Nuclear question....

[Skidmore]

I've been spending my downtime watching scifi movies in which our fine military solves cosmic threats by sending nukes into space to blow crap up. I know these are just movies but if something like this was really done and a nuke was exploded beyond the earth's atmosphere, how would the explosion really behave? Would materials fall to earth? Or would they stay in outer space? Would such an explosion really look like the big flat white donut flash I just saw portrayed in the last molvie? Just curious about how materials behave in space.

[TheWraith]

1. A nuclear detonation would have much less power in space than on the ground.

Much of their destructive force comes from the thermal and overpressure blast waves, burning and smashing things in their path. Thus, you'd have to get a nuke much closer to the target, and even then it wouldn't have as much kick.

Also, the amount of residual radioactive particles from a space-based detonation would be relatively low, since the fallout is primarily from dirt and debris sucked up by the explosion and exposed to neutron flux. That's why an "airburst," detonation of a nuclear weapon a couple thousand feet up, produces very little radioactive fallout as compared to a "ground-burst," meaning detonation at or near the ground. Given the size of space and the behavior of a microgravity environment, very little of the detonation byproducts would likely return to Earth.

The explosion would probably look simply like a very large, painfully bright flash, followed by a rapidly-expanding spherical cloud of superheated particles.

[Skidmore]

2. Thanks for educating me. I am always mildy amused by these

blow crap up with nuke solution films, in space or anywhere on earth. Just got to thinking about it and wondered how much grounded in reality science-wise these movies are.

[TheWraith]

3. Depends a lot on what they're trying to do with the bomb.

For instance, using nuclear weapons to deflect an asteroid away from the Earth is actually a scientifically valid idea. In fact, nuclear explosions have been contemplated as a potential form of spacecraft drive, known as "Project Orion." Deflecting an asteroid would work much the same way, in effect giving it a "kick" to move it into a different orbit, one which hopefully didn't hit the Earth.

Similarly, the use of nukes as a weapon for combat between spacecraft is also fairly practical, although sometimes they fail to realize that outside of an atmosphere, a nuclear detonation does not produce an electromagnetic pulse.

Other uses of nukes as a solution to scientific problems... not so much.

[Lionel Mandrake]

4. The effects depend on altitude.

There is no particular altitude where the atmosphere ends and space starts. The higher the altitude, the less atmospheric and the more space-like the environment is.

There have been thermonuclear explosions altitudes up to 300 miles, which could reasonably be called space, but the effects from such explosions are caused mainly by gamma rays which travel to lower altitudes before interacting with the atmosphere.

For details, browse:
http://en.wikipedia.org/wiki/High-altitude_nuclear_explosion

There have been no nuclear explosions in deep space, which is where they would be needed to deflect a comet or asteroid heading toward the Earth.