Alternatively, an asteroid that was going to barely miss or splash into the ocean could be persuaded to hit the part of the planet which the controlling government wants destroyed.

Aha, you’ve read Stephen Baxter’s novel ‘Titan’ when China destroys the Earth with exactly this idea in mind – except the Chinese leaders miscalculate the impact size – too then?

Oh I dunno – there are some places I can think of that might benefit everybody by being hit by an asteroid and turned into smoking craters!

As the article hints, the major problem with using a tether is that asteroids rotate. There’s no stable point to fix the tether to. Rotation also means that landing a rocket and using it push the asteroid is basically a non-starter too.

I don’t feel like working out the numbers but my guess is that you can’t stop the rotation and then fix a tether because the energy requirements would be ‘astronomical’.

Mike.

I’m think one advantage of the gravity tractor over a tether system for a sail or whatnot is that you don’t need to actually land anything on the asteriod or attach anything to it. So there is no need to worry about the added complexities involved, or the addition of more mechanical parts that might fail.

As for the Gravity Tractor, why bother? Use spider thread or carbon fibres or fine steel wire to moor the sail to the asteroid. The small acceleration shouldn’t be a bother and it would reduce the need to keep the sail nearby or limit it’s size.

tOM

So it seems to me that the nuclear option is clearly the best choice if the threat is imminent and there isn’t much time. Faced with that kind of crisis, I think the political roadblocks will fall by the wayside quite rapidly. And the possibility of a messy aftermath can be dealt with, in the aftermath (whereas if you did not act, there would be no aftermath to worry about because we’d all be dead).

If we have a lot of time, techniques like a gravity tractor have the advantage of giving us very precise and long-term control over the asteroid in question. We’ll not only be able to deflect it so that it misses the earth, we can theoretically steer it into any orbit we want, leaving us the option of exploiting it in the future.

By the way have a look at this video from CNET:
http://cnettv.cnet.com/cnet-top-5-real-life-star-trek-gadgets/9742-1_53-29457.html

As a friend said:
“…Hehe that means there are more Trekkies in the world than people realise.”

PS. Warp drive is not so close yet though

Then earlier this year at the Planetary Defense Conference in Granada, the ADRC presented a poster on further analysis of Nuclear Ablation that in conjunction with another paper presented by David Dearborn from LLNL increased the effectiveness of Nuclear Ablation to 1,000 times the Second Best Alternative.

To deflect a 1,000 meter asteroid 2 cm/sec with Nuclear Ablation would require only a 1 ton nuclear device payload detonated in proximity to the asteroid whereas using a Gravity Tractor (2nd Second Best Alternative) would require a mission mass of 25,000 tons for the same result.

I’m just sayin’, when NEOPucker Time comes, and it’s your children and grandchildren at
Ground Zero would you want the-powers-that-be using a 1,000 times Second Best Alternative to save your gene pool? How about if it were only second best by a factor of 2?

Sometimes what is elegant is just not practical.

DonQ

@Brian That is a depressingly accurate description of how we often deal with problems. Do you work in government or something?

[Next they will ages] becomes [Next they will spend ages].

I don’t mean the problem is that we have to know that many years in advance (although of course that might be an issue). No, the problem is political.

How many governments or large organizations respond well to problems that can be solved by the consistent application of a manageable amount of resources over many years? And yet require that effort to start quickly? Not many.

These large entities are driven by political considerations. In that environment it’s always the crisis that gets the attention, resources, time and funding. And the crisis is always changing.

If you go to one of these large agencies with a message like “we are 80% sure that a large asteroid will hit Earth in 50 years. If we start right now it will cost $10 billion USD to solve the problem with high certainty”. The agency will first ask you to refine your estimate from 80% accuracy to 99.9% accuracy. Then they will ask for a cheaper solution. Then they will question the timeframe. Later they will ask if new technology (either bleeding edge or not yet invented) could solve the problem both quicker and cheaper. Next they will ages arguing who’s responsibility it really is. Then they will kick it to the international stage and ask for funding from every large body or country out there.

You’ll be lucky to get an expedition started in 40 years. Because only then will it have become a crisis.