Planetary Defense Experiment

[Bomb#20]

I don't understand why Armagedon gets bad rap for blowing up asteroid.

Innumeracy. You know what the gravitational binding energy is of an asteroid the size of the one in that movie? Blowing it up with a big nuke is blowing up Mt. Everest with a firecracker.

 

[steve_bank]

What if they deflect one object that hits another object that then hits the Earth?

If you want to traslate motion and change the vector you have to hit at the center of mass, otherwise it spins. Sounds low probaility of sucess.

I'd think it would have to be a set of thrusters coordinated to move the object in a predictable manner.

The experiment sounds like an exercise in Newtonian mechanics.

The chance of deflecting one object into another to cause it to hit is minuscule. There are two problems with thrusters: First, you have to match orbits with the target first--unless we have a long lead time that very well might be impossible. Second, they are an inefficient use of your launch mass. You will get more deflection per pound launched by ramming.

Anyway, if there is a seriously threatening object out there the real answer is neither of these. Instead, nuclear-tipped interceptors, fused for standoff detonation. Keep the warheads small enough you don't risk disrupting the target if it turns out to be a pile of gravel. The essence of an Orion drive.

How is momentum of the object changed by a standoff nuke? Heat could vaporize some of the object causing a force. but it would be unpredictable.

Drop a hook from a rocket and pull it.

If there is an actual threat, I think in the end somebody has to go there to make it happen.

 

[Loren Pechtel]

I don't understand why Armagedon gets bad rap for blowing up asteroid. They argue that few smaller asteroids hitting the Earth are worse than one big one. I don't think it's true.
Rocks below certain size becomes harmless because they don't reach even upper atmosphere. So if is too late, than blowing it up is a good option. Of course even that had to be done relatively far from Earth - months before impact.

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option. For close-in defense against a city-killer I think putting a seeker on an ICBM could work if you have an accurate enough fusing system. Think of what happened to Chelyabinsk--that boom was half a megaton but killed nobody and all injuries were from people who didn't realize what was happening and were looking at it and got hit with flying glass when the shockwave arrived. Duck and cover would have provided close to 100% protection.

However, against big rocks that's absolutely not what you want to do. Even a Tsar Bomba won't blow the Armageddon rock into small enough bits that they will burn. So long as it's coming down in big pieces the important factor is that blast damage goes at the 2/3 power of blast energy. (Blast energy is spread in all directions and thus drops off at the third power of distance. However, the area hit by the blast goes at the square of the blast radius.) If you have an incoming rock and blast it into 8 equal pieces each piece does 1/4 the damage of the original--but you have 8 of them, for twice the total damage. Blow it into 64 equal pieces and you have 4 times the total damage. Less overkill and less energy expended on digging craters.

Even worse is that above 20 megatons additional blast energy is very inefficient at doing damage. Note how other than the 100Mt totally impractical chest-thumping Tsar Bomba nobody has built a bomb bigger than that.

 

[Loren Pechtel]

What if they deflect one object that hits another object that then hits the Earth?

If you want to traslate motion and change the vector you have to hit at the center of mass, otherwise it spins. Sounds low probaility of sucess.

I'd think it would have to be a set of thrusters coordinated to move the object in a predictable manner.

The experiment sounds like an exercise in Newtonian mechanics.

The chance of deflecting one object into another to cause it to hit is minuscule. There are two problems with thrusters: First, you have to match orbits with the target first--unless we have a long lead time that very well might be impossible. Second, they are an inefficient use of your launch mass. You will get more deflection per pound launched by ramming.

Anyway, if there is a seriously threatening object out there the real answer is neither of these. Instead, nuclear-tipped interceptors, fused for standoff detonation. Keep the warheads small enough you don't risk disrupting the target if it turns out to be a pile of gravel. The essence of an Orion drive.

How is momentum of the object changed by a standoff nuke? Heat could vaporize some of the object causing a force. but it would be unpredictable.

Drop a hook from a rocket and pull it.

If there is an actual threat, I think in the end somebody has to go there to make it happen.

Heat blasts material off the surface. For every reaction there is an equal and opposite reaction. You can do it with chemical explosives (very inefficient, the flight test couldn't go very far, it's been tested with nuclear blasts, but not sustained--they were piggybacking their test on bombs that were going to go off anyway. For an improvised system I've seen an estimate 10% of the energy of the bomb can go into propulsion and it's possible to do considerably better with purpose-built bombs.

 

[barbos]

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option.

That's what I said.

 

[steve_bank]

Humans will still be debating as the next killer rock enters the atmosphere.

Why deflect it? Seems like you could accelerate it with the same effect., changing the tie of intersecting Earth's orbit.

 

[barbos]

Calculated amount of energy required to disintegrate 10km diameter asteroid with 2000/m^3 density - 2 MT of TNT. This is assuming 100% efficiency.

If asteroid has a lot of ice in it then efficiency could be quite high, you just need to put 50MT nuke inside of it, which could be a problem.

and energy requirements are behave as ~R^5. So disintegrating 1km asteroid would require 20 tons of TNT.

 

[barbos]

Why deflect it? Seems like you could accelerate it with the same effect., changing the tie of intersecting Earth's orbit.

That's still called deflection. Accelerating would change orbit too, not just time.

 

[Loren Pechtel]

Humans will still be debating as the next killer rock enters the atmosphere.

Why deflect it? Seems like you could accelerate it with the same effect., changing the tie of intersecting Earth's orbit.

Accelerating it is a form of deflection, although it might be harder to do because it's ass is probably pointed away from us.

 

[barbos]

I don't understand why Armagedon gets bad rap for blowing up asteroid.

Innumeracy. You know what the gravitational binding energy is of an asteroid the size of the one in that movie? Blowing it up with a big nuke is blowing up Mt. Everest with a firecracker.

Well, such asteroids are astronomically unlikely to ever become dangerous.
But for D=10km I calculated it to be only 2MT of TNT.
and 1km is only 20 tons of TNT. Basically even tiny nuke will blow 1km asteroid with ease.
the only problem is putting it inside of it.

 

[Jimmy Higgins]

I don't understand why Armagedon gets bad rap for blowing up asteroid.

Innumeracy. You know what the gravitational binding energy is of an asteroid the size of the one in that movie? Blowing it up with a big nuke is blowing up Mt. Everest with a firecracker.

Well, such asteroids are astronomically unlikely to ever become dangerous.
But for D=10km I calculated it to be only 2MT of TNT.
and 1km is only 20 tons of TNT. Basically even tiny nuke will blow 1km asteroid with ease.
the only problem is putting it inside of it.

The "only problem". Kind of like the "only problem" with fusion for domestic energy production is containing the reaction.

What about trojans? Is there any feasible way to scout them for potential candidates to project towards incoming asteroids? Biggest trouble with asteroids is quite simply inertia. So we need rocks with similar or greater size to handle them (likely greater to deal with the most likely lower velocity of a bumper). The trojans are already in motion (and there are a lot of them), so we aren't starting from stand still and they are naturally deployed in space, so no problems with launching massive masses off the face of the planet.

Slap ion engines to them and create a matrix of ready to go bump the incoming asteroid. A bit science-fictiony, but there are only a few things that address the inertia issue, and one of them is well... more inertia.

 

[steve_bank]

The fact that a rich guy can put a lot of money into developing a space station for profit and take a joy ride into space, and NASA has a meager budget for planetray defense appropriated by congress says it all.

Climate change is elevated because there are immediate observable consequences. Even at that there is a lot of restance in spendig money.

I'd say we are failing the Darwin Test. After the next mass extinction event maybe evolution will do something with lizards.

 

[Loren Pechtel]

I don't understand why Armagedon gets bad rap for blowing up asteroid.

Innumeracy. You know what the gravitational binding energy is of an asteroid the size of the one in that movie? Blowing it up with a big nuke is blowing up Mt. Everest with a firecracker.

Well, such asteroids are astronomically unlikely to ever become dangerous.
But for D=10km I calculated it to be only 2MT of TNT.
and 1km is only 20 tons of TNT. Basically even tiny nuke will blow 1km asteroid with ease.
the only problem is putting it inside of it.

There's also an efficiency problem. I'll assume your binding energy numbers are accurate, but you have a big problem with converting your bomb energy to dispersing it. You're liable to end up expending a lot of energy on a weak spot, leaving behind very large chunks that don't get all that much velocity.

 

[steve_bank]

In the asteroid scifi movies a hole is drilled for a nuke. The explosion and expanding gas from vaporized material has to work against something.

In a car a small amount of gas exploding in a cylinder moves the car. In the open air it doesn't do much.

Perhaps multiple nukes inside an asteroid could break it up This all should be able to be simulated accurately.

 

[Jimmy Higgins]

All we’ll need is a sample of the asteroid.

 

[Shadowy Man]

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option.

That's what I said.

You’d still be depositing a lot of energy into the atmosphere. Whether it comes down in one chunk or in pieces it’s still raining devastation if it’s big enough and the pieces enter together.

 

[barbos]

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option.

That's what I said.

You’d still be depositing a lot of energy into the atmosphere. Whether it comes down in one chunk or in pieces it’s still raining devastation if it’s big enough and the pieces enter together.

If they are 200km apart they would burn in the atmosphere separately.

 

[barbos]

I don't understand why Armagedon gets bad rap for blowing up asteroid.

Innumeracy. You know what the gravitational binding energy is of an asteroid the size of the one in that movie? Blowing it up with a big nuke is blowing up Mt. Everest with a firecracker.

Well, such asteroids are astronomically unlikely to ever become dangerous.
But for D=10km I calculated it to be only 2MT of TNT.
and 1km is only 20 tons of TNT. Basically even tiny nuke will blow 1km asteroid with ease.
the only problem is putting it inside of it.

There's also an efficiency problem. I'll assume your binding energy numbers are accurate, but you have a big problem with converting your bomb energy to dispersing it. You're liable to end up expending a lot of energy on a weak spot, leaving behind very large chunks that don't get all that much velocity.

Yes, I mentioned efficiency. That's why I suggest biggest nuke you can get there.

 

[Shadowy Man]

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option.

That's what I said.

You’d still be depositing a lot of energy into the atmosphere. Whether it comes down in one chunk or in pieces it’s still raining devastation if it’s big enough and the pieces enter together.

If they are 200km apart they would burn in the atmosphere separately.

If they are coming in at escape velocity how long do you think the time difference is between impacts only 200km apart?

 

[barbos]

If they are coming in at escape velocity how long do you think the time difference is between impacts only 200km apart?

5 km/hour, it would take 40 hours, 2 days.

LOL, you meant they go one behind the other. No that's not how blowing up an asteroid works. They are blown up in all directions. And it does not take much time for remnants to separate enough. In fact, they would have enough time to separate so far that most of the rocks will miss the earth.