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Comment by ano-ther | Hacker News Reader

Tangential question: if we send a nuclear bomb to divert a meteor from its way to earth, how does the bomb transfer energy to the meteor? On earth I guess you can detonate in the vicinity because the air helps to push. But how does this happen in a vacuum? Does the bomb have to touch the meteor?

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Perhaps the mechanism is to explode the bomb close enough to the surface of the asteroid to heat it with the x-ray pulse and cause ejection of debris from the surface--that would impart a reaction force on the asteroid. That's suggested in this article: https://www.llnl.gov/news/nuclear-impulse-could-deflect-mass...

Thank you - very helpful article

http://www.projectrho.com/public_html/rocket/spacegunconvent... is a great website from the Before Times that includes long treaties on subjects like this (I first found it through a thing about stealth in space); when it comes to nukes, it does say the falloff is a lot higher than on earth, so yes it would have to touch the meteor. It's about using nukes to attack spaceships but the premise is the same.

> Nuclear weapons will destroy a ship if they detonate exceedingly close to it. But if it is further away than about a kilometer, it won't do much more than singe the paint job and blind a few sensors. And in space a kilometer is pretty close range.

> Please understand: I am NOT saying that nuclear warheads are ineffective. I am saying that the amount of damage they inflict falls off very rapidly with increasing range. At least much more rapidly than with the same sized warhead detonated in an atmosphere.

> But if the nuke goes off one meter from your ship, your ship will probably be vaporized. Atmosphere or no.

That’s a great site - thank you

Same way a rocket works in vacuum. Small particles at high speed and the law of conservation of momentum.

Imagine a large combined bomb and asteroid at rest before it explodes, so combined momentum has to stay at zero after.

If explosion happens when not combined, particles from the bomb hit the asteroid and transfer their momentum to the rocket.

But the total amount of mass in a nuclear weapon is actually very small. Even obscenely large weapons like the Tsar Bomba are tiny compared to the rockets that were used to travel to the moon.

Nuclear weapons can do interesting things like fusion, but it isn't going to create persistent mass when detonated.

The actual proposed weapon was a W25, with a yield of 1.7 kilotons. That size of weapon is so small may non-nuclear explosions eclipse it.

The kinetic energy works of ejected mass, not just the mass of the bomb. The bomb provides energy for acceleration of said mass - you vaporize and eject a big chunk of rock with the bomb if correctly placed. Which is why placing the bomb underground a'la Armageddon is much more effective at diverting it.

The bomb itself doesn’t have to touch the meteor but you do want it as close as possible so the radiative energy from the explosion doesn’t fall off too much. If there’s enough time you would want to build a bomb that acts like a shaped charge and release most of that energy in one direction and you would probably add a heavy element to it that could be energized and pushed in the direction of the asteroid.

Is it even possible to direct that much energy is a specific direction?

Yes. Orion was a credible bomb powered rocket plan. The energy released is mostly thermal, metallic mirror will work to reflect it and if there are superheated gasses involved, you can direct these with rocket nozzles for example. The problem will be attaching that reflector so that it does not fly off.

https://en.m.wikipedia.org/wiki/Nuclear_shaped_charge

Imagine a meteor made of ice. A nuclear bomb bombards the surface with immense radiation, vaporizing huge swaths of the surface. This superheated steam explodes off the surface of the meteor, and the meteor itself moves the opposite direction.

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