Watching this flick, Armageddon Outa Here got me thinking again about explosions in space. You take a kilo of TNT, set it down ten feet from you and set it off, AMF. However, if you do the same thing in space, other than shrapnel and a sharp spray of photons, would it have any effect?
From what I understand of physics, which is very little, a shock wave is a disturbance of molecules… it needs a medium through which to travel.
Virtually no molecules in space, therefore, no shockwave… only a spray of shattered material from whatever it is that exploded.
[Bracing myself for a lashing from SDMB physicists].
Assuming you’re setting off a kilo of TNT, sans container, the only shrapnel you might get would be bits of unexploded TNT and by-products. However, you also get a fairly large quantity of hot gas evolving from the reaction.
Right. That gas would cool rapidly as it expands, so you might see an expanding ball for a few seconds. There were atomic tests done in space that show that.
Hmmm. Do you need an oxidizer for TNT, or does it carry its own? Some rocket fuels don’t need oxygen; when you put the two chemicals together, they react. They’re called hypergolic fuels, and I think that’s a cool word.
Do you have a cite for this, or more info? Are you talking nuclear-bomb-type tests, or what?
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I don’t think there has ever been an atomic weapon exploded in space…do you have a cite for this?
Hypergolic doesn’t mean that no oxygen is needed, it just means the fuels don’t need an ignition source - they ignite spontaneously on contact. The ascent engine on the Apollo lunar module used hypergolic fuel.
Now, on to the OP. Trucido gets it essentially right. According to the people at my company who design the explosives used to separate rocket stages, the rocket structure feels the explosion through two mechanisms: first, the explosives are in contact with the structure, so the structure itself transmits shock, and second, the shock waves and sound transmitted through the ‘cloud’ of gas generated by the explosive reaction are significant. The fact that the explosion occurs when the rocket is out of the atmosphere doesn’t reduce the effect of the explosion much.
In 1962 the Operation Dominic series of nuclear tests included one detonation, Starfish Prime, at an altitude of 248 miles (about the same altitude as the International Space Station). The test was apparently easily visible from Hawaii and Kwajalein, respectively 800 and 1600 miles from the launch point on Johnston Island.
This was discussed in some detail in this thread: Space Nuke Testing. Operation ARGUS predated Operation DOMINIC by four years.
Typically, an explosive does have it’s own oxygen.
An entire stick of Dynamite, or block of C4, basically “combusts” (burns) almost instantaneously. (More on that in a moment.) It would take a roomful of air to provide the oxygen, were the explosive not supplying it’s own.
Now, an explosive “works” (to put it simply) by “burning up” extremely quickly. X amount of explosive burns and turns into Y amount of hot gasses and residues. Since it happens so quickly, the resulting mass of hot gas is at a very high pressure, and rushes outward just as the air does when you pop a balloon.
It’s this expanding “bubble” of high-pressure gas that does the “work” of an explosive.
Dynamite, AmFO and other “industrial” type explosives, have a relatively slow wave front, in the 16,000 to 25,000 foot-per-second range. C4, RDX and mercury fuminate (primer compound) blow much faster- in the order of 100,000 to 250,000 feet per second.
Think of it this way- Dynamite will knock a brick wall over. But C4 will shatter it into dust and fragments.
If you lit a stick of Dynamite (somehow) in space and tossed it gently so it was only 20 feet away when it blew, the blast would certainly affect you, but due to the lack of atmosphere, only the explosives’ own gasses would push on you. You’d likely live, you might even get away without a rip in your suit. (Somebody might have to run get you with a jet-pack though.)
But if a block of C4 went off 20 feet away, even without the atmosphere to push against, it would very likely implode your visor (and probably your eyeballs too) possibly break bones, and generally inflict severe trauma to both the suit and your internal organs. Whats left would probably be accellerated to several hundred miles an hour, too.
Yes, there’d be an effect in space… The effective “blast radius” would be lessened because the hot gasses would not have surrounding air that it can compress and use to transmit the wave front, but there would still BE a blast.
Even if that Kilo of TNT went off 100 feet away, it’d definitely nudge a spacewalker a little, though I doubt it’d have any effect on a hundred tons of Shuttle.
By the way- most of the more spectacular explosions you see in space movies… The ones with balls of red flame and black smoke? Those are fuel explosions, like using gasoline or kerosenes. Which would, of course, be nearly impossible in space. 
Ah, missed that one. Here’s more information on Operation Argus.
A “brilliant but eccentric physicist”… Clandestine nuclear testing… “Top Secret Task Force 88”… “The world’s largest scientifc experiment”, creating artificial Van Allen belts…
Wow! This is real Mad Scientist stuff here.
Yes, yes, yes! This has always been a pet peeve of mine. The oxygen in the ship would provide a means of fueling the explosion for a few seconds, but after that, you’d just see a big, broken hull.
THe game Wing Commander 3 got this right… when one of those massive, multi-hundred-meter long ships went down, there was a brief flare-up, but that’s all. The explosions you see in Star Trek are so bogus it’s laughable.
Interesting question!
Explosives need no atmospheric oxygen - they contain their own. Sometimes they are physical mixtures of a fuel and an oxidiser, e.g. ANFO (ammonium nitrate is the oxidiser, fuel oil is the fuel.) Othertimes the fuel and oxidiser species exist on the same molecule, e.g. TNT.
TNT is actually a little oxygen-poor, so the reaction byproducts include a cloud of unburned carbon powder. So you would be hit by a cloud of expanding gas and fine carbon dust. How damaging this would be at 10ft from a kilo of TNT is a tough question. Of course, if your TNT is in a container and you catch some frag, you’re talking big trouble at 10 ft or 10000 ft. (For that matter, if you’re really, really unlucky you could be hit by an orbiting piece of frag 5 years later on a different mission!)
hypergolic fuels most chemical rockets generate a high velocity exhaust by reacting a fuel and an oxidant (exception - catalysed peroxide decomposition rockets). Typical fuels are kerosene, methanol, liquid hydrogen. Typical oxidants are hydrogen peroxide, nitric acid and liquid oxygen. Most combinations of these aren’t hypergolic, and so need an igniter. Also, while not all of them use elemental oxygen, they do carry chemically bound oxygen in the oxidant.
However, hydrazine-based fuels are hypergolic. The classic rocket propellant combination is hydrazine and di-nitrogen tetroxide. Again, the rocket is carrying “oxygen” to burn the hydrazine fuel, but it’s chemically bound in the tetroxide.
Doc Nickel:
The velocity figures you give are for the detonation wave which propagates the reaction through the body of the explosive. Detonation velocities roughly correlate to peak pressure, which correlates to the “brisance” or shattering power of the explosion. (The Vdets you gave for RDX, C4 and fulminate seem a tad high to me. Well, factor-of-ten high, actually!)
However, brisance is a very short range effect, generally affecting materials within a few inches of the explosive. The initial overpressure drops off very rapidly with initial expansion, after which it begins to approximate to adiabatic expansion of a compressed gas. At 20 ft, I can’t see C4 doing more damage than the equivalent energy charge of dynamite. I might not be thinking this through properly, however.
Thanks for the cites, guys. This stuff is wild, and I had no clue about any of it!
Just for the record, that’s what I said. “…when you put the two chemicals together, they react.”
How is this any different (except for the magnitude) than the proposed nuclear-propelled spacecraft powered by dropping exploding atom bombs out the back? It seems to me that conventional explosives should propel you just as easily–just with less bang per pound.
I don’t think using chemical bombs to propel your spacecraft would be any different (in principle) from using nuclear bombs. It’s just that using bombs of any kind to propel a spacecraft isn’t really very efficient. If you’re going to be using chemical reactions, you might as well use a nice well-designed rocket engine. The point of the Orion nuclear-bomb drive was that, sure, it was inefficient as hell, but hey, these are thermonuclear explosions we’re talking about, so who needs efficiency? Even a very inefficient use of the power of thermonuclear explosions can (theoretically) send a quite large spaceship jetting all over the Solar System.
By the way, why doesn’t NASA do important experiments like this? Dammit, they should haul a thousand pounds of TNT into space on the next shuttle, toss it out the airlock, train a half-dozen high-powered HDTV cameras on it, and then detonate the sucker.
I guaran-damn-tee you that NASA could make bank by selling the stock footage to Hollywood’s sci-fi space movies for years to come.
Sorry SPOOFE, I dunna thin’ so. Hollywood wouldn’t want the stock footage of a real space explosion. It would be too boring. Blappp, poof that’s about it.
People are used to the traditional KerrrrBlammmmieee, kerbleww, rumble, rumble, rumble… they wouldn’t like real science-like space stuff. Not Hollywood anyway. Even in their “hardest” SF (really sci-fi, but don’t quibble), Hollywood insists you can hear the spaceship’s engines in space as they go to “warp”.
But it would be way-cool to see a real space explosion, like you said SPOOFE.
Well, not a real real space explosion, like the ISS going up (or down, depending), but a real staged explosion. Explosions are cool.
AFAIK, NASA is not allowed to make money.