# Redirect asteroid by mining it for reaction mass?

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54 minutes ago, Xd the great said:

Well, if the asteroid breaks apart, its surface area increases, so more of the asteroid should be burnt away.

But you now have 2 or more smmaller nukes incoming, rather than 1...

theres still the heat transfer problem. all the ke of the astroid or its parts is going to turn into heat when it hits the atmosphere. dump enough heat and you could cause a catastrophic climate change event.

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12 minutes ago, Nuke said:

theres still the heat transfer problem. all the ke of the astroid or its parts is going to turn into heat when it hits the atmosphere. dump enough heat and you could cause a catastrophic climate change event.

That needs scientific proof.

I am more worried about the shockwaves.

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14 hours ago, Xd the great said:

That needs scientific proof.

Not sure what you mean.

If an asteroid or its parts is stopped in the atmosphere, all of the kinetic energy of the asteroid will turn into heat.  That's a given.  That's how this works.

If there's enough heat, it can disrupt climate patterns.  How much heat?  Enough to do the job.

What kind of "scientific proof" are you looking for?

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Well, let's run the numbers.  Let's take a 1km spherical asteroid, and assume a density of 5,000 kg/m3.  The chelyabinsk meteor came in at about 19km/s.  That gives us enough to calculate the kinetic energy.

Mass of asteroid: 5,000 * 5.23x10^8 m3 =2.62 x 10^12 kg

Kinetic Energy of 1km asteroid: E = 0.5 *mV^2 = 0.5 * 2.62 x 10^12 x (1.9x10^4)^2 = 4.73 x 10^20 J

By comparison, a one-megaton nuclear bomb releases about 4.18x10^15J, so this asteroid has about 100,000 times as much energy.  The sun imparts 174 petawatts (10^15) on the earth, so about 45 minutes of sunlight is equal to the energy of the asteroid.  I could be wrong on this next part, but if you assume that the asteroid entirely burns up in the atmosphere (i.e. no surface impact), it wouldn't have a long-term impact on the climate.  The earth would heat up slightly, start radiating more heat into space, and over a few months all that energy would get dissipated.

Of course, an asteroid that hits the atmosphere at such an exact re-entry angle and burns up without exploding is hypothetical--at that speed, by the time it would have vaporized, it would have long since exited the atmosphere.

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4 minutes ago, zolotiyeruki said:

Kinetic Energy of 1km asteroid: E = 0.5 *mV^2 = 0.5 * 2.62 x 10^12 x (1.9x10^4)^2 = 4.73 x 10^20 J

By comparison, a one-megaton nuclear bomb releases about 4.18x10^15J, so this asteroid has about 100,000 times as much energy.

According to the infallible wiki, Krakatoa released ~8*10^17J and left the world without a summer that year.  I'd strongly suspect any dramatic effects to involve at least temporary cooling.  On the other hand, I don't think the Tsar Bomba (~2*10^17J) test had any effect on the climate.  It mostly depends on how much dust is kicked up to reflect sunlight outside the atmosphere.

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4 hours ago, wumpus said:

According to the infallible wiki, Krakatoa released ~8*10^17J and left the world without a summer that year.  I'd strongly suspect any dramatic effects to involve at least temporary cooling.  On the other hand, I don't think the Tsar Bomba (~2*10^17J) test had any effect on the climate.  It mostly depends on how much dust is kicked up to reflect sunlight outside the atmosphere.

I think Krakatoa's effects were due to the vast amount of ash spewed into the atmosphere, rather than the raw energy released.  Tsar Bomba would be 1/2000th of the hypothetical asteroid.

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4 hours ago, wumpus said:

According to the infallible wiki, Krakatoa released ~8*10^17J and left the world without a summer that year.  I'd strongly suspect any dramatic effects to involve at least temporary cooling.  On the other hand, I don't think the Tsar Bomba (~2*10^17J) test had any effect on the climate.  It mostly depends on how much dust is kicked up to reflect sunlight outside the atmosphere.﻿﻿

Main problem with an major asteroid impact is pretty much like Krakatoa, it will kick up so much dust its like an nuclear winter or worse the KT event who was caused by an asteroid.
Yes you could airobrake one, however its some chance it will break up in the atmosphere, this increase air resistance and increase the chance of more break up, this is how asteroids air burst.
its also how the previous 4 Kerbal civilizations failed.

The paperwork for doing it will probably out mass the asteroid, doing it with an killometer sized cargo ship would be way easier.

Last someone who arobrake so much stuff in their atmosphere it affect climate is pretty close to an Kardashev 1 civilization, they are less concerned with global warming as the US or EU is about famine. Very easy to block sunlight if you tend to handle gigaton of stuff in orbit.

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These are what I mean by scientific proof

If someone actually have control over an asteroid and can aerobrake it/use it as a nuke, it will cause a global power imbalance. Aka all out war.

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We would not forget about the specific thin volcanic ash which is continuously rising up with hot air flows.
The thinner is a powder, the wider can be the cloud, as lightweight particles can float and be spread by winds.
So, not sure if volcanic and explosion clouds are really the same.

4 hours ago, Xd the great said:

If someone actually have control over an asteroid and can aerobrake it/use it as a nuke, it will cause a global power imbalance. Aka all out war.

If someone has so much energy at once, he doesn't need an asteroid.
If vice versa he needs decades to deorbit it, the asteroid can be redirected to his own roof.

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1 hour ago, kerbiloid said:

We would not forget about the specific thin volcanic ash which is continuously rising up with hot air flows.
The thinner is a powder, the wider can be the cloud, as lightweight particles can float and be spread by winds.
So, not sure if volcanic and explosion clouds are really the same.

If someone has so much energy at once, he doesn't need an asteroid.
If vice versa he needs decades to deorbit it, the asteroid can be redirected to his own roof.

Explosion dust depends on the environment.

True, but the 20m asteroid in russia in 2013(probably this year, i forgot) caused massive destruction. It is the velocity, not the mass, that does the most damage.

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16 minutes ago, Xd the great said:

It is the velocity, not the mass, that does the most damage.

It is released energy, velocity should be just greater than several km/s (supersonic in solid bodies, to consider any rock as a cloud of particles)

Edited by kerbiloid

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Just now, kerbiloid said:

It is released energy, velocity should be just greater than several km/s (supersonic in solid bodies)

The one in russia was like 19km per s.

When it slows down, the speed decreases to several km/s, so the change is like 15km/s. Both the change in PE and KE means that velocity is the main component and contributes to the crazy explosions. KE=1/2mv squared.

So its like 225000000 joule released per kg. In a few minutes.

Dont forget i just used the ke. Including PE, its like another 1000 joule per kg.

So there you go, the released eneegy is absurdly high, cause the change in velocity is crazy.

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11 minutes ago, Xd the great said:

S﻿o there you go, the released eneegy is absurdly high, cause the change in velocity is crazy.

Sonic speed in solid bodies is ~5 km/s.
Meteorite typical velocity is 20..70 km/s.
So, that 19 km/s is at the very bottom of meteorite speed range. And right above the supersonic (in solids) limit.

A nuke releases a lot of energy in a limited volume, with zero initial speed.
As the energy can't release quickly, it is dissipating for seconds, while the heated air stays very hot.
Asteroid at 10 km/s or 70 km/s would release its energy also in less than a second, and its dissipation time would depend only on released energy, not on velocity.
Because in both cases fireball is not a nuke/asteroid material, it's a sphere of heated air got opaque due to ionization.

Edited by kerbiloid

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1 hour ago, kerbiloid said:

Sonic speed in solid bodies is ~5 km/s.
Meteorite typical velocity is 20..70 km/s.
So, that 19 km/s is at the very bottom of meteorite speed range. And right above the supersonic (in solids) limit.

A nuke releases a lot of energy in a limited volume, with zero initial speed.
As the energy can't release quickly, it is dissipating for seconds, while the heated air stays very hot.
Asteroid at 10 km/s or 70 km/s would release its energy also in less than a second, and its dissipation time would depend only on released energy, not on velocity.
Because in both cases fireball is not a nuke/asteroid material, it's a sphere of heated air got opaque due to ionization.

What causes the released energy? SPEED.

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40 minutes ago, Xd the great said:

What causes the released energy? SPEED.

Nothing can cause energy. It just is. The energy can be just redistributed, like also impulse.

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well most of that energy comes from its speed, not its mass.

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17 minutes ago, Xd the great said:

well most of that energy comes from its speed, not its mass.

Energy comes from energies and impulses which have thrown the asteroid to its orbit, and from the energy of chemical bounds between the fuel atoms.
Velocity is just how this energy from time to time manifests.

Edited by kerbiloid

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30 minutes ago, kerbiloid said:

Energy comes from energies and impulses which have thrown the asteroid to its orbit, and from the energy of chemical bounds between the fuel atoms.
Velocity is just how this energy from time to time manifests.

Ok lets start this.

A bunch of stuff were orbiting their CoM. Some of the stuff collapse and formed the Sun. The rest of the stuff formed planets and asteroids and comets.

Thats how asteroids velocity comes from.

Anyway, the released energy is transformed from the velocity and the gravity potential energy. What causes these energy to be stored inside I am not sure (something about our solar system is a leftover from other stars... Conservation of angular momentum?)

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40 minutes ago, Xd the great said:

A bunch of stuff were orbiting their CoM. Some of the stuff collapse and formed the Sun. The rest of the stuff formed planets and asteroids and comets.

Original total energy has been stored partially in form of mechanical energy (orbital speed and radius), partially in form of chemical compounds appeared when the planets were forming.

You release some energy stored in fuel chemical bounds, and take some amont of total mechanical energy of the asteroid, putting it into an orbit with lower mechanical energy.
It follows down, it's total mechanical energy redistributes between the raising velocity and lowering radius.
Energy and angular momentum conservation laws define that.
(In fact, the latter is a particular case of more common impulse and coordinates combination, but for calculations you don''t need to get so deep).

When the asteroid hits the Earth, the total mechanical energy gets released, and velocity just defines how fast this will be happening, how much energy will harmlessly dissipate, and how much will release at once at the very end. For asteroid-scale size and velocities this almost doesn't play role, because anyway almost all energy will be released very quickly.

Edited by kerbiloid

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1 hour ago, kerbiloid said:

Original total energy has been stored partially in form of mechanical energy (orbital speed and radius), partially in form of chemical compounds appeared when the planets were forming.

You release some energy stored in fuel chemical bounds, and take some amont of total mechanical energy of the asteroid, putting it into an orbit with lower mechanical energy.
It follows down, it's total mechanical energy redistributes between the raising velocity and lowering radius.
Energy and angular momentum conservation laws define that.
(In fact, the latter is a particular case of more common impulse and coordinates combination, but for calculations you don''t need to get so deep).

When the asteroid hits the Earth, the total mechanical energy gets released, and velocity just defines how fast this will be happening, how much energy will harmlessly dissipate, and how much will release at once at the very end. For asteroid-scale size and velocities this almost doesn't play role, because anyway almost all energy will be released very quickly.

How did we get to this lol.
Anyway, most of that energy comes from the speed.

A wrecking ball smashing into the ground does much less damage than that asteroid, even with same weight.

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36 minutes ago, Xd the great said:

Anyway, most of that energy comes from the speed.

You can drop a 10 t asteroid at 40 km/s, or a 40 t asteroid at 20 km/s, and results will be more or less the same.

P.S.
If originally type "les" (it will recognize LES and probably adds a tip), and then edit and add "s", the "less" is still highlighted.
(Probably, a tag is inserted and the tip stays there).

Edited by kerbiloid

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1 minute ago, kerbiloid said:

You can drop a 10 t asteroid at 40 km/s, or a 40 t asteroid at 20 km/s, and results will be more or less the same.

You are comparing asteroids with asteroids.

I am comparing asteroid speeds with daily life speeds.

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On 6/22/2018 at 4:08 PM, zolotiyeruki said:

This is one of those "please tell me what I'm missing, and how I'm horribly wrong and/or stupid for even coming up with this" questions

Could you take a NERVA plus some mining equipment, and use an asteroid's mass for reaction mass?  NERVAs are usually expected to run off hydrogen for efficiency, but you'd need to heft a whole lot of hydrogen to redirect a very large asteroid.  What if instead, you fed the nuclear reactor ground-up asteroid as a propellant?  Off the top of my head, I can think of a few issues, like "how to feed a solid into an engine", and making sure you don't melt the engine itself when vaporizing the asteroid dust.  But those seem like solvable issues.

Or, as an alternative, could you use some other sort of mass driver (catapult of some sort?) to hurl chunks of the asteroid away, gradually changing its path with each launch?

How to feed a solid into a nuclear reactor? Try feeding coal into a ramjet. Basically the same only hotter than hell. On another note, the "mass driver" is basically like saying you can make a rocket go faster solely from the stage ejections, only with much weaker force. Plus, you would need PERFECTLY aligned drives in order to negate any chance of thrust misalignment, which would result in a spinning rock.

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1 hour ago, Lego_Prodigy said:

Plus, you would need PERFECTLY aligned drives in order to negate any chance of thrust misalignment, which would result in a spinning rock.

That’s the easy part, simply gimbal  the drive “barrel” or have multiple barrels splayed out around a central one. After several shots from each barrel to calibrate the system, the computer should be able to help keep the thrust more or less through the CoM (which will tend to move anyway as the roid is mined) and negate any spin that starts to develop.

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