(Repost from RPG.SE, per the community's suggestion.)

A friend recommended I post this question here - said I'd be more likely to get a useful response than, say, from Reddit.

My question is: How would a nuclear explosion operate in the vacuum of space?

Battlestar: Galactica and Mobile Suit Gundam SEED both portrayed nuclear weapons (or fusion/fission technology in general) in an outer-space environment. In one episode of BS:G, the Galactica gets nailed by a thermonuclear warhead that managed to penetrate its curtain of defensive fire, but (to my surprise) the ship survived being crippled or destroyed outright.

I've been digging into a tabletop RPG system called Mongoose Traveller over the last few months. Its hard science fiction approach reminds me of The Expanse. The more I dig into it, I find myself daydreaming about the reality of combat in space. No atmosphere to conduct sound, so combat is mostly quiet; ship attack from long distances takes minutes, even longer at extreme ranges. Combat in a hard-sci environment takes on some qualities I'm not used to in most sci-fi settings, and I like it.

So, what about explosions, especially and specifically ones from fission warheads? I have a few specifics I'd like to get some insight on:

  1. How would a vacuum affect a nuclear explosion (or, really, any explosion)? Would the lack of atmosphere cause it to snuff out sooner? For a nuclear blast, which stages of the detonation/fallout would experience significant change? Would the effective blast radius be likely shrink or expand?
  2. Would the shockwave from a nuclear blast travel far through a vacuum, or would it exist at all? In general situations, I believe you'd see an explosion but hear and feel nothing; with something of this magnitude, is that still true? Is space truly a vacuum through which nothing can transmit?
  3. Traveller considers radiation exposure in open space as fairly harmful over short periods of time; without the proper shielding, space travel over long periods of time is extremely hazardous, and space walks without protective layering are reckless. Would the radiation released from a nuclear explosion be more or less considerable in a vacuum?

I appreciate your consideration, and any insightful answers (or even hypothesis) would be fantastic. I don't know much about physics really (outside of the enjoyable what-ifs I read from xkcd!) so I'm at a loss.

  • $\begingroup$ Given that there have been nuclear explosions in outer space (google, say, Starfish Prime), they clearly can happen. The impact of such an explosion is different than in the atmosphere, but that is mainly because the energy output in the form of x-rays, gammas, and neutrons propagates and interacts differently between space and atmosphere. $\endgroup$ – Jon Custer Jul 10 '19 at 15:29

A space explosion of an atomic or nuclear weapon would be very different from the same explosion on the earth, for the following reasons.

In space, there is no atmosphere in which acoustic and shock waves can propagate. The only matter being "thrown" outward by the blast is that which originated from the bomb, which is very small compared with the energy release in the explosion itself. To experience blast damage from a space explosion would require you to be so close to the detonation point that you'd be incinerated by the fireball before being physically torn to pieces.

In space, there is no large mass of rock and dirt to render radioactive via mechanisms like neutron activation, so the only residual radioactivity would be that carried by the components of the bomb's casing and internal parts (including, in the case of an atomic blast, unfissioned plutonium or uranium) which would be small compared to the energy release. No planetary surface next to the detonation point also means no shock wave reflections and no seismic waves either.

In space, the radiation and stray neutrons produced by the explosion would suffer no absorption or attenuation by air, because there'd be no air in the way. This means that the x-rays, neutrons, and other ionizing radiation would remain lethal out to a larger radius.

In an air burst explosion on earth, the air immediately surrounding the detonation point gets heated so hot by the initial blast that it becomes opaque to infrared radiation, which traps a lot of the energy release inside the fireball until such time as the fireball has expanded and cooled enough to become transparent again. With no air around the detonation point, the energy release can stream directly out of the explosion and the time evolution of the fireball and its size, etc. would be very different.

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  • $\begingroup$ Several (admittedly picky) points to consider. (1) lots of neutrons are produced (I mean lots), calling them 'stray' seems to be an understatement. (2) I'm not sure I'd consider there to be a 'fireball' in space, but I'm not a weapons output person. (3) Objects will still be subject to shock, but it will be caused by directly absorbing the freely-propagating x-rays/gammas/neutrons, not by an atmosphere absorbing them and then transmitting the pressure wave. $\endgroup$ – Jon Custer Jul 10 '19 at 18:20

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