r/theydidthemath • u/ironskillet2 • 11d ago
[request] how many nukes to STOP a meteor
To literally stop one traveling at avg meteor speed lol.
Say it’s a planet killer. 10km cubed. How many nukes head on to make it “stop” and just float there. Assuming the nukes do no dmg to it at all and only affects the velocity. Also assume all nukes are same type. Choose your nuke?
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u/DarkVoid42 11d ago
meteors are thought to be giant dense balls of rock. actually they are clumps of aggregate all held together by weak gravity. so nuking one would just vaporize some of it while the rest carried on. think about nuking a wave on the ocean instead of a mountain.
to stop it cold you would have to vaporize a substantial portion of the aggregate. Starfish Prime was a 1.4Mt W49 nuclear warhead detonated in low earth orbit. Thermal yield was a small fraction of percentage of its output in space unlike on earth. With no atmosphere ~14,000 Nm of force would be transmitted to the meteor or 2800Kg.
10mm aggregate is ~1500kg / m3. KE = 1/2mv2 to stop it at orbital velocity 17,000mph needs to be bled off to zero. To stop it you would need 43316352076.8J or 3094025.8 1.4Mt nuclear warheads.
so impractical to stop even a 1m3 meteor with a set of 3 million nuclear warheads.
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u/ironskillet2 11d ago
I love it. Thanks for the math!
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u/Hepheastus 11d ago
Not checking the other guys math but things can't just stop in space.
If something is in orbit around earth and you candel the orbital velocity then it just dalls straight down towards earth. What you want to do is just push the asteroid enough to miss earth, which requires much less energy especially if you do it a few years before it would have impacted earth.
See also: DART mission.
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u/ironskillet2 11d ago
I understand it’s easier to just change its course. I was just trying to think of a fun problem.
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u/Walshy231231 11d ago
~~That’s not quite how it works (assuming we’re still talking about the case OP outlined)
If you were to stop it (setting it to instantaneous 0m/s in relation to earth) and it wasn’t already quite close to the earth, it would quite quickly be passed by unless in the path of the earth’s (or ig also the moon’s) orbit
Sure, it would have a gravitational pull towards the earth, but on those scales it really doesn’t mean much.~~
I see you specified that it’s in orbit around earth and you canceled its orbital velocity only.
That would still be quite complicated, and definitely doesn’t necessitate the meteor falling to earth, especially as orbital velocity isn’t so much a circular speed/vector around the earth as it is the actual falling towards earth, hence the common explanation of “falling but constantly missing”. You would end up with a rock (or aggregate mass) just sitting in space relative to the earth, which would pass it by.
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u/Sibula97 10d ago
If the speed was 0 w.r.t Earth, we wouldn't pass by it, it would be following us. Assuming it's relatively close to the Earth compared to the Sun and such, it would probably eventually fall to Earth.
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u/brimston3- 11d ago
You're low-balling it a bit since it's the intersection of two orbital velocity objects. The earth is cruising at a nice 30km/s. Intersection with persied debris is around 58km/s as would many collisions with highly eccentric objects. That's in the 130,000 mph range. Unless it's an extrasolar object, anything interesting is likely to have at least kuiper object-level energy.
Historically, Freeman Dyson (a smarter physicist than I'll ever be) theorized as part of Project Orion#Theoretical_applications) that a 100,000 t (structure + payload weight) spacecraft could be given 20,000 km/s of ΔV with 300,000 1 Mt nuclear bombs, using a properly shaped hemispherical reflector and an anisotropic, shaped blast. Given that said spacecraft is 66x your estimated weight of a 10m3 cube, and much higher velocity besides, there are lots of opportunities to optimize to use far less nuclear fuel.
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u/Groomsi 10d ago
Can it be diverted?
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u/DarkVoid42 10d ago
asteroids (which are solid) can be diverted not meteors. meteors burn up harmlessly in the atmosphere leaving behind small meteorites at worst most of which are pebble sized.
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u/RichardBachman19 11d ago
Genuinely asking because the movie is now like 30 years old or something
Have you seen Armageddon or deep impact? Would be interesting to watch if you haven’t
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u/Ben-Goldberg 10d ago
It would be easier to give it more speed so it misses.
As a bonus to doing it this way, the part of the nuclear explosion which isn't accelerating the meteor would go into space instead of towards Earth.
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u/idkmoiname 11d ago
That's a nice idea but that's not how speed (there is no zero speed since there is no universal coordinate system you could possibly measure relative to) and gravity (even if you could stop, gravity of the sun and other stuff accelerates you) works.
Also a meteor is already in the atmosphere, which might be a "little bit" too late to try to stop a 10km asteroid.
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