explosions in space

Inspired by SPOOFE’s thread.

We’ll all seen scenes in Sci Fi movies and television where some nearby explosion rocks a star ship similar to depth charges shaking a submarine. It occurs to me that this might not happen. Since space is a near vacuum, there would not be the same type of shockwave from the detonation of a thermonuclear blast found when one is detonated terrestrially. What would the effect of a nearby nuclear blast be on a space bearing vessel, assuming the bomb throws little or no shrapnel? I’d assume there would be little or no structural damage due to the blast, but that the ship could sustain considerable damage caused by the absorption of energy released as radiation (the ship wouldn’t be blown apart, but it might cook). Am I right? Wrong? What would happen?

Depends on a lot of things. You need to look at what you’re blowing up. Let’s say you blow up something with a lot of atoms by sending these atoms in 4 pi steradian directions at incredible speeds. This shockwave will most certainly have an effect on a neighbor, perhaps depth-charge-like. In a perfect vacuum, said effect will reduce in intensity candela-like (1 over r^2)… Closer you are, more you rock. This is different than on Earth where the intervening materials have an effect on how intense you feel a quick dispersion of material.

However, you said “little or no shrapnel”. I don’t see how it is possible to assume this happens. How does one destroy an object and cause no shrapnel? The stuff you’re blowing up has to go somewhere!

If there is no physical medium there is no shock wave. If you assume that no particles from the explosion itself, debris and expanding gas, hit your vessel you’ll see but not hear or feel the explosion. You will of course feel any radiation from the blast including infra red but our old pal the inverse square law comes into play here so the intensity will all depend on distance.

I think he meant no shrapnel in the sense that bomb itself doesn’t eject many pieces, not the ship… I mean, in an atomic bomb explosion, wouldn’t most of the metal casing be melted/vapourized?

What I am thinking of is a thermonuclear tipped cruise missile against some ship about the size of two aircraft carriers. On Earth, that vessel would be destroyed if the missile is detonated, say, 100 yards away because of the shockwave propagating through the air, land, and water. A hundred yards in space is a whole different story. In either case, the shrapnel from the missile itself does little damage because of the size of the two objects. It may poke a few holes in the ship but the mass of the device seems negligible when it comes to any real damage on a large craft - it’s the energy released, not the shrapnel that does the damage. But in space that energy may be as militarily effective as a giant flashbulb.

And further, there have been some proposals for space craft that use nuclear explosions for propulsion (ORION comes to mind). Wouldn’t the concave propulsion chamber have to have some sort of reaction mass in it (such as water vapor) in order to transform the energy released via the bomb into kinetic energy for the ship? If all the ship is doing is throwing H-bombs out the back, how is the energy transfered to the ship if there is a near vacuum between the blast and the ship? In ORION, are the atoms from the bomb casing itself enough to drive the ship? Seems doubtfull. I am aware that photons can exert force (like using a solar sail), but it seems remarkably inefficent to use H-bombs to merely generate photons. What am I missing?

I am currently reading a book on the Orion project and they discussed this very thing. There needs to be something for the bomb to push into the pusher plate and they went into specifics that it needed to be ‘opaque’ (energy wouldn’t just pass through it and such. My memory cannot recall specifics here, but if people are interested, I can look it up.

I’m skeptical that without air, the damage will be less. The energy for the air blast comes from the bomb. Without the air, all that energy will hit the starship directly, with (I’d expect) similar effects.

You are right, Zen, to a point… the less dense the intervening material, the more energy that can be transferred and not dissipated. This is why powerful bombs are detonated while in the air. Without air, the damage is likely to be more at the same distance.

Shockwaves can be created by things other than air (parts of the bomb, specifically). When you create projectiles out of atoms, you create very damaging things. Any energy that is not transferred directly to the projectiles will be released and, given properly dense and unshielded targts, will be absorbed.

Also, vaporization is a moot point. Whatever form the matter is in, it is still mater and it still has mass and it still has imparted kinetic energy.

There would still be heating from the radiant energy of the blast. If the explosion is close enough, you could damage the ship that way.

Even more, the gamma rays and fast ionized particles emitted during nuclear fusion would do a lot of damage. When absorbed by the metal, they can create a cascade of charged particles which can short out the electronics in the ship. This is the so-called electromagnetic pulse or EMP effect. It’s happened in Earth-orbiting satellites during big solar stroms; the surge can fry electronics.

Remember that nuke weapons are only about 4% efficient: That is to say the mass-defect is 4% of the mass of the fissile material. So all the rest of that mass will form a roughly sphereical shell expanding outwards at balst speeds. Additionally, all the non-bomb materials will also be converted to plasma, joining the unexpended bomb fuel in it’s rapidly cooling expansion. Even on the lightest of ‘cruise missiles’, this is around a thousand pounds of material, moving at a very high speed. It would hit like a high-speed slap, and the imparted KE would be dependant on the density of the blast-front, thus, the distance from the point of detonation, and would potentially be extremely destructive to surface fixtures. At sufficiently close ranges, it might even slap into the target with enough force to crush it like a tin can.

However, I’d be more interested in electromegnetic effects at any less than extremely near misses. Beyond all but the closest of misses, I would also neglect heat damage, as while the blast front may be very hot in degree (depending on distance), it will be too diffuse to carry much in the way of quantity of heat.

The better portion of the shockwave from a nuclear blast is created by the fireball, an intensly hot plasma which disrupts the air it pushes against. The fireball is basicly nearby air heated by high energy x-rays produced by black-body radiation from the superheated mass of nuclear fuel and bomb casing. Without the air to absorb these x-rays and produce a fireball, my guess is that their would radiate until they hit the hull of a ship, vaporizing the exposed surfaces and creating a fireball on its own, right against the ship’s side. Without the intervening air medium converting the thermal heat into kinetic force, a side of the ship itself would become the fireball (hence the reason that, as stated earlier, an intermediary substance would have to be used for an Orion-type engine).

By initial reaction would be that a nuclear blast in space would be more devistating than here on earth because of the lack of an atmosphere to absorb the energy and scatter it.

I concur. My totally nonexpert observation: Witness how much stronger the radiation from the Sun is in low Earth orbit compared to on the surface, just a few 10s of miles below. I know there are some strong magnetic forces at work, but even so the atmosphere absorbs a tremendous amount of energy. I would have to think it would be the same for an atomic bomb. The energy has to go somewhere.

Try this site from CalTech.