out of its orbit, and would be essentially a one shot weapon.

Putting the first two together, I wonder if a lunar base wouldn’t be a better idea. You’d only have to get the spot down to the size of the destruciton zone (say several miles in diameter), rather than some relatively tiny spot if you’re relying on the blast for destruction, so this makes up for the additional beam spreading from a Lunar distance. Plus, you’ve got the potential of firing the weapon multiple times.

20

No reason why our death beams can’t be bomb-pumped one-shots. Of course that begs the question “If you’ve got a bomb that big, why aren’t you using it, instead?” I assume the answer would have to be something along the lines of “Let’s not crap-up the planet”.

Of course, The Death Star works for me, too. It has the advantage of having lots of room for my motorcycle collection and hareem. :wink: