bombs in space

When a bomb goes off on earth (even a nuclear one) it seems that it is the expansion of air that knocks buildings down. In space or on the moon, there is no air. Its a vacuum. Would a bomb be more or less harmless there since there is no air or other medium to knock things down? While it might damage something its in contact with, if you’re just a short distance away, nothings going to hit you except particles of the bomb itself.

Well, explosions usually involve an emission of heat, so depending on how hot and how close, that could be a problem. And the expanding material from the bomb itself - gases and fragmentary solids - will travel a lot further, since there is no friction with the atmosphere to slow it down. So it might be dangerous at a greater distance than it would have been if the bomb had exploded on earth.

A nuclear bomb will also emit quite a large amount of harmful radiation.

I thought the blast wave in a nucelar bomb was caused by the rapid heating of the surrounding air by X-Rays?

Depending on the type of explosive there could be differences due to the lack of air pressure confining the reaction. I expect for high explosives that difference would hardly matter, but for slower explosives the bomb might expand rapidly enough to disperse the reactants before they react completely.

One of the more interesting effects is that charged particles from the bomb can interact with the magnetic field of the Earth (or some other body). This is how ElectroMagentic Pulse (EMP) effects occur in explosions above the atmosphere*. Different effects are responsible for EMPs from atmospheric nuclear explosions.

Pretty much all the above.

For a conventional explosive, the shrapnel pattern would retain energy longer since the fragments wouldn’t be pushing through an atmosphere. But they’ll still be becoming less dense at the same inverse square of the distance from explosion to target. Overall the net effect is to expand the radius at which any given severity of injury / damage occurs. But also to increase the shotgun effect whereby one person gets badly hit and the person next to them is unscathed.

The blast overpressure effects of conventional explosives are enhanced in close but are reduced at a distance in the same fashion. At a good distance there simply isn’t enough hot expanding gas to push very hard on the target. Whereas had their been an atmosphere to transfer the force through, there would be.
Nukes are anther matter. As **AK84 **effectively said, a nuke is essentially a very bright X-ray flashbulb and a couple hundred pounds of plasmafied solids.

For a burst well away from any other solid objects a nuke in a vacuum is pretty much just the X-rays and a puny little puff of expanding gas. But those X-rays are very powerful, and absent an atmosphere, they travel many thousands of miles instantly at an intensity sufficient to kill people or destroy machinery.

The expanding cloud of plasma/gas is a lot like the shrapnel of a conventional explosive. In a vacuum it retains dangerous velocity to a greater distance, but can’t overcome the inverse square law. Given that most man-made structures in space are A) flimsy and B) not designed against high veolicty gas impingement, you’d expect the lethal radius to be bigger than might be naively assumed. IMO compared to the X-ray flux damage the gas impingement damage will be a rounding error.

If a vacuum burst happens near something solid, like the surface of a moon or a ship, those X-rays will couple to the surface just like they do in a non-vacuum. Resulting in a big crater, lots of vaporized rock or ship, a moonquake, etc. And all that vaporized or pulverized rock & ship will become part of a much bigger shrapnel cloud expanding without an atmosphere to slow it down.

I suspect at a certain distance, the gamma ray and neutron radiation will do more harm to humans than the expanding cloud of plasma. (Humans in spacecraft or spacesuit, that is.)

I’ve read somewhere (can’t remember where) that the optimal space weapon is – wait for it-- sand! Just throw it out from your spacecraft, in a path that will cross your enemies’! The relative velocities will account for the damage.

Provided you have a sufficient difference in orbital velocities, even a grain of sand could be destructive and a large mass of it would be devastating. Figure 9 of this paper shows the result of what is believed to be a paint chip on the Shuttle Orbiter Vehicle windshield. A large amount of even fine dust could do sufficient damage to radiator surfaces, solar arrays, and antenna to render a spacecraft useless. An object as large as a quarter inch nut could literally punch right through the structure of the ISS, destroying anything in its path.

As for bombs, it is true that the destructive overpressure wave that we observe on Earth is due to rapid heating of the atmosphere, which expands beyond sonic velocities creating a highly densified pressure front that is essentially a solid wall. (Although the nebulous “force fields” of science fiction have no real world counterpart, a blast front can be considered a type of force field, creating the effect of solid material literally out of “thin” air.) However, a nuclear weapon detonated in space still releases the same amount of energy; it just isn’t thermalized (turned into mechanical energy), and so it travels as high energy radio waves (x-rays or gamma rays), alpha and beta particles, and neutrons, depending on the balance of the reaction. The flux of the radiation will vary as an inverse square of the distance from the source just as with light or any other omnidirectional radiation, so you can guesstimate the amount of a target may receive. However, during the Strategic Defense Initiative, concepts for focusing the radiative output or using it to power a free electron laser that could be applied as a directed energy weapon against ICBMs or reentry vehicles. While none of these were ever tested in space or in full scale space-like conditions, it is certainly possible to focus some of the energy directionally. Similarly, in multistage nuclear weapons, a certain amount of the radiative output form the primary is redirected, using the X-rays to compress and heat the fusion secondary, although this all happens in the few tens of nanoseconds before the entire weapon is energetically disassembled and disappears into a cloud of radioactive gas.

Stranger

Of the approx. 528 nuclear warheads that have been detonated above ground, roughly 20 of those were in space.

The former Sentinel/Safeguard antiballistic missile system used a 5 megaton W-71 warhead on the Spartan missile to intercept ICBMs. Various sources place the kill radius at 10 to 30 miles: https://en.wikipedia.org/wiki/W71, http://www.gutenberg.us/articles/spartan_(missile).

The kill mechanism was thermal X-rays, not blast:
http://en.citizendium.org/wiki/W71_(nuclear_weapon)
http://www.nuclearabms.info/Spartan.html

Fixed links:

http://en.citizendium.org/wiki/W71_(nuclear_weapon)
http://www.gutenberg.us/articles/spartan_(missile)