Alien Invasion

Actually -- let me add to that with this analogy.


If you think of a nuke in terms of destructiveness, there's a limited amount of destructive effect on "matter" in general.
I'm not sure how to calculate what percentage of nonspecific matter it would have an effect on, but if you compare a nuke to something like a black hole which effects ALL matter, so you can say there were hypothetical 'forces' that can exist in reality that could effect something else regardless of what format it came in. I mean that our 'haymaker' would be the analogous equivalent to the black hole.....something that does destructive stuff to matter.

 

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http://en.wikipedia.org/wiki/Tsar_Bomba

 

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I don't believe there's a theoretical limit to how powerful you can make a Teller–Ulam type nuclear bomb. You can just keep adding more and more stages, making the explosion bigger and bigger. Of course, eventually you will run into the practical limitation that the bomb weighs so much that you don't have an effective way to move it to the target...

Alternatively, if we had to fight in space then I would guess that nuclear warheads coupled t x-ray laser assemblies would probably be the way to really put the hurt on an enemy spaceship. Any guess about the actual damage that they could do would probably just be speculation, though. http://en.wikipedia.org/wiki/Project_Excalibur

 

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Guerilla warfare

 

Or. Burry are heads in sand

 

You don't need explosions.
Rick Robinson's First Law of Space Combat states that "An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT." In other words there are 4,500,000 joules in one kilogram of TNT (3,0002m/s * 0.5 = 4.5e6). This means a stupid bolder traveling at 2,000 km/sec relative has about 400 kilo-Ricks of damage (i.e., each ton of rock will do the damage equivalent of 2e12 / 4.5e6 = 400 kilotons of TNT or about 20 Hiroshima bombs combined).
http://www.rocketpunk-manifesto.com/2009/08/space-warfare-vi-kinetics-part-1.html
http://www.rocketpunk-manifesto.com/2009/08/space-warfare-vii-kinetics-part-2.html

Relative velocity will do a lot of damage.

 

On the other hand, a W-88 nuclear warhead can deliver energy equal to well over 1 million times its mass in TNT. I know which one I would prefer to shoot at our alien foes.

Also, I would guess that if the alien starships are able to get here in a reasonable time then it's pretty unlikely that they'll be threatened by small kinetic projectiles. If they had to worry about running into stuff at high speed, their ship would probably get toasted by random space crap while it was cruising to our solar system at some significant fraction of C. They would probably have to either have materials science that allowed them to make armor able to shrug off such hits, or they would have some fancy system to destroy/deflect stuff before it hit their ship.

 

3 km/ sec is a trivial difference: the more the difference the greater the energy delivered. Any ship coming into the Solar System from outside will have a tremendous velocity, even while decelerating. And the problem with a nuke is that it delivers its energy into a volume.
It's cheaper and easier to put a lot of inert objects into a ship's path at high velocity than it is to deliver nukes.
(This was part of the thinking behind the Rods from God idea).

 

I guess it depends on the motivations of the aliens. Are they here to extract mineral "x"..or they looking for a new home world because theirs is about to be destroyed? Do they value other life forms, or do they consider us to be like cockroaches? or are they here to collect slaves to work the dilithium mines of Rura Penthe? What their intentions are would effect their tactical decisions...and would also effect how we would defend against them.

 

I thought of a very easy way to terraform the Earth and get rid of the pesky infection that's here. If they can get here, then they can build a sun shield, and basically freeze out the existing biosphere, then remove it and thaw out a clean world for the taking.

 

You would need to get an object up into the thousands of km/sec before the kinetic energy began to approach the energy delivered by a nuclear weapon. It doesn't seem very plausible to me that we could do that with Earthling technology of the foreseeable future.

Sure, perhaps you could use the enemy ship's own velocity against it, but that would mean you're engaging it pretty far away. With our own relatively pitiful space propulsion technology, we would have to launch our box of ball bearings far in advance so that it had time to spend weeks or months coasting through space to the intercept point. An invading alien starship would almost necessarily be capable of incredible dV. If the enemy ship makes any random course changes on its way in, our weapons probably wouldn't have the dV to adjust. If you wait to launch until they are close enough that the enemy starship's dV advantage doesn't let it easily dodge, then the alien ship is probably almost done slowing down.

No, that's the advantage of a nuke. You don't have to actually make hard contact with the enemy ship. Close doesn't count with kinetic projectiles.

I don't think that it's easier to make projectiles hit an alien ship at a high enough relative velocity for it to be competitive with nukes. You either need amazing propulsion technology that we don't have, or you have to launch months in advance and hope that the alien ship is still where you expect it to be when the projectiles arrives.

Rods from god are great if it's not feasible to use nukes for political/ethical/whatever reasons. I don't think we would have any such issues with nuking the alien menace.

 

Why? What do they want Earth for?

We need means, motive, and opportunity. You haven't given us one, yet alone all three.