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MartinB comments on 60m Asteroid currently assigned a .022% chance of hitting Earth. - Less Wrong
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Any kinetic energy an object has, it has to get first. If you compare the size of satellites with their respective rocket it looks difficult to make an object of any reasonable mass get any significant speed. You can trick a bit with swing by maneuvers, but as far as I understand no man made object makes any more than a little sound at the atmosphere while entering. You could however poison the planet with a nice substance.
On the other hand it might be possible to use a man made satellite to deflect a bigger object so that it crashes into earth. But please do not try this on your home.
A fair point. <nods> On the subject of pulling vast quantities of energy from nowhere, does any one country currently possess the knowledge and materials to build a bomb that detonated on the surface could {split the Earth like a grape}/{smash the Earth like an egg}/{dramatic verb the Earth like a metaphorical noun}?
And yes, not something to try in practice with an inhabited location. Perhaps a computer model, at most... actually, there's a thought regarding morbid fascination. I wonder what would be necessary to provide a sufficiently-realistic (uninhabited) physical (computer) simulation of a planet's destruction when the user pulled meteors, momentum, explosives et cetera out of nowhere as it pleased. Even subtle things, like fiddling with orbits and watching the eventual collision and consequences... hm. Presumably/Hopefully someone has already thought of this at some point, and created such a thing. <curiously goes looking>
Can we? Probably not, there don't seem to be enough fissiles available: http://www.coarsegra.in/?p=95
There's also scale issues at play - as your bomb gets larger and larger, relatively more of its energy escapes into space and isn't directed into the ground.
The link in question analyzes the possibility of creating a doomsday weapon that could launch a projectile that would destroy all life on another earth sized planet remotely. That is a far more difficult task than just destroying life on the planet the bomb is on. The limiting factor in question is also fission materials to serve as triggers for the primary explosion in each of hundreds of thousands of shaped thermonuclear explosions. The massive numbers of distinct explosions are needed to progressively accelerate the Orion device but for a single explosion the ration of fissile trigger to fusion material need not be the same.
Mind you the Orion weapon is just intended to obliterate all life. That task becomes comparitively trivial when you aren't trying to do it across space via projectile. But if Multipartite literally wants to smash the earth into pieces I suspect he is out of luck for now!
He wants something which would crack the planet's crust; you're not going to get that with widely dispersed efficient-life-killing thermonuclear strikes (leaving aside the obvious question 'what do you do about the vents and spores etc'). To do that, you need a lot of energy, whether it's a kinetic projectile or a fireball & shockwave. A Project Orion kinetic strike would probably be more efficient than a pile of gigaton nukes since each explosion can be smaller and more energy extracted than it.
Where on earth did widely dispersed efficient-life-killing thermonuclear strikes come into it? Multi was considering a bomb (or cluster thereof) at a single location. The closest to 'dispersion' was when you brought Orion into it, with it's chain of bombs spread out over the launch distance.
Or, alternately, it would be overwhelmingly inefficient because the projectile is aimed away from the planet - or at best along the surface of it.
I incidentally dispute your efficiency claim anyway. I'd be willing to bet that if you collect every one of the bombs you were using for your Orion weapon and place them in single location then it would be more capable of slippiting the planet than the projectile would have been. Even if you managed to make it target the earth directly. If necessary you would of course use several years worth of the entire earth's production of steel (and maybe lead, gold and anything else hard or heavy) and use it to cover the bomb and keep the energy around a tad longer.
Why does it need to be aim along the planet? Use orbital mechanics: Send your spacecraft on an orbit such that it hits the planet it launched from at the fast point of a very long elliptical orbit. Or even just at the far side of the current planet's orbit, whatever. It can't be that hard to get an impact at whatever angle you'd prefer with most of the Orion vehicle's energy, launching direction barely seems to matter.
No particular reason. It's just that the arbitrary task of planetary self destruction that Multipartite specified happens to be that of destroying the planet with a bomb on the surface. If you were just trying to destroy the planet then doing so from the surface seems like a terrible idea.
(For thoroughness, noting that the other approach was also wondered about a little earlier. Surface action is an alternative to look at if projectile-launching would definitely be ineffective, but if the projectile approach would in fact be better then there'd no reason not to focus on it instead.)
As I already said, the scaling laws mean the larger the bomb, the less efficient it becomes. Piling together 200 bombs just means you get inefficiency and possible fratricide from the explosion themselves or neutron emission. (Looking briefly at my old notes, underwater explosions have an exponent of tonnage raised to 2/3 for the resultant overpressure wave.)
If we had some convenient test planets handy I would bet against you when it came to optimal planetary suicide methods.
Orion's is a great idea for a different task but just not the solution to this problem.
/shrug
I'm the one who has read in detail about basic equational descriptions of nukes by their tonnage, targeting concerns, the engineering involved in going to megatonnage or gigatonnage range, etc. (I wanted to make a nuke simulation game), so you'll pardon me if I put more weight on my opinion than yours.
And you must pardon me if I find that:
Whatever mass of theoretical expertise you may have behind you, you most decidedly haven't applied it coherently here. To the extent that if you had just made an assertion and appealed to your own authority I may have believed you but given that you explained details that are clearly wrong I have to dismiss it out of hand.
Doubtful. Breaking the earth up is hard. The biggest explosion ever made is this one: http://en.wikipedia.org/wiki/Czar_bomb