Visual effects of Nukes in Space

[ph4tman]

Hello all,

I hope I'm posting in the right sub-forum here, because I'm quite new and don't really know my way around yet. Not to mention that the topic encompasses quite a few different areas.

The subject is nukes in space.

Or more specifically, the visual effects they should produce while in space. Now, on the forums I hang out, it's quite normal to assume a nuke in space will look like a single giant blinding flash. And if you see such a nuke detonation in, say, a movie, it should look exactly like that. I very intense pulse of light. But is that really so?

I mean, the EM-radiation will of course travel at the speed of light, and the bomb detonation should take a measly amount of time (wikipedia states that the Tsar Bomba expelled all it's energy in 39 nano-seconds, for instance, but it's wiki, so take it with a grain of salt). So, why should there be a visible flash? The eye shouldn't have time to even register the light before it's all been emitted. Glowing material from the bomb? I don't think so, it should've been vaporized and thrown across the four corners of space long before your eye has a chance to catch it (never mind a videocamera with a very low frame-rate).

Can anyone explain this to me?

For your convenience, I'll give you a more specific scenario, answer what you think the effects will look like.

You're in deep space, far outside our own solar system. You have a camera with you that has a frame-rate of 35 frames per second. 10km in front of you there is a nuke that's about to be detonated (fission, fission/fusion, it does not matter). You yourself and the camera will remain unharmed for some odd reason, your eyes will not be burned out by the flash and they'll not exhibit lingering effects on it due to biological/mechanical limitations. They'll see what's there, unedit and real.)

Boom.

What did the camera see? What did you, with your eyes, see?

 

[Astronuc]

So, why should there be a visible flash?

Because the ionized atoms recombine and emit photons, and atoms excited by collisions, a consequence of the thermal energy, will also decay and emit visible light.

There will also be bursts in the gamma and X-ray range. The gammas coming from fission products, brehmssrahlung and neutron absorption reactions, and the X-rays coming from electrons dropping back into the K and L shells.

The vaporized mass will rapidly expand in space.

 

[ph4tman]

The vaporized mass will rapidly expand in space.

Indeed, and this is key, I think. Take the specific range I gave - 10km - that's not a whole lot in space. The vaporized material should have expanded so fast that it has passed you before a single frame on the camera takes a picture. So, if there's no more mass directly in front of you, how could there be radiation eminating from something there? Even at longer ranges, the density of the vaporized mass should drop so quickly that it'd look like a spread out cloud in no time flat.

Don't get me wrong, I know the EM-radiation flash will be there, the flash will just be so brief that your brain wouldn't have time to percieve it and the camera with the limited frame-rate wouldn't have time to catch it.

Or am I missing something?

 

[Astronuc]

How fast does on think the blast front will move. 1 km/s? At that rate, the blast front would take 10 sec to reach the camera or person at 10 km. Or is the blast front velocity 10 km/s, in which case one will have only 1 sec.

Also remember that the mass toward the outer surface will move fastest, and the mass further in, more slowly since it has to push the outer mass away. Well inside the nuclear detonation, the material would expand slower because is has the inertia of the outer mass holding it back.

One would have to look at the equations of state for the various materials and geometries involved. One can approximate the velocity of the nuclear detonation by using a resonable approximation of the temperatures.

 

[ph4tman]

One would have to look at the equations of state for the various materials and geometries involved. One can approximate the velocity of the nuclear detonation by using a resonable approximation of the temperatures.

Well, the results are varied, but we seem to be talking about over a million degrees kelvin at the hypocenter, at least. http://hypertextbook.com/facts/1999/SimonFung.shtml" .

But generally, the explosive velocity of even normal explosives are quite high, TNT has an explosive velocity of 6.9 km/s, for instance.

 

[vanesch]

I think that what you are missing, is that the eye (and a ccd camera) is an integrating detector. So it looks at the total integrated flux during a "timeframe" that arrives. If that's spread over milliseconds, or in just one nanosecond doesn't matter: it is the integral.

 

[Astronuc]

I think that what you are missing, is that the eye (and a ccd camera) is an integrating detector. So it looks at the total integrated flux during a "timeframe" that arrives. If that's spread over milliseconds, or in just one nanosecond doesn't matter: it is the integral.

Plus the fact that the photons are moving at the speed of light (obviously) so the gamma, X-ray, visible light, infrared will happen instantaneously with detonation. The flash will be a bright point of light in microseconds and grow quickly as the ball of high temperature gas expands rapidly. Most of the fissioning will be done in less than one second.

 

[vceinc]

NPR just did a piece on Nukes In Space, July 4, 2010

http://io9.com/5578016/heres-what-it-looks-like-when-you-blow-up-nukes-in-space