Explosions in space.

[cb92]

Some may consider this a stupid question, but I want to know. When I watch Science Fiction shows about asteriods threatening the Earth, they sometimes show missiles with nuclear weapons breaking up the asteriod.
My question is, does an explosion really do any damage in the vacuum of space? A nuclear explosion is mostly a heat engine, isn't it? Heat can radiate thru a vacuum, but will that really destroy an asteriod, or just sear it, or maybe crack it with expansion?
This also connects with the idea of using nuclear explosions to propel spaceships. On the first part, I don't see how they expect a craft to survive such a sudden thrust, if that could even happen in a vacuum. Secondly, why waste so much energy, when very little of it could be captured by the backside of the ship, even if it were flared?
I just want to get some straight facts if I ever discuss this socially.

 

[IRstuff]

Since you're mechanical, it should be clear that the objective must be to drive the warhead some distance into the rock before detonation, just as in earthbound mining. Energy is released, of which some is absorbed, which results in kinetic energy.



TTFN

FAQ731-376

 

[rb1957]

personally, i can't envision an opportunity to discuss this topic socially ...

 

[cb92]

I read a lot of sci-fi when I was young, and it has been inspiration for inventions, mine and others I'm sure. An author needs credibility in his stories if he's going to keep the readers coming back and buying more books. I've asked this question because I really want input on how the vacuum of space relates to explosions, nuclear and conventional.
I've seen plenty of things start in sci-fi and end up in reality. Those that are credible happen, bad science doesn't get anywhere.

 

[RPstress]

I've often wondered the same. In an atmosphere you get a shockwave which does a lot of the damage, whereas in a vacuum...what are the effects of an explosion, of any sort?

There must be quite a few people in the US DOD and elsewhere studying these things rather intensively for space war purposes.

For a nuclear explosion in a vacuum there would be the usual tremendous release of heat in the form of various wavelengths of electromagnetic radiation. What else happens? Apart from irradiating a comet/asteroid what would be the physical effects on it?

 

[jedward]

The radiation from a nuclear explosion set off near an asteroid would subject the asteroid, or any material, to an intense short pulse (less than a microsecond) of radiation which would have several effects. Intense heating near the surface would result in evaporation of part of the surface. he resulting vaporized material would generate an impulsive force on the material, thus acting somewhat as a rocket with an "open" nozzle.
Other than thermal effects, which could be very intense, a rocky asteroid would probably not suffer much unless there was a direct hit. Most of the energy would be deposited with the first few inches of the surface. Seems that this is not an effective means of destroying asteroids.
If the asteroid were to be shattered, where would the remains go?

 

[IRstuff]

Breaking up an object has two effects.

> The smaller chunks more easily burn up in the atmosphere.

> There may be sufficient delta_v to miss Earth altogether.

TTFN

FAQ731-376

 

[KENAT]

Yeah, I seem to recall one sci fi film where rather than just firing missiles at the asteroid they actually landed on it, drilled into its surface and buried the nuke(s).

Point being to break up the asteroid for the reasons IRstuff said.

I recall some one doubting the benefit firing nukes at an asteroid but for the reasons IRstuff lists I always thought it may make sense.

Not only will the smaller chunks burn up more in the atmosphere, possibly completely, but I suspect will do less overall damage. Partly because there will be less net mass impacting the earth (as some mass 'burnt' off) but also because smaller impacts will probably only have local effects while larger ones may have more widespread results.

For instance one asteroid hundreds of meters across hitting the ocean might be expected to cause a tsunami. Hundreds of smaller impacts in the ocean probably wouldn't have the same net effect.

If you're talking about the idea of detonating the nuke say next to the asteroid in order to try and give it an impulse then you may have more of a point. If you look at how ion engines etc work I'd expect it would put an impulse on the rock but I'm not sure how big it would be, even for a multi megaton warhead.

You could maybe make a special warhead that acts a bit like a shot gun. The nuke could have material around it (or just at one orientation pointed to the asteroid) that although it gets vaporized by the explosion will still have significant impulse. This impacting on the asteroid may work.

KENAT, probably the least qualified checker you'll ever meet...

 

[IRstuff]

Oh, oh, I know. Would that be Armageddon, Alex?

http://en.wikipedia.org/wiki/Armageddon_(film)

Starring Bruce Willis, Ben Affleck, LIV, Billy Bob Thornton, Will Patton, Steve Buscemi, and Michael Clarke Duncan


TTFN

FAQ731-376

 

[KENAT]

I believe so, I didn't see the whole thing.

http://news.cnet.com/Meteor-warning-system-needed,-says-panel/2100-11397_3-6160316.html

Here's an idea for diverting the asteroid.

http://abcnews.go.com/Technology/story?id=4271344&page=1

If you have that much time why not strap an ion engine to the darn thing and divert it that way, or am I missing something.

KENAT, probably the least qualified checker you'll ever meet...

 

[IRstuff]

Sure, 20 yrs, I read that one when it first came out and was ROTFLOL. Not all astronauts qualify as rocket scientists.

TTFN

FAQ731-376

 

[FieldTeam]

I would hope that anyone really qualified to speak on this topic would not do so as their clearances would prevent them from even speculating.
Oh yeah, the movie with the line "one summer...at band camp.....!"

 

[KENAT]

Well, I studied rocket science & orbital mechanics at school. But no FieldTeam you're right I'm sure I'm not qualified.

You could maybe calculate it out from first principles.

KENAT, probably the least qualified checker you'll ever meet...

 

[RPstress]

It would be nice if a physicist could lay out the basics, though. That can't be sensitive. (As a related aside, see the "relativistic ravioli" discussion at

http://leonbrooks.blogspot.com/2005_09_01_archive.html

for a fascinating description of impacts at velocities from the mundane to the relativistic.)

 

[KENAT]

I worked it out.

You make a little spaceship/lander that has a big old ion engine, a nuclear power source and a plasma torch type device.

You land it on the asteroid, the plasma torch is used to generatate the 'fuel' for the ion engine from the asteroid itself.

How much do you recon NASA will pay me for saving the world?

KENAT, probably the least qualified checker you'll ever meet...

 

[whansen02]

hey Kenat, do I have to go to school for this or what? I'll join you in saving the world if we get to play in a spaceship/lander with nuclear power & a plasma torch!!! Will

 

[KENAT]

First we need to discover a big rock that's timed to hit the earth in about 20 years time.

KENAT, probably the least qualified checker you'll ever meet...

 

[kontiki99]

I just listened to some ideas on this in an Astronomy audio book. The author suggested the asteroid strike was likely to happen way before the sun swells and consumes the planet.

He advocated for early detection with minor deflection. We probably won't be around for any of it though. Given the huge number of species went extinct before we even arrived, the odds of us lasting are very slim.

Boy, I feel like the life of the party now!

 

[ASEI]

One approach to pushing an asteroid out of the way would be to have a nuclear rocket vehicle (such as a NERVA engine) match velocity with it, "land" on the side and apply thrust.

There may be ways to rig a nuclear explosive to dump the radiation energy into a propellant tank and produce impulse. Nuclear warheads produce a lot of energy. If it could efficiently be channeled into gas, it would make for a lot of impulse. To move a large asteroid (think manhattan island in orbit - hundreds of thousands, if not millions of tons), you need a lot of impulse.

To push an asteroid out of the way, if it is on an earth collision course, the most efficient method of doing so would be to send your device to rendezvous with it at apogee, about 0.5-2 years before impact (depending on it's orbit). Small changes in velocity there would amount to planet-radii of change in orbital path at impact. This requires a year or two before that of warning to launch whatever interception device scheme you have in mind.