# Thread: Nukes in Space - Visible from the ground?

1. ## Nukes in Space - Visible from the ground?

I'm not entirely sure if this is the right section for this... if there's somewhere else more appropriate, could a Mod kick it over?

Anyway. I'm writing some science fiction, and in one scene there is a battle in Earth orbit--about 4,000 km altitude. Nuclear missiles are used to blow up a ship, and what I'm trying to determine is if this would be visible from the surface of the planet.

I know from other sources that a nuclear weapon detonated in the atmosphere has the big, brightly-glowing long-lasting fireball because the air is absorbing the x-rays emitted and re-emitting them as visible light over a longer period of time. There's obviously no air to do this in space, so most of the energy of the weapon would instead be released as a single flash of x-rays.

The upper atmosphere of the Earth is opaque to x-rays. Would this make the nuclear detonations effectively invisible from the surface, or would the x-rays be converted into visible light after being absorbed and re-emitted by the air?

Finally, if the nukes would be visible, how bright would they be from that distance if they were, say, 100 kilotons in yield, 500 kt, 1 megaton and 10 Mt. Oh, and it's nighttime on the surface below.

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Hi Jim; Your analysis seems correct. Let's start with 100 kilotons = 1/10 megatons at a distance of 5000 kilometers. The flash may be more noticeable if it is not exactly over head. The missile that carries the nuke and the target will convert perhaps 0.1% of the x-rays to visible light = perhaps ten trillion watts = 10E13 average over one millisecond = about as long as digital camera flash = 1000 watts 10E3 of visible light. The visible light is equal to 10E10 flash tubes. If we increase the distance from 50 meters to 5000 kilometers = 100 000 times 10E5: the brightness decreases 10E10 times so the flash should be about as bright as a digital camera flash 50 meters away = noticeable in low light conditions, but not impressive. Higher yield nukes won't vaporize proportionally more material (except for extremely large targets) and the pulse of light will be little or no longer, so bigger nukes will produce only slightly brighter flash, I think. The 10,000 trillion 10E16 watts of x-rays was a wild guess, so perhaps someone can correct that. The 1000 watts from the digital camera flash is more likely a high than a low estimate and the camera flash is somewhat directional. Also more than half of the light energy is lost in Earth's atmosphere, which I don't think will x-ray to visable brighten noticeably, except for 1000 megaton detonations 4000 kilometers away. Neil

3. So net conclusion is that it's barely visible from the surface unless you vaporize a lot more mass, or you use a really huge warhead. Alright then, so the missile detonations themselves won't be visible...

...what about the half-a-megaton's worth of starship they vaporize? Would that show up better?

4. I like the approach taken, but regardless of the x-ray pulse, you've got a cuple of tons of warhead mass that you are vaporizing and energetically stimulating to release energy. Even at 4000km that's going to make a visible flash and fading glow. I doubt it would cast shadows, but if you are looking in that direction, the strobes should be easily noticeable.

5. ## Look at posts in an earlier thread

There was a thread a while back based on the
question, "Would a nuclear explosion on Earth
be visible from the moon?"

http://www.bautforum.com/off-topic-b...seen-moon.html

I suggest you read it, especially this post:

http://www.bautforum.com/off-topic-b...ml#post1187706

Short answer: yes, a nuclear explosion on the Earth
could be seen from the Moon (easily if done at night
on Earth), and vice versa.

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Now, I know nothing of any formulae to calculate the brightness of nuclear explosion. However, at the altitude of...say...the Hubble, it should be quite easily visible. It may show up in daylight but I wouldn't say it comes anywhere close to the brightness of the sun. From my thinking, it would have a magnitude of between -10 and -4. I could be wrong though.

7. Starfish Prime was a nuclear test that took place at the same altitudes as what is considered low earth orbit, and it was definitely visible from the ground.

8. Accounts and photos of a nuclear test in space here
http://en.wikipedia.org/wiki/Starfish_Prime
the Starfish Prime bomb was detonated at 400km altitude, about the same height as the ISS.

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It's perhaps worth pointing out that Iridium flares (clearly visible at night, and also detectable in daylight) are just a reflection of the sun's surface, a couple of metres square and at 800km altitude.
A nuclear explosion in air produces a fireball with a surface brightness five times greater than the sun's during its first few milliseconds, and during that very early time the mass of luminous material must come predominantly from the bomb components.

So I think we're talking something very roughly comparable to an Iridium flare. The descriptions at the link given by ravens_cry and eburacum45 suggest the flash was significantly brighter, which makes sense from the reasoning above.

Grant Hutchison

10. A lot of the afterglow from Starfish Prime seems to have come from an artificial aurora, the very thin atmosphere at that height glowing because of excitation. In very deep space the aurora effect would be minimal. But even between the stars there is some gas and dust.

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Originally Posted by eburacum45
A lot of the afterglow from Starfish Prime seems to have come from an artificial aurora, the very thin atmosphere at that height glowing because of excitation. In very deep space the aurora effect would be minimal. But even between the stars there is some gas and dust.
4000 km is not deep space, though. The Starfish Prime glow was visibly shaped by geomagnetic field. Therefore, with an explosion in upper magnetosphere of Earth, could the visible glow be dim in the vicinity of explosion (because the gases are sparse there) and much brighter where the charged particles do hit upper atmosphere?

12. Good point. From underneath, it would be difficult to tell the difference between a glow in space and a glow where particles hit the top of the atmosphere.

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Originally Posted by eburacum45
Good point. From underneath, it would be difficult to tell the difference between a glow in space and a glow where particles hit the top of the atmosphere.
Underneath? The magnetic field lines are not vertical except at geomagnetic poles. Looking at a clear air image
http://en.wikipedia.org/wiki/File:Op...from_plane.jpg

it is clearly a shaped object and not fireball. Where was the air zero in that aurora?

14. It would look like lightning. In regards to brightness and duration. Looking straight at a high yeald explosion could burn your retina (Eye.) No fire ball, no noise. Just a flash. A lingering after glow of burnt material... and some debris into our atmosphere over the next hour or so... at 4000 km distance, very little danger to us, or none.

15. Originally Posted by astromark
It would look like lightning. In regards to brightness and duration. Looking straight at a high yeald explosion could burn your retina (Eye.) No fire ball, no noise. Just a flash. A lingering after glow of burnt material... and some debris into our atmosphere over the next hour or so... at 4000 km distance, very little danger to us, or none.
pretty sure the lower yeilds would be free from retina burn at 4000km, but yeah as the yeilds creep up into the multiMT range that is probably an issue. It would still be a quick flash and slightly lingering afterglow, and there would probably be some upper atmosphere excitation directly below the blast (due to x-ray pulse - but it would be diffuse and widespread, unsure that it would be visible even in the case of extremely large warheads) and you'd probably pump up the aurora's a bit for that night. Uncertain as to other effects, certainly shouldn't be an immediate health risk to anyone on the surface of the planet, EMP effects would probably be significant at least in orbit near the detonations, probably have to worry about taking out some satellites.

16. Mostly what I'm looking for is to have people on the surface see the flash in the night sky and wonder what's going on, so it needs to be bright enough to catch attention even if they're not looking directly at it.

17. Originally Posted by Jim Starluck
Mostly what I'm looking for is to have people on the surface see the flash in the night sky and wonder what's going on, so it needs to be bright enough to catch attention even if they're not looking directly at it.
I'd have to actually break out a reference book and a calculator to approximate real numbers but I don't think you'd have to be looking directly at the spot to notice the strobe and the fading afterglow would probably be visible for a second or two after the flash even on the smaller yeild nukes, if you utilize some larger yeilds (guessing ~20MT) and had several of them detonating over a period of tens of seconds or more, you'd probably get the reaction you seem to be looking for,...unless it was on the Fourth of July or New Year's Eve. Have to get some more details and work some hard numbers to get much better than this type of guessing.

18. http://en.wikipedia.org/wiki/Starfish_Prime

These are pretty visible, and just 1.4 MT.

Originally Posted by Trakar
I'd have to actually break out a reference book and a calculator to approximate real numbers ...
As I wrote in this very thread, 12 posts earlier, there's
an example of exactly this sort of numerical calculation
in an earlier discussion in the forum. Go read

this post

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Nuclear warheads aren't all the same. They vary greatly in energy distribution of each radiation type, based on bomb design.

E.g, a conventional fission weapon detonated within the atmosphere might break down this way:

By contrast a neutron bomb detonated also within the atmosphere might be 50% prompt radiation, 30% blast, 20% thermal radiation.

If a neutron bomb was detonated in space (and 4,000 km is far higher than any previous nuclear test), the already-reduced blast and fireball effects were be further greatly reduced.

Anyone using nukes in space would select the optimal type. It would appear a neutron or enhanced radiation design is best, as there's no atmosphere to convey the blast or cause a fireball.

I've seen speculation that a neutron warhead detonated in a hard vacuum (which 4,000 km altitude is) would just be a very quick blueish flash, not that bright. It would seem reasonable you could see it at night from earth's surface. Maybe also during the day, but it might depend on yield, cloud cover, sun angle, etc.

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## Nukes in Space

There is a cool commercial DVD you can get - "Nukes in Space" by Peter Kuran. It has some amazing declassified video from many upper atmosphere and space detonations.

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Hey Jim,

While it may not directly answer your question a good site for these sorts of hard scifi questions is AtomicRocket. That's a link to the nuclear weaponry section of the site.

My understanding on your question is that while the nuclear explosion is primarily X-rays the vaporisation of the warhead and the explosives used to start the reaction are likely to create a bright and extremely short lived flash. So if you're throwing around a few dozen people on the surface will probably be seeing star sized flashes strobing from the sky.

23. Originally Posted by Twisted Mentat
Hey Jim,

While it may not directly answer your question a good site for these sorts of hard scifi questions is AtomicRocket. That's a link to the nuclear weaponry section of the site.

My understanding on your question is that while the nuclear explosion is primarily X-rays the vaporisation of the warhead and the explosives used to start the reaction are likely to create a bright and extremely short lived flash. So if you're throwing around a few dozen people on the surface will probably be seeing star sized flashes strobing from the sky.
Yeah, I've already used them as a reference repeatedly. Very handy. That's why I figured that the explosion was largely X-rays and thus invisible to the naked eye.

I suppose, then, that the only visible stuff will be when whole ships go up, providing a lot more mass to vaporize than just warhead casing.

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Originally Posted by Jim Starluck
...I suppose, then, that the only visible stuff will be when whole ships go up, providing a lot more mass to vaporize than just warhead casing.
Unless it's a direct hit, a very near miss, or a gigantic nuke, the ship wouldn't be vaporized. Rather the neutron and x-ray flux would kill everybody in the ship and disable the electronics.

Even a nuclear warhead requires a pretty close hit to vaporize a sizeable target. Yet if that accuracy is available, you probably wouldn't use a nuke.

E.g, some modest size Navy ships survived a 23 kiloton detonation a few hundred yards away: http://en.wikipedia.org/wiki/File:Cr..._explosion.jpg

Much of that damage was blast, which is non-existant in space. Due to the inverse square law, even a multi-megaton warhead would have to be pretty close to totally vaporize a ship in space.

25. Detonations are within a hundred meters most of the time. In this particular instance, the ships in question are getting hit with considerably more firepower than they're built to withstand.

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Originally Posted by Jim Starluck
Detonations are within a hundred meters most of the time. In this particular instance, the ships in question are getting hit with considerably more firepower than they're built to withstand.
In the Operation Crossroads atomic test, the transport ship USS Gilliam was only 47 yards away from surface zero. It sank within one minute (likely from atmospheric blast damage), but was by no means vaporized.

It's hard to believe anything could be a stone's throw from an atomic detonation and only suffer severe damage, vs being disintegrated. However that's how it is for vehicles of significant mass whether naval or space ships.

If you were double the distance (say 100 meters), it would require 4x the yield to do the same damage via radiation as at 50 meters. At 3x the distance (about 150 meters) it would require 9x the yield. At 200 meters it would require 16x the yield.

To vaporize a decent size space vehicle at 100 meters would probably require an immense nuke -- maybe 10s of megatons or more.

However strict adherence to this level of technical detail may not be necessary for science fiction.

27. Originally Posted by joema
To vaporize a decent size space vehicle at 100 meters would probably require an immense nuke -- maybe 10s of megatons or more.

However strict adherence to this level of technical detail may not be necessary for science fiction.
Note that spacecraft likely to get shot at with nukes may very well be equipped with ablative armor to minimize heat absorption from nearby nuclear blasts...so although no significant portion of the ship is likely to vaporize, there may be quite a large amount of material that does get vaporized.

Also, an anti-spacecraft nuke might be a bit like one of the propellant charges for an Orion vessel...relatively small charge and a lot of material that gets vaporized and directed at the target, allowing direct blast damage to be inflicted.

28. 'Laser' rods could (in theory) direct the energy of a nuclear explosion as an X-Ray pulse
http://www.nytimes.com/1983/11/15/sc...=&pagewanted=1
however I believe the test results of this technology were somewhat disappointing...

29. Originally Posted by eburacum45
'Laser' rods could (in theory) direct the energy of a nuclear explosion as an X-Ray pulse
http://www.nytimes.com/1983/11/15/sc...=&pagewanted=1
however I believe the test results of this technology were somewhat disappointing...
I wouldn't be too disappointed by that. A lot of progress in design and fabrication of the glasses and other materials needed for this sort of thing has been made since (https://www.llnl.gov/str/September03/Moses.html), and of course, further development suffered from the fact that the devices would require nuclear warheads, developing them would require test detonations, and they didn't really fill a near-term need.

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That ignition facility isn't working with X-ray lasers IIRC. X-ray lasers are harder to pump--and gamma ray lasers harder still...

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