Well a 10 kg mass traveling at .1c has 1 MT of energy in it. Make it out of iron and that’s a cube 10cm per side. Nasty. Make it out of a sub critical fission material and you can add nasty fission by products once it hits.
That would be ‘starworld’, the final book in the ‘to the stars’ trilogy I believe. And the defending general was almost blisteringly incompetent there… (heat-seeking defensive missiles proved no protection against the first assault, so what did he do? Send out three times as many defensives.)
With regards to the explosives argument… correct me if I’m wrong, but isn’t the fact that fuel and oxidizer are mixed together the basic element that distinguishes an explosive detonation from a fire?? A flame, in itself, is self-limiting… it can only burn as fast as oxygen can get to it. Some kind of explosions (such as after those car crashes in movies,) depend on surrounding air mixing with flammable fumes to create the key elements for an explosion. But I thought that everything we think of as being ‘an explosive’ had at least partial oxidizers built in, or they would just be called ‘flammable stuff’ 
This may be a bit off the OP, but how could you even conduct combat in space? So, you’ve fired some sort of projectile at the enemy. It reaches the target and the target explodes. Now, you’ve got gazillions of little tiny pieces of the enemy all over the place. Many of those tiny pieces will be zooming right back at you. It seems that your weapon may be just as dangerous for you as for the enemy.
Suppose your projectile misses. Now, it’s going to continue out into space literally forever, packing the same hurt as it started with. At least on Earth, the stray bullets eventually hit the ground and stop.
If you’re on a planet and a large something is coming in at you, you’re no better off shooting at it. If you hit it with something, you’ll have a bunch of smaller somethings with the same mass (roughly) as the original large something.
It seems that the only weapon in space that would be effective would be something that can totally consume the target and render it into something harmless. It would have to be like the old Star Trek phasers where the target simply glows and vanishes. I have no idea how one could accomplish this, however.
Not exactly. Deflagrants often contain their own oxydizer. For instance, black powder used potassium nitrite as the oxidizer. In this case, the actual reaction does free oxygen to be used in the reaction, but other elements, most notibly flourine, can also work. Oxygen and oxygen-based compounds are used because oxygen is so readily available and has a high electronegativity. The “burning” is a reaction between little fragments of carbon, sulphur, and saltpeter. You can’t just throw chunks of the stuff together, either; you have to grind them into tiny, tiny fragments. They react by releasing heat.
You can use atmospheric oxygen for an explosion, which is the principle behind fuel-air bombs and silo explosions, but you have to highly aeriate the explosive or you won’t have enough oxidizer to get a good mixture; sort of like running your carbuerator too lean.
As this wiki on gunpowder briefly explains, the practical difference between low and high (detonation) explosives is the rate of propagation of the reaction. A blackpowder bomb or a truck full of ANFO can make a loud boom and a big crater, but if you want to, say, cut through steel beams to cause a controlled implosion of a building, you gotta use high explosives.
The chemistry of high explosives is more complicated, and frankly, out of my league from a technical standpoint, but it basically involves making a compound (or compounds) that are metastable. When a sufficent physical, thermal, or electrical shock is imparted, a chain reaction occurs where the near “layer” of explosive undergoes reaction, causing the next layer to fall, and so forth, like dominos. An improperly shaped explosive charge can potentially blow a lot of its mass away without properly detonating (especially something as stable as C4) and so much expertise is required to correctly shape and place the charge for desired effect.
Perhaps someone with a background in chemistry or chemical engineering can correct (:o) and expand my explaination.
Stranger
That seems to be assuming that everything is on collision courses in space, which isn’t necessarily the case. For instance… a romulan ship warps into my star system, cruises on impulse to take on a medium-low orbit around my planet, and says to hand over all my dilithium or they’ll destroy all my cities with plasma torpedoes. I fire off a planetary defense ray and turn the romulan ship into a pile of scrap metal in orbit. Good enough. Some pieces of that scrap may eventuall fall down into my atmosphere due to stratospheric drag or something, but most of them will burn up and not hurt anybody.
A lot of the same arguments apply to shooting missiles at a ship that’s coming towards you. Yes, if you miss, they might end up travelling to somewhere you didn’t intend or even swing on a wide orbit around a large gravitational mass in the area and back to you, but a time-detonator could blow them up after a certain time and just turn them into debris. (There’s a lot of debris in space, though it’s pretty widely scattered. What’s a little more.)
Sure, if you destroy the ship, the wreckage of it is still coming straight at you. But it can no longer make course corrections and should be fairly easy to avoid, though you might still get hit by small bits as small as micrometeoroids. (And if you don’t have something capable of dealing with those, you shouldn’t be out in space LOL.) The point in space combat would not be to vaporize things, so much as keep them from shooting projectiles at you or adjusting their course.
On the other hand, the whole ‘blow the meteor/comet up so it doesn’t crash into the earth’ thing is a bigger problem, literally. Unless you got a really impressive explosion far enough away that the debris would spread out and stream through the vicinity of the earth, a pile of rubble crashing into us would probably be more deadly than a single impact. Better to get some kind of a rocket motor to dock with the asteroid and gently push it aside. 
Bah…the trick for that is to send up oil drillers in specially made titanium shuttles to land on whatever it is and drill a hole in it and drop a nuke inside. Only way to be sure!
Now, now. I believe they retracted that editorial on July 21, 1969.
Yeah, but it serves as a good reminder, every time somebody says “You’ll never be able to do that because of such-and-such”.
We don’t know practically nuthin’ ‘bout nuthin’…and most journalists don’t even know nothin’ about what we do know.
There aren’t any jouranlists around here, are there?
Stranger
I’ve been “on the inside” of a half dozen new stories over the last twenty years, both at the national and local level. In each case, the journalists got the facts wrong. Grossly wrong, in half the cases.
It makes me deeply suspicious of the stories I don’t have the inside take on…
Ummm… be sure of what exactly?? I’ve just gotta ask.
If you just want to blow ‘whatever it is’ to kingdom come, see above regarding the fact that matter is hardly ever destroyed - even with nukes. You still have a bunch of rubble and dust heading for the earth.
If you want the explosion to send a small chunk of it one way, and push the rest of it the other… well, that has a shot, but you’d really need to be very careful with a maneuver like that. 
Partly correct. All explosives that use a combustion reaction include fuel and oxidiser components. In some cases these are physical mixtures of fuel and oxidiser, such as the aforementioned black powder. In other cases the explosive consists of molecules that have a fuel component and oxidiser component, for example the “nitro” group NO[sub]2[/sub] provides the oxygen in TNT and nitroglycerol.
However, as always, all is not so simple! Black powder merely burns very fast. It will only explode if confined, and the explosion mechanism is simply the rupture of the confinement releasing high pressure gas, similar to the gas tank that took out Jaws. Or to blowing up a balloon till it bursts.
Explosives that explode without being confined are called detonating explosives, yet many of them can be burnt in small quantities without exploding. C4 has allegedly been used as a cooking fuel in place of hexamine tablets. You need a detonator to inject a shockwave and get the explosion going in these materials.
Finally, there are some explosives that don’t involve a combustion reaction at all - their molecules contain a high level of bond stress and they simply ping apart when given a helping start. One example is acetylene gas, which can’t be stored at high pressure because it spontanously explodes by disintegration, no oxygen required. The acetylene gas in oxy-acetylene torches is dissolved in acetone within the tank for this reason.
I’m digressing. I tend to do that. Of course, I’m meant to be working…
You have had several good posts in this thread, but I have to take issue with this, ironically the the point you had a nitpick with someone else on. It is true we do not say " air friction," we say skin friction, but it is the same thing. It is a major component of drag. Individual particles interact with the surface of the body, and the sum of these interactions is termed friction. Friction does, in fact, occur in fluids.
Man, talk about “reports of my death have been greatly exaggerated.” I eagerly await his input to this thread.
Psh. What fun would that be?