Double digit percentage of C

This is the fucking best.

"My Lord Xarnog! There seems to be...these... holes in the earth...many of them. Should we concentrate our laser fire on them?"

"Nonsense Nod! Those puny earth weapons are too slow! They would never reach us on time."

*meanwhile back on earth*

How many do we have loaded?!
U-Um about fifty sir!
FIRE ZEM ALL! NOW NOW NOW!

*the sounds of earth trembling*

"XARNOG THEY AREN'T ROCKETS THEY ARE CANNO-"

*PTHOOOOOOOOOOOOOOOOOM*

Rods from God? Meet the Devils Finger.

And how would you aim it? Or you would have to wait for them to pass above you?

There's probably one built under the White House, just in case.

this better be a plot of an action movie in my lifetime

Would blasting a giant copper disk at relativistic speeds have a noticeable pushback effect on the earth?

IT'S NOT CAPITAL c!!!1

No. Not even close.

Good lord no

I don't see the point. If you are using nukes anyway the most energy you are going to get out of it is your yield, so you might as well just nuke them. You can aim it and most of the nuke's energy is going to the target, unlike the cannon that may sink energy into the earth. Sure, you might miss or be hit, but it's much easier to build nukes than relativistic canons.

>I don't see the point. If you are using nukes anyway the most energy you are going to get out of it is your yield, so you might as well just nuke them.
brainlets, when will they learn.

10 newtons on a needle does more damage than 10 newtons from your palm.

I'd rather make a big fucking hole than a tiny puncture. It's unlikely there's anything that could withstand a nuclear explosion at point blank anyway, and if there was we'd all be screwed no matter what we did.

>a copper ball travelling at more than 0,1c
>a tiny puncture

Choose one

This makes me wonder, has any military run scenarios where Earth is attacked by a technologically superior force?

except we built bunkers designed to withstand direct nuclear strikes on earth already, the idea that a true space faring civ wouldnt be able to build a vessel capable of withstanding that level of energy is kind of laughable

Pretty sure the dish would just disintegrate or something

afaik yeah there is but its pretty much only applicable if they are near our level of tech, otherwise its time to bend over

because air resistance will slow things down dramatically, could you evacuate air above the projectile via controlled explosions?

something like a weather balloon tethered with detcord?

>Double digit percentage of c
>Tsar Bomba

The biggest estimates for the Tsar Bomba puts it at 25 petajoules. If it needs to reach 0.1c, the projectile can weigh an absolute max of about 55 kg, and that's at 100% efficiency. The biggest russian warheads are about 100 petajoules (thanks wikipedia), that's 220 kg projectile weight. 220 kg of copper is a lot, but it's not an amazingly big projectile - something like a sphere that's half a meter across. Even if you do a disk and use a lighter material, your hole in the ground will only be a few meters wide, and at that point you're just blowing a hole in the concrete with the nuke since the water won't be able to contain the explosion well.

I do like the idea of a manhole cover being launched to relativistic speeds by a nuclear explosion, but I don't think it's particularly viable unless your bomb is huge. Way bigger than anything we currently have.

Big fucking bulky bunkers that never need to move and just sit beneath a fuck load of soil. Warships will always be better light and maneuverable than bulky armored and slow for the simple fact that if you found a material good enough to withstand a blast you can just use that same material to build you missiles or slugs to puncture a hole in your armor. That besides your need to transport all that mass to another star, accelerating and decelerating, makes armor, as we currently understand physics, useless in spaceships. A better strategy of invasion is releasing relativistic kill vehicles before you start your deceleration and deal with whatever is left after that.

So, relativistic canons are a bad idea because 1) they can't aim, 2) they lose a lot of energy to the ground and to the atmosphere and 3) missiles are better at it.

Tons. At least for the US, it's the only department I can speak knowledgeably about. They made all these cold war indoctrinated military strategists trained into rigorousness cold-thinking math brains, turned them into one a think tank, and churned out scenario after scenario of "what-if" events. Before they started running scenarios, their initial models identified the approximate threat level of "the unknown", and it was so significant that it made them assume that the absence of evidence for unlikely things didn't allow the opportunity to ignore the possibility that it may happen.

Therefore they methodically charted endless scenarios about things such as Magic, ESP, Aliens, Secret civilizations, Godzillas, and so on. Drew up plans for everything, treating each scenario with complete seriousness. It's not regular business though, so it's something they pull up out of a database when the time comes, not something some Admiral is walking around with a head full of knowledge of. I've heard discussions about these plans being constantly updated realtime by sitrep, but I think that's a myth. They're probably categorized by degrees of likelyhood with all other "what-if" scenarios and only the ones calculated to be the most relevant get constant real-time updates, such as maybe "imminent nuclear exchange" and other conventional scenarios. Everything probably falls under periodic review with intervals depending on need. But again, I don't know so much about that, I'm just guessing off of what I know could be physically possible.

As it goes, being attacked by a previously-unknown technologically superior force is their biggest fear. It's literally in the foundation of the US modern approach to defense

>The genesis of that mission and of DARPA itself dates to the launch of Sputnik in 1957, and a commitment by the United States that, from that time forward, it would be the initiator and not the victim of strategic technological surprises.

No. Blasting all the copper on the earth at relativistic speeds at once might.

You can see the nuke coming easy. You can see the thing coming from the explosion as easily, and have far less time to deploy counter measures.

We are talking about relativistic speeds, and a projectile.

The difference between "copper manhole cover" and "copper particles traveling in the same general direction" is semantics.