Asteroid Fragmenting and Re-entry?

[SilentP]

In a discussion in the TNZ about keeping nuclear weapons in stock for use in asteroid defence, I raised the idea of using railguns (once the tech for them is nailed down) to pulverise asteroids into smaller chunks burn up in atmosphere, when someone stated this wasn't the case, since apparently it would be worse for us. It was almost a week after before I saw the thread, so I decided against necroposting, and decided maybe it was a question better placed to ask here.

Now, I would have been under the impression that if an asteroid is reduced to smaller elements, it would be the case that each section would burn up quicker than a single larger whole, since there's a larger surface area that can suffer friction from the atmosphere, thusly quicker to burn up during re-entry.

Am I wrong here?

 

[Psion]

If you pulverized a rock into the equivalent mass of sand, that sand would still release the same amount of energy upon hitting the Earth's atmosphere as the original rock.

But ...

All that sand might not re-enter at the same time. Some of it might not even hit the planet. And after being hit with nukes or railguns, debris from the original isn't likely to hit with the same original force.

 

[Jadzia]

This is true as far as I understand. Small fragments can burn up, and large fragments will at least burn down to something smaller that is less devastating than they originally were.

However, if these fragments are also of sufficiently deadly size, you'd end up with a cluster bomb, which is (possibly) worse than the original, as the devastation is spread further.

Small asteroid -- May burn up. If not, it will cause a small amount of damage, comparable to a conventional missile.

Medium size asteroid -- Potentially devastating to a city, as much as a medium-large sized nuclear warhead would devastate a city. Best to break it up into smaller fragments, which may in themselves burn up, or if they don't, will be equivalent to a handful of conventional missiles raining down.

Larger asteroid -- Potentially devastating within a few hundred kilometers. But break it up and you have something that will behave like a cluster bomb, which may cause devastation across five times the area.

Huge asteroid -- Everybody dies whatever you do.

 

[All Seeing Eye]

I think it depends on the size of the asteroid you hit. If it breaks apart but each part is still large enough to reach Earths surface then the damage will be wider spread and possibly more damaging.

If there's time to hit the asteroid and then strike the smaller fragments again into even smaller pieces then the Earth would not be devastated.

 

[SilentP]

If you pulverized a rock into the equivalent mass of sand, that sand would still release the same amount of energy upon hitting the Earth's atmosphere as the original rock.

Ah, while there is the kinetic energy, the atmosphere is now in a 'position' to bleed off the kinetic energy far easily by applying friction/drag on to each individual sand particle.

Though now that I think about it, what environmental problems would the Earth suffer if such a large quantity of dust was suddenly scattered over the Earth?

But ...

All that sand might not re-enter at the same time. Some of it might not even hit the planet. And after being hit with nukes or railguns, debris from the original isn't likely to hit with the same original force.

True. Some of the dust could even be scattered by solar winds, if solar wind can do that?

This is true as far as I understand. Small fragments can burn up, and large fragments will at least burn down to something smaller that is less devastating than they originally were.

However, if these fragments are also of sufficiently deadly size, you'd end up with a cluster bomb, which is (possibly) worse than the original, as the devastation is spread further.

Small asteroid -- May burn up. If not, it will cause a small amount of damage, comparable to a conventional missile.

Medium size asteroid -- Potentially devastating to a city, as much as a medium-large sized nuclear warhead would devastate a city. Best to break it up into smaller fragments, which may in themselves burn up, or if they don't, will be equivalent to a handful of conventional missiles raining down.

Larger asteroid -- Potentially devastating within a few hundred kilometers. But break it up and you have something that will behave like a cluster bomb, which may cause devastation across five times the area.

Huge asteroid -- Everybody dies whatever you do.

Gotcha

I think it depends on the size of the asteroid you hit. If it breaks apart but each part is still large enough to reach Earths surface then the damage will be wider spread and possibly more damaging.

Very true, which is why (supposedly) any plan to fragment any dangerous asteroid would require you to keep breaking down the fragments until they're a 'manageable' size for the atmosphere to burn up.

If there's time to hit the asteroid and then strike the smaller fragments again into even smaller pieces then the Earth would not be devastated.

Aye.

 

[Christopher]

It's just generally better not to multiply the number of potentially hazardous bodies out there in space. It's cluttered enough as it is. Instead of being slaves to testosterone and defaulting to "blowy-uppy stuff is good," it's better to go for a subtler approach. If you detect the asteroid soon enough, all you need to do is tweak its course a tiny bit. It takes the Earth just over seven minutes to travel a distance equal to its own diameter. So if you delay the asteroid just enough that it takes seven minutes longer to reach Earth's orbit, the problem's solved. Same if you tweak its orbit by a fraction of a degree while it's still very far away -- the farther it is, the smaller the necessary deflection to get it to miss. And there are lots of ways to make such alterations. Land a rocket thruster on the asteroid. Attach a solar sail to it. Paint it white so that radiation pressure from the Sun affects it more. Park a space probe next to it and let the probe's gravity pull on it for a few months. Plenty of nice, simple, subtle solutions.

 

[SilentP]

Aye, I've heard of these subtler approaches, especially the gravity tug method. One could in theory use a railgun of sorts to deliver the payload faster to the asteroid, reducing the travel time.

I only suggest this method, since it's something you can have ready waiting in orbit, inert, ready to start dealing with any threat as soon as it's detected. Though this idea of preparedness doesn't prevent the same idea of having gravity tug probes ready and waiting in orbit to be sent off for same. Probably be easier to convince the international community of these tugs over a kill sat. Not sure how easily viable the options for solar sail (we're having difficulty with deploying them at the moment), painting it white (requires some extra AI over a simple gravity tug, or ability to act instantly) or strapping a rocket (extr AI for course corrections at the correct time) to it would be.

However, my personality for problem solving is subtle as an antimatter brick through a glass window, so railguns would occur to me first

A point that your ideas on even just slowing down the asteroid, would any projectiles launched, even if not fired fast enough to shatter/break up the asteroid, do much in the way of adding momentum in the opposite direction to slow down an asteroid? Or would the size of planet killer asteroids prohibit the use of this method too?

 

[strongmind]

In a discussion in the TNZ about keeping nuclear weapons in stock for use in asteroid defence, I raised the idea of using railguns (once the tech for them is nailed down) to pulverise asteroids into smaller chunks burn up in atmosphere, when someone stated this wasn't the case, since apparently it would be worse for us. It was almost a week after before I saw the thread, so I decided against necroposting, and decided maybe it was a question better placed to ask here.

Now, I would have been under the impression that if an asteroid is reduced to smaller elements, it would be the case that each section would burn up quicker than a single larger whole, since there's a larger surface area that can suffer friction from the atmosphere, thusly quicker to burn up during re-entry.

Am I wrong here?

You are correct.

Energy would be spread out in both space and time.

Same as blunderbuss.Spreads the energy out over a larger volume and distributes it over time.

>>>>>>>> . <<<<<<<<<< energy concentrated in a point generates hugh shock wave.

>>>>>>> O <<<<<<<<<<<, energy spread over bigger space and also over time...shock waves less intense.

 

[All Seeing Eye]

Is this a bad time to mention my rail line on the moon idea to quickly propel an object into the outer reaches of the solar system?

 

[PurpleBuddha]

I would guess many of you have seen this, but here is a video of Neil DeGrasse Tyson discussing these issues.

http://www.youtube.com/watch?v=1-ReuLZ2quc&feature=related

He tends to be against the blow it up or fragment it approach and favors the gravity tug as a better and perhaps easier solution. I think he has a few good points.

 

[Trekker4747]

Is this a bad time to mention my rail line on the moon idea to quickly propel an object into the outer reaches of the solar system?

There's never a good time to mention ANY of your ideas.

 

[SilentP]

Is this a bad time to mention my rail line on the moon idea to quickly propel an object into the outer reaches of the solar system?

There's never a good time to mention ANY of your ideas.

Strictly speaking though, the idea is relevant, and not as bad as other ones, though I'd say in this case, one based in orbit would be preferable.

 

[All Seeing Eye]

Is this a bad time to mention my rail line on the moon idea to quickly propel an object into the outer reaches of the solar system?

There's never a good time to mention ANY of your ideas.

Strictly speaking though, the idea is relevant, and not as bad as other ones, though I'd say in this case, one based in orbit would be preferable.

Well, not necessarily. If it's on the moon it doesn't need fuel for keeping in orbit and could use Moon based Helium3 power plants to power the EM rail line, there'd also be enough stretch of EM rail line on the Moon to make sure the object being propelled gains more speed before it gets released so it reaches the target asteroid more quickly and also hits it with a large enough force. Once the projectile is released it could have its course continually adjusted using tiny rockets to make sure it heads on target correctly.
There could either be one single rail line that travels the entire circumference of the Moon or many smaller rail lines located in different directions (perhaps a network of rail lines) to allow the release of the projectile in many different directions.

 

[Christopher]

If it's on the moon it doesn't need fuel for keeping in orbit...

For the most part, nothing needs fuel to stay in orbit. Orbit, by definition, is an unpowered freefall trajectory. Satellites in low orbit sometimes need thrusters to counter the drag induced by the tenuous atmosphere at those altitudes, but that's it. Planets don't need fuel to orbit the Sun, moons don't need fuel to orbit planets, so why should anything else? The problem is we've been conditioned by Star Trek and other sci-fi to believe that orbit is something you'll fall out of if your engines shut down.

and could use Moon based Helium3 power plants to power the EM rail line, there'd also be enough stretch of EM rail line on the Moon to make sure the object being propelled gains more speed before it gets released so it reaches the target asteroid more quickly and also hits it with a large enough force.

What you're proposing could be more easily achieved with an orbital tether. Velocity would be imparted by momentum transfer, and the tether would be self-powered as it moved through the Earth's magnetic field.

 

[All Seeing Eye]

If it's on the moon it doesn't need fuel for keeping in orbit...

For the most part, nothing needs fuel to stay in orbit. Orbit, by definition, is an unpowered freefall trajectory. Satellites in low orbit sometimes need thrusters to counter the drag induced by the tenuous atmosphere at those altitudes, but that's it. Planets don't need fuel to orbit the Sun, moons don't need fuel to orbit planets, so why should anything else? The problem is we've been conditioned by Star Trek and other sci-fi to believe that orbit is something you'll fall out of if your engines shut down.

and could use Moon based Helium3 power plants to power the EM rail line, there'd also be enough stretch of EM rail line on the Moon to make sure the object being propelled gains more speed before it gets released so it reaches the target asteroid more quickly and also hits it with a large enough force.

What you're proposing could be more easily achieved with an orbital tether. Velocity would be imparted by momentum transfer, and the tether would be self-powered as it moved through the Earth's magnetic field.

So when I said that we should build an EM rail line in Earth orbit that circles the entire Earth why was I told it would not stay in orbit without the need for rockets to keep it there? I also said that the orbital rail line should move at a different speed to the Earth to allow coils to pass through the Earths magnetic fields and produce power.
If something can stay in orbit without the need for rockets to keep them there then why would the orbital rail line not stay in orbit?

 

[Trekker4747]

Because your stupid orbital rail-line whould be subject to atmospheric drag and would need to be boosted up every so often like out satellites do.

The moon isn't subject to any atmospheric drag so it can stay in orbit forever around the Earth, same for the Earth and the sun.

The shuttle? Satellites? The ISS? All have to occasionaly use thrust to stay in orbit. The astronauts in the shuttle aren't floating in the shuttle due to lack of gravity, they're floating because they're falling back to Earth.

 

[John Picard]

Can't use a railgun in space, since every action has an equal and opposite reaction. Fire that sucker and guess what? The rail gun will be headed the other way.

 

[SilentP]

Can't use a railgun in space, since every action has an equal and opposite reaction. Fire that sucker and guess what? The rail gun will be headed the other way.

That doesn't rule out using one, you'd just need a stabilising system (i.e. rocket thrusters to fire in the opposite direction) to reestablish the position of the satellite the railgun is mounted on, or at least prevent it from sending itself barrelling off it's orbit.

 

[Lindley]

I suppose if you made the railgun fire in opposite directions at the same time it would work. That does make it useless for hitting anything that's not in a direction tangent to its current position over the Earth, though.

 

[Zulu Romeo]

I suppose if you made the railgun fire in opposite directions at the same time it would work. That does make it useless for hitting anything that's not in a direction tangent to its current position over the Earth, though.

Unless of course there's something strategically placed on Earth that you want to destroy too...