What are the real chances of an asteroid hitting Earth?

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Jun 1, 2020
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Helio, am I not correct in saying that the tractor system requires a large mass (and hence great fuel consumption) ...
[I missed this one. :)]

Yes, that has to be the big question that must be addressed. I don't know the answer, though the math wouldn't be all that hard to add to the analysis. It must not be too bad because I think it is still considered a valid possibility. Perhaps fuel supply ships would be needed for the extended tractoring efforts. These resupply vessels would be helpful since we would already know a lot more about the object from the first arriving vessel (tractor).

Another advantage with this method is that the tractor would allow for even greater trajectory projections, critical to any game plan.
 
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Catastrophe

Approaching asteroid? Is this THE one?
Feb 18, 2020
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[I missed this one. :)]

Yes, that has to be the big question that must be addressed. I don't know the answer, though the math wouldn't be all that hard to add to the analysis. It must not be too bad because I think it is still considered a valid possibility. Perhaps fuel supply ships would be needed for the extended tractoring efforts. These resupply vessels would be helpful since we would already know a lot more about the object from the first arriving vessel (tractor).

Another advantage with this method is that the tractor would allow for even greater trajectory projections, critical to any game plan.
The supply ships could latch on to the main tractor to add to its mass.
 
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Catastrophe

Approaching asteroid? Is this THE one?
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This is the first book I picked up; edited by an Astronomer Royal - Martin Rees, but I have seen exactly the same diagrams and explanations in many books.

Quote
The effect of a collision between asteroids depends on the sizes of the bodies involved. If a very small body hits a larger one it will produce a crater on the surface. The crater will be about ten times the size of the incoming body. As asteroids are much smaller than planets, the material blasted out of the crater will escape and move off into an independent orbit around the Sun. This orbit will. however, be very similar to that of the impacted asteroid, and there is a good chance that the ejected material will hit the cratered asteroid again.
A bigger impactor can break up the asteroid that it hits. But so much energy is used to do this that the resulting fragments cannot escape from the gravitational field, and they will all fall back to form an irregular ball of rubble. Subsequent minor impacts will break up the surface, covering the asteroid in a dusty, rocky layer. A casual observer will not realize that the underlying asteroid is actually in pieces.
A large impactor will not only shatter the asteroid, but the fragments will also escape. These will form a family of asteroids that eventually spreads out around the orbit of the original body.
Quote

Source: Universe: The Definitive Visual Guide, Gen. Editor Martin Rees.DK 2012.

Of course, this is in the context of your last resort nuke.

Cat :)

P.S. I still doubt the feasibility of getting a large enough mass tractor to the target in time to have any effect against any asteroid large enough to do serious damage.
 
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Catastrophe

Approaching asteroid? Is this THE one?
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Given an asteroid that was not too big (definitely not safe, but not so large that we could not divert it) I would 100% support diverting by change of momentum. Tractor efforts - I would resign myself to certain death.

Cat :)

P.S. And an addition to the asteroid collision (with another asteroid) story. I wish I had found this first, as it encapsulates the situation very succinctly:

Fig. 10. Stages in the fragmentation history of a moderately large asteroid. Originally composed of strong rock (1), the asteroid is cratered (1,2), and then, catastrophically fragmented by a more energetic impact (3). Most of the ejects fail to reach escape velocity, and the body is reassembled (4) Later impacts (4,5) further fragment the body, converting it into a gravitationally bound pile of boulders. Finally, (5,6), a sufficiently gigantic collision occurs to completely disrupt and destroy the asteroid. My emphasis.

The New Solar System ed. Beatty et ali., Book Club Associates.

Last one. There are many more:
Asteroids by Michael J Shepard, Cambridge University Press, 2015.
Discussion of both these and other methods.
"The technology to ram an asteroid has been demonstrated, with the Deep Impact mission, which slammed a 370 kg missile into Comet Temple I in July 2005.
The difficulty is (I am being very fair :) ) is that if the asteroid is a pile of rubble, it does not work. Nature of the asteroid, critically, must be known.

Of the tractor method he writes: "The main technological hurdle with this method is launching something as heavy as possible with enough fuel (or the ability to be refuelled) to maintain the gravitational pull for decades."
 
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Jun 1, 2020
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Given an asteroid that was not too big (definitely not safe, but not so large that we could not divert it) I would 100% support diverting by change of momentum. Tractor efforts - I would resign myself to certain death.
If tractoring takes place, can I have your K&E slide rule in advance of this "certainty", or do you have another brand? ;)

Fig. 10. Stages in the fragmentation history of a moderately large asteroid. Originally composed of strong rock (1), the asteroid is cratered (1,2), and then, catastrophically fragmented by a more energetic impact (3). Most of the ejects fail to reach escape velocity, and the body is reassembled (4) Later impacts (4,5) further fragment the body, converting it into a gravitationally bound pile of boulders. Finally, (5,6), a sufficiently gigantic collision occurs to completely disrupt and destroy the asteroid. My emphasis.
The escape velocity is determined by the mass of the asteroid, so for small asteroids, escape velocity is likely reached, IMO.

The other element not mentioned is the time frame for reassembly, which can be quicker than one might think but for deflection we are talking months not years. Recall that at least the mass of Moon did not reassemble onto Earth but formed the Moon. Hopefully it doesn't reassemble. ;)

Of the tractor method he writes: "The main technological hurdle with this method is launching something as heavy as possible with enough fuel (or the ability to be refuelled) to maintain the gravitational pull for decades."
Yes, but my math (subject to change w/o notice ;)) demonstrates that diversion is possible given enough time (implying distance as well).

But, yes, the heavier the tractor the better the deflection. I found a paper that uses the clever idea of using the tractor to grab a sizeable mass from the asteroid to augment its mass. This is called EJT (Enhanced Gravity Tractor) technique. See this paper.

The tractor becomes a type of wheel or crawler space loader, I suppose. [A wheel loader is actually a tractor with a bucket digging/lifting/dumping system.]

But I would expect any such trips to include all the tools to affect orbital change. Lasers, for instance, hold promise since they can trigger out-gassing to cause the asteroid itself to provide thrust. An array (ie drones) dispersed by the tractor should be easy to properly control the lasers given that the control is there and not remote from Earth.
 
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