Here’s one news tsory on the missile shoot-down of a failed satellite. In the link below, they claim some witnesses saw an explosion. How can you have an explosion in space? (They say the satellite was still above the atmosphere.)
http://wjz.com/national/satellite.missile.shoot.2.658441.html
Where’s the O2 come from to make fire? 
There’s no O2 in a light bulb either, but you get light when you add energy. When you have an satellite travelling 17,000 mph getting hit by a kill vehicle with similarly high speed, that’s a huge amount of energy - enough to shatter both and heat the fragments to incandescence.
If you think about it, all those underwater explosions are fake too.
Explosion or not (the missile wasn’t equipped with a warhead but relied instead on speed of impact), would the disintegration of the satellite caused by the collision result in the widespread tumbling of debris that, as it reflects sunlight, would maybe mimic the signature of an explosion?
The same way that you can have an explosion underwater, or inside a sealed airtight bomb/shell/container of choice - by using something explosive.
Well, it may be already present bound up in an explosive compund, or there may not have been any 02 involved at all but some other similar element. Or they may have seen all the Hyrdazine fuel vaporizing and decomposing. Or the eyewitnesses may not have seen an actual explosion but just something that looked like one (e.g. a spray of shrapnel or gas).
edit: dammit, beaten again
Steam explosion
No fire is needed.
Ruptured pressure vessel…
What slaphead said. The combustion in a detonation happen far too fast to get their oxygen from their environment; it has to be part of the energetic material’s molecule. One of the key attributes analyzed in an energetic material is its oxygen balance, that is, what percentage of oxygen does it have compared to what it needs for complete combustion.
However, since there was no warhead, there was no explosion. As other posters have said, there may have been something that looked like an explosion, but it could not have been one, per se.
Hydrazine just needs a catalyst to allow it to decompose and release energy. That’s one of the reasons that it is popular for attitude control systems. It keeps things simple.
This is known as a monopropellant, i.e. a propellant that decomposes with thermal impulse or catalyzation and then self-oxidizes . As mks57 says, it keeps things very simple, instead of requiring valving, tankage, pressurization, ullage, et cetera, for an oxidizer. Hydrazine (N[sub]2[/sub]H[sub]4[/sub]), for instance, decomposes into ammonia and molecular nitrogen, and then self-oxidizes. It is used for spacecraft propulsion because unlike many other liquid monopropellants (such as highly concentrated peroxide) it has a low rate of spontaneous decomposition and thus is pretty stable. The downside is that it is much lower performance than bipropellants, but that is counteracted by less complexity of the propellant system and resultant high reliability, which is desirable in satellites and spacecraft where you can’t inspect or repair the system once it is deployed. Hydrazine is also used for hot gas generation systems to provide pressure to drive actuators or thrust vector control systems.
Of course, in vacuum, the liquid propellant is going to vaporize and expand rapidly, which might give the impression of an explosion or fast combustion. Given that most monopropellants don’t generally decompose and combust well under low pressure, I’d guess that this is what transpired.
Stranger
Uh, I’ve worked with ruptured pressure vessels. You’re merely describing the failure of the integrity of the tin can floating in space. That is nothing more than a bursting balloon. This answer alone does not address the OP.
You’re missing the point…of course anything can explode under high enough pressure. Explode - i.e., rupture in a violent manner. That’s not the crux of the OP.
You’re missing the point of the question…
True, I didn’t consider that. I’m picturing a fireball-type of explosion.
But there was an explosion. Explosions aren’t just of the “combustiblie detonation” type. Any rapid enough increase in the volume of something is an explosion, whether there’s a chemical reaction going on or not. Note the reference to steam explosions above.
And about steam explosions not being relevant to the OP… Jinx, I think it is completely relevant. It goes to show that an explosion can take place through mechanical means only, without energetic chemical reactions having to take place. The impact of the missile with US 193 was an incredibly energetic event…the kinetic energy in the missile/satellite system, liberated by their collision, was insane. If I throw a water balloon against a wall with just the kinetic energy I can muster, the spash verges on being eligible for “explosion” status. If that water balloon was instead a half-ton sphere of hydrazine, and the impact was not at 50 mph, but at 22,000 mph, i think it’s easy to see how its contents could be spread so rapidly that it would be an explosion from mechanical forces alone.
I don’t know if the hydrazine in the satellite’s tank would have undergone any reactions due to the impact or not. Did it break down, and self-oxidize rapidly enough to explosively detonate? I don’t know. But my point is that it doesn’t need to to be considered a bona fide explosion.
One of these threads here somewhere, I calculated the heat released in the collision.
It’s equivalent to about 150 pounds of dynamite.
Whatever it was, in the video that military guy showed it sure looked like a typical explosion. Flashy lights, expanding glowing cloud, etc.
Let’s look at it: what you have, is metal kill vehicle smashing into mostly metal satellite. When you smash metal into metal at thousands of miles per hour you have a result of very hot, very dense metal. What very hot and dense metal do when left alone? Expands violently in all directions. The effect IS explosion - with particles of red hot vaporised or semi-vaporised metal creating an expanding fireball. No O2 extra needed. Just a lot of pressure and temperature.