Using nukes to push an incoming meteoroid off course

Question

It's often said (or at least, I have read it somewhere on some occasion), that using nukes to combat a potential incoming meteoroid is not viable because it may split it into multiple incoming bogies.

Some questions though:

1. If the nuke was detonated on one side of it, or several were detonated on one side, wouldn't that be enough to push it slightly off course and it would then sail right on by the earth. It would have to be done when it's still some distance away so that even a small nudge would have an effect.

2. Even if it was split into a gazillion pieces - surely this would be better than one big ass piece as those gazillion pieces would just burn up in the atmosphere and some lucky gits will see the meteor shower of the century.

Answer 1

If you have enough warning, there are more gentle and much more predictable approaches than using a nuke. If you don't have enough warning, then you're probably only going to get one shot at it, so you definitely don't want the unpredictability of a nuke imparting unknown velocities to unknown size pieces, only one of which would need to be large enough to be a significant threat to make this a risky venture. If you know that the object is not a rubble pile, e.g. a metallic asteroid, and you have very little time to get it off course, then a nuke might be a good option.

You certainly shouldn't throw nukes out of your toolbox, but their application needs to be considered very carefully. That statement probably applies to all potential uses of nukes.

Answer 2

As for the first part:

Nukes have one great advantage over any other scheme that has been proposed. Every other suggested system requires matching orbits with the target before you can attempt to move it. So long as your guidance system is good enough a nuke doesn't need this.

Your target is closing on the Earth at 10 km/sec, you have to fly out there, then cancel your outbound velocity and add 10 km/sec back towards Earth before you've done anything--and at that point even with the biggest booster your payload is awfully small. Your nuke, however, doesn't care if it's going 20 km/sec relative to the target. So long as the fuse explodes it at the right altitude it does it's job.

There's also the little detail that nukes pack an awful lot of energy per kg and the number of kg we can get to the target is limited.

As for the second part of this question:

The reason breaking it up is a very bad thing is the square-cube law. The energy expends in all three dimensions, thus it drops off at the third power of distance. We live on the surface, though, the area goes up only at the square of the distance.

Look at what happens if we split a rock into 8 equal parts. Energy = 1/8, distance = 1/2, area = 1/4. Each piece does 1/4 the damage of the whole rock but there are 8 pieces for a total of twice the damage. (More energy is expended on blowing things up, less on making a crater.)

Breaking the rock up is the worst thing you can do unless you can break it small enough the pieces expend their energy in the atmosphere.

Answer 3

Judging by the amount of rock vaporized in underground nuke tests, and the size of an average asteroid, todays nuclear weapons are easily capable of vaporizing all but the most massive of asteroids.

The largest nuclear detonation by the US was Castle Bravo at 15Mt. This created a crater 2km in diameter and 75m deep. Thats 3.1x10^8 cubic meters. But thats a cone shape, so a lot of energy radiated in upward directions. Lets say very approximately half, giving 6x10^8 m^3 of rock vaporization and/or dispersal. That volume is equivalent to a sphere of radius 530m, assuming we send Bruce Willis to bore a hole to the center of the asteroid. According to wikipedia, there are about 31 million asteroids of less than that size, and about 1m greater. So given that the Russian Tsar Bomba was several times larger again, I think its fair to say that with the most powerful of todays nukes detonated at the core we are talking about enough energy to totally vaporize the vast majority of asteroids. Any chunks that might remain would be blown outwards at high speed by the extremes of pressure in the center of the vaporized and rapidly expanding plasma cloud, and so be thrown far enough from the original impact trajectory that they'd miss earth (assuming you hit it some weeks or months away).

i didnt manage to find much more than speculation regarding the effects of nuclear detonations in open space, beside an asteroid. Lacking any atmosphere for blast waves, the energy is released as radiation, which would likely vaporize the surface of the asteroid, propelling it sideways and off course.

I also found this, which seems interesting, although i didnt watch all of it.

Answer 4

Nukes are a horrible idea to use for asteroids. First nuclear detonations do not work the same way in space as they do in atmosphere. In space a nuclear device creates a large deadly cloud of radiation but not much more. It loses all of its blast component and with no atmosphere to heat, most of its thermal component. So basically if you use a Nuke on an asteroid all that will result is you will have a very large highly irradiated asteroid on the same course. Maybe you might be able to use them if you coul drill a hole and fill it with a reactive gas like oxygen or hydrogen so you could get some of the blast and thermal component back, but this would take weeks possibly months to accomplish and the end result isn't guaranteed and would only work on asteroids that weren't very dense. Against a nickle/iron asteroid it would have very reduced to no effect at all.