[grey-area]

Couldn’t you make an ablative heat shield possibly from waste materials on the same asteroid? Then lob your metal toward a shallow sea on earth?

Or take it back to some stable earth orbit then pick it up there?

Do we know what their reentry plan is?

[Loughla]

I am not super comfortable with a company whose purpose is figuring out pinpoint meteor strikes.

That seems like a recipe for acquisition by the military? Who needs nukes when you can lob a hunk of iron at a city?

[tsimionescu]

Iron rods from heaven is a fun idea, but it's very unlikely to be a practical weapon. It's not hard to change the orbit (and thus the landing spot) of an object in space that is small enough for us to control. And no country will allow any other country to store weapons in orbit, as soon as someone put one there, it would get blown out of the sky.

The reason we have ICBMs is that we can store them safely on the ground, and launch them on an unpredictable trajectory, with minutes of travel time to their destination, preferably launched in a swarm that makes them even harder to track and individually stop.

[MattExSci]

I get asked this all the time. And in short — no way in hell we can change the orbit of an asteroid that is large enough to make a massive impact. Cool (I guess) to think about, but physics make this impossible for our size craft.

[Scubabear68]

Hmm…see also The Moon is a Harsh Mistress.

If you have the energy to mine in space, you have a massive kinetic energy well to “throw rocks” into.

[tsimionescu]

The positions and velocities of every human ship in space are well known and easy to track. And any journey from space to Earth takes a long time. And anything that a single rocket that went out for mining (or even a dozen or a hundred rockets) could move back towards earth as a weapon can easily be moved slightly to hit a different destination using other weapons.

So if anyone tried to send rockets to fling back pieces of asteroid or of the Moon as weapons to Earth will be easily observed, tracked, and countered. And anyway, we're very far off being able to send a chunk of rock towards Earth that wouldnt entirely burn up in the atmosphere, nevermind one that could level a city.

[itishappy]

> And anything that a single rocket that went out for mining (or even a dozen or a hundred rockets) could move back towards earth as a weapon can easily be moved slightly to hit a different destination using other weapons.

There's a lot of complexity here you're ignoring. You can nudge a rock into a collision course with Earth using a slow ion thruster, but you're not going to stop it with one. Time is not on your side, you need to get your affecter to the rock, during which the rock will be getting closer and (assuming it came from the asteroid belt) faster, both of which make the required impulse higher. Higher impulse means more mass and/or propellant, which means even more time and cost!

This is not a symmetrical problem, but defense rarely is. The fact we can shoot bullets at supersonic speeds doesn't make it any easier to stop them.

[tsimionescu]

We absolutely can't, with current technology, move an asteroid of any dangerous size towards (or away from) a collision with the Earth - and even more so not with a single engine that has to have fuel for the entire duration of the flight. It would take thousands of years to get an ion engine on an asteroid to move it back to the Earth, and you'd have to constantly send fuel with it. And controlling where it will land is an entirely different problem.

And many years of the engine running would still be easily reverted by one or two high energy impacts, like a fusion bomb hitting the asteroid just right.

Consider this as well from an energy diff perspective - to hit a city with the same energy as a nuclear bomb, you have to have the final mass times the final speed squared about equal to the energy of the fusion bomb. And to get that, you have to put in energy that's proportional to the mass before burning up in the atmosphere times the square of the delta of the speed difference between its original speed and its speed on a collision course with the Earth. So you need to find an asteroid that's pretty close to hitting the Earth, and still put in the energy to move its full mass the extra distance.

You're right this is not fully a symmetrical problem, but it's asymmetrical in the opposite direction: defense is a lot easier than offense in this case, simply because of the massive inertia of the weapon. To alter your metaphor of the bullets, there's a reason why we shoot explosive rockets instead of just hurling huge rocks at our enemies. And it's precisely the same reason why a nuclear weapon is much better than an asteroid.

[MattExSci]

Destroying civilization by redirecting an asteroid is not on the current roadmap.

[sonofhans]

You should frame this and put it on a wall somewhere.

[Smithalicious]

Why would you? Space weapons are also very definitively illegal. I don't see what you could accomplish this way that a nuke couldn't, and it's not like there's a shortage of nuclear firepower. Plus, this seems really slow to deploy.

[pengaru]

> I don't see what you could accomplish this way that a nuke couldn't

The nuke poisons the land, a metallic asteroid just makes a conventional mess you cleanup and rebuild under your own flag...

[tsimionescu]

You realize that both Hiroshima and Nagasaki are huge, inhabited cities, and have been without interruption, right?

[pengaru]

Elevated rates of leukemia and other cancers don't prevent cities from existing or even thriving...

[tsimionescu]

Even if that's true, it still means that there is at best a tiny advantage to an asteroid weapon compared to a nuclear weapon - and a gigantic disadvantage in terms of energy cost of moving an asteroid from its orbit to Earth's surface, and in terms of the months or years it would take to deploy (in which time your enemy might even find a way to stop you, or at least launch all of its nuclear arsenal on you if that's not possible, MAD style).

[grey-area]

That’s already possible but not that interesting as a weapon except for pinpoint strikes.

Clearly they would need permission as for any landing.

[thatcat]

That would just be a shittier, illegal version of the oreshnik system

[grey-area]

Clearly you would need permission from the government who owned the sea, in which case it would not be illegal.

Capsules land with shaped ablative heat shields all the time so it seems proven but the hard part would be making one off earth.

Maybe they’ll just send a small capsule up though and return the metals with that.

[thatcat]

https://en.m.wikipedia.org/wiki/Outer_Space_Treaty I was referring to military application

Existing system https://m.youtube.com/watch?v=pYKDNSYw1NQ