The Elegant Way to Save Earth From Asteroid Destruction

By Eric Wolff | September 4, 2009 5:10 pm

The one fact in Deep Impact that we can all agree on is that we should not allow the Earth to get hit by a large meteor. Depending on its size, it could potentially destroy anything from a city to the entire planet. And nations it doesn’t destroy outright would still have to deal with big atmospheric and weather problems caused by dust and debris. General badness all around.

Where common sense and the film divide is just how best to dodge an oncoming meteor. I wrote a while back on the idea of painting one side of the asteroid black while beaming heat onto it, causing the asteroid to shift course. It’s a neat idea, but not nearly as neat as the gravity tractor, not just because this approach is more elegant, but because there’s a British company called EADS Astrium that announced last week that they could actually build one if it were needed.

solar-sail.jpgThe idea for the tug first proposed by NASA scientists Edward Lu and Stanley Love in a paper in Nature in 2005. The pair realized that sure, we could change an asteroid’s course by docking a rocket onto the asteroid and pushing it, but landing on an asteroid is really hard: The asteroid is an extremely fast-moving target, and often it rotates asymmetrically around its axis, meaning that a lumpy part of the asteroid could smash a relatively teeny rocket in its rotational path. But, the scientists argued, the spaceship could hover 200 meters or more above the asteroid and use their mutual gravitational attraction to form a “towline” between the two. Then ship could use its own propulsion to slowly pull the asteroid to another course. It would have to push very gently to avoid breaking the bond and flying away, but over the course of 15 to 20 years, the asteroid could be persuaded to miss our planet.

The idea of a gravity tractor has been refined (PDF) by scientist Bong Wie, working at Arizona State University, who proposed the use of solar sails to eliminate the problem of fuel capacity on the satellite. (Love and Lu’s proposal relied on nuclear energy generators for power in their design.) Solar sails capture the momentum from photons of solar radiation to provide propulsion. By properly angling the sail (Wie proposes 35 degrees), the body of the space ship can be moved in the desired direction. The sail can take months to build up significant velocity, but since it has a long time to accomplish its tugboat-like task, this isn’t inherently a showstopper. That said, solar sail technology is still in its infancy—it’s only been tested on a very small scale by American and Japanese scientists in space—so it’s not ready for large-scale deployment just yet.

EADS Astrium’s design uses four ion thrusters of the sort used on Deep Space 1.  Each is aligned to keep the device hovering above the asteroid while gently pulling the asteroid via it’s gravitation “towline” off course. The ship will be 30 meters (about 98 feet) across and weigh about 10 tons. In news articles, Astrium representatives say they haven’t even built a prototype yet, but they’re convinced they can bang one out if necessary.

All of which puts us back to the question of whether there’s enough capacity to provide the necessary early warning to build and launch a gravity tractor in time to have it work. Since NASA currently tracks about 6,000 asteroids, of the 100,000 out there, I’m going to go with no.

CATEGORIZED UNDER: Apocalypse, Astronomy

Comments (21)

  1. You mean we can’t just count on Bruce Willis and Ben Affleck to save us?

  2. Of course we can! They can totally pilot the space ship with the gravity beam for 20 years. I think we’d all be into that, right?

  3. To worry about asteroid destruction at this point in humankind’s history is similar to a terminally ill person standing on the seashore and worrying about a tsunami. An asteroid is coming, of course, but humankind has already done enough to drive our species extinct without the intervention of an asteroid.

    Humankind has a bleak future. Extinction looms ahead.

    It is a tragedy, of a sort, but not so tragic as what humans have done to the planet and all the thousands of species that our activities have already driven extinct, along with all those ecosystems eradicated for the sake of an unsustainable unhealthy economy, and the horrors which humankind routinely inflicts upon each other for a million different foolish reasons.

    Our civilization is collapsing, the human population bubble will reach its apex and then collapse follows immediately, and from there on humankind will live in a humiliated and diminished role as the planet transforms from hospitable home to something not quite so benign.

  4. 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.

  5. Brian

    You know what the problem with this? It’s the 15 or 20+ years required to make it happen.

    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.

  6. Brian

    The embedded edit function isn’t working for me.

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

  7. @David Coincidentally, I have exactly this argument with a close friend of mine. He argues we need to invest more in asteroid detection, I tell him we should worry less about what might happen then what is currently happening right now with global warming.

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

  8. DonQ

    In 2007 NASA’s PA&E reported that Nuclear Ablation would be 100 times more effective than the Second Best Alternative (Kinetic Impactor) for deflecting asteroids.

    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.


  9. Dan42day

    But setting off nukes is so risky and socially irresponsible. What we need to do is send thousands of environmentally aware, politically correct persons up to hug the asteroid, changing its center of gravity and throwing it off on a new course!

  10. nobody

    @David (September 4th, 2009 at 6:27 pm):
    Am I the only one who sees a bright (a la Star Trek) future for the human kind? We have made some huge progress in the last century, and I don’t mean only technologically but also politically.

    By the way have a look at this video from CNET:

    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

  11. JJG

    EADS Astrium is not a British compagny but an European Company. Interesting article by the way.

  12. Steve from Baltimore

    Brilliant idea Dan. I’d like to nominate David to be the captain of the first mission.

  13. amphiox

    The nuclear options are particularly good at getting a lot of energy focused into a small target, in a short period of time. The technical drawback primarily is control and predictability, when compared with other methods.

    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.

  14. Seems to me nuclear explosion or Kinetic Impactor assume the asteroid is a solid mass rather than an agglomeration of bits and pieces loosely bound together. Why would you assume that all the pieces would go off in the right directions?

    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.


  15. amphiox


    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.

  16. #14

    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’.


  17. Petrolonfire

    The one fact in Deep Impact that we can all agree on is that we should not allow the Earth to get hit by a large meteor.

    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! 😉

  18. Asimov fan

    @4. Lab Lemming Says:

    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? 😉

  19. Kolus

    A mixture of the technologies already present are going to have to be employed and used at the interval best suited for them. IE: a nuclear payload detonated at the breaking point and the point of no return are useless, however, used in deep-space where other tools can also be used are feasible. The gravity tractor alone seems to be interesting and a lot of people are pretty hell-bent on it. How about this though, a gravity tractor in orbit around the object to be moved, in an elliptical orbit use to not only put mass in use for gravity, but also centrifugal force much like the moon as it orbits the Earth?
    Again, I would pose that this would only be a partial solution and we would have to use more that one solution to make this a final solution.

  20. Sunny

    in space every particle moves at a contant velocity according to the Newton’s law… if its direction is altered by some smart diversion technique then we avoid the asteroid from hitting the earth.

  21. As for how to improve its visitors, the person correct above me had some great ideas. Also, I’d suggest linking to your blog in your forum signatures (this is assuming you’ve several accounts on some forums).


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