Earth-grazing asteroids as a military resource

Excellent suggestion.! Needs some clever maths calcs though...

Silly suggestion. You'd have to plan your wars 30 years in advance, and you couldn't sign a peace treaty with the thing a week away from hitting earth.

We can launch a nuke in 20 minutes.

You wouldn't have just one of them, and the trick would be to have a bunch of them in orbits that could easily (and quickly) shifted from earth grazing to earth impacting. You might mot be able to shift it back into earth grazing in a week, but you could probably get it to hit the Pacific ocean rather than your enemy's territory.

And everybody can see where it came from. Junk in the asteroid belt is anonymous, and an asteroid hitting the earth will vapourise anything that might otherwise have been traceable back to you.

Timing is everything in orbital dynamics.

The Earth is moving along it's orbit at 30km/s and the impactor is similar or possibly faster depending on its orbital parameters. IOW just a couple of minutes difference between a direct hit and a miss.

Its actually better than that since glancing impacts will skim off the upper atmosphere like a stone does off off a pond. And only iron or stone ones coming in at relatively steep angles get to reach the ground. Many are loose aggregates of ice and pebbles that disintegrate on entry.

One of those peppered part of France with stones just after their Royal Academy had declared conclusively that "Nothing ever falls from the sky"

Modern NEO surveys get most of the potential impactors in plenty of time. The ones that can sneak up on us tend to be dirty sooty black comet residues but even they can't hide from thermal infrared.

There is of course a catalogue of such objects:

Or milliseconds.

Drones are more sensible weapons.

In The Expanse series of novels, asteroids are used as weapons, and it took them months. Of course, you need the proper drive (which we don't have). I'm not sure they calculated the hit place.

Ok, it is fiction, but calculated fiction.

Same core issue, on a smaller scale, "The Moon is a Harsh Mistress".

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Joe

If you're planning to maintain anonymity and convincing deniability (as your final statement suggests) then you aren't really in a position to use the asteroid as a bargaining chip in a war, are you?

You can't contact your enemy's leader and say "Well, an asteroid that we have absolutely nothing to do with, and have no power over, is going to smash your capital city in a few weeks... unless you make peace with us. Then, we promise to pray to the Flying Spaghetti Monster to divert it to a place where it will only kill a lot of fish and cause tsnuamis that flood numerous uninvolved nations. That won't be our fault since we have no control over it."

In addition to that... if you really want a bunch of them moved into Earth-grazing orbits, it'll require a truly huge industrial effort to loft the necessary number of "engines" to divert them into those orbits (e.g. by gravity-tug effect, ablative lasers, etc.). Do you really expect that any nation can do such a thing, and not have it detected and traced back to the nation in question? Outer space is a lot more "visible" than something like the Manhattan Project was.

A counter to this sort of gambit would be for the targeted nation to make it clear that their own retaliatory counter-force (ICBMs, atomic-tipped cruise missiles, etc.) has been put into a deadman switch of sorts, and will be launched if the asteroid strikes.

It'd be just another round of "Mutually Assured Destruction", without a bunch of the existing safeguards (two-man firing rule, the ability to hit a destruct switch up until the last moment, etc.) to stave off Armageddon.

That's not to say that somebody military won't propose it... but I doubt that it will fly.

You can afford about 300ms error and still annihilate a target.

Make a mess of the surrounding countryside too. No fallout but for a very big asteroid impact cloud cover might make it an extinction event.

Serious effort is made to spot anything that might one day intersect with the Earth in its orbit. Quite a lot of Earth crossing asteroids.

Fortunately Jupiter acts as a cosmic vacuum cleaner for the solar system catching comets and tearing them apart. A la Shoemaker Levy 9. (back in the good old days when humans spotted them first)

Autonomous ones look a bit too much like Terminator for my liking.

I haven't done the calculations - but then again neither have you.

My guess is that sort of ion drives that you'd use wouldn't be all that big, and you'd power them with solar cells. They'd need to keep pushing for quite a while. The first stage would be to stop the asteroid tumbling and get it spinning on an axis that more or less pointed at the sun so that the solar cells could stay illuminated for most of the time.

You might have ship up more reaction mass from time to time. Using theasteroid mass as your reaction mass might be practicable, but it would be an additional complication.

But there is a lot of it, and most of the action would be happening a long way away from the earth - more than 93 million miles, on average.

Which only works if you can correctly identify the source of the threat.

In the same way that the Germans thought that an atomic bomb was impracticable.

Russell's teapot :-p :-)

Not exactly. My claim was simply that observation would be difficult - not impossible - in the same way that it isn't impossible to intercept an intercontinetal ballasitc missile in mid-flight, but that the practical difficulties mean that nobody is trying to do it.

Reagan's "Star Wars" proposal pretended that it was practical.

The thing is, it is impossible to prove that there are no objects out there in an intercept orbit with earth.

If you find one, you have proved it exists, but you can not prove the negative.

And you'd be mad to try. Meteorites hit the earth every day, so there are clearly lots of small objects out there with intercept orbits with earth.

Larger objects hit the planet and make it down to the surface less often, and the frequency drops off with size. A really big one killed off the dinosaurs about 65 million years ago.

In this particular case you couldn't prove the negative because there isloads of evidence to the contrary. People like Trump do make that kind of assertion from time to time, and some people do seem to take them seriously, but that's all about influencing the hopelessly gullible.

A drone that could create the Barringer Crater

A 50-metre diameter asteroid is a bit too big to be any kind of practical weapon. Something smaller and lighter would be easier to shift into an earth-impacting orbit.

Obviously I refer to objects of a dangerous size.

Isn't Russian-occupied Ukraine already a mined wasteland? You think Putin gives a damn?

Throwing rocks? It may come to that, if the conflict goes on long enough without aid. Look at Gaza.

Aid that is already withdrawn isn't a threat or bargaining chip, it's simple betrayal.

RL

And that means that you don't know what you are talking about.

There's a whole distribution of space junk up there. The bigger they are, the more damage they can do when they hit the surface of the earth.

The historical record - in terms of meteor craters big enough to have survived for a few million years - demonstrates that big earth grazing asteroids are pretty rare. I imagine that somebody has worked out what the distribution is, at least roughly.

A really small meteor - one only just big enough to make it the surface of the earth - could still kill you if it hit your head.

It seems to have been a stony asteroid, rather than a lump of nickel-iron, and seems to have come apart at an altitude of of between five and ten kilometres.

It does tend to be full of Russian cannon fodder, which is starting to run out, whence the admixture of North Korean cannon-fodder.

Putin won't give a damn about the lives lost, but he won't be pleased about having to find more cannon fodder.

It's tricky to get rocks to move as fast as a chunk of earth impacting asteroid.

So Trump is traitor. As if we didn't know that already.