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Comment by vortico | Hacker News Reader

It works for small <10m astroids, but for anything bigger than that, its own gravity will pull the segments back together after the explosion since they do not reach escape velocity, and nothing will have changed due to conservation of momentum. A better method is to detonate an astroid up to 100m away so it heats up the surface. The heat will blow off small particles at more than escape velocity, so by conservation of momentum the astroid will be pushed in the opposite direction.

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Can you explain why the nuke option wouldn't work? It seems to me that most of Earth's protection against asteroids is them burning up in the Earth's atmosphere.

Let's assume that you did blow up an asteroid, and the constituent parts loosely reassembled. Wouldn't they they break apart again as soon as they started to experience the turbulent effects of the Earth's atmosphere? And once they did, the surface area to mass ratio of the asteroid matter would be an order of magnitude or higher, pretty much guaranteeing all of the mini-asteroid parts would burn up.

No doubt I'm wrong. I'm a programmer, not a physicist or an astronomer. So I'm seeking to get 'educated' more than I am to argue with you.

Something the size of a dinosaur killer is going to cause a devastating shockwave at the surface, even if you manage to break it into small parts. Plus, breaking it into many small parts of known trajectory, with a very small standard deviation in size, is going to be a much more difficult problem than nudging one big part. Once the no-doubt irregularly-shaped chunks start interacting and banging into each other, all bets about impact sites are going to be off. You'd much rather miss the planet entirely instead of running the risk of a larger-than-average chunk hitting New York or Beijing.

On top of that, nudging it out of a collision trajectory is going to require a lot less energy than disintegrating it, particularly if you can arrange to do the nudge a long way off. What's easier, pushing a runaway shopping cart so it doesn't bang into your car, or tearing the cart into parts small enough that they don't do any damage when they hit?

Neal Stephenson's latest novel, Seveneves has some discussion of this (on a much larger scale, granted).

Another issue that is usually the first objection is that receiving a thousand highly radioactive rocks at very high velocity is a very efficient way for us humans to die in large numbers. Just one radioactive meteor would cause a lot of damage and be very difficult to seal off, but a thousand?

I think you're a bit confused by nuclear scare-mongering. Large fusion H-bombs put out stuff all radiation. And radiation isn't very deadly anyway.

Are there really asteroids so big that a nuke could not even chip off a small fraction at escape velocity? If ablative impulse could cause enough of a course change to miss earth, then why would detonative propulsion not do that job even better?

Why would mass only a bit larger than 10m in diameter have so much gravitational pull?

Hey, that's a really cool idea! Using an asteroid as its own propellant.

Yeah! Has anyone actually investigated this or written about it??

https://en.wikipedia.org/wiki/Asteroid_impact_avoidance#Hist... - Project Icarus is almost 50 years old. There was a paper about laser ablation 2 years ago. Lot of literature on many different collision avoidance strategies.

There was a talk this year at LLNL showcasing a few methods, each with high resolution mesh-based simulations. Hopefully that's enough information so you can find the slides online.

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