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# Divide and Collide

Make one big asteroid into lots of little ones with its own rotation.
 (+1) [vote for, against]

(Inspired by "Cutting asteroid in sections to save earth" by [SolarDon])

This idea is intended to reduce a large, solid iron asteroid on a collision course with Earth into many small chunks that will burn up in the atmosphere instead of hitting the ground. It needs a year or two to work, though.

An asteroid is going to be rotating in almost all cases. (I think I've read at least three different references to that (if something comes into view and it isn't rotating, it is most likely a spacecraft).)

A ship pulls up next to the asteroid, and fires a grappling hook/magnet onto the equator. The rotation carries the grapple around, until the grapple's cable is wrapped around the equator a few times. A team of intrepid robots equipped with mighty lasers (and magnetic treads) rides the end of the cable down to the asteroid. The team secures the end of the cable, girdling the equator.

The robots then use the lasers to slice the asteroid in half from pole to pole--into east and west hemis, not north and south--and the cable keeps it from splitting. (Solar power or nuclear power, it's going to take a while.)

The robots then cut the cable, letting the two halves of the asteroid separate at the right time, which causes them to go out from the trajectory, no explosives needed, just the centrifugal force of the rotation. (In some cases, the two halves could separate far enough to go on each side of the Earth, as in [SolarDon]'s idea.)

In this idea, half the robots go with each half of the asteroid. They use their lasers to blast away little bits of their respective asteroid halves, steering and accelerating them. And, of course, cutting grooves to weaken the asteroid and prepare it to break into chunks.

The two halves will theoretically come back together again after one orbit of the sun in their now-independent orbits. (Based on my understanding of orbital dynamics.) The speed of the collision would be the speed with which the two halves went away from each other, but the brave little robots have had a year to work. Their goal is to have the two halves collide as quickly and as accurately as possible, and in as fragile a state as possible.

The collision would reduce the asteroid into many small chunks, which would supposedly not reach the surface of the Earth.

The robots would bail before the collision, re-enter the Earth's atmosphere in a blaze of glory, and parachute down to their ticker-tape parade and beeping groupies.

(This goes halfbaked when you consider that a whole lot of small meteoroids will now be headed into the artificial satellites in orbit around Earth, but that's better than one big one hitting the planet. The meteoroid swarm could be in a slightly different orbit than originally, of course. Practically, the asteroid could be moved by the robots almost as well if it stayed whole. I just wanted to do something with my realization that the rotation would carry the two halves away, but they would come back together again.)

 — baconbrain, Feb 29 2012

Cutting asteroid in sections to save earth Cutting_20asteroid_...20to_20save_20earth
Cutting an asteroid with a wire saw. [baconbrain, Feb 29 2012]

NEO spin-up NEO_20spin-up
Due to popular(?) demand [Ling, Mar 02 2012]

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Shoemaker-Levy 9
 — lurch, Feb 29 2012

 Those are some mighty robots indeed. Where do they get the power to run these high-powered lasers nearly continuously for a year or more? Are they large enough to each contain a small nuclear reactor?

Actually, that gives me an idea...
 — Alterother, Feb 29 2012

 Um, they bring down a couple of nuclear reactors to the asteroid, and run off cables connected to them. The cables would centrifuge up, not drag along the surface.

The reactor shielding would serve as the heat shield for re-entry. Maybe. (Or at least for aerobraking into Earth orbit.)
 — baconbrain, Feb 29 2012

//Shoemaker-Levy 9// , Jupiter nil.
 — MaxwellBuchanan, Feb 29 2012

If the asteroid is made of iron, you could simply construct a very large electromagnet in Basingstoke to render the impact beneficial.
 — MaxwellBuchanan, Feb 29 2012

Multi-legged robots would probably fare better than tracked robots. Asteroid topography can be pretty rugged. That might cause problems with the power cables getting tangled in rock formations, too. Better to have them fully autonomous, IMO.
 — Alterother, Feb 29 2012

//An asteroid is going to be rotating in almost all cases.// Well, all asteroids are rotating, since zero rotational velocity has zero probability; the question is what proportion are rotating fast enough.
 — spidermother, Feb 29 2012

If you have robots that can do all this, why waste the iron? Build a fleet of self-replicating Von Neuman asteroid miners.
 — mouseposture, Feb 29 2012

Do you have to be that close to slice and dice with lasers? Why not have an outpost with a well-aimed laser beam?
 — RayfordSteele, Feb 29 2012

 [RayfordSteele], I want to slice a rotating asteroid along a meridian, and can't really see doing that from a distance. Yeah, slicing into the equator would be possible. Maybe if we parked a ship off one of the poles and stuck in a rotating laser mount.

 Okay, I think we just worked out another way to laser an asteroid:

 Park a long ship (or two with precise relative positioning) even with the equator, parallel to the asteroid axis. Scan and map/model the asteroid. Fire two powerful lasers so they converge at their cutting depth below the surface of a bit of the asteroid. The rotation will carry the surface under the lasers, and the converging beams will cut out a shape much like a cucumber-pickle spear (or potato wedge (or chip (if you are English)). (Let's call it a chip, as that's what it would be called in a metal cutter.)

 The chip will be blasted loose and centrifuge outward. The asteroid will move a bit in the other direction. The chip will burn up if it hits atmo.

No robots, no cables, no contact. Just a slight chance of a late-breaking chip smacking into the ship, if we use the long one (better use the two ships, then). I may post that as an idea, after some research...
 — baconbrain, Feb 29 2012

Uneven topography and variations in composition and density will result in wildly fluctuating penetration, unless you have a very clever computer that will analyze and correct for such things. Very, very clever.
 — Alterother, Feb 29 2012

You don't want to arm a computer that clever with a powerful laser.
 — mouseposture, Mar 01 2012

Or arm a stupid one either.
 — AusCan531, Mar 01 2012

Why bother cutting? Spin the asteroid up until it explodes...
 — Ling, Mar 01 2012

 //Spin the asteroid up until it explodes...//

That's an interesting idea. The advantage of that approach is that the angular momentum of the asteroid acts as an accumulator for whatever energy you can supply, until it's sufficient to split the asteroid. This means that you don't need to supply all the energy in one big bang. Quite an elegant idea.
 — MaxwellBuchanan, Mar 01 2012

Hear hear. Post that one, [Ling], so we can vote for it.
 — mouseposture, Mar 01 2012

That is good. It would take time though.
 — 2 fries shy of a happy meal, Mar 01 2012

 // Spin the asteroid up until it explodes... //

Post!
 — baconbrain, Mar 02 2012

OK, OK....
 — Ling, Mar 02 2012

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