I have heard some scientists explain that a nuclear weapon could possibly be used to altar the course of a dreaded “doomsday” asteroid. Is it even possible to create a nuclear chain reaction in outer space?
I think that is probably just “Hollywood”. You need all 3 elements (no, not earth, wind & fire!) Fuel, Heat, and Oxygen! Something “outerspace” is decidedly short on.
A nuclear chain reaction only requires that there is enuf fissionable material to induce the reaction. There might not be the mushroom cloud and shockwaves in space but the same energy is released instantaneously. Without the atmosphere to aid its destructive explosion, maybe thats why you have to bury the nuke into the asteroid to get effective results.
Of course it is. None of the parts of an atomic bomb require the presence of either oxygen or gravity. In general, an atomic bomb is detonated by compressing a hunk of fissionable material to a critical mass, using conventional high-explosives. There are a number of ways to do this, and all have been used during the history of the development of these weapons, however, most modern high-yield bombs use the technique of compressing a hollow sphere of fissionable plutonium with the detonation of a shell of high explosive around it. For more info, go here.
A nuclear chain reaction happens when you put together a critical mass of fissile material. So if there is a natural or artificial mechanism that concentrates U-235 or something like that, then yes, a chain reaction will happen.
The reason nuclear weapons can push an asteroid is that if detonated close to an asteroid, the heat will vaporize the surface. The evaporating gas will function as rocket exhaust and push the asteroid. You do not want to drill a hole and plant a weapon deep inside an asteroid, contrary to what certain movies have said.
The answer to this is a most emphatic yes! How do you think the sun operates? It is essentially a gigantic fusion explosion hanging in space.
Chemical reactions require things like oxygen (or other catalysts) to make them go. Nuclear reactions only need the nuclear fuel (such as hydrogen for fusion) to work (along with a helluva lot of pressure and heat).
Actually, didn’t the US do some nuke tests in space? Starshine or something?
Oh, and it would take far more than a single atomic bomb to divert an asteroid that was big enough to seriously damage earth.
Is the sun not a giant nuclear chain-reaction?
Depends on how big the bomb is, and how far away the asteroid is. If the asteroid isn’t going to hit for 100 years, then you wouldn’t have to devert it very much to make it miss.
No.
Er, actually, yes. Well, it wasn’t called “Starshine”, but pretty close.
“Starfish Prime”, part of the Operation Dominic (or Operation Fishbowl) test series in 1962, was a 1.45 megaton bomb detonated 248 miles out in space. There were some other high-altitude shots as part of Operation Fishbowl as well; “Checkmate” was over 90 miles up, and “Kingfish” was over 60 miles up.
The earlier Operation Argus, in 1958, detonated several smaller warheads (1.7 kilotons each) at distances as far out as 466 miles.
Ummm, then what’s this documentary about then?
Even a conventional warhead (plain chemical explosives) would work just as well in space as it would on Earth: Everything, both the fuel and the oxidizer, is contained in the explosive and the detonator. If bombs relied on atmospheric oxygen to explode, the best they could manage would be a quick, rather incomplete burn.
For the same reason, a conventional gun will fire in space.
Anyway, nuclear weapons all use conventional charges (explosives shaped in precisely the right way) to initiate the reaction by slamming two pieces of a fissile metal (usually either Uranium or Plutonium) into each other to form a whole that is both massive enough and dense enough to produce a fission chain reaction of appreciable magnitude.
In a plain nuclear bomb, also called an A-bomb, that’s it. In a thermonuclear device, also called a hydrogen bomb or an H-bomb, the fission chain reaction triggers the fusion reaction of a layer of heavy Hydrogen (Deuterium or Tritium) covering the core. That fusion reaction greatly increases the bomb’s yield in terms of blast force and radiation produced.
In a boosted bomb, there is a small amount of heavy Hydrogen placed between the two pieces of fissile metal. This creates a very small fusion reaction during the first stages of the fission reaction, a process that greatly increases the bomb’s yield by making the fission reaction more efficient. (The fusion liberates large amounts of neutrons, which are dumped into the ongoing fission reaction.) The Hiroshima bomb, a plain fission weapon that used Uranium, achieved roughly 2% efficiency in its use of the Uranium. A boosted bomb can approach 100% efficiency. (Those numbers are from memory, BTW, but I can assure you they are accurate to within an order of magnitude.)
Given that a nuclear weapon or twenty would work just dandy to alter the course of an asteroid, how quickly could we retarget existing ICBMs to counter a known asteroid threat? 2000YT (or whatever the latest worldkiller is called) is approaching: When can we deflect it?
Could a Minuteman (to pick an example) achieve orbit?
We can’t. ICBMs are designed for suborbital flights. Some have been converted into orbital launchers, but it takes a lot more power to go beyond earth orbit and reach an asteroid. Also, ICBMs do not have the necessary thrusters and sensors to navigate in deep space. It would be easier to take the warhead and mount it on an interplanetary probe, assuming you can find one.
Anyway, even the largest hydrogen bomb can only deflect the asteroid by a small amount. That means it must be done months or years before the actual impact.
Not quite. The heavy hydrogen (deuterium, or, rarely tritium) is stored in the bomb as a salt of some light metal, usually lithium, as in lithium deuteride, e.g. Being combined with other elements does NOT inhibit fusion reactions among hydrogen isotopes, but does allow their storage at higher densities. Pure deuterium or tritium are gasses; but lithium deuteride or tritide are solids at room temp.
A recent NASA probe was landed on an Asteroid, carrying a payload of instruments which were mostly finished what they were designed to do, and were just sitting in the probe. The mass and volume of a fair sized nuke is certainly no larger than the entire scientific payload of a probe.
That entire project lasted less than a decade. The asteroid landing was just an afterthought. If we don’t already have the hardware on the shelf, it would be simple engineering to assemble it into an appropriate guidance and maneuvering package no larger than the aforementioned probe. Shuttle it up to LEO, and boost it on into space on a two or three year voyage to soft land right on the killer asteroid.
Now, deciding just when, and where to blow that sucker, that’s a whole different problem.
Tris
Lithium is itself fusible. IIRC, it is even better than hydrogen, releasing more energy.
Fuel and oxidiser? 
I am not aware that explosives such as TNT contain oxidiser at all.
An explosive substance is, by definition, a self-contained mixture of fuel and oxidizer. If it is just fuel, the reaction speed will be limited by how fast air can get to the reaction site. That’s combustion, not explosion. Pure hydrogen is not explosive; a hydrogen/air mixture is.