New Cosmic Defense Idea

[zandore]

In a Space Age version of fighting fire with fire, French scientists have suggested using one asteroid to destroy another rather than letting Earth get pummeled.

The offbeat plan is intentionally incomplete and would allow the planet to be showered by fragments. But it might be better than a civilization-ending whack.

No asteroids are presently known to be on collision courses with Earth. But existing holes in the ground suggest that inevitably one will eventually be found. There is no firm plan for how to deflect or destroy an incoming asteroid, though scientists have pondered firing rockets at them, moving them gently with solar sails, or nudging them with nuclear explosions.

Lock and load

The new idea is to capture a relatively small asteroid—perhaps 100 feet (30 meters) wide—by sending a robot to it.

The robot would heave material from the asteroid's surface into space, and the reaction force would gradually direct the asteroid to a Lagrange point, one of a handful of nodes along Earth's orbit where the gravity of Earth and the Sun balance out. Scientists know that object can be kept stable at a Lagrange point with little or no energy.

The captured rocky weapon would be held there, traveling around the Sun ahead of or behind the Earth, held until needed.

Then, if a large asteroid threatens to hit us, the small one is moved into its path, using the same heaving technique. The rocks collide, and the big one is broken into somewhat less harmless bits.

The collision disperses the fragments of the incoming asteroid, so that not all of them hit the planet.

But …

Depending on the relative masses of the two objects, between 10 and 20 percent of the incoming asteroid mass would still hit, "but the fragments would be dispersed all over the Earth and, hopefully, none would be large enough to reach the ground with a large remaining destructive power," said Didier Massonnet of the CNES research center in France.

Massonnet and colleague Benoit Meyssignac say the collision should be engineered to occur at least 620,000 miles (1 million kilometers) from Earth and would take about eight months to execute from the Lagrange point.

The plan is detailed in the July-September, 2006 issue of the journal Acta Astronautica. The researchers first floated it at a scientific conference last fall.

One small asteroid that could fit the bill already been identified; it is called 2000 SG344, and Massonnet suspects there are many others that would work.

Fuel for thought

The researchers admit their entire scheme is not quite ready for prime time.

"We are more confident in our capability to capture the asteroid than in our capability to redirect it to an incoming body," Massonnet told SPACE.com. "The scenario of this last stage requires further studies on the very unstable trajectories which will be required."

Meanwhile, there is another aspect to the plan that could make it appealing.

Material mined from a small, nearby asteroid could provide liquid oxygen for other space missions more efficiently than mining it from the Moon, which other researchers have proposed. Liquid oxygen could be used as fuel at a cosmic gas station that would allow spacecraft to be launched from Earth with much smaller tanks and therefore more cheaply.

Space.com

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Sort of reminds me of the game "Asteroids"

[Waspie_Dwarf]

Depending on the relative masses of the two objects, between 10 and 20 percent of the incoming asteroid mass would still hit, "but the fragments would be dispersed all over the Earth and, hopefully, none would be large enough to reach the ground with a large remaining destructive power," said Didier Massonnet of the CNES research center in France.

I'm not sure I like the use of the word "hopefully". This seems a bit hit and miss, literally. If the asteroid fragments into large enough pieces then multiple large impacts around the world could potentially be more damaging than a single huge impact.

It seems to me that if we can develop the technology to use robots to move asteroids into different orbits the most sensible thing to do would be to place all the earth crossing asteroids into safe orbits.

This could have a use as a sort of emergency back up plan.

[Lilly]

Hmm...so we chuck a rock at a rock? I guess it could help in a pinch. However, I prefer Love and Lu's idea...a gravitational tractor,

Killer asteroid heading your way? Who ya gonna call? Call Love and Lu's Tractor Service!

[Bone_Collector]

Ridiculous idea. Why the pain of sending a robot, capturing an asteroid and holding it eternally till we *hopefully* hurl it at the incoming asteroid with precision, when we can point a rocket to the asteroid directly? And god knows if the capptured asteroid is big enough or capable enough to blast an incoming asteroid to smithereens or not.

If we are good enoiugh to capture and hurl an asteroid with a robot in space, then we're probably god enough to hurl a powerful rocket at it.

[frogfish]

Lots of asteroids are actually "rubble piles", a balls of miuniature asteroids. The shock from the thrown asteroid would just be absorbed and it would keep on moving.

[Waspie_Dwarf]

Lots of asteroids are actually "rubble piles", a balls of miuniature asteroids. The shock from the thrown asteroid would just be absorbed and it would keep on moving.

Actually these rubble piles could possibly be disrupted by the method proposed. However you would have to hit it hard enough that enough energy was imparted on the rubble pile so that the individual components would be thrown off with sufficient velocity that gravity could not draw them back together. Throwing a big rock at a rubble pile could be a better option than throwing a nuke at it. However if you don't hit it hard enough frogfish would be exactly right, nothing would happen. It is all too hit and miss for my liking. I still think that if we can develop the technology to move asteroids then move the ones that present a threat.

There is another, useful aspect to this technology. The asteroids are moved by drilling into them and expelling waste rock like a rocket exist. Such technology could usefully extract useful ores whilst doing this and hollow out a small asteroid. Move the asteroid to earth orbit and when it arrives it is hollowed out as a ready made space station with all the raw materials already mined. This idea is not mine (I wish I could claim it but I'm not that bright) and has been around for a while. I'm not sure who first suggested it.