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#1
Old 02-14-2015, 07:23 PM
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Do explosions not "travel" in the vacuum of space?

If an explosive blast wave requires a medium such as air or water in which to spread out, or ripple through, then does this mean that you could stand a few yards away from a detonating TNT bomb in space vacuum and no blast wave would reach you?


(The shrapnel, of course, would still hurt or kill you.)
#2
Old 02-14-2015, 07:38 PM
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An explosion consists of liquid or solid rapidly oxidizing into gas, which expands rapidly and with hot temperatures. No medium is required, except for some novelty explosives (such as thermobaric weapons) which lack an oxidizer. If you stood next to a block of exploding TNT in space, you would die.
#3
Old 02-14-2015, 08:13 PM
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Quote:
Originally Posted by Velocity View Post
If an explosive blast wave requires a medium such as air or water in which to spread out, or ripple through, then does this mean that you could stand a few yards away from a detonating TNT bomb in space vacuum and no blast wave would reach you?


(The shrapnel, of course, would still hurt or kill you.)
you'd have to be in close vicinity of the detonating object. On the planet, the "blast wave" is the supersonic detonation compressing the air around it and that compression wave traveling outwards. if the pressure wave you experience is 60 psi or greater you're in danger of serious injury or death.

in space, there's nothing to compress so there's no blast wave.
#4
Old 02-14-2015, 08:34 PM
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Quote:
Originally Posted by The Joker and the Thief View Post
An explosion consists of liquid or solid rapidly oxidizing into gas, which expands rapidly and with hot temperatures. No medium is required, except for some novelty explosives (such as thermobaric weapons) which lack an oxidizer. If you stood next to a block of exploding TNT in space, you would die.
So the exploding material is it's own medium.
#5
Old 02-15-2015, 10:04 AM
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The difference being that in a vacuum the sphere of expanding gases from the explosion will rarify quickly as they expand. So the lethal overpressure radius will be much smaller in a vacuum than it would be in our atmosphere. It's not zero, but it is much smaller.

Going in the other direction, this is why underwater explosions have a much larger lethal radius. The much denser and almost incompressible water transmits the explosive force more effectively and farther than does our atmosphere.

I'd have to do some research and some math to determine the lethal radius of a typically efficient TNT explosion in a vacuum. I'm too lazy today. But it could be done.

Last edited by LSLGuy; 02-15-2015 at 10:06 AM.
#6
Old 02-15-2015, 11:05 AM
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Originally Posted by LSLGuy View Post
The difference being that in a vacuum the sphere of expanding gases from the explosion will rarify quickly as they expand. So the lethal overpressure radius will be much smaller in a vacuum than it would be in our atmosphere. It's not zero, but it is much smaller.

Going in the other direction, this is why underwater explosions have a much larger lethal radius. The much denser and almost incompressible water transmits the explosive force more effectively and farther than does our atmosphere.

I'd have to do some research and some math to determine the lethal radius of a typically efficient TNT explosion in a vacuum. I'm too lazy today. But it could be done.
Your statemernt is precisely the opposite of the one made by Paul Brickhill in The Dam Busters, his book about the famous WWII effort to destroy German dams with highly innovative bombs and bombing technique. According to the folks who worked on those bombs, one problem with using explosives underwater is that the water acts to restrict the range of explosives -- that's one reason destroying dams is so difficult. You can'tg simply drop the bombs in the laske behind the dam and expect it to do significant damge to the dam, because the water workls against you by inhibiting the explosive effect.

But if you could arrange to have your explosive detonate right against the dam, then the water helps you. Since it is restricting the range of the explosion, all of that explosive force gets vented in a smaller area, and its effect is amplified. The best situation, then, is to maske sure that you bomb is right next to the dam (underwater) when it goes off. That was the entire point of their effeorts -- why they used the crazy skipping-over-the-water bombs and the counterrotating spin, and the carefully calculated height and speed of the drop -- it guaranteed that the bomb would be there.



As far as explosions in space, as noted above, they sre certainly deadly, since the explosion itself sends out gases and solid material at very high speed away from the explosion. This is, in fact, the theory behind some explosive space propulsion schemes. Comservation of momentum meansd that if you send out a lot of small material at a high speed in one direction, it can push a much large mas in the other direction, and this is as true is you use an explosion instead of a rocket motor to do iot. Thus, you had Arthur Kantrowitz' laser propulsion, which used a laser to first ablate material from a surface and then pump in energy via inverse brenstrahlng to start a Laser-Sustained Detonation Wave (way different from using simple laser light pressure). It's also the idea behind the Orion spacecraft's idea of throwing small nuclear bombs out the back of your ship and having them detonate near a resistance-coupled pusher plate. It would have let us get huge payloads off the ground, although at cost in radioactive contamination. I guarantee you wouldn't want to be near one of these in operation in space.
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Old 02-16-2015, 07:48 AM
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So how close could you be to a nuke and survive the blast? (Ignore radiation exposure and choose whatever size of device you would like to.)
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Old 02-16-2015, 10:46 AM
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Like others have said, the propagation of the shock wave through the air is what causes a lot of the damage on earth.

Underwater, I don't know if you really get a shock wave, with the water being incompressible and all. However, IIRC, the reason it's so lethal to people and fish is because while water's incompressible, your innards are very compressible, and the shock does that very well.

In space, there's no shock wave, since there's no air to compress. There is the sphere of rapidly expanding gas, but it become much less dense very quickly, since it's expanding in a sphere. You'd have to be close enough for that gas to actually impact you directly with enough force to do damage.

Fragments are going to be more effective in space, since they have no atmosphere to slow them.

There's probably some radiative heat, but for chemical explosions, that would be more or less negligible. For nukes, the heat and radiation are probably the biggest effects unless you're nearly in contact with the nuke when it goes off.
#9
Old 02-16-2015, 11:00 AM
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Quote:
Originally Posted by bump View Post
Like others have said, the propagation of the shock wave through the air is what causes a lot of the damage on earth.

Underwater, I don't know if you really get a shock wave, with the water being incompressible and all. However, IIRC, the reason it's so lethal to people and fish is because while water's incompressible, your innards are very compressible, and the shock does that very well.

In space, there's no shock wave, since there's no air to compress. There is the sphere of rapidly expanding gas, but it become much less dense very quickly, since it's expanding in a sphere. You'd have to be close enough for that gas to actually impact you directly with enough force to do damage.

Fragments are going to be more effective in space, since they have no atmosphere to slow them.

There's probably some radiative heat, but for chemical explosions, that would be more or less negligible. For nukes, the heat and radiation are probably the biggest effects unless you're nearly in contact with the nuke when it goes off.
I'm not a nuclear weapons expert, but I had the impression from reading that much of the thermal output of a fission (or fusion) explosion comes from the primarily soft X-ray energy output of the reaction being absorbed by atmosphere and re-radiated as heat (as well as the shockwave). Without atmosphere, I expect most of the energy would continue to be the crazy high-spectrum stuff. (Of course, that means that any target would absorb a physically destructive load of hard radiation instead of heat and vaporize anyway.)
#10
Old 02-16-2015, 11:08 AM
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Originally Posted by D18 View Post
So how close could you be to a nuke and survive the blast? (Ignore radiation exposure and choose whatever size of device you would like to.)
According to the Atomic Rockets website (scroll down a little to "Warhead"), about a kilometer. They also have a good explanation of why.

This is assuming you're in a spaceship of some description, of course. If you aren't in a spaceship, you've probably got other problems to worry about, even without the nuclear ordnance going off around you.
#11
Old 02-18-2015, 11:21 AM
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If you want to see what a shock wave looks like in space, try the Ring Nebula.
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