Doug's Darkworld

War, Science, and Philosophy in a Fractured World.

Posts Tagged ‘rope trick effect

What The Hell Is That?

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The answer is in a very first few lines so the gentle reader should stop reading now if they wish to guess.

Picture identification day on Doug’s Darkworld, what the hell is that thing? A wormhole opening? A UFO? A ghost? Nope, it’s a photograph of a small nuclear explosion about 3 milliseconds after detonation. I wouldn’t have had a clue either. The fireball is about 20 metres in diameter at this point. It was taken by a very special camera at an exposure of about 3 microseconds, that’s three one millionths of a second. Pretty amazing technology for the early 1950s, and I am especially curious as to how the camera survived the blast. Or even how the film survived the initial burst of radiation and light, which had already passed it when this picture was “snapped.” My admittedly limited research into this didn’t yield an easy answer at least.

Moving right along though, the image has a number of features that bear explaining. This bomb was set off atop a tower, the base of the tower can be seen below the explosion. As well as a number of downward projecting spikes, the first oddity that demands explanation. This is called the rope trick effect, and only occurs in blasts where the bomb was on a tower stayed by guy lines, never in air bursts or ground bursts or underground bursts. It was theorized that these are the remains of the guy lines that were vaporized and blasted away by the initial flash of light the explosion generated, the brighter than a million suns light  ignites anything flammable close to the explosion light. To test this, bombs were set off with the guy lies painted in reflective paint or covered in tin foil. No rope trick effect in such blasts, theory proved. Yes, a flash of light so strong that it can vaporize and propel steel cables through the air, scary.

So what exactly are we seeing here anyhow, aside from the rope trick effect? The surface of the explosion is the actual blast wave, or hydrodynamic shock front, propagating outward. The surface of the sphere is glowing because at this stage the blast wave is so strong that it is literally compressing and igniting the atmosphere ahead of it. As the shock wave expands and grows weaker it stops igniting the air and becomes invisible, a process known as breakaway. Scientists studying bombs still wanted to study the shock wave after it becomes invisible, and thought of a way to do this. Look for the upright white spikes below and to the right of the blast. These are smoke trails made by small rockets fired off a few seconds before the bomb itself. As the shock wave passes though these smoke trails they will be visually distorted, and thus the shock wave can be timed and studied even though it is invisible. Slicker than whale shit as we used to say in the service.

Lastly, what accounts for the mottled appearance of the surface of the shock wave? Well, the bomb itself and its mount are made out of matter, and this matter is literally turned into clouds of particles being blasted outwards at tens of kilometres per second by the explosion. Then these clouds of matter “splash” against the back of the shock wave, and are mottled because the matter around the bomb varies in amount and density. Yes, these are clouds of atomized, not just vaporized, matter.

Now I wouldn’t swear to this, but I think this is basically the moment when the nuclear explosion essentially starts to act like a normal explosion. The nuclear part of the explosion is over, and what is pictured here is a ball of incredibly hot gas under unimaginable pressure. It’s going to make a huge mess as it dissipates.

Is there a point to this post? Not really. I just thought the photo and the explanation for the features of it were fascinating. Well, maybe an implied comment about the obsessive lengths humans take to devise ever more efficient methods of killing each other. In that vein, yes, there’s something terribly terribly wrong with this picture.

(The above image is Public Domain under US copyright law, being produced by a Federal employee in the course of their duties. The bomb pictured above was one of a series of bomb tests called Operation Tumbler-Snapper, conducted in 1952. Yes, this bomb no doubt created some fallout, one of the reasons most nuclear tests are conducted underground these days. Also, the fallout from an above ground burst could give important information about the nature of the bomb to other nations, something else that no doubt contributed to the USA’s willingness to go to underground testing.)


Written by unitedcats

December 11, 2011 at 8:58 pm